properties of selected soils in the gooburrum - moore park ... · properties of selected soils in...

C S I R O L A N D a nd WAT E R

Properties of selected soils in the

Gooburrum - Moore Park area of Bundaberg

Kirsten Verburg, Bryan J. Bridge, Keith L. Bristow and Brian A. Keating

CSIRO Land and Water, Canberra

Technical Report 9/01, April 2001

Properties of selected soils in the

Gooburrum – Moore Park area of Bundaberg

Kirsten Verburg1, Bryan J. Bridge2, Keith L. Bristow3, and Brian A. Keating4

1 CSIRO Land and Water, Bruce E Butler Laboratory, GPO Box 1666, Canberra, ACT 2601

2 CSIRO Land and Water, c/- The Leslie Research Centre, P.O. Box 2282, Toowoomba, Qld 4350

3 CSIRO Land and Water, Private Mail Bag, PO Aitkenvale, Qld 4814

4 CSIRO Tropical Agriculture (now CSIRO Sustainable Ecosystems), Long Pocket Laboratories, 120

Meiers Road, Indooroopilly, Qld 4068

CSIRO Land and Water, Canberra

Technical Report 09/01, April 2001

2001 © CSIRO Land and Water

ISBN 0 643 06092 8

Corresponding author:

Kirsten Verburg

CSIRO Land and Water

Bruce E Butler Laboratory

GPO Box 1666

Canberra, ACT 2601

Tel (02) 6246 5954

Fax (02) 6246 5965

E-mail [email protected]

Cover photograph:

Mr Denis Orange taking disk permeameter measurements in the soil pit at the SCH site. Photo courtesy

of Dr Bryan Bridge..

Citation:

K. Verburg, B.J. Bridge, K.L. Bristow, and B.A. Keating. 2001. Properties of selected soils in the

Gooburrum – Moore Park area of Bundaberg. Technical Report 09/01, CSIRO Land and Water,

Canberra, Australia.

CLW Technical Report 09/01: Soil properties Gooburrum – Moore Park area of Bundaberg 1

Table of Contents

Table of contents ....................................................................................................................................... 1 Summary.................................................................................................................................................... 2 1. Introduction................................................................................................................................................ 3 2. Methods ..................................................................................................................................................... 7

2.1 Profile description.............................................................................................................................. 7 2.2 Particle size distribution .................................................................................................................... 7 2.3 Chemical analyses ............................................................................................................................. 7 2.4 Bulk density ..................................................................................................................................... 10 2.5 Water retention ................................................................................................................................ 10 2.6 Near-saturated hydraulic conductivity............................................................................................. 11

3. Measured Soil Properties......................................................................................................................... 13 3.1 FRA and WIL sites (Oakwood) ....................................................................................................... 13 3.2 SCH site (Otoo sandy variant) ......................................................................................................... 23 3.3 PAO site (Otoo) ............................................................................................................................... 33 3.4 SFF site (Gooburrum)...................................................................................................................... 37 3.5 TOW site (Alloway) ........................................................................................................................ 44 3.6 FA1 site (Moore Park) ..................................................................................................................... 50 3.7 FA2 site (Fairymead) ....................................................................................................................... 56 3.8 EWA site (Flagstone) ...................................................................................................................... 62

4. Concluding Remarks................................................................................................................................ 68 5. Acknowledgements.................................................................................................................................. 70 6. References................................................................................................................................................ 71 7. Appendices .............................................................................................................................................. 73

7.1 List of Tables ................................................................................................................................... 73 7.2 List of Figures.................................................................................................................................. 76


Summary

A study into the development of sustainable intensive crop production systems for the sugarcane growing area around Bundaberg (Queensland, Australia) involved two sugarcane cropping trials and several small-scale field experiments. These experiments provided a wealth of data on the soil properties of five soil types in the Gooburrum – Moore Park area of Bundaberg. A compilation of the data is presented here and includes soil profile descriptions, particle size and chemical analyses, bulk density, water retention and hydraulic conductivity measurements. The presentation contains a discussion of the uncertainty associated with experimental data focussing on bulk density, for which several methods were employed.

To interpret and extrapolate the results of the cropping trials, simulation analysis was employed. The data presented in this report were collected to parameterise the hydraulic property functions of two models, SWIMv2 (Soil Water Infiltration and Movement version 2, Verburg et al., 1996) and APSIM-SWIM (Agricultural Productions Systems Simulator, McCown et al., 1996). For this purpose the water retention data were fitted using the smoothed-Brooks-Corey function. The fits were generally good. Most soils in this study exhibited, however, a marked increase in wet-end hydraulic conductivity at potentials below the air-entry point. This feature is not supported by the Brooks-Corey conductivity function, but needs to be taken into account when wet conditions are simulated.

The data presented here would be suitable for other modelling exercises, provided these are general and not site-specific, in which case additional measurements would be required.


1. Introduction

The Gooburrum – Moore Park area of Bundaberg was the focus of a Land and Water Resources Research and Development Corporation (LWRRDC) funded project, CTC6 “Development of sustainable intensive crop production systems”, managed by Dr Brian Keating of CSIRO Tropical Agriculture. The project dealt with the potential conflict between the need for an adequate nitrogen supply for the sugar and horticultural industries and the requirement for a healthy drinking water supply. Bundaberg depends for 84% of its drinking water on groundwater.

Two of the aims of the project were to (1) assess the likely impact of current sugarcane and horticultural cropping practices on future groundwater quality, and (2) identify soil, crop and fertiliser management strategies for sugarcane and intensive horticultural industries that reduce the risk of groundwater contamination. In order to achieve these aims it was necessary to estimate how much and how often nutrients are leached below the root zone in the various soils in the region. To assess this so-called leaching potential the project combined field measurements with simulation modelling.

Many experiments and measurements were carried out as part of the LWRRDC project and a previous project funded by Sugar Research and Development Corporation (SRDC, CSC7S) “A modelling framework to integrate research on nitrogen management of sugarcane”. It has resulted in a wealth of data on the major soil types in the Gooburrum – Moore Park area of Bundaberg. A series of three Technical Reports documents these experiments and measurements. This is the first report in the series, which provides a compilation of soil property data. The two other reports describe the results of the various experiments and their analysis using simulation modelling (Verburg et al. 2002a,b).

Field experiments

Two sites were chosen for detailed study of nutrient cycling in sugarcane cropping systems. One of the sites was at the farm of Des Schulte on Moore Park Road (SCH). During two cropping seasons (1992-1994) nitrogen in the crop and soil were frequently monitored under different fertiliser and irrigation treatments. In addition, the movement of bromide was followed in the two-year trial and a number of small-scale bromide leaching experiments were carried out. The soil at this site is classified in the Australian system (Isbell, 1996) as a Red Dermosol (see Table 1).

The second site of detailed study was at the farm of John Francis (FRA), also on Moore Park Road. The soil at this site is a Red Kandosol (Isbell, 1996) (see Table 1). A two-season sugarcane cropping trial similar to that at the SCH site was carried out from 1994 to 1996. In addition, a number of small-scale experiments were carried out to study the movement of water and bromide.

The FRA site was also chosen for the installation of two large in situ drainage lysimeters. These formed part of a two-year project on the re-use of sewage biosolids managed by Mr Ted Gardner of the Queensland Department of Natural Resources (Barry et al., 1998). The drainage and leaching data of the lysimeters were used for model testing within the LWRRDC project.

At both sites a detailed soil physical characterisation was carried out. This included disk permeameter measurements in the field to determine the near-saturated hydraulic conductivity, drainage plots, and sampling for water retention, bulk density, particle size distribution, and organic carbon determinations. The measurements and samples were taken in and near two soil pits dug at different positions within the cropping trials.

As it was not possible to study all major soil types in the region in detail as described above, “minimum” data sets were obtained to characterise seven other sites (see Table 1 and Fig. 1). Here soil physical characterisation was limited to one soil pit and the number of sampling depths reduced. In addition, bromide leaching experiments were carried out under fallow conditions, and the redistribution of water was followed in drainage plots.


The sites were selected in collaboration with experienced pedologists, Mr Peter Wilson, Mr Terry Donnolan and Mr Peter Zund (Queensland Department of Natural Resources, DNR, Bundaberg), who were involved with the (1:50 000) land resource survey of the Gooburrum-Moore Park area of Bundaberg. The soil pits dug at the various sites were used for detailed profile descriptions and additional chemical analyses were carried out by DNR for six of the soil types.

Presentation of data

The number of replicates of the various measurements was not statistically based, but logically constrained. In general, more replicates were taken at the two sites of detailed study (FRA, SCH). Many units in this report are non-SI units reflecting instead those used by the SWIM model, namely cm for distance and hour for time.

Soils and geology of the area

Soil groups based on geology and geomorphology, derived from the DNR soils map of the Gooburrum – Moore Park area, are shown in Fig. 1. These broader soil groupings were necessary at this scale. Six of the sites were on soils developed in the Tertiary Elliott formation, which is comprised of sandstone, conglomerate, siltstone, mudstone and shale (Robertson, 1979). Soils are developed in marine and alluvial material below an escarpment that is clearly visible in the landscape. Three experimental sites were located in this geological unit.

Simulation analysis

The field measurements described above were complemented with simulation modelling. The SWIMv2 water and solute transport model (Verburg et al., 1996) was used to analyse the small-scale bromide leaching and drainage experiments. The analysis of these experiments provided a characterisation of the different soil types in terms of their water and solute transport properties. At the same time, the SWIMv2 simulations established a tested set of soil input parameters that could then be used for whole-system simulations with the APSIM model (McCown et al., 1996). The SWIMv2 model has been interfaced with the APSIM model and this APSIM-SWIM combination was satisfactorily tested against the data of the two sugarcane cropping trials and then used to make longer-term predictions of nitrate leaching under different management systems (hypothetical scenarios). The simulations are described in the two other reports in this series (Verburg et al., 2002a,b).

Outline of the report

Chapter 2 of this report provides details of the various experimental methods and laboratory procedures used in these studies. Only those methods relating to the soil characterisation are discussed. Chapter 3 summarises the results for each of the sites. A few concluding remarks are made in Chapter 4. Most of the data in this report are presented in tables and figures, which are listed in the Appendices.


Table 1: Experimental sites in Gooburrum – Moore Park area of Bundaberg (24.8°S, 152.3°E).

Site Local classification

Australian classification (Isbell, 1996)

Great Soil Group1 (Stace et al., 1968)

Sugarcane trial

Soil hydraulic properties

Drainage experiment

Br drip experiment4

Br leaching experiment5

FRA Oakwood Red Kandosol Red earth � �detailed � � �

WIL Oakwood Red Kandosol Red earth �

SCH Otoo2 Red Dermosol Red podzolic soil � �detailed �

PAO Otoo Red Dermosol Red podzolic soil �3 � �

SFF Gooburrum Red Dermosol Red podzolic soil � � �

TOW Alloway Chromosolic Redoxic Hydrosol Gleyed podzolic soil � � �

FA1 Moore Park Semiaquic Podosol Podzol � � �

FA2 Fairymead Sulfidic Redoxic Hydrosol Humic gley � � �

EWA Flagstone Black Dermosol Prairie soil � � �

1 included for comparison 2 sandy variant, see Section 3.2 3 soil surface only 4 bromide applied using a drip infiltrometer 5 bromide applied using an injector, followed by natural rainfall


FRA and WIL sites

N

Bundaberg

Moore Park

KolanRiver

Burnett River

SCH siteSFF site

PAO site

TOW site

FA2 site

FA1 site

EWA site

Pacific ocean

Elliot formation; upper slopes (Kandosols)Elliot formation; upper slopes (Dermosols)Elliot formation; mid to lower slopesElliot formation; drainage depressionsAlluvial plains; older alluviaAlluvial plains; recent alluviaMarine sediments; beach ridgesMarine sediments; plainsWetlands

Figure 1: Location of experimental sites and soils groups of the Gooburrum – Moore Park area of Bundaberg (derived from Gooburrum – Moore Park Soils 1: 50 000, 1998, P.R. Zund, T.E. Donnollan, and S.A. Irvine).


2. Methods

2.1 Profile description

The soil profiles were described following the procedures in the second edition of the Australian Soil and Land Survey Field Handbook (McDonald et al., 1990). The profiles were classified according to the Australian Soil Classification (Isbell, 1996). Classifications following the Great Soil Group scheme (Stace et al., 1968), the Factual Key (Northcote, 1979), and a local classification used in the Gooburrum-Moore Park area of the Bundaberg Land Resource Survey (1: 50, 000) are also included in Table 1. The profiles of the FRA, SFF, TOW, FA1, FA2, and EWA sites were described in situ from a fresh face in the soil pits. The profile of the SCH site was compiled later from notes taken in the field when the soil pits were dug, with soil physical properties determined on stored samples. The profile of the PAO site, where no pit was dug, was obtained from a soil core of 5 cm diameter.

2.2 Particle size distribution

The particle size analysis is a measurement of the size distribution of individual soil particles. It was determined for each soil sample by first removing the coarse fragments (> 2 mm) and then using either the pipette and sieve method (Coventry and Fett, 1979; Gee and Bauder, 1986) or the hydrometer method (Piper, 1942; Gee and Bauder, 1986; Baker and Eldershaw, 1993) for soil textural analysis of the remaining soil fraction. The size fractions reported in Chapter 3 are coarse fragments (>2 mm), coarse sand (2 mm > cs >0.2 mm), fine sand (0.2 mm > fs >0.02 mm), silt (0.02 mm > s >0.002 mm) and clay (< 0.002 mm). All samples were air-dried before the particle size analysis.

For most sites, two measurements were made. One in the CSIRO Land and Water Townsville Lab (pipette and sieve method) and one as part of the chemical analysis carried out by DNR (hydrometer method). The samples analysed in Townsville were taken from the soil pits at the depths corresponding to those of the disk permeameter measurements (FRA, SFF, TOW, FA1, FA2, and EWA sites) or at 20-cm intervals (SCH). The DNR samples were taken from common depths (0-10, 10-20, 20-30, 50-60, 80-90, 110-120 cm), except when an important soil horizon boundary occurred within these depths (Beattie and Gunn, 1988).

2.3 Chemical analyses

The SFF, TOW, FA1, FA2, and EWA samples sent to Townsville for particle size analysis were also analysed for organic carbon using the Heanes wet oxidation method (Heanes, 1984; Rayment and Higginson, 1992). Total carbon for the FRA site was determined by dry combustion using a Europa ANA mass spectrometer (Barry and Prosser, 1996). The FRA samples came from the first and second soil sampling in the cropping trial. The first soil sampling was before the farmer applied mill mud to his field, the second sampling occurred a few weeks after application of the mill mud. Mill mud is the ‘solid’ material left after filtering cane juice, which has high levels of nutrients and water contents ranging from 60-85%.

Samples from the two soil pits at the SCH site were used to determine the EC of 1:5 soil/water extracts. Method S3A1 of the Australian Laboratory Handbook of Soil and Water Chemical Methods by Rayment and Higginson (1992) was followed.

For a number of soil samples from the cropping trials at the SCH and FRA sites, the pH of 1:5 soil/water extracts were determined (Raymond and Higginson, 1992, Method S4A1).

A selected number of soil cores from the cropping trial at SCH were used to determine the exchangeable bases Ca, Mg, K, and Na. The cations were extracted using 1M ammonium chloride at pH=7.0 (Rayment and Higginson, 1992, Method S15A1). The measurements were carried out using inductively coupled plasma mass spectrometry (ICPMS).


The chemical analysis carried out by DNR for the SFF, TOW, FA1, FA2, and EWA sites involved a number of methods, which are listed in Table 2. Most of the analyses followed standard methods described in Rayment and Higginson (1992). The methods are described in detail in Baker and Eldershaw (1993).


Table 2: Methods used for chemical analysis by DNR.

Analysis Unit Method description Drying condition Method number1 pH-H2O - pH of 1:5 soil/water suspension Air dry S4A1 EC mS/cm Electrical conductivity of 1:5 soil/water extract Air dry S3A1 Cl mg/kg Soluble chloride in 1:5 soil/water extract Air dry S5A2 15 Bar % 15 bar (15000 cm) pressure plate gravimetric water content 24 h at 105°C Dispersion ratio (R1) - % readily dispersed (silt + clay) / % total (silt+clay) Air dry Total P, K, S mg/kg Total phosphorus, potassium, sulfur - pressed powder, X-ray fluorescence 65°C pH - CaCl2 - pH of 1:5 soil/0.01M calcium chloride extract Air dry S4B1 OrgC % Organic carbon - Walkley & Black, colorimetry Air dry S6A1 TotN % Total nitrogen - semimicro Kjeldahl, colorimetry Air dry S7A2 Acid Extract P mg/kg Acid-extractable phosphorus - 0.005M H2SO4, colorimetry Air dry Bic Extract P mg/kg Bicarbonate-extractable phosporus - 0.5M NaHCO3, colorimetry Air dry S9B2 K meq/100g 0.005M HCl extractable potassium Air dry Fe, Mn, Cu, Zn mg/kg DTPA extractable iron, manganese, copper and zinc - ICP Air dry SO4-S mg/kg 0.01M Ca(H2PO4)2 extractable sulfate sulfur - ICP Air dry S10B3 ECEC meq/100g Effective cation exchange capacity = Exchangeable

(Ca+Mg+K+Na+Al+H) Air dry

Exchangeable Ca, Mg, Na, K

meq/100g Exchangeable bases - aqueous 1M NH4Cl at pH7.0 Air dry S15A1

1 Method number in Rayment and Higginson (1992)


2.4 Bulk density

Different methods were used to determine the bulk density of the soils. In situ samples were taken at different depths in the soil pits using a 10 cm diameter x 5 cm long thin-walled push tube and cutting box (Loveday, 1974). Four sample replicates were taken at each depth in the soil pits at the SCH site, and two replicates were taken at each depth in the other soil pits (FRA, SFF, TOW, FA1, FA2, and EWA sites). The determination of bulk density using these in situ samples is relatively accurate, but the disadvantage of sampling on one occasion in a soil pit is that it does not provide information about variation in space beyond the soil pit and time.

As part of the regular monitoring of the cropping trials at the FRA and SCH sites, continuous soil cores (42-45 mm diameter) were taken to 150 cm or deeper. Often a first core was taken to 100 cm depth, followed by a core with slightly smaller diameter to 150 cm or deeper. Each core was sectioned into depth intervals (e.g., 0-20, 20-40, 40-60, 60-100, 100-150 cm at the FRA site). All the soil from each depth interval was retained, with a number of soil cores bulked. Row and interrow samples were kept separate. In the laboratory the soil was mixed and sub-sampled for determination of the gravimetric water content. By taking into account the core diameter and section lengths, this sampling procedure allows the calculation of a bulk density for each depth interval, position (row vs. interrow) and sampling time. These bulk density values suffer, however, from inaccuracies due to compaction and errors in sectioning of the continuous cores. The bulk density depth profile from a single core, therefore, often exhibits a jagged pattern. This can be minimised if the results of a large number of cores are combined. The number of samples that will be required depends on the soil sampling conditions. In non-optimal conditions more samples will be required. Here we have combined the data from different cores to present median values. These are thought to be more appropriate than average values, as they give less weight to outliers.

If there are no systematic errors and the number of outliers is small, then this method can provide useful information about variations in bulk density in space and time. In addition, it gives a detailed picture of the bulk density profile. This is not always possible using in situ sampling, as it is usually restricted to a few selected depths.

The small-scale bromide leaching experiments were also sampled using continuous cores to a depth of 150 - 200 cm. The background cores (taken at the beginning of the experiments) were bulked (four replicates). The cores taken during and at the end of the experiments were kept separate. Again only the median bulk density values are presented here.

In this report both the in situ and core estimated bulk density values are presented. This allows an evaluation of the methods and shows that they are often complementary. Best estimate “field average” curves were drawn by eye for each soil type based on the available data. These curves were used in the simulations, and in the experiments to convert measured gravimetric water contents into volumetric water contents (Verburg et al., 2002a,b). It should be noted that none of the methods made a correction for coarse framents. Where the percentage of coarse fragments is large (e.g. subsoil at TOW site), the listed bulk density values should not be used to calculate soil porosity.

2.5 Water retention

The relationship between matric potential (or suction) and water content was determined on undisturbed soil cores 3 cm in diameter x 3 cm long. Four replicate soil cores were taken from different depths in the soil pits. Four additional depths were sampled at the SCH site (outside the soil pits) with six replicates. The matric potentials ranged from -1 cm to -3000 cm using suction and pressure plates (McIntyre, 1974), and -15000 cm using a thermocouple psychrometer.

The smoothed Brooks-Corey function (Brooks and Corey, 1964, 1966; Hutson and Cass, 1987) was fitted to the water retention data.

( ) ( )θ θθ θ

ψ ψ ψψ

ψ ψψ ψ

−−

= =−

≤≥ >

−r

s r

eb

i

i

Sc

/1/

21 0 (1)


where,

a = 2b / (1 + 2b), ψi = ψe a–b (ψi ≤ 0), c = (1-a) / ψi

2

and

θ = volumetric water content [cm3/cm3] θs = saturated volumetric water content [cm3/cm3] (theta-s) θr = residual volumetric water content [cm3/cm3] (theta-r) ψ = matric potential [cm] (ψ ≤ 0) ψe = air entry potential [cm] (ψe ≤ 0) (psie) b = constant (b)

When plotted on a log-log scale, Eq. (1) results in a linear function with slope b below ψi (Fig. 2a). θr, θs, ψe, and b are usually determined using curve-fitting procedures to measured data. Equation (1) overcomes the unrealistic, sharp discontinuity of the regular Brooks-Corey function by replacing the exponential function by a parabolic one near saturation.

2b+3

-2-3/bKs

ψi

log (water content) log (suction)

log

(co

nd

uct

ivit

y)

log

(co

nd

uct

ivit

y)

Ks

θs (c)

(b)

-1/b

ψi

θs

log

(w

ater

co

nt.

)

log (suction)

(a)

ψe

ψe

KT

Figure 2: Brooks-Corey hydraulic property functions: (a) water retention curves, and (b) and (c) related hydraulic conductivity functions. Dashed curve in (c) is an example of an additional function to deal with “macroporosity”.

2.6 Near-saturated hydraulic conductivity

Near-saturated hydraulic conductivities were obtained from disk permeameter measurements (Perroux and White, 1988). The measurements were made on undisturbed soil, either at the soil surface, at the bottom of the soil pits, or on shelves dug in the walls of the soil pits (see Fig. 3). There were eight replications per depth at each site. Good contact with the soil surface was obtained through the use of sand pads (Coughlan et al., 1991). The disk permeameters were made such that the supply potentials (-4, -3, -2, and -1 cm H2O) could be applied to a single measurement pad. The analysis was done according to the method of Reynolds and Elrick (1991). This method uses a piecewise exponential fit to the steady state flow data from the disk permeameters at the supply potentials used. It uses numerically determined shape factors that account for the interaction effects between flow geometry and soil properties, and has the advantage of also allowing an estimate of the saturated hydraulic conductivity. The latter is obtained through extrapolation of the piecewise exponential fit, based on the measurements made at –1 and –2 cm suction. Accuracy of the extrapolated value will depend somewhat on soil structure, and needs to be treated with care. The calculated near-saturated hydraulic conductivities apply to an “average” potential between steps. In the presentation of the results (Section 3), the potentials are, therefore, given as -3.5, -2.5, -1.5 and 0 cm H2O.


In the simulations (Verburg et al., 2002a,b) the soil hydraulic conductivity function was assumed to be described by an equation related to Eq. (1) (Brooks and Corey, 1964, 1966; Campbell, 1974, 1985) such that

( )K K S Ksb

sr

s r

b

= = −−

++

ψ θ θθ θ

2 32 3

(2)

Equation (2) is shown schematically in Fig. 2b and implies that the slope of the conductivity function on a log-log plot (2b+3) can be derived from the water retention curve (-1/b, Fig. 2a). A single hydraulic conductivity measurement (Ks or another point) can then be used as a ”matching” or “scaling” point to define the whole function.

Most soils in this study exhibited a marked increase in wet-end conductivity below the air-entry point (Fig. 2c), a feature which is not supported by Eq. (2). The phenomenon is generally ascribed to the presence of sparse macropores of small total volume, that do not significantly affect the water retention curve. The effect on hydraulic conductivity near saturation can, however, be considerable. For some of the simulations, an extra macropore function was therefore added to Eq. (2) in the form of a simple one-parameter exponential function. Details of this function are described in the SWIMv2.1 User Manual (Verburg et al., 1996).

Figure 3: Bryan Bridge and Denis Orange taking disk permeameter measurements in a pit at the SFF site.


3. Measured Soil Properties

3.1 FRA and WIL sites (Oakwood)

3.1.1 Site details

The FRA experimental site was located on the farm of John Francis on Moore Park Road. From July 1994 to November 1996 a cropping trial was carried out in blocks 11 and 12. Three replicate areas (Reps 1, 2 and 3) were established, half of each for use in 1994/95 and half reserved for 1995/96. The three blocks or replicates for use in 1994/95 and the three for use in 1995/96 were each divided into three plots. Each plot (9 m x 56 m) represented a different N-fertiliser rate (0, 120, or 240 kg N/ha).

In July 1995 two soil pits were dug within the sugarcane of Reps 1 and 2 of the 1994-1995 season of the cropping trial. In and around these soil pits several soil physical measurements were made. Half-way between Rep 1 and Rep 2 an area of approximately 10 x 6 m2 was cleared for bromide leaching experiments with a drip infiltrometer (“drip experiments”; four 1 m2 plots). Two drainage plots were situated here as well.

A longer term bromide leaching study (“leaching experiments”) was carried out from December 1995 to February 1996 at the WIL site. The WIL site was in a fallow field on the farm of Alex Wilson on Gin Gin Road. The soil at this site was the same as that of the FRA site and the distance between the experiments at the WIL site and Rep 3 of the FRA cropping trial (1995-1996) was less than 50 m.

More details about the bromide experiments and cropping trials are provided in the second and third reports of this series (Verburg et al., 2002a,b).

3.1.2 Profile description

A photo and profile description of the Oakwood soil at the FRA site are presented in Fig. 4 and Table 3, respectively. Both are of the first soil pit (in Rep 1 of cropping trial). The soil profile of the second soil pit (in Rep 2 of the cropping trial) was similar, although the A horizon contained more sand with a sandy light clay texture and massive structure. Sandstone rock in the size range from 20-60 mm was present as a single occurrence in the pit face in the upper B at 45 cm depth.

The Oakwood soil is found on level plains and the upper slopes and crests of rises on the sedimentary rocks of the Elliott formation (Robertson, 1979).

Table 3: Profile description of the Oakwood soil at the FRA site (by T.E. Donnollan, DNR).

MAPPING UNIT CODE: Ok SITE NO. Z1 A.M.G. REFERENCE: 430 476 mE 7 251 394 mN ZONE 56 GREAT SOIL GROUP: Red Earth LANDFORM ELEMENT TYPE: Hill crest PRINCIPAL PROFILE FORM: Uf6.71 AUSTRALIAN SOIL CLASSIFICATION: Red Kandosol CONDITION OF SURFACE SOIL WHEN DRY: Firm

HORIZON DEPTH (cm) DESCRIPTION Ap 0 - 32 Dark reddish brown (10R3/3); light clay; moderate 2-5 mm polyhedral; dry;

moderately firm. Clear, smooth to – B21 32 - 55 Dark reddish brown (2.5YR3/6); light clay; massive; moderately moist;

moderately firm; common medium manganiferous soft segregations. Gradual, smooth to –

B22 55 - 100 Dark red (10R3/6); light medium clay; massive; moderately moist; moderately weak; very few fine manganiferous soft segregations. Gradual, smooth to –

B23 100 - 150 Dark red (10R3/6); light clay; weak 2-5 mm polyhedral; moderately moist; moderately weak.


Figure 4: Photo of the Oakwood soil at the FRA site (photo by T.E. Donnollan).

3.1.3 Particle size distribution

The particle size distributions of the Oakwood soil (Table 4) confirmed that the soil in the second soil pit contained more sand, as was observed in the soil profile descriptions. There was a significant increase in clay content in the subsoil.

Table 4: Particle size distribution of the Oakwood soil at the FRA site (Townsville analysis).

Soil pit Location Depth (cm) > 2 mm Coarse sand Fine sand Silt Clay (% of total) (% of < 2 mm fraction)

1 Row Surface < 1 30 32 15 23 15-20 < 1 30 32 15 23 Interrow Surface < 1 29 35 13 23 15-20 < 1 30 33 15 23 40-50 < 1 25 28 13 33 80-90 < 1 22 25 11 42 160-170 < 1 19 22 10 48

2 Row Surface < 1 39 27 13 21 15-20 < 1 37 28 13 22 Interrow Surface < 1 39 26 13 21 15-20 < 1 36 28 14 22 40-50 < 1 33 24 12 31 80-90 < 1 33 22 6 39 160-170 < 1 29 21 10 40


3.1.4 Chemical analysis

Total carbon in the Oakwood soil was determined by dry combustion (see Section 2.3) on selected samples from the first and second soil sampling of the cropping trial. In between these two sampling dates the farmer applied mill mud to the field, which caused the increase in % C in the top soil (Table 5). The reasons for the increase in % C at depth are unclear, so the data should be used with care. The pH was determined on samples of the first and final soil samplings of the 2-year cropping trial. As there was no significant change in pH during the trial, only the results of the final soil sampling are shown here (Table 6).

Table 5: Total carbon of selected soil samples of the Oakwood soil at the FRA site.

Depth (cm) % C first sampling second sampling (before mill mud) (after mill mud)

0-20 0.850 1.119 20-40 0.514 0.834 40-60 0.340 0.399

60-100 0.276 0.294 100-150 0.203 0.232

Table 6: Soil pH at the final soil sampling (November 1996) of the cropping trial at the FRA site.

Depth (cm) pH Average St. dev.

0-20 7.1 0.3 20-40 6.4 0.3 40-60 5.5 0.3

60-100 5.7 0.2 100-150 5.9 0.1 150-200 5.9 0.1 200-250 6.1 0.1 250-300 6.1 0.1

3.1.5 Bulk density data

As explained in Section 2.4, different methods were used to determine soil bulk density. At the FRA and WIL sites all methods were employed. The in situ measurements using bulk density rings at different depths in the soil pits resulted in two similar bulk density profiles (Table 7), with the exception of a shallow hardpan that was more evident in soil pit 1 than in soil pit 2 (higher bulk density at 15 cm depth in the interrow). Bulk density in the row at shallow depth was lower than between the rows. The maximum bulk density in the two profiles occurred at 40 cm depth. At depths below 40 cm the bulk densities decreased (Fig. 5a).

Table 7: Bulk density of the Oakwood soil obtained from in situ samples in the soil pits at the FRA site.

Bulk density (g/cm3) Location Depth (cm) Soil pit 1 Soil pit 2 Average St. dev.

Rep 1 Rep 2 Rep 1 Rep 2 Row Surface 1.25 1.38 1.40 1.37 1.35 0.07

15-20 1.57 1.53 1.48 1.54 1.53 0.04 Interrow Surface 1.53 1.56 1.59 1.59 1.57 0.03

15-20 1.74 1.73 1.58 1.66 1.68 0.07 40-50 1.78 1.67 1.81 1.74 1.75 0.06 80-90 1.64 1.74 1.74 1.72 1.71 0.05 160-170 1.61 1.69 1.63 1.64 1.64 0.04


The median bulk density data from the soil samplings during the first season of the cropping trial (1994-1995) (Table 8) corresponded well with the in situ bulk densities of Table 7, as shown in Fig. 5a. The bulk density values in the column labelled “Average” were obtained by averaging the median of the row samples and median of the interrow samples. These values were used for the (one-dimensional) simulations with APSIM-SWIM (see Verburg et al., 2002b).

Table 8: Bulk density of the Oakwood soil obtained from soil samples taken during the first season of the cropping trial at the FRA site (FRA1).

Bulk density (g/cm3) Depth (cm) Median of all1 Median of row Median of interrow "Average"2 surface hill 1.66 1.50 1.68 1.59

0-20 1.58 1.49 1.68 1.59 20-40 1.72 1.68 1.72 1.70 40-60 1.73 1.73 1.74 1.74 60-100 1.71 1.69 1.73 1.71

100-150 1.67 1.68 1.68 1.68 150-200 1.67 1.67 1.67 1.67 200-250 1.66 1.68 1.68 1.68 250-300 1.72 1.74 1.73 1.74

1 Includes data from preliminary soil sampling, before preparation of rows and interrows. 2 Average of median of row and median of interrow.

The bulk density values obtained in the small scale leaching experiments (drip and leaching experiments, see Verburg et al., 2002a) were rather variable (Table 9). In some cases (e.g. the medians of the samples of the drip and leaching experiments; D median and L median, respectively) the error due to inaccurate slicing of the soil core caused the bulk density to fluctuate strongly from one layer to the next. This suggests that the number of samples used in the calculation of the median value did not compensate for errors induced by the method. It is not clear why the bulked background of the drip experiments (D background) gave lower bulk density values. The column labelled “Field average” was used in the simulations with the SWIMv2.1 model (Verburg et al., 2002a) as the best estimate based on all available data (Fig. 5b).

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(a) (b)

Figure 5: Comparison of bulk density data for the Oakwood soil: (a) in situ bulk density vs. median bulk density for the first year of the cropping trial at the FRA site (FRA1), (b) bulk density obtained using various estimates for the FRA and WIL sites (note different depth scale).


Table 9: Bulk density of the Oakwood soil obtained from soil cores taken as part of the small scale bromide leaching experiments at the FRA and WIL sites and the best estimate “field average”.

Depth (cm) Bulk density (g/cm3) Leaching experiments Drip experiments "Field Bulked median of bulked median of average” Background 16 samples background 14 samples

0-5 1.44 1.52 1.58 1.44 1.48 5-10 1.40 1.77 1.44 1.51 1.56

10-20 1.68 1.69 1.53 1.58 1.63 20-30 1.67 1.68 1.54 1.66 1.68 30-40 1.71 1.73 1.61 1.81 1.72 40-50 1.76 1.73 1.75 1.71 1.74 50-60 1.73 1.74 1.76 1.73 1.74 60-70 1.78 1.68 1.66 1.78 1.73 70-80 1.67 1.68 1.72 1.76 1.72

80-100 1.70 1.76 1.60 1.84 1.70 100-120 1.72 1.64 1.55 1.70 1.69 120-140 1.70 1.73 1.60 1.81 1.68 140-160 1.62 1.67 160-180 1.60 1.67 180-200 1.57 1.67

3.1.6 Illustrations of the effect of uncertainty in bulk density

Bulk density values are often used to convert gravimetric water content into volumetric water content. Hence, uncertainty in bulk density data results in uncertainty in the calculated volumetric water contents. This is illustrated in Fig. 6, which shows the volumetric water content profiles of two plots of the drip experiments. The volumetric water contents were calculated by multiplying the gravimetric water contents (assumed to be fairly accurate) with the various values for bulk density. In the first graph of each plot (D plot1 and D plot2) the bulk density values of each individual core section were used. While spatial variability plays a role, the jagged behaviour of the curves suggests that measurement error due to inaccurate slicing of the cores dominated the results. Use of any of the other bulk density data (In situ from Table 7; D background, D median, or “Field average” from Table 9) led to much smoother curves. The actual position of these curves varied with the method used, but the maximum difference was 0.04 and in general of the same order as the differences between replicates.


Drip Plot 1individua l core

bulk de nsityprofiles

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Figure 6: Effect of uncertainty in bulk density on the volumetric water content profiles in the drip experiments. For each of the two plots shown (Plot 1 top row and Plot 2 bottom row) three replicate profiles are given (curves connect data points at the mid points of sampled layers).


3.1.7 Water retention curves

The water contents at different matric potentials for the different depths in the two soil pits are presented in Table 10. The data are averages of four replicate determinations, with the standard deviation given in parentheses. Plots of the average water retention curves are shown in Fig. 7. Note that the curves become flatter with depth as the texture becomes heavier with increasing clay content. There were slight differences between the soil pits, but these were small. The most spectacular differences were between the row and interrow samples in the surface layers, particularly at low suction where the row samples had much higher water contents. This is a reflection of differences in structure (macroporosity) between the two sampling positions. Also shown in Fig. 7 are the Brooks-Corey fits of the data. The fitted Brooks-Corey parameters (Eq. 1) are given in Table 11.

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Figure 7: Brooks-Corey fits of water retention data for the Oakwood soil at the FRA site.


Table 10: Water retention data for the Oakwood soil at the FRA site. Values represent average volumetric water contents (four replicate measurements, standard deviations are given in parentheses).

Matric potential (cm) Soil pit Location Depth (cm) -1 -3 -10 -20 -50 -100 -330 -670 -1000 -3000 -15000

1 Row Surface 0.45 0.41 0.36 0.30 0.23 0.19 0.16 0.15 0.14 0.12 0.10 (0.05) (0.03) (0.02) (0.02) (0.01) (0.00) (0.00) (0.00) (0.00) (0.00) (0.00)

15-20 0.42 0.41 0.39 0.35 0.28 0.24 0.21 0.19 0.18 0.16 0.13 (0.04) (0.04) (0.03) (0.03) (0.02) (0.01) (0.01) (0.01) (0.01) (0.00) (0.00)

Interrow Surface 0.44 0.43 0.41 0.36 0.28 0.23 0.19 0.17 0.16 0.14 0.12 (0.05) (0.04) (0.04) (0.03) (0.02) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01)

15-20 0.32 0.32 0.32 0.31 0.28 0.25 0.22 0.20 0.19 0.17 0.14 (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.00) (0.00) (0.00) (0.00) (0.00)

40-50 0.36 0.35 0.33 0.31 0.28 0.27 0.24 0.23 0.22 0.20 0.18 (0.06) (0.05) (0.04) (0.03) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01)

80-90 0.38 0.38 0.38 0.36 0.35 0.33 0.30 0.28 0.27 0.25 0.23 (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.00) (0.00) (0.00) (0.00) (0.00)

160-170 0.38 0.38 0.38 0.37 0.34 0.32 0.29 0.27 0.26 0.24 0.21 (0.02) (0.02) (0.02) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01)

2 Row Surface 0.44 0.41 0.37 0.32 0.25 0.21 0.17 0.15 0.14 0.12 0.10 (0.04) (0.04) (0.03) (0.02) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.00)

15-20 0.42 0.40 0.37 0.33 0.24 0.21 0.18 0.17 0.16 0.14 0.11 (0.05) (0.04) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.00) (0.00)

Interrow Surface 0.38 0.38 0.36 0.33 0.26 0.22 0.19 0.17 0.16 0.14 0.12 (0.06) (0.05) (0.05) (0.03) (0.02) (0.01) (0.00) (0.00) (0.00) (0.00) (0.00)

15-20 0.30 0.29 0.29 0.29 0.26 0.22 0.19 0.17 0.17 0.15 0.12 (0.02) (0.02) (0.02) (0.02) (0.01) (0.01) (0.01) (0.00) (0.01) (0.00) (0.00)

40-50 0.31 0.31 0.30 0.29 0.26 0.25 0.23 0.22 0.21 0.19 0.16 (0.02) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.00)

80-90 0.38 0.38 0.37 0.35 0.32 0.30 0.27 0.26 0.25 0.23 0.20 (0.01) (0.01) (0.00) (0.01) (0.01) (0.01) (0.01) (0.00) (0.00) (0.00) (0.00)

160-170 0.37 0.37 0.36 0.35 0.33 0.30 0.27 0.26 0.24 0.22 0.20 (0.01) (0.01) (0.01) (0.01) (0.00) (0.00) (0.00) (0.00) (0.00) (0.00) (0.00)


Table 11: Smoothed Brooks-Corey parameters (Eq. 1) for the Oakwood soil at the FRA site.

Soil pit Location Depth (cm)

theta-r theta-s psie b

1 Row Surface 0.09 0.44 4.9 2.6 15-20 0.10 0.42 7.9 3.4 Interrow Surface 0.11 0.43 10.6 2.5 15-20 0.07 0.32 17.7 5.3 40-50 0.07 0.36 5.2 8.1 80-90 0.00 0.38 11.1 13.4 160-170 0.04 0.38 11.3 10.4

2 Row Surface 0.07 0.43 5.9 3.2 15-20 0.11 0.41 7.7 2.4 Interrow Surface 0.09 0.38 10.4 3.1 15-20 0.09 0.30 19.0 4.0 40-50 0.00 0.31 6.7 12.2 80-90 0.10 0.38 8.1 7.7 160-170 0.07 0.37 12.3 7.9

Combined Row Surface 0.08 0.43 5.3 2.9 15-20 0.11 0.42 7.7 2.9 Interrow Surface 0.10 0.41 10.5 2.7 15-20 0.08 0.31 18.3 4.6 40-50 0.04 0.33 5.7 9.8 80-90 0.05 0.38 9.0 10.4 160-170 0.06 0.38 11.8 8.9

3.1.8 Near-saturated hydraulic conductivity data

The near-saturated soil hydraulic conductivity values obtained by disk permeameter measurements are presented in Table 12. The soil was reasonably permeable to the depth of measurement at 160 cm. Infiltration through the profile would be limited by the B21 and B22 horizons (40 cm measurements). The data suggest that these compacted horizons (cf. Table 7) would be the “throttle” for flow. The saturated conductivity, Ksat , was, however, still around 5 cm/h.

The variability of the measurements was high, with coefficients of variation around 30% to 80%. This is normal for disc permeameter measurements and we feel that the use of eight replicates was adequate to obtain a reasonable mean. From a statistical point of view, the values of the near-saturated conductivities for the B horizon all came from the same population, i.e. no significant differences were present between 40, 80 and 160 cm depth (for a given potential).

The high near-saturated hydraulic conductivity values of the A horizon reflected the structure of the surface soil. The conductivity values were reduced up to 8-fold in the interrows compared with the row data. Even so, Ksat was still around 10 cm/h for the surface soil in the interrows. Similar trends were found at 15 cm depth, but not as marked.

Figure 8 illustrates the marked increase in K near saturation and the difference between row and interrow positions. The four matric potential values (0, -1.5, -2.5, and -3.5 cm) were all above (wetter) the air-entry values (psie) that were obtained by fitting the Brooks-Corey functions to the water retention data (see Table 11). The observed increase in K was, therefore, not consistent with the Brooks-Corey description of the hydraulic conductivity (Section 2.6). An extra macro-pore function would have to be added on to the Brooks-Corey function to describe the sharp increase in conductivity due to macropores (see Section 2.6; Verburg et al., 1996).


Table 12: Near-saturated hydraulic conductivity (cm/h) of the Oakwood soil obtained from disk permeameter readings at the FRA site.

Potential (cm) Depth (cm) Surface 15 cm 40 cm 80 cm 160 cm Row Interrow Row Interrow

-3.5 2.6 1.2 7.7 2.0 0.60 0.85 1.0 (1.6) (0.3) (6.4) (1.5) (0.40) (0.27) (0.3)

-2.5 7.3 1.8 15.8 3.7 1.0 1.0 1.6 (3.9) (0.8) (12.6) (2.1) (0.3) (0.4) (0.5)

-1.5 24.6 4.8 19.3 8.3 3.1 2.3 3.4 (10.4) (1.6) (12.8) (4.7) (1.0) (0.8) (1.7)

01 85.7 10.8 41.2 17.4 8.7 4.7 6.8 (39.7) (5.9) (29.6) (11.0) (3.7) (2.6) (5.1)

1 extrapolation

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Figure 8: Effect of structure (macroporosity) on the relation between near-saturated matric potential and hydraulic conductivity; (a) 0-5 cm and (b) 15-20 cm layers of the Oakwood soil at the FRA site.


3.2 SCH site (Otoo sandy variant)

3.2.1 Site details

The SCH experimental site was established in August 1992 on the farm of Des Schulte on Moore Park Road. The first year of the cropping trial involved two replicates (Rep 1 and 2), which each received two irrigation treatments and four N fertiliser rates. The second year was limited to one irrigation regime, but with the original 4 N-rates each split into two treatments with or without new fertiliser.

In June 1993 some preliminary disk permeameter measurements were conducted in one subplot (no. 80, Rep 2) and some cores taken back to the lab for moisture retention measurements. A full physical characterisation was carried out in September 1993, approximately 6 weeks after harvest of the first crop. This characterisation consisted of measurements in and around two soil pits, one in subplot 26 (Rep 1) and one in subplot 86 (Rep 2). The soil pits were also used for a two-dimensional sampling of the bromide applied at the beginning of the trial (Verburg et al., 2002b).

In April 1994 an area of approximately 9 x 4.5 m2 inside the cane of Rep 2 was cut at ground level and removed. Within this area four short-term and two long-term bromide leaching experiments were carried out using a drip infiltrometer. More details about the bromide experiments, the two-dimensional sampling, and the cropping trial are provided in the second and third reports of this series (Verburg et al., 2002a,b).


The soil profile at the SCH site was not typical of the Otoo soil profile class as it had a sandy loam surface (Table 13). The typical A horizon of Otoo has a sandy clay loam to clay loam surface (see PAO site, Section 3.3). The profiles at the SCH site were, therefore, best described as an Otoo sandy variant. The two soil pits were similar with only slight differences in texture, colour and pH. A visual impression of the soil profile is provided in Fig. 9. This photo also shows the procedure of the two-dimensional soil sampling (see Verburg et al., 2002b). The blocks are 20 cm high and wide. The AP, A2 and B horizons are clearly discernible.

The Otoo soil is found on the plains and upper slopes and crests of rises on the sedimentary rocks of the Elliott formation (Robertson, 1979). Its surface soil is similar to the Kepnock soil (Yellow Dermosol) in that it is hard-setting when dry.

Figure 9: Photo of the Otoo sandy variant soil at the SCH site; also shown the markings for the 20x20 cm blocks for the two dimensional sampling.


Table 13: Profile description of the Otoo sandy variant soil at the SCH site; (a) first soil pit, and (b) second soil pit (by K.J. Smith, CSIRO Tropical Agriculture).

(a) MAPPING UNIT CODE: Ot SITE NO. CSIRO soil pit 1 A.M.G. REFERENCE: 428 871 mE 7 256 141 mN ZONE 56 (SCH site) GREAT SOIL GROUP: Red podzolic soil LANDFORM ELEMENT TYPE: Plain PRINCIPAL PROFILE FORM: Gn3.64 AUSTRALIAN SOIL CLASSIFICATION: Red Dermosol CONDITION OF SURFACE SOIL WHEN DRY: Hard setting

HORIZON DEPTH (cm) DESCRIPTION Ap 0 - 40 Dark greyish brown (10YR4/2); fine sandy loam; massive; dry; moderately

firm; few worm channels; few pieces charcoal; few patches of yellowish A2; common medium roots; pH6.0. Abrupt, wavy to –

A2e 40 - 80 Light yellowish brown (10YR5/4) (dry 10YR7/4); fine sandy clay loam; massive; dry; moderately strong; common medium yellowish orange mottles; few worm channels; few fine roots; pH 5.0. Gradual, smooth to –

B21 80 - 100 Yellowish brown (10YR5/6) with red (3YR4/8); medium clay; 5-10mm moderate angular blocky; dry; moderately strong; common medium ferruginous nodules near boundary with A2; pH 4.8. Diffuse to –

B22 100 - 160 Dark red (2.5YR3/6) with common distinct mottles of yellow (7.5YR6/6); medium to heavy clay; 5-10mm moderate to strong polyhedral; dry; moderately strong; common 2-20mm ferruginous nodules; few vertical yellow channels (drainage lines?); very few fine roots running down channels; pH 4.8.

(b) MAPPING UNIT CODE: Ot SITE NO. CSIRO Soil pit 2 A.M.G. REFERENCE: 428 871 mE 7 256 141 mN ZONE 56 (SCH site) GREAT SOIL GROUP: Red podzolic soil LANDFORM ELEMENT TYPE: Plain PRINCIPAL PROFILE FORM: Gn3.64 AUSTRALIAN SOIL CLASSIFICATION: Red Dermosol CONDITION OF SURFACE SOIL WHEN DRY: Hard setting

HORIZON DEPTH (cm) DESCRIPTION Ap 0 - 40 Dark greyish brown (10YR4/2); sandy loam; massive; dry; moderately firm;

few worm channels; few pieces charcoal; few patches of yellowish A2; common medium roots; pH6.5. Abrupt, wavy to –

A2e 40 - 78 Light yellowish brown (10YR5/4) (dry 10YR7/4); sandy clay loam; massive; dry; moderately strong; common medium yellowish orange mottles; few worm channels; few fine roots; pH 5.7. Gradual, smooth to –

B21 78 - 90 Yellowish brown (10YR5/8) with red (2.5YR5/8); medium to heavy clay; 5-10mm moderate angular blocky; dry; moderately strong; common medium ferruginous nodules near boundary with A2; very few fine roots; pH 5.5. Diffuse to –

B22 90 - 135 Red (2.5YR4/6) with common distinct mottles of brownish yellow (10YR6/6); medium to heavy clay; 5-10mm moderate to strong polyhedral; dry; moderately strong; common 2-20mm ferruginous nodules; few vertical yellow channels (drainage lines?); very few fine roots running down channels; pH 5.0. Diffuse to –

B23 135 - 160 Red (2.5YR4/6) with common distinct yellow and grey mottles; medium to heavy clay.



The particle size distributions of the A-horizons of both soil pits at the SCH site were similar, but at depth the soil in the second soil pit contains more clay and less gravel (Table 14).

Table 14: Particle size distribution of the Otoo sandy variant soil at the SCH site (Townsville analysis).

Soil pit Depth (cm) > 2 mm Coarse sand Fine sand Silt Clay (% of total) (% of < 2 mm fraction)

1 0-20 2 36 38 19 7 20-40 2 35 38 19 8 40-60 2 34 37 19 9 60-80 2 33 36 19 12 80-100 12 24 27 16 33 100-120 21 23 27 17 33 120-140 15 18 19 13 50

2 0-20 3 34 40 18 9 20-40 4 34 39 18 9 40-60 3 32 38 20 11 60-80 14 27 32 18 22 80-100 10 14 17 10 59 100-120 10 10 13 10 67 120-140 4 7 12 10 71


Electrical conductivities were determined on extracts of soil samples taken as part of the two dimensional sampling. The EC values were low (Table 15) as would be expected under a high rainfall regime plus supplementary irrigation. There was no significant change in pH during the trial, so an average profile is given (Table 16).

Table 15: Electrical conductivity (EC) of the Otoo sandy variant soil at the SCH site.

Depth (cm) EC (1:5 extract) (mS/cm) Soil pit 1 Soil pit 2

0-20 0.03 0.04 20-40 0.03 0.03 40-60 0.07 0.05 60-80 0.09 0.04

80-100 0.08 0.09 100-120 0.05 0.14 120-140 0.08 0.16

Table 16: Average pH at the SCH site (1992-1994).

Depth (cm) pH Average St. dev.

0-20 5.7 0.6 20-40 5.1 0.3 40-60 5.0 0.6 60-90 5.2 0.6 90-120 5.0 0.6

120-150 4.6 0.2 150-200 4.5 0.2 200-250 4.5 0.1 250-300 4.6 0.1


Exchangeable cations were determined on samples taken towards the end of the first cropping season (6th soil sampling) from three locations, two of which were inside the trial (Table 17).

Table 17: Exchangeable cations of the Otoo sandy variant soil at the SCH site (3 locations).

Location Depth (cm) Ca Mg Na K cmolc/kg of OD soil

Sample 0-20 0.21 0.17 0.07 0.16 near 20-40 0.07 0.09 0.10 0.63

weather 40-60 0.02 0.04 0.02 0.03 station 60-90 0.11 0.05 0.12 8.27

90-120 1.21 0.54 0.11 0.15 120-150 1.69 1.25 0.09 0.19 150-200 0.71 1.29 0.06 0.14 200-250 0.40 1.45 0.08 0.08 250-300 0.33 1.61 0.05 0.06 300-350 0.30 1.93 0.02 0.04

SL6 (1af) 0-20 1.65 0.27 0.07 0.10 (Rep 1) 20-40 0.38 0.06 0.03 0.06

40-60 0.34 0.09 0.05 0.02 60-90 0.53 0.11 0.01 0.02 90-120 3.05 0.98 0.13 0.04 120-150 1.58 1.52 0.13 0.03

SL6 (25af) 0-20 1.87 0.25 0.07 0.17 (Rep 1) 20-40 1.78 0.27 0.06 0.16

40-60 0.23 0.05 0.05 0.03 60-90 0.48 0.10 0.04 0.03 90-120 2.19 0.52 0.19 0.02 120-150 1.42 1.15 0.25 0.02


Bulk density cores were taken from the two soil pits during the September 1993 physical characterisation. The bulk density values obtained from these cores were very high (Table 18), especially in the sandy loam A and B21 horizons to about 1 meter depth. In the mottled, well structured, gravelly B22 horizon densities were lower. Note that soil pit 2 had a higher density at 100 cm depth than soil pit 1, but this had a higher variability associated with it.

Table 18: Bulk density of the Otoo sandy variant soil obtained from in situ samples in the soil pits at the SCH site.

Depth (cm) Bulk density (g/cm3) Soil pit 1 Soil pit 2 Combined

Average1 St. dev. Average1 St. dev. Average St. dev. Surface 1.812 1.692 1.75 20-30 1.87 0.04 1.75 0.07 1.81 0.08 60-70 1.83 0.05 1.82 0.03 1.82 0.04

100-110 1.56 0.04 1.76 0.08 1.66 0.12 160-170 1.60 0.06 1.62 0.04 1.61 0.05

1 Average over four replicates, except for surface layer. 2 Only one sample taken for surface layer.


During the first year of the cropping trial soil samples were taken from positions on the row and in the interrow, 1 and 2 m into the subplots. The number of cores taken from these positions varied throughout the season (see Verburg et al., 2002b). The cores were bulked to give three samples, one for the row 1 m into the subplot (af), one for the row 2 m into the subplot (bf), and one for the interrow (i). The medians of the bulk densities from all the soil samples obtained during the first season of the cropping trial (SCH1) are given in Table 19. There was not much difference between the various positions, although near the surface the bulk density was higher in the interrow, as would be expected given the traffic of farm machinery in the interrow and the presence of roots in the row. The “Average” was obtained by first averaging the two row positions (af and bf) and then averaging the row and interrow data. The latter calculation took into account two factors, representing the relative area corresponding to these two sampling positions (0.52 for row and 0.48 for interrow).

Table 19: Bulk density of the Otoo sandy variant soil obtained from soil samples taken during the first season of the cropping trial at the SCH site (SCH1). Sampling positions af, bf, and i are explained in the text.

Depth (cm) Bulk density (g/cm3) Median of af Median of bf Median of i "Average"

0-20 1.54 1.56 1.60 1.57 20-40 1.64 1.66 1.65 1.65 40-60 1.76 1.77 1.78 1.77 60-90 1.69 1.69 1.71 1.70

90-120 1.57 1.57 1.59 1.58 120-150 1.58 1.57 1.63 1.60

Comparison of the in situ bulk densities obtained in the soil pits with the median bulk densities in Table 19, shows that the former were much higher, especially near the surface (Fig. 10a). These in situ samples were taken in the interrow and, in addition, were taken only a few weeks after harvest. It is, therefore, possible that these high values were influenced by compaction due to harvesting traffic. Alternatively the differences may be due to different diameter cores and over-consolidation of the soil.

The various soil cores taken as part of the small scale bromide leaching experiments with the drip infiltrometer also resulted in bulk density data (Table 20). There were four short-term plots, around each of which background cores were taken and bulked. At the end of these short-term experiments, one 25-cm diameter core was taken from the middle of each plot. Two adjacent long-term plots were only sampled at the end of the experiments, using one 25-cm diameter core and three 4.5-cm cores in each plot. As these median bulk densities were rather variable but generally enveloping the “Average” of SCH1 (Fig. 10b), the “Field average” column is drawn by eye through the SCH1 “Average” data.


Table 20: Bulk density of the Otoo sandy variant soil obtained from soil cores taken as part of the small scale bromide leaching experiments with the drip infiltrometer at the SCH site and the best estimate “field average”.

Depth (cm) Bulk density (g/cm3) Background 4.5 cm cores 25 cm cores "Field average" median of 4 median of 6 Median of 6

0-10 1.50 1.58 1.39 1.54 10-20 1.67 1.65 1.55 1.59 20-30 1.74 1.59 1.54 1.63 30-40 1.74 1.64 1.70 1.68 40-50 1.82 1.69 1.73 1.75 50-60 1.83 1.75 1.59 1.77 60-70 1.63 1.79 1.81 1.73 70-80 1.76 1.62 1.97 1.70 80-90 1.57 1.72 1.73 1.66

90-100 1.47 1.48 1.68 1.62 100-120 1.28 1.57

0

20

40

60

80

100

120

140

160

1.0 1.2 1.4 1.6 1.8 2.0Bulk density (g/cm3)

De

pth

(cm

)

In situ, soilpit 1

In situ, soilpit 2

"Average" SCH1

Median, SCH2

0

20

40

60

80

100

120

140

160

1.0 1.2 1.4 1.6 1.8 2.0Bulk density (g/cm3)

De

pth

(cm

)

Background

4.5 cm cores

25 cm cores

''Field average''

(a) (b)

Figure 10: Comparison of bulk density data for the Otoo sandy variant soil at the SCH site: (a) in situ samples from the soil pits vs. average and median of samples taken during the SCH1 and SCH2 cropping seasons, (b) median bulk density of samples taken in the drip experiments.


At the SCH site samples for water retention determinations were taken on two occasions. In June 1993 samples were taken near the surface and at about 50 cm depth in subplot 80 of the cropping trial. This was followed up in September 1993 by sampling in two soil pits (1: subplot 86 in Rep 1, 2: subplot 26 in Rep 1) at intermediate and deeper depths. The measured water contents at different matric potentials are presented in Table 21. The data are averages of six (subplot 80) and four (soil pits) replicate measurements. Plots of the water retention curves are shown in Fig. 11. Also shown in Fig. 11 are the Brooks-Corey fits to the data. The fitted Brooks-Corey parameters are given in Table 22 and 23.


0

0.1

0.2

0.3

0.4

0.5

0 1 2 3 4 5log (suction, cm)

Vo

l. w

ate

r c

on

t. (

m3/m

3)

1-4 cm

5-8 cm

Plot 80, surface

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ate

r c

on

t. (

m3/m

3)

pit 1 pit 2

20-30 cm

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ate

r co

nt.

(m

3/m

3)

pit 1 pit 2

60-70 cm

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ate

r c

on

t. (

m3/m

3)

pit 1 pit 2

100-110 cm

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ate

r c

on

t. (

m3/m

3)

pit 1 pit 2

160-170 cm

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ate

r co

nt.

(m

3/m

3)

51-54 cm

55-58 cm

Plot 80, A2 horizon

Figure 11: Brooks-Corey fits of water retention data for the Otoo sandy variant soil at the SCH site.


Table 21: Water retention data for the Otoo sandy variant soil at the SCH site. Values represent average volumetric water contents (six replicate measurements for the subplot 80 samples and four replicates for the samples from the two soil pits*, standard deviations are given in parentheses)

Location Depth (cm) Matric potential (cm) 1 3 10 20 50 100 330 667 1000 3000 15000

Subplot 80 1-4 0.29 0.28 0.28 0.27 0.23 0.20 0.17 0.14 0.13 0.09 0.06 (0.02) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.00) (0.00) (0.00)

Subplot 80 5-8 0.35 0.34 0.33 0.31 0.23 0.19 0.16 0.14 0.12 0.09 0.06 (0.03) (0.02) (0.02) (0.02) (0.01) (0.01) (0.00) (0.00) (0.00) (0.00) (0.00)

Soil pit 1 20-30 0.28 0.27 0.25 0.25 0.22 0.19 0.17 0.15 0.13 0.09 0.06 (0.01) (0.01) (0.02) (0.02) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.00)

Soil pit 2 20-30 0.30 0.29 0.27 0.27 0.23 0.19 0.16 0.14 0.13 0.09 0.06 (0.02) (0.02) (0.01) (0.02) (0.01) (0.01) (0.01) (0.01) (0.01) (0.00) (0.00)

Subplot 80 51-54 0.25 0.25 0.24 0.23 0.20 0.19 0.17 0.15 0.14 0.10 0.08 (0.03) (0.03) (0.02) (0.02) (0.01) (0.01) (0.00) (0.00) (0.01) (0.01) (0.01)

Subplot 80 55-58 0.25 0.25 0.23 0.22 0.20 0.18 0.17 0.15 0.14 0.10 0.08 (0.05) (0.05) (0.03) (0.02) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01)

Soil pit 1 60-70 0.30 0.29 0.25 0.24 0.21 0.19 0.17 0.15 0.13 0.09 0.07 (0.04) (0.03) (0.02) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01)

Soil pit 2 60-70 0.26 0.26 0.23 0.22 0.19 0.18 0.16 0.14 0.13 0.09 0.06 (0.02) (0.02) (0.02) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.00)

Soil pit 1 100-110 0.47 0.45 0.42 0.41 0.40 0.38 0.37 0.36 0.36 0.35 0.33 (0.05) (0.04) (0.02) (0.02) (0.02) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01)

Soil pit 2 100-110 0.37 0.36 0.34 0.34 0.32 0.31 0.30 0.29 0.29 0.27 0.26 (0.03) (0.03) (0.03) (0.03) (0.03) (0.03) (0.03) (0.03) (0.03) (0.03) (0.02)

Soil pit 1 160-170 0.49 0.47 0.43 0.42 0.40 0.38 0.37 0.36 0.36 0.35 0.34 (0.05) (0.04) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01)

Soil pit 2 160-170 0.43 0.42 0.39 0.39 0.37 0.35 0.34 0.34 0.33 0.32 0.30 (0.03) (0.03) (0.02) (0.02) (0.02) (0.02) (0.02) (0.02) (0.02) (0.02) (0.03)

* Soil pit 1 was located in subplot 86 (Rep 2) and soil pit 2 in subplot 26 (Rep 2).


The water retention curves in the top soil (Fig. 11) were similar for the two soil pits and also for the different depths. The main differences between depths were near saturation (< 10 cm suction). The differences near saturation between the samples from 1-4 and 5-8 cm depth were similar to the findings at the FRA site (Section 3.1) and likely due to macropores. In the subsoil the differences between the two pits were larger and the curves flatter due to the heavier texture of the material.

Table 22: Smoothed Brooks-Corey parameters (Eq. 1) for the Otoo sandy variant soil at the SCH site (subplot 80).

Location Depth (cm) theta-r theta-s psie b Subplot 80 1-4 0.00 0.28 21.0 4.6

5-8 0.00 0.34 11.1 4.2 51-54 0.00 0.25 19.5 6.4 55-58 0.00 0.24 10.1 7.5

Table 23: Smoothed Brooks-Corey parameters (Eq. 1) for the Otoo sandy variant soil at the SCH site (soil pits).

Location Depth (cm) theta-r theta-s psie b Soil pit 1 20-30 0.00 0.27 15.4 5.5

60-70 0.00 0.30 4.6 6.4 100-110 0.00 0.47 0.6 26.5 160-170 0.00 0.49 0.5 23.9

Soil pit 2 20-30 0.00 0.29 15.1 4.9 60-70 0.00 0.26 5.4 6.7 100-110 0.00 0.37 1.6 26.4 160-170 0.00 0.44 0.6 25.9

Combined 20-30 0.00 0.28 15.1 5.2 60-70 0.00 0.30 5.0 6.5 100-110 0.00 0.42 0.8 26.7 160-170 0.00 0.47 0.6 24.8


During the preliminary physical characterisation in subplot 80 (June 93), disk permeameter measurements were made in three positions: on the surface in the row and interrow and at 50 cm depth. The interrow measurements included the effect of a surface crust. This reduced the hydraulic conductivity significantly (Table 24). However, even if this surface crust was broken, the limitation for flow would be in the deeper horizons, with a maximum hydraulic conductivity of less than 3 cm/h at 50 cm depth.

Additional disk permeameter measurements were made in and around the soil pits a few months later (September 93). In this case the measurements were all carried out in the interrow. The results (Table 25) show that the hydraulic conductivity at higher tensions (-3.5, -2.5 cm H2O) down the profile was quite low, and the limiting layer was around 20 cm depth in the A horizon. At zero tension, Ksat was limited by the surface soil, at around 0.4 - 1.0 cm/h. In the B21 horizon it increased to 1.6-2.5 cm/h and reached a maximum in the lateritic B22 horizon of 3.0 - 5.0 cm/h. Note that there was no significant effect of surface crusting. The hydraulic properties of the two soil pits were similar, so that we could assume the whole field was uniform for modelling purposes.

Overall the June and September data compared quite well. Especially the data from soil pit 1, which was at a neaby location. For example the 20 cm depth (Table 25) compared well with the interrow data in June (Table 24) and the 60 cm depth data from September matched those of the 50 cm depth in June.


Table 24: Near-saturated hydraulic conductivity (cm/h) of the Otoo sandy variant soil obtained from disk permeameter readings in subplot 80 of the cropping trial at the SCH site (values represent averages of eight replicates, standard deviations in parentheses).

Potential (cm) Depth (cm) Surface 50 cm Row Interrow

-3.5 0.70 0.42 0.36 (0.88) (0.25) (0.07)

-2.5 0.85 0.63 0.58 (0.27) (0.29) (0.20)

-1.5 3.48 1.04 1.34 (1.52) (0.50) (0.49)

01 13.1 1.87 2.81 (10.4) (1.72) (1.19)

1 extrapolation

Table 25: Near-saturated hydraulic conductivity (cm/h) of the Otoo sandy variant soil obtained from disk permeameter readings in and around the two soil pits at the SCH site (values represent averages of eight replicates, standard deviations in parentheses).

Soil pit Potential (cm) Depth (cm) Surface 20 cm 60 cm 100 cm 160 cm crust no crust

1 -3.5 0.23 0.29 0.14 0.29 0.44 0.46 (0.10) (0.15) (0.06) (0.17) (0.13) (0.17)

-2.5 0.34 0.35 0.16 0.55 0.79 0.62 (0.13) (0.21) (0.07) (0.26) (0.34) (0.20)

-1.5 0.57 0.55 0.58 1.26 1.63 1.47 (0.16) (0.24) (0.23) (0.47) (0.38) (0.84)

01 1.06 0.78 1.83 2.56 3.38 3.23 (0.49) (0.42) (1.16) (1.04) (1.15) (2.55)

2 -3.5 0.26 0.25 0.10 0.31 0.69 0.56 (0.09) (0.07) (0.04) (0.09) (0.36) (0.32)

-2.5 0.27 0.32 0.19 0.37 1.11 0.94 (0.20) (0.08) (0.09) (0.09) (0.42) (0.47)

-1.5 0.50 0.35 0.32 0.86 2.59 1.87 (0.13) (0.06) (0.17) (0.24) (1.32) (0.74)

01 0.77 0.45 0.72 1.64 5.68 3.79 (0.23) (0.11) (0.44) (0.63) (3.34) (1.80)

1 extrapolation


3.3 PAO site (Otoo)

3.3.1 Site details

The fallow PAO site was used from December 1995 to March 1996 for a bromide leaching experiment and a drainage experiment. It was selected because of its similar soil properties to the SCH site. It was the best alternative for experiments complementary to those presented in Section 3.2, as we were unsuccessful at the time in finding a fallow field with the same soil properties as the SCH site on the farm of Des Schulte. The PAO site was on the farm of Dean De Paoli on Horsleys Road. Soil physical characterisation was limited to the surface layer. Details of the experiments are described in the second report of this series (Verburg et al., 2002a).


As no soil pit was dug at the PAO site, the profile description (Table 26) was based on a soil core taken next to the experimental plots. The soil was similar to that at the SCH site, but the A horizon was less sandy and the transition to heavier texture subsoil was at a shallower depth (40 cm vs. 80 cm, cf. Table 13).

The Otoo soil is found on the plains and upper slopes and crests of rises on the sedimentary rocks of the Elliott formation (Robertson, 1979). Its surface soil is similar to the Kepnock soil (Yellow Dermosol) in that it is hard-setting when dry.

Table 26: Profile description of the Otoo soil at the PAO site (by P.R. Zund, DNR).

MAPPING UNIT CODE: Ot SITE NO.: 703 A.M.G. REFERENCE: 425 752 mE 7 256 463 mN ZONE 56 GREAT SOIL GROUP: Red podzolic soil LANDFORM ELEMENT TYPE: Plain PRINCIPAL PROFILE FORM: Gn3.71P LANDFORM PATTERN TYPE: Gently undulating plains AUSTRALIAN SOIL CLASSIFICATION: Red Dermosol CONDITION OF SURFACE SOIL WHEN DRY: Hard setting

HORIZON DEPTH (cm) DESCRIPTION AP 0 - 40 Greyish yellow-brown (10YR4/2); fine sandy clay loam; massive; moderately

moist; moderately weak. Clear to – B11 40 - 55 Yellowish brown (10YR5/6); light clay; massive; moderately moist;

moderately weak. B12 55 - 80 Bright brown (7.5YR5/6); few medium distinct red mottles; light clay; weak

2-5mm subangular blocky; moderately moist; moderately weak; common medium ferruginous nodules. Gradual to –

B2 80 - 140 Bright reddish brown (5YR5/6); many medium prominent red mottles, medium prominent yellow mottles; light clay; strong 2-5mm polyhedral; moderately moist; moderately firm; common medium ferruginous nodules.


As no soil pit was dug at the site, particle size was only obtained for the surface layer (Table 27). The analysis was similar to that of the surface layer of the soil at the SCH site (Table 14). The percentages of clay, silt, and sand matched well, but the proportion of fine sand to coarse sand was higher at the PAO site.

Table 27: Particle size distribution of the Otoo soil at the PAO site (Townsville analysis).

Depth (cm) > 2 mm Coarse sand Fine sand Silt Clay (% of total) (% of < 2 mm fraction)

10 1 27 47 17 9



Organic carbon was only determined for the surface layer. The resulting 0.73 % C was an estimate of total organic carbon content, because the Townsville analysis employed Heanes wet oxidation (see Section 2.3).


In situ samples for bulk density were only obtained for the surface layer (Table 28). The average in situ bulk density value compared well with the bulk density data obtained from the soil cores that were taken as part of the bromide leaching experiments (Fig. 12). These are reported as the bulk densities of the bulked background cores taken at the beginning of the experiment, and the medians of samples taken during and at the end of the experiments (Table 29). As explained in Section 2.4 these data suffered from errors due to inaccurate sectioning of the cores. Despite this, the bulk density profile with depth was reasonably well defined. The best estimate “field average” curve was drawn by eye in Fig. 12.

Comparison of the “field averages” of the soils at the PAO and SCH sites (Fig. 10 and 12), confirms that the transition to heavier textured subsoil occurs at a shallower depth at the PAO site than at the SCH site.

0

20

40

60

80

100

120

140

160

180

1.0 1.2 1.4 1.6 1.8 2.0

Bulk density (g/cm3)

De

pth

(cm

)

In situ

Background

Median

SCH

"Field average"

Figure 12: Comparison of bulk density data for the Otoo soil at the PAO site; also shown is the best estimate “field average” of the Otoo soil at the SCH site.

Table 28: Bulk density of the Otoo soil obtained from in situ samples near the soil surface at the PAO site.

Depth (cm) Bulk density (g/cm3) Rep 1 Rep 2 Average

10-15 1.66 1.55 1.61


Table 29: Bulk density of the Otoo soil obtained from soil cores taken as part of the bromide leaching experiments at the PAO site and the best estimate “field average”.

Depth (cm) Bulk density (g/cm3) bulked median of "Field background 16 samples average"

0-5 1.49 1.33 1.35 5-10 1.44 1.50 1.50 10-20 1.85 1.62 1.62 20-30 1.73 1.76 1.76 30-40 1.70 1.83 1.80 40-50 1.67 1.74 1.70 50-60 1.57 1.59 1.59 60-70 1.50 1.46 1.48 70-80 1.35 1.43 1.40

80-100 1.48 1.58 1.53 100-120 1.58 1.53 1.58 120-140 1.58 1.73 1.62 140-160 1.65 1.65 160-180 1.68 1.68


The water retention data for the surface layer of the Otoo soil at the PAO site (Table 30, Fig. 13) corresponded well with those determined for the surface layers at the SCH site (compare Table 31 with Tables 22 and 23).

Table 30: Water retention data for the Otoo soil at the PAO site. Values represent average volumetric water contents (four replicates, standard deviations in parentheses).

Depth (cm) Matric potential (cm) -1 -3 -10 -30 -100 -330 -1000 -3000 -15000

10-15 0.36 0.36 0.34 0.32 0.23 0.18 0.14 0.10 0.06 (0.06) (0.06) (0.03) (0.02) (0.02) (0.01) (0.01) (0.01) (0.00)

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ater

co

nt.

(m

3 /m3 ) 10 cm

Figure 13: Brooks-Corey fit of water retention data for the Otoo soil at the PAO site .

Table 31: Smoothed Brooks-Corey parameters (Eq. 1) for the Otoo soil at the PAO site.

Depth (cm) theta-r theta-s psie b 10-15 0.00 0.35 20.0 4.0



The hydraulic conductivity data obtained for the Otoo soil at the PAO site were somewhat higher than those measured at the SCH site in and around the soil pits (compare Table 32 and Table 25). They were intermediate to the row and interrow values obtained in subplot 80 of the SCH cropping trial (Table 24). As the hydraulic conductivity of surface layers is highly dependent on factors such as rainfall and surface management prior to the measurements, these differences are not unreasonable.

Table 32: Near-saturated hydraulic conductivity (cm/h) of the Otoo soil obtained from disk permeameter readings at the PAO site (values represent averages of eight replicates, standard deviations in parentheses).

Potential (cm) Depth (cm) 10 cm

-3.5 0.36 (0.42)

-2.5 1.1 (0.4)

-1.5 6.0 (3.3)

01 31.3 (27.3)

1 extrapolation


3.4 SFF site (Gooburrum)

3.4.1 Site details

The SFF site was located along the same road as the PAO site (Horsleys Road) on the farm of Ron Schiffke. It was, however, part of a different mapping unit (Gooburrum) on the local soils map. The site was in use from December 1995 until March 1996 and was in fallow condition during this time. It consisted of four bromide leaching plots, a drainage plot and a soil pit (March 1996) for soil physical characterisation. More information about the experiments and their results can be found in the second report of this series (Verburg et al., 2002a).


The profile description of the Gooburrum soil at the SFF site is given in Table 33, with a photo of the soil profile in Fig. 14. The Gooburrum soil is found on the plains and upper slopes and crests of rises on the sedimentary rocks of the Elliott formation (Robertson, 1979). The structured B2 horizon distinguishes it from the Kandosol. Its soil colour is a stronger red indicating that the soil is better drained than the Otoo soil.

Table 33: Profile description of the Gooburrum soil at the SFF site (by P.R. Zund, DNR).

MAPPING UNIT CODE: Gb SITE NO.: BAB 9003 A.M.G. REFERENCE: 426 930 mE 7 256 130 mN ZONE 56 GREAT SOIL GROUP: Red podzolic soil LANDFORM ELEMENT TYPE: Plain PRINCIPAL PROFILE FORM: Gn3.12p LANDFORM PATTERN TYPE: Gently undulating plains AUSTRALIAN SOIL CLASSIFICATION: Red Dermosol SLOPE: 1% CONDITION OF SURFACE SOIL WHEN DRY: Firm

HORIZON DEPTH (cm) DESCRIPTION AP1 0 - 20 Dark brown (10YR3/3); sandy loam; massive; dry; moderately weak. Clear,

wavy to – AP2 20 - 45 Dull yellowish brown (10YR4/3), bright brown (7.5YR5/6); sandy clay loam;

massive. Clear, wavy to – A3 45 - 80 Bright brown (7.5YR5/6); sandy clay loam; massive; moderately moist;

moderately weak; very few fine ferruginous nodules. Gradual, wavy to – B1 80 - 95 Reddish brown (2.5YR4/6); common medium faint red mottles; clay loam;

weak 2-5mm subangular blocky; moderately moist; moderately weak; few medium ferruginous nodules. Gradual, wavy to –

B2 95 - 140 Dark reddish brown (2.5YR3/6); light clay; strong 2-5 mm polyhedral; moist; moderately weak; very many medium ferruginous nodules.


Particle size distributions were determined by two laboratories. The depths of the samples analysed in Townsville corresponded with the depths of the water retention determinations and the disk permeameter measurements (Table 34). The samples analysed by DNR were part of the soil survey, which used standard depth, unless these occurred on layer boundaries (Table 35). The two analyses matched reasonably well. The proportion fine to coarse sand was slightly higher in the DNR analysis of the surface layers, but silt and clay contents corresponded well.


Figure 14: Photo of the Gooburrum soil at the SFF site (photo by P.R. Zund).

Table 34: Particle size distribution of the Gooburrum soil at the SFF site (Townsville analysis).


10-15 < 1 50 31 13 7 50-55 < 1 47 30 13 10

161-166 4 22 11 7 60

Table 35: Particle size distribution of the Gooburrum soil at the SFF site (DNR analysis).

Depth (cm) Coarse sand Fine sand Silt Clay (% of < 2 mm fraction)

0-10 44 36 12.0 9 20-30 49 35 7 11 50-60 43 34 14 10 80-90 37 29 9 23

110-120 17 12 6 65



Organic carbon contents of three samples were measured in Townsville (Table 36). A complete chemical analysis was carried out for the samples that were taken as part of the DNR soil survey (Table 37). The organic carbon contents given in Table 36 are not directly comparable with those reported in Table 37, as different methods were used (Walkley & Black in DNR analysis vs. Heanes in Townsville analysis). Strictly speaking the Heanes method should result in higher values, as it ensures complete oxidation of OC, whereas the Walkley & Black method generally only achieves recoveries of 75-80% depending on soil type and depth (Rayment and Higginson, 1992). In this case the lower value reported in Table 36 could be due to the slightly deeper depth of sampling, because organic carbon content usually decreases sharply with depth.

Table 36: Organic carbon of the Gooburrum soil at the SFF site (Townsville analysis).

Depth (cm) % C 10-15 0.76 50-55 0.19

161-166 0.25


Table 37: Chemical analysis of the Gooburrum soil at the SFF site (method description in Table 2).

Total element Depth pH-H2O EC Cl 15 Bar R1 P K S pH-CaCl2 OrgC TotN

cm mS/cm mg/kg % mg/kg % % B 0-10 5.7 0.04 BQ 4.6 1.4 .08 0-10 6.3 0.03 BQ 3 0.74 0.031 0.042 0.013 4.6

10-20 6.0 0.02 BQ 4.7 20-30 5.5 0.03 BQ 3 0.80 0.018 0.042 0.013 4.3 50-60 4.6 0.04 BQ 3 0.22 0.006 0.037 0.014 4.1 80-90 5.2 0.04 0.002 7 0.15 0.007 0.039 0.010 4.8

110-120 6.1 0.07 0.006 0.012 0.090 0.019 6.0

HCl extractable DTPA extractable Exchangeable cations Depth Acid P Bic P K Fe Mn Cu Zn SO4-S ECEC Ca Mg Na K

cm mg/kg mg/kg cmolc/kg mg/kg mg/kg cmolc/kg cmolc/kg B 0-10 7.0 7.0 0.18 51.0 10.0 0.09 0.31 4.0 0-10 2 1.3 0.87 0.07 0.10

10-20 20-30 1 0.54 0.53 0.06 0.01 50-60 1 0.14 0.62 0.06 0.01 80-90 2 0.99 0.70 0.11 0.02

110-120 6 1.8 4.3 0.28 0.03 B = subsample from nine bulked samples taken from a triangle around the site < 50 m from the site; BQ = below limit of quantification.



The bulk density data obtained from the two different sources (in situ Table 38, derived from soil cores Table 39) matched well at the SFF site (Fig. 15). This suggests that the sampling frequency minimised the effects of inaccuracies of sectioning of the soil cores resulting in a smooth bulk density depth profile.

Table 38: Bulk density of the Gooburrum soil obtained from in situ samples in the soil pit at the SFF site.


10-15 1.59 1.57 1.58 50-55 1.64 1.79 1.71

161-166 1.55 1.66 1.61

Table 39: Bulk density of the Gooburrum soil obtained from soil cores taken as part of the bromide leaching experiments at the SFF site and the best estimate “field average”.


0-5 1.32 1.47 1.47 5-10 1.24 1.54 1.54 10-20 1.55 1.73 1.70 20-30 1.72 1.77 1.77 30-40 1.76 1.79 1.79 40-50 1.83 1.79 1.78 50-60 1.72 1.74 1.73 60-70 1.70 1.72 1.72 70-80 1.70 1.70 1.70

80-100 1.61 1.54 1.56 100-120 1.53 1.55 1.54 120-140 1.60 1.65 1.62 140-160 1.72 1.62

0

20

40

60

80

100

120

140

160

180

1.0 1.2 1.4 1.6 1.8 2.0


De

pth

(cm

)

In situ

Background

Median

"Field average"

Figure 15: Comparison of bulk density data for the Gooburrum soil at the SFF site.



The water retention data for the Gooburrum soil (Table 40, 41 and Fig. 16) highlighted the marked differences between the A and B horizons. In particular the slopes of the curves (b) were notably different. The different water retention characteristics matched the differences in structure (massive vs. structured; Table 33) and in particle size distribution (low vs. high clay content; Tables 34 and 35). As a result, the clayey subsoil had a higher saturated water content and a slower decrease in water content with increasing suction (Fig. 16). The 15000 cm (15 Bar) gravimetric water contents measured as part of the chemical analysis (Table 37) corresponded well with the gravimetric water contents that formed the basis of Table 40 (data not shown).

Table 40: Water retention data for the Gooburrum soil at the SFF site. Values represent average volumetric water contents (four replicates, standard deviations in parentheses).


10-15 0.32 0.32 0.31 0.23 0.17 0.13 0.10 0.08 0.05 (0.03) (0.02) (0.02) (0.02) (0.01) (0.01) (0.00) (0.00) (0.00)

50-55 0.27 0.26 0.25 0.20 0.16 0.13 0.10 0.08 0.06 (0.02) (0.02) (0.02) (0.01) (0.01) (0.01) (0.01) (0.01) (0.01)

161-166 0.41 0.41 0.40 0.39 0.37 0.36 0.34 0.33 0.30 (0.03) (0.03) (0.03) (0.03) (0.02) (0.02) (0.02) (0.02) (0.02)

Table 41: Smoothed Brooks-Corey parameters (Eq. 1) for the Gooburrum soil at the SFF site.

Depth (cm) theta-r theta-s psie b 10-15 0.01 0.32 8.6 3.7 50-55 0.00 0.27 7.3 5.1

161-166 0.00 0.41 10.2 25.0

0

0.1

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0.4

0.5


Vo

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ater

co

nt.

(m

3 /m3 ) 10 cm

0

0.1

0.2

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0.4

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Vo

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ater

co

nt.

(m

3 /m3 ) 50 cm

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ater

co

nt.

(m

3 /m3 ) 161 cm

Figure 16: Brooks-Corey fits of water retention data for the Gooburrum soil at the SFF site



The trends in hydraulic conductivity with depth were highly dependent on the matric potential. At saturation the lowest conductivity was observed in the subsoil, whereas at higher suctions, the surface soil limited the flow. This illustrates the marked effect of macropores on hydraulic conductivity near saturation (Fig. 17). These are not captured by the Brooks-Corey model because the increases occur below the air-entry point (psie in Table 41).

Table 42: Near-saturated hydraulic conductivity (cm/h) of the Gooburrum soil obtained from disk permeameter readings at the SFF site (values represent averages of eight replicates, standard deviations in parentheses).

Potential (cm) Depth (cm) 10 cm 50 cm 161 cm

-3.5 0.43 0.97 1.1 (0.40) (0.76) (0.4)

-2.5 0.64 1.7 1.7 (0.60) (1.4) (0.5)

-1.5 5.5 4.1 3.8 (3.1) (2.3) (0.9)

01 36.4 10.3 7.5 (30.6) (6.1) (2.4)

1 extrapolation

0

5

10

15

20

25

30

35

40

-4-3-2-10


Co

nd

uct

ivit

y (c

m/h

)

0

5

10

15

20

25

30

35

40

-4-3-2-10Matric potential (cm)

Co

nd

uct

ivit

y (c

m/h

)

(a ) (b)

Figure 17: Effect of structure (macroporosity) on the relation between near-saturation matric potential and hydraulic conductivity of the Gooburrum soil at the SFF site; (a) 10 cm and (b) 161 cm depth.


3.5 TOW site (Alloway)

3.5.1 Site details

The TOW site was located at the end of Vecellios Road on a block of land belonging to the Townson family. From December 1995 until March 1996 it was used for bromide leaching experiments. In March 1996 a soil pit was dug for soil physical characterisation and a drainage experiment carried out. Details and results of the experiments are reported in the second report in this series (Verburg et al., 2002a).


A photo of the Alloway soil at the TOW site is presented in Fig. 18, with the corresponding profile description in Table 43. The Alloway soil is found in drainage depressions of plains and lower slopes of rises on the sedimentary rocks of the Elliott formation.

Table 43: Profile description of the Alloway soil at the TOW site (by P.R. Zund, DNR).

MAPPING UNIT CODE: Al SITE NO.: BAB 9004 A.M.G. REFERENCE: 421 350 mE 7 261 580 mN ZONE 56 GREAT SOIL GROUP: Gleyed podzolic soil LANDFORM ELEMENT TYPE: Plain PRINCIPAL PROFILE FORM: Dg2.42 LANDFORM PATTERN TYPE: Plain AUSTRALIAN SOIL CLASSIFICATION: Chromosolic Redoxic Hydrosol SLOPE: 1% CONDITION OF SURFACE SOIL WHEN DRY: Hardsetting

HORIZON DEPTH (cm) DESCRIPTION Ap 0 - 25 Brownish grey (10YR5/1); sandy loam; massive; dry; very weak. Clear, wavy

to – A21e 25 - 50 Dull yellowish orange (10YR7/2); sandy loam; massive; dry; very weak.

Abrupt, wavy to – A22e 50 - 70 Pale yellow (2.5Y8/3); few medium distinct yellow mottles; sandy loam;

massive; moderately moist; very weak; few coarse ferruginous nodules. Gradual, wavy to –

A23e 70 - 95 Pale yellow (2.5Y8/4); common medium distinct brown mottles; sandy loam; massive; moderately moist; very weak; few coarse ferruginous nodules. Gradual, wavy to –

B2 95 - 140 Light grey (10YR8/1); many medium distinct brown and red mottles; light clay; strong 2-5mm polyhedral; moderately moist; moderately weak; very many coarse ferruginous nodules.


The two analyses of particle size distribution (Tables 44 and 45) corresponded fairly well for matching layers. The Townsville analysis unfortunately did not include a sample of the B2 horizon, which had a much higher clay content.

Table 44: Particle size distribution of the Alloway soil at the TOW site (Townsville analysis).


10-15 4 28 53 13 6 30-35 3 28 54 12 6 75-80 9 25 45 14 17


Figure 18: Photo of the Alloway soil at the TOW site (photo by P.R. Zund).

Table 45: Particle size distribution of the Alloway soil at the TOW site (DNR analysis).


0-10 25 56 13 10 50-60 26 58 8 8 80-90 24 51 13 10

110-120 18 28 7 44


Organic carbon contents as measured in Townsville are presented in Table 46. The results of the complete chemical analysis of the samples analysed by DNR are presented in Table 47.

Table 46: Organic carbon of the Alloway soil at the TOW site (Townsville analysis).

Depth (cm) % C 10-15 N/A 30-35 0.31 75-80 0.21


Table 47: Chemical analysis of the Alloway soil at the TOW site (method description in Table 2).


cm mS/cm mg/kg % mg/kg % % B 0-10 5.6 0.03 BQ 4.2 1.8 0.06 0-10 6.6 0.05 BQ 3 0.44 0.025 0.053 0.022 5.6

10-20 7.0 0.04 BQ 5.6 30-40 6.8 0.02 BQ 5.7 50-60 7.2 0.01 BQ 1 0.77 0.003 0.019 0.008 5.6 80-90 6.5 0.01 BQ 2 0.81 0.005 0.045 0.026 5.6

110-120 6.3 0.04 .002 0.010 0.080 0.016 5.6


cm mg/kg mg/kg cmolc/kg mg/kg mg/kg cmolc/kg cmolc/kg B 0-10 6.0 4.0 0.08 74.0 15.0 0.06 0.60 4.0 0-10 4 2.4 1.1 0.06 0.12

10-20 30-40 50-60 1 0.31 0.81 0.04 0.01 80-90 1 0.25 0.74 0.05 0.01




Bulk density values of the Alloway soil at the TOW site were extremely high in the subsoil (Table 49). This is most likely due to the many coarse ferruginous nodules found in this horizon (B2, see Table 43). These bulk density values should therefore not be used or calculatin of porosity without a correction for the coarse fragments. The very low bulk density values in the surface 20 cm of the bulked background were caused by recent tillage and were ignored when establishing the best estimate “field average”. The different bulk density values (Table 48 and 49) corresponded reasonably well and provided a clear picture of the changes in bulk density with depth (Fig. 19).

Table 48: Bulk density of the Alloway soil obtained from in situ samples in the soil pit at the TOW site.


10-15 1.44 1.31 1.37 30-35 1.78 1.69 1.74 75-80 1.89 1.71 1.80

Table 49: Bulk density of the Alloway soil obtained from soil cores taken as part of the bromide leaching experiments at the TOW site and the best estimate “field average”.


0-5 0.81 1.23 1.23 5-10 0.76 1.24 1.30 10-20 1.04 1.33 1.43 20-30 1.49 1.63 1.63 30-40 1.74 1.76 1.76 40-50 1.66 1.68 1.68 50-60 1.63 1.62 1.62 60-70 1.82 1.61 1.61 70-80 1.83 1.61 1.80

80-100 1.57 2.14 2.14 100-120 1.39 2.18 2.18 120-140 2.24 2.19 2.19 140-160 2.23 2.23

0

20

40

60

80

100

120

140

160

0.6 1.0 1.4 1.8 2.2


De

pth

(cm

)

In situ

Background

Median

"Field average"

Figure 19: Comparison of bulk density data for the Alloway soil at the TOW site.



The water retention curves for the three depths that were analysed at the TOW site differed only slightly in slope (b) (Table 51, and Fig. 20). The saturated water content was much higher in the surface layer than in the other two layers. The missing sample for the B2 layer subsoil would presumably have had a much higher b value, possibly similar to that of the Gooburrum subsoil (Section 3.4). The 15000 cm (15 Bar) gravimetric water contents measured as part of the chemical analysis corresponded well with the gravimetric water contents that formed the basis of Table 50 (data not shown).

Table 50: Water retention data for the Alloway soil at the TOW site. Values represent average volumetric water contents (four replicates, standard deviations in parentheses).


10-15 0.48 0.47 0.46 0.33 0.20 0.15 0.10 0.09 0.05 (0.09) (0.08) (0.08) (0.02) (0.00) (0.00) (0.00) (0.01) (0.00)

30-35 0.29 0.29 0.29 0.26 0.19 0.15 0.11 0.08 0.05 (0.02) (0.02) (0.02) (0.02) (0.01) (0.01) (0.01) (0.01) (0.01)

75-80 0.33 0.33 0.32 0.26 0.19 0.14 0.09 0.07 0.05 (0.03) (0.03) (0.03) (0.01) (0.02) (0.02) (0.02) (0.02) (0.02)

Table 51: Smoothed Brooks-Corey parameters (Eq. 1) for the Alloway soil at the TOW site.

Depth (cm) theta-r theta-s psie b 10-15 0.04 0.47 11.6 2.3 30-35 0.00 0.29 18.4 4.0 75-80 0.00 0.33 13.5 3.6

0

0.1

0.2

0.3

0.4

0.5


Vo

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ater

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(m

3 /m3 ) 10 cm

0

0.1

0.2

0.3

0.4

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Vo

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ater

co

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(m

3 /m3 ) 30 cm

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ater

co

nt.

(m

3 /m3 ) 75 cm

Figure 20: Brooks-Corey fits of water retention data for the Alloway soil at the TOW site



The hydraulic conductivity values of the three depths were not unlike those of the Gooburrum soil at the SFF site (compare Table 52 and 42). Data on the B2 layer subsoil were, however, lacking.

Table 52: Near-saturated hydraulic conductivity (cm/h) of the Alloway soil obtained from disk permeameter readings at the TOW site (values represent averages of eight replicates, standard deviations in parentheses).


-3.5 0.90 1.2 5.2 (0.79) (0.6) (1.8)

-2.5 3.6 1.6 5.9 (1.7) (0.4) (1.5)

-1.5 11.7 2.1 6.8 (3.9) (1.1) (1.8)

01 39.5 3.1 7.8 (26.8) (2.1) (2.3)

1 extrapolation


3.6 FA1 site (Moore Park)

3.6.1 Site details

The FA1 site and the FA2 site (Section 3.7) were located on the same block of cane. The area is part of the Fairymead Plantation run by the Bundaberg Sugar Co. The boundary between two soil types occurs in the middel of the block, with the Moore Park soil of the FA1 site being on a former beach ridge, whereas the FA2 site, classified as Fairymead soil, was in a lower lying area. Both sites were under fallow conditions during the bromide leaching experiments that ran from December 1995 until March 1996. During this time the water table fluctuated between 150 cm and 70 cm (FA1) or 30 cm (FA2) depths. A soil pit was dug at each site in March and two drainage experiments were carried out at that time. Further details on the experiments and their results can be found in the second report of this series (Verburg et al., 2002a).


The Moore Park soil at the FA1 site is found on the beach ridges in the marine sediments. A photo of the profile is given in Fig. 21, and its profile description in Table 53.

Table 53: Profile description of the Moore Park soil at the FA1 site (by T.E. Donnollan, DNR).

MAPPING UNIT CODE: Mp SITE NO.: BAB 9001 A.M.G. REFERENCE: 430 160 mE 7 261 250 mN ZONE 56 GREAT SOIL GROUP: Podzol LANDFORM ELEMENT TYPE: Beach ridge PRINCIPAL PROFILE FORM: Uc5.11 LANDFORM PATTERN: Marine plain AUSTRALIAN SOIL CLASSIFICATION: Semiaquic Podosol HORIZON DEPTH (cm) DESCRIPTION

Ap1 0 - 15 Greyish yellow-brown (10YR4/2); sandy loam; massive; dry; very weak; common fine roots. Clear, smooth to –

Ap2 15 - 35 Brownish grey (5YR4/1); sandy loam; massive; moderately moist; very weak; common fine roots. Clear, smooth to –

B21s 35 - 60 Yellowish brown (10YR5/6); few fine prominent brown mottles; sandy loam; massive; moist; very weak; few fine manganiferous nodules; few fine roots. Gradual, wavy to –

B22s 60 - 75 Dull yellowish orange (10YR6/3); common medium prominent brown mottles, red mottles; sandy loam; massive; moist, very weak, few fine manganiferous nodules; few fine roots. Gradual, irregular to –

B23s 75 - 100 Yellowish brown (10YR5/6); common medium prominent brown and grey mottles, sandy loam; massive; moist; very weak; few fine roots. Diffuse, irregular to –

B24s 100 - 140 Bright yellowish brown (10YR6/6); common medium prominent grey mottles; sandy loam; massive; moist; very weak; few fine roots.


The Moore Park soil consisted predominantly of sand, with close to 50% of the soil particles in the fine sand category and another 30% as coarse sand (Table 54 and 55. The Townsville and DNR particle size analyses corresponded reasonably well, although the distribution between coarse and fine sand was slightly different. Reasons for this difference are not clear.

Comparison with Tables 64 and 65 shows the marked textural differences between the Moore Park and Fairymead soils.


Figure 21: Photo of the Moore Park soil at the FA1 site (photo by T.E. Donnollan)

Table 54: Particle size distribution of the Moore Park soil at the FA1 site (Townsville analysis).


Surface < 1 34 50 7 9 10-15 < 1 30 52 8 9 42-47 1 33 45 7 15 67-72 < 1 36 45 6 14

Table 55: Particle size distribution of the Moore Park soil at the FA1 site (DNR analysis).


0-10 26 58 6 10 20-30 28 55 8 10 50-60 25 54 4 15 80-90 28 56 4 12

110-120 25 56 3 19


Organic carbon content (Table 56) showed a decrease with depth as expected. The values of the Townsville analysis were lower than that of the DNR analysis (Table 57), despite the fact that the Haines procedure in Townsville is supposed to have higher recoveries than the Walkley & Black method used by DNR. The EC and pH results of the 0-10 sample from the soil pit and those of the bulked samples around the site (B 0-10) are different. The paddock in which this site and the FA2 site were located was fertilised with liquid dunder, a by-product of ethanol and rum production. It is possible that uneven application of this potassium-rich material affected the results.

Table 56: Organic carbon of the Moore Park soil at the FA1 site (Townsville analysis).

Depth (cm) % C Surface 0.67 10-15 0.58 42-47 0.15 67-72 0.08


Table 57: Chemical analysis of the Moore Park soil at the FA1 site (method description in Table 2).


cm mS/cm mg/kg % mg/kg % % B 0-10 6.2 0.28 0.019 5.5 0.80 0.04 0-10 5.8 0.09 BQ 3 0.63 0.094 1.69 0.020 4.9

10-20 5.7 0.05 BQ . 4.9 20-30 6.3 0.04 BQ 3 0.70 0.089 1.64 0.018 5.6 50-60 8.0 0.10 0.004 5 0.65 0.023 1.73 0.008 7.0 80-90 7.9 0.11 0.006 4 0.76 0.014 1.83 0.009 7.2

110-120 7.9 0.08 0.003 0.013 1.68 0.010 6.7


cm mg/kg mg/kg cmolc/kg mg/kg mg/kg cmolc/kg cmolc/kg B 0-10 178 180 1.2 87.0 40.0 61.0 1.6 38.0 0-10 4 2.4 1.3 0.06 0.36

10-20 20-30 5 3.4 1.1 0.13 0.07 50-60 5 3.1 1.3 0.49 0.05 80-90 4 1.9 1.7 0.49 0.03




As soil sampling of the bromide experiments occurred on a few occasions under saturated conditions, the bulk density values obtained from these cores were rather variable (Tables 58 and 59, Fig. 22). By taking the median of these values, outliers were excluded, but the pattern of change in bulk density with depth was not as well defined as for some of the other soils (e.g. Gooburrum soil, Section 3.4, or the Flagstone soil, Section 3.8). The in situ bulk density values were, therefore, given more weight when the best estimate “field average” curve was drawn by eye.

Table 58: Bulk density of the Moore Park soil obtained from in situ samples in the soil pit at the FA1 site.


10-15 1.62 1.54 1.58 42-47 1.76 1.84 1.80 67-72 1.64 1.67 1.66

Table 59: Bulk density of the Moore Park soil obtained from soil cores taken as part of the bromide leaching experiments at the FA1 site and the best estimate “field average”.

Depth (cm) Bulk density (g/cm3) bulked median of "Field background 16 samples1 average"

0-5 1.23 1.05 1.25 5-10 1.15 1.32 1.50 10-20 1.51 1.49 1.58 20-30 1.62 1.58 1.65 30-40 1.67 1.74 1.74 40-50 1.63 1.67 1.78 50-60 1.76 1.60 1.70 60-70 1.73 1.65 1.66 70-80 1.70 1.70 1.70

80-100 1.83 1.85 1.80 100-120 1.77 1.93 1.80 120-140 1.74 1.83 1.80 140-190 1.85 1.80

1 6 samples at depths below 1 m.

0

20

40

60

80

100

120

140

160

180

1.0 1.2 1.4 1.6 1.8 2.0


De

pth

(cm

)

In situ

Background

Median

"Field average"

Figure 22: Comparison of bulk density data for the Moore Park soil at the FA1 site.



Water retention data were determined for three depths. A subsoil sample was, unfortunately, missing. The curves for these three depths were fairly similar, reflecting similar soil texture and structure (Table 60, 61, and Fig. 23). The 15000 cm (15 Bar) gravimetric water contents measured as part of the chemical analysis (data not shown) corresponded well with the gravimetric water contents that formed the basis of Table 60.

Table 60: Water retention data for the Moore Park soil at the FA1 site. Values represent average volumetric water contents (four replicates, standard deviations in parentheses).


10-15 0.38 0.39 0.38 0.32 0.19 0.15 0.12 0.10 0.06 (0.07) (0.06) (0.06) (0.02) (0.01) (0.00) (0.00) (0.00) (0.01)

42-47 0.32 0.32 0.32 0.29 0.23 0.19 0.16 0.13 0.10 (0.02) (0.02) (0.02) (0.01) (0.01) (0.02) (0.02) (0.01) (0.01)

67-72 0.34 0.33 0.33 0.28 0.17 0.13 0.10 0.09 0.07 (0.04) (0.04) (0.04) (0.02) (0.03) (0.03) (0.03) (0.03) (0.03)

Table 61: Smoothed Brooks-Corey parameters (Eq. 1) for the Moore Park soil at the FA1 site.

Depth (cm) theta-r theta-s psie b 10-15 0.05 0.39 16.9 2.3 42-47 0.03 0.32 15.7 5.2 67-72 0.07 0.34 19.1 1.7

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ater

co

nt.

(m

3 /m3 ) 10 cm

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ater

co

nt.

(m

3 /m3 ) 42 cm

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ater

co

nt.

(m

3 /m3 ) 67 cm

Figure 23: Brooks-Corey fits of water retention data for the Moore Park soil at the FA1 site



Hydraulic conductivity values were determined for five different depths (Table 62). The measurements in the subsoil (155 cm) were, however, complicated by the presence of a water table, reducing the hydraulic conductivity values significantly. Downward flow at this site would be limited by the AP2 or B21 horizons, with conductivity values at -3.5 cm H2O around 0.70 cm/h. The effect of near-saturation potential was not as marked as for some of the other soils (e.g. Oakwood, Section 3.1; Fairymead, Section 3.7; or Flagstone, Section 3.8). Measurements made at 155 cm are not reported as these were an underestimate due to being too close to the water table.

Table 62: Near-saturated hydraulic conductivity (cm/h) of the Moore Park soil obtained from disk permeameter readings at the FA1 site (values represent averages of eight replicates, standard deviations in parentheses).

Potential (cm) Depth (cm) Surface 10 cm 18 cm2 42 cm 67 cm

-3.5 2.2 1.6 0.70 0.72 3.7 (1.2) (1.0) (0.55) (0.50) (0.7)

-2.5 4.4 2.9 2.0 1.3 4.5 (1.0) (1.0) (0.8) (0.5) (1.6)

-1.5 8.6 7.5 5.4 2.1 6.3 (3.0) (4.6) (0.8) (0.9) (2.7)

01 14.3 17.6 11.7 3.4 8.5 (6.9) (16.9) (1.5) (1.6) (4.6)

1 extrapolation 2 four replicates only


3.7 FA2 site (Fairymead)

3.7.1 Site details

The FA2 site was located on the same block of cane as the FA1 site (Section 3.6). The area is part of the Fairymead Plantation run by the Bundaberg Sugar Co. The boundary between two soil types occurs in the middel of the block, with the Moore Park soil of the FA1 site being on the Beach ridge, whereas the FA2 site, classified as Fairymead soil, was in a lower lying area. Both sites were under fallow conditions during the bromide leaching experiments that ran from December 1995 until March 1996. The water table was during this time fluctuated between 150 cm and 30 cm (FA2) or 70 cm (FA1) depths. A soil pit was dug at each site in March and two drainage experiments were carried out at that time. Further details of the experiments and their results are described in the second report in this series (Verburg et al., 2002a).


The Fairymead soil is found in the plains and swales of the marine sediments. Its profile description is given in Table 63, and a photo in Fig. 24.

Table 63: Profile description of the Fairymead soil at the FA2 site (by T.E. Donnollan, DNR).

MAPPING UNIT CODE: Fm SITE NO.: BAB 9002 A.M.G. REFERENCE: 430 220 mE 7 261 540 mN GREAT SOIL GROUP: Humic gley LANDFORM ELEMENT TYPE: Plain PRINCIPAL PROFILE FORM: Uf6.41 LANDFORM PATTERN TYPE: Marine plain AUSTRALIAN SOIL CLASSIFICATION: Sulfidic Redoxic Hydrosol CONDITION OF SURFACE SOIL WHEN DRY: Self mulching

HORIZON DEPTH (cm) DESCRIPTION AP 0 - 30 Brownish black (10YR3/2); medium clay; strong 5-10mm subangular blocky;

moderately moist; moderately firm; few very fine roots. Clear, smooth to – B21 30 - 55 Greyish yellow-brown (10YR5/2); many medium prominent red mottles,

brown mottles; medium clay; strong 5-10mm subangular blocky; clay skins; moderately moist; moderately firm; few very fine roots. Gradual, wavy to –

B22 55 - 90 Greyish brown (7.5YR5/2); many medium prominent yellow and brown mottles; medium clay; strong 10-20mm subangular blocky; clay skins; moist; moderately firm; few very fine roots. Gradual, wavy to –

B23 90 - 140 Greyish brown (7.5YR 4/2); many medium prominent yellow mottles (jarosite); medium clay; strong 10-20mm subangular blocky; clay skins; moist; moderately firm; few very fine roots. Clear, wavy to –

D1 140 - 150 Sandy light clay; wet.


The particle size distributions of the two samples included in the Townsville analysis matched reasonably well with corresponding layers of the DNR analysis, except for the balance between silt and clay in the surface soil layer (Tables 64 and 65). The Fairymead soil is characterised by a very low coarse sand content and a very high clay content throughout the profile.


Figure 24: Photo of the Fairymead soil at FA2 site (photo by T.E. Donnollan)

Table 64: Particle size distribution of the Fairymead soil at the FA2 site (Townsville analysis).


10-15 1 4 23 31 41 37-42 < 1 3 24 28 46

Table 65: Particle size distribution of the Fairymead soil at the FA2 site (DNR analysis).


0-10 4 24 21 48 20-30 3 23 27 46 50-60 3 23 23 52 80-90 3 31 19 48

110-120 1 34 19 45


The Townsville analysis of organic carbon and the full chemical analysis by DNR are presented in Tables 66 and 67, respectively. The EC and pH results of the 0-10 sample from the soil pit and those of the bulked samples around the site (B 0-10) are different. The paddock in which this site and the FA1 site were located was fertilised with liquid dunder, a by-product of ethanol and rum production. It is possible that uneven application of this potassium-rich material affected the results.

Table 66: Organic carbon of the Fairymead soil at the FA2 site (Townsville analysis).

Depth (cm) % C 10-15 1.9 37-42 0.68


Table 67: Chemical analysis of the Fairymead soil at the FA2 site (method description in Table 2).


cm mS/cm mg/kg % mg/kg % % B 0-10 4.8 0.36 0.031 4.2 1.5 0.12 0-10 5.1 0.13 0.002 19 0.61 0.043 1.11 0.058 4.1

10-20 4.9 0.10 0.001 4.0 20-30 5.0 0.14 0.004 20 0.61 0.050 1.13 0.058 4.0 50-60 4.4 0.36 0.015 22 0.50 0.020 1.28 0.292 3.6 80-90 4.1 0.49 0.030 21 0.51 0.022 1.53 0.709 3.4

110-120 4.2 0.48 0.027 0.018 1.24 0.051 3.5


cm mg/kg mg/kg cmolc/kg mg/kg mg/kg cmolc/kg cmolc/kg B 0-10 25.0 41.0 1.1 175 15.0 0.91 0.85 119 0-10 11 6.3 3.3 1.2 0.36

10-20 20-30 11 5.7 3.2 0.87 0.85 50-60 7 2.5 2.6 2.1 0.24 80-90 7 0.75 3.0 2.7 0.29

110-120 7 0.41 3.5 2.8 0.38 * B = subsample from nine bulked samples taken from a triangle around the site < 50 m from the site



Bulk density data obtained from the soil cores of the bromide leaching experiments were highly erratic below 60 cm depth (Table 69 and Fig. 25). This was due to the wet sampling conditions caused by a water table which fluctuated between 150 and 60 cm depth. In drawing the best estimate “field average” curve more emphasis was, therefore, given to the in situ data from the soil pit (Table 68).

Table 68: Bulk density of the Fairymead soil obtained from in situ samples in the soil pit at the FA2 site.


10-15 1.23 1.18 1.20 37-42 1.36 1.38 1.37

Table 69: Bulk density of the Fairymead soil obtained from soil cores taken as part of the bromide leaching experiments at the FA2 site and the best estimate “field average”.

Depth (cm) Bulk density (g/cm3) bulked median of "Field background 4 samples1 average"

0-5 1.12 0.83 1.12 5-10 0.98 0.83 1.17 10-20 1.14 1.18 1.22 20-30 1.25 1.26 1.26 30-40 1.33 1.24 1.35 40-50 1.29 1.35 1.31 50-60 1.29 1.36 1.30 60-70 1.26 1.13 1.27 70-80 1.32 1.14 1.32

80-100 1.31 0.96 1.31 100-120 1.27 1.11 1.27 120-140 1.26 1.42 1.26

1 average of 2 samples at depths below 60 cm.

0

20

40

60

80

100

120

140

0.8 1.0 1.2 1.4 1.6


De

pth

(cm

)

In situ

Background

Median

"Field average"

Figure 25: Comparison of bulk density data for the Fairymead soil at the FA2 site.



The water retention curves for both depths were characterised by high b values (slope) and high saturated water contents (Table 70, 71, and Fig. 26). These are typical for soil with a high clay content. The 15000 cm (15 Bar) gravimetric water contents measured as part of the chemical analysis (data not shown) corresponded well with the gravimetric water contents that formed the basis of Table 70.

Table 70: Water retention data for the Fairymead soil at the FA2 site. Values represent average volumetric water contents (four replicates, standard deviations in parentheses).


10-15 0.46 0.45 0.42 0.38 0.36 0.33 0.31 0.28 0.22 (0.05) (0.04) (0.03) (0.02) (0.02) (0.01) (0.01) (0.01) (0.01)

37-42 0.45 0.46 0.46 0.45 0.44 0.42 0.39 0.35 0.28 (0.02) (0.02) (0.02) (0.02) (0.02) (0.02) (0.03) (0.02) (0.02)

Table 71: Smoothed Brooks-Corey parameters (Eq. 1) for the Fairymead soil at the FA2 site.


0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ater

co

nt.

(m

3 /m3 ) 10 cm

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ater

co

nt.

(m

3 /m3 ) 37 cm

Figure 26: Brooks-Corey fits of water retention data for the Fairymead soil at the FA2 site.



The hydraulic conductivity was fairly low at the higher suctions, but increase dramatically towards saturation, with an increase of more than 100-fold in the surface layer (Table 72).

Table 72: Near-saturated hydraulic conductivity (cm/h) of the Fairymead soil obtained from disk permeameter readings at the FA2 site (values represent averages of eight replicates, standard deviations in parentheses).

Potential (cm) Depth (cm) 10 cm 37 cm

-3.5 1.4 0.90 (1.1) (0.76)

-2.5 6.5 2.5 (3.6) (1.6)

-1.5 32.1 7.5 (14.9) (5.4)

01 161 33.0 (78) (36.9)

1 extrapolation


3.8 EWA site (Flagstone)

3.8.1 Site details

The EWA site was the experimental site closest to Bundaberg city and the Burnett river. It was located on a cane block, along a dirt road off Waterview Street. The block was managed by Mr Ewald and, outside the experimental area, under field peas for the duration of the bromide leaching experiments from December 1995 until March 1996. A soil pit was dug in March 1996, at which time a drainage experiment was run as well.


A profile description and photo of the Flagstone soil at the EWA site are given in Fig. 27 and Table 73, respectively. The Flagstone soil is found in plains and swales of the quaternary alluvium along the Burnett River.

Table 73: Profile description of the Flagstone soil at the EWA site (by T.E. Donnollan, DNR).

MAPPING UNIT CODE: Fs SITE NO.: BAB 9005 A.M.G. REFERENCE:435 210 mE 7 251 280 mN ZONE 56 GREAT SOIL GROUP: Prairie soil LANDFORM ELEMENT TYPE: Scroll PRINCIPAL PROFILE FORM: Uf6.32 LANDFORM PATTERN TYPE: Alluvial plain AUSTRALIAN SOIL CLASSIFICATION: Black Dermosol CONDITION OF SURFACE SOIL WHEN DRY: Hard setting

HORIZON DEPTH (cm) DESCRIPTION Ap1 0 - 5 Brownish black (10YR3/2); light clay; strong 2-5mm platy; dry; moderately

weak; few very fine roots. Abrupt, wavy to – Ap2 5 - 18 Dark brown (10YR3/3); light clay; strong 50-100mm prismatic parting to 2-

5mm subangular blocky; dry; very firm; few very fine roots. Clear, wavy to – Ap3 18 - 25 Brownish black (10YR3/2); light clay; strong 20-50mm subangular blocky

parting to 2-5mm subangular blocky; many clay skins; moderately moist; moderately firm; common fine roots. Gradual, wavy to –

B21 25 - 55 Brownish black (10YR3/2); light medium clay; strong 5-10mm subangular blocky; many clay skins; moderately moist; moderately weak; very few fine manganiferous soft segregations; common fine roots. Gradual, wavy to –

B22 55 - 140 Brown (7.5YR4/3); light medium clay; strong 5-10mm subangular blocky; moderately moist; moderately weak; few very fine roots.


The particle size distribution is uniform down the profile, with essentially no coarse sand, close to 50% fine sand and the remaining percentage split roughly equally between clay and silt (Tables 74 and 75). Near the surface the ratio clay: silt is 50:50, at depth this changes to 60:40. The deepest sample included in the Townsville analysis suggests that the proportion of fine sand may increase at this depth at the cost of the silt fraction. The two analyses (Townsville and DNR) compared well.

Table 74: Particle size distribution of the Flagstone soil at the EWA site (Townsville analysis).


10-15 < 1 1 48 25 26 40-45 < 1 1 43 25 31

166-171 < 1 1 57 17 25


Figure 27: Photo of the Flagstone soil at the EWA site (photo T.E. Donnollan).

Table 75: Particle size distribution of the Flagstone soil at the EWA site (DNR analysis).


0-5 1 49 24 27 20-25 1 45 22 33 50-60 < 1 52 20 30 80-90 < 1 46 22 33

110-120 1 47 20 33


The Townsville analysis of organic carbon and the full chemical analysis by DNR are presented in Tables 76 and 77, respectively.

Table 76: Organic carbon of the Flagstone soil at the EWA site (Townsville analysis).

Depth (cm) % C 10-15 1.3 40-45 0.91

166-171 0.41


Table 77: Chemical analysis of the Flagstone soil at the EWA site (method description in Table 2).


cm mS/cm mg/kg % mg/kg % % B 0-10 6.7 0.07 BQ 5.4 1.1 0.09

0-5 6.7 0.11 0.004 11 0.49 0.107 1.58 0.023 5.4 10-20 6.6 0.05 0.001 5.1 20-25 6.9 0.05 0.001 14 0.56 0.089 1.51 0.023 5.4 30-40 7.5 0.04 0.002 6.1 50-60 7.2 0.05 0.003 13 0.52 0.052 1.52 0.015 6.2 80-90 7.8 0.06 0.004 14 0.63 0.059 1.48 0.014 6.2

110-120 7.7 0.06 0.004 0.058 1.46 0.015 6.3


cm mg/kg mg/kg cmolc/kg mg/kg mg/kg cmolc/kg cmolc/kg B 0-10 186 130 0.40 96.0 56.0 2.3 2.3 8.0

0-5 15 8.8 5.3 0.49 0.49 10-20 20-25 18 12.0 4.9 0.65 0.23 30-40 50-60 17 13.0 3.4 0.68 0.18 80-90 19 15.0 3.4 0.80 0.19




The bulk density profile with depth was well defined by the in situ samples and by those taken as part of the bromide leaching experiments (Tables 78 and 79, Fig. 28). The two measurements compared well.

Table 78: Bulk density of the Flagstone soil obtained from in situ samples in the soil pit at the EWA site.


10-15 1.59 1.43 1.51 40-45 1.51 1.54 1.52

166-171 1.61 1.60 1.60

Table 79: Bulk density of the Flagstone soil obtained from soil cores taken as part of the bromide leaching experiments at the EWA site and the best estimate “field average”.

Depth (cm) Bulk density (g/cm3) bulked median of “Field background 10 samples average"

0-5 1.22 1.20 1.22 5-10 1.40 1.29 1.40 10-20 1.50 1.44 1.50 20-30 1.55 1.50 1.51 30-40 1.57 1.55 1.52 40-50 1.50 1.53 1.53 50-60 1.60 1.55 1.54 60-70 1.62 1.56 1.55 70-80 1.50 1.55 1.55

80-100 1.59 1.61 1.60 100-120 1.59 1.60 1.61 120-140 1.60 1.64 1.61 140-160 1.61 1.61 160-180 1.63 1.61

0

20

40

60

80

100

120

140

160

180

1.0 1.2 1.4 1.6 1.8 2.0


De

pth

(cm

)

In situ

Background

Median

"Field average"

Figure 28: Comparison of bulk density data for the Flagstone soil at the EWA site.



The water retention properties of the Flagstone soil did not change much with depth (Table 80, 81, and Fig. 29), as was expected given the uniformity in structure and texture (Tables 73, 74, 75). The 15000 cm (15 Bar) gravimetric water contents measured as part of the chemical analysis (data not shown) corresponded well with the gravimetric water contents that formed the basis of Table 80.

Table 80: Water retention data for the Flagstone soil at the EWA site. Values represent average volumetric water content values (four replicates, standard deviations in parentheses).


10-15 0.40 0.39 0.39 0.37 0.34 0.31 0.28 0.25 0.17 (0.03) (0.03) (0.03) (0.02) (0.02) (0.02) (0.01) (0.01) (0.00)

40-45 0.40 0.40 0.40 0.38 0.36 0.34 0.32 0.29 0.21 (0.02) (0.02) (0.02) (0.02) (0.02) (0.02) (0.02) (0.02) (0.01)

166-171 0.42 0.42 0.41 0.40 0.37 0.34 0.29 0.24 0.18 (0.01) (0.01) (0.01) (0.01) (0.01) (0.00) (0.01) (0.01) (0.00)

Table 81: Smoothed Brooks-Corey parameters (Eq. 1) for the Flagstone soil at the EWA site.


166-171 0.00 0.41 66.8 7.2

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ater

co

nt.

(m

3 /m3 ) 10 cm

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ater

co

nt.

(m

3 /m3 ) 40 cm

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ater

co

nt.

(m

3 /m3 ) 166 cm

Figure 29: Brooks-Corey fits of water retention data for the Flagstone soil at the EWA site.



The hydraulic conductivity decreased rapidly with increasing suction, in particular near the surface, where the drop was more than 100-fold (Table 82). The hydraulic conductivity also decreased with depth.

Table 82: Near-saturated hydraulic conductivity (cm/h) of the Flagstone soil from disk permeameter readings at the EWA site (values represent averages of eight replicates, standard deviations in parentheses).


-3.5 1.0 0.49 0.57 (0.6) (0.37) (0.20)

-2.5 4.7 2.0 1.3 (3.5) (0.8) (0.5)

-1.5 24.0 8.3 3.1 (15.6) (2.3) (0.8)

01 127 35.1 7.0 (85) (14.2) (2.1)

1 extrapolation


4. Concluding Remarks

The compilation of data presented in this report gives a broad picture of the soil properties of the major soil types in the Gooburrum – Moore Park area of Bundaberg. To conclude this report we would like to add a few comments about the usefulness of the methods and the data obtained, as well as some comparisons between soil types.

Profile description

The profile descriptions proved useful in providing a picture of the various horizons of the soils and of differences in horizon depths between different locations of the same soil type (e.g. Otoo soil at the SCH and PAO sites).

Particle size distribution

Whenever two analyses of particle size distribution were carried out, they generally matched well. The particle size distributions were useful to distinguish soil types or soil layers, whereas field texture was not sufficient.

Bulk density

The two bulk density measurements (in situ and those derived from soil cores) were often complementary. The derived bulk density values provided the depth interpolation between in situ values, where the two agreed. In case of discrepancies, it could usually be argued why one or the other method was deficient. The in situ method was accurate, but had a disadvantage that it was valid for only one point in time and space. On the other hand, the derived median bulk density values were unreliable in cases where the soil was not optimal for sampling (e.g. FA2 site).

Water retention

The water retention curves were generally well-defined with little variability between replicates. The 15000 cm data point determined using a thermocouple psychrometer corresponded well with the measurement made as part of the chemical analysis using the pressure plate technique, indicating no osmotic effect. This is consistent with the very low EC values found.

The water retention curves of the various soil types and layers often exhibited “textbook” shapes. Compare, for example, the contrast between the sandy clay loam A3 and light clay B2 horizons of the Gooburrum soil (Fig. 16; 50 and 161 cm depth; no. 3 and 7 in Fig. 30) with Fig. 2.2 of Marshall and Holmes (1979), Fig. 5.6 of Hillel (1982), or Fig. 2.13 of Jury et al. (1991). Clay rich materials are characterised by a high saturated water content and high b values (resulting in flat slopes in figures of water content vs. matric suction), whereas sandy soils have lower saturated water contents, lower b values, and often a more sudden drop in water content. The comparison of a number of water retention curves in Fig. 30 illustrates this. The loamy soil materials had lower saturated water contents and relatively steep slopes with b values of 5 or less (No. 3,4, and 8). The soil layers with higher clay contents had higher saturated water contents and b values as high as 25 (No. 1,2,5,6,and 7).

Comparisons between the loamy or clay soils were less straight forward. The comparison of curves 5, 6, and 7 in Fig. 30 suggests that the b value is governed by the clay content, but structure plays a role as well, as seen by comparing curves 1 and 5. Clearly the particle size data are highly correlated to the b value, which is one reason why they are often used in pedotransfer functions that estimate water retention data from readily available soil properties. (e.g. Rawls et al., 1991; Williams et al., 1992; Paydar and Cresswell, 1996; Smettem and Gregory, 1996; Bristow et al., 1999).


0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ater

co

nt.

(m

3 /m3 )

0

0.1

0.2

0.3

0.4

0.5


Vo

l. w

ater

co

nt.

(m

3 /m3 )

6

7

5

8

2

3

1

4

No. Soil Depth Field texture Particle size Structure b 1 Fairymead 37 cm medium clay Cs 2.7, fs 24.2, s 27.5, c 45.5 strong 5-10mm subangular blocky 10 2 Flagstone 40 cm light medium clay Cs 0.7, fs 43.1, s 25.1, c 31.2 strong 5-10mm subangular blocky 11 3 Gooburrum 50 cm sandy clay loam Cs 47.1, fs 29.8, s 13.4, c 9.7 massive 5 4 Moore Park 42 cm sandy loam Cs 33.3, fs 45.2, s 6.6, c 14.8 massive 5 5 Oakwood 160 cm light clay Cs 19, fs 22, s 10, c 48 weak 2-5 mm polyhredral 8 6 Flagstone 166 cm light medium clay Cs 0.8, fs 56.6, s 17.4, c 25.2 strong 5-10mm subangular blocky 7 7 Gooburrum 161 cm light clay Cs 21.7, fs 11.3, s 6.9, c 60.1 strong 2-5 mm polyhedral 25 8 Moore Park 67 cm sandy loam Cs 35.6, fs 44.8, s 6.0, c 13.6 massive 2

Figure 30: Comparison of selected water retention curves.

Near-saturated hydraulic conductivity

A significant feature of the hydraulic conductivity measurements was the increase in conductivity near saturation in all soils. The effect was most marked in the surface layers and in structured soils (Oakwood, Fairymead, Flagstone). As the increases often occurred below the air-entry point (psie, Eq. 1), this behaviour is not described by the Brooks-Corey hydraulic conductivity function (Eq. 2). It suggests that complete description of the hydraulic conductivity requires an extra macro-pore function to be added on to the Brooks-Corey function (see Verburg et al., 1996). Whether this makes a difference to the simulations will depend on the scenario being modelled; in particular, whether or not saturated conditions occur for lengthy periods (Verburg et al., 2002a).

While the Fairymead and Flagstone soils have the largest extrapolated saturated hydraulic conductivity (Ksat), at a slight suction their conductivity drops below that of the Oakwood soil. The Moore Park soil has the highest subsoil unsaturated conductivity, but a water table at shallow depth limited its drainage. Of the seven soil types studied, therefore, the Oakwood soil was the most permeable soil, as was confirmed by simulations of the relative leaching potential (Verburg et al., 2002b).

Use of the data for modelling

The data presented in this report were used to parameterise the hydraulic properties required by the SWIMv2 and APSIM-SWIM models for the simulations of field experiments and different climate and management scenarios (Verburg et al., 2002a,b). The data would be suitable for other modelling exercises, especially if evaluating “what if” scenarios. Care would still be needed for site specific analyses, which would probably require the use of locally measured data.


5. Acknowledgements

Many people contributed to the collection of data presented in this report. The authors would like to thank Jody Biggs, Vic Catchpoole, May Ling Goode, Charlie McEwan, Keith Smith and Keith Weier for all their efforts in the two sugarcane cropping trials at the SCH and FRA sites, including field sampling under not always optimal weather conditions and tedious processing of samples in the lab. Denis Orange was involved with the soil physical characterisation of all the sites, with help from Jody Biggs, Vic Catchpoole, Keith Smith, and John Molomby. Thanks very much for your hard work digging shelves in the soil pits and listening to the disk permeameter commands on the tape recorder over and over again. The WIL, PAO, SFF, TOW, FA1, FA2, and EWA sites were selected with the help of Peter Wilson, Terry Donnollan and Peter Zund of DNR Bundaberg, who also carried out the soil survey for the new land resource map of the Gooburrum-Moore Park area of Bundaberg. Jim Sullivan (BSES) and Trevor Wilcox (Canegrowers) helped selecting the sites, which was not easy because of the requirements for a fallow management treatment and a level field. It was an interesting exercise. Thank you for your help. Thanks also for the chemical analysis of five of the sites, arranged through the DNR Chemical Analysis Lab. The Townsville analyses were carried out by Eva-Jane Ford, Ron Russo and the Townsville Chemistry Laboratory. Neil McKenzie is acknowledged for his helpful comments on an earlier draft of this report. Last but not least, thanks to all the farmers who allowed us to carry out experiments on their fields, including digging deep soil pits: John and Charlie Francis, Alex Wilson, Des Schulte, Dean De Paoli, Ron Schiffke, Chris Townson, Peter Maidment of Brisbane Sugar Co., and Mr Ewald.

The experiments were carried out as part of two studies funded in part by the Sugar Research and Development Corporation (CSC7S) and the Land and Water Resources Research and Development Corporation (CTC6). Their funding is gratefully acknowledged.


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Barry, A., and S.J. Prosser. 1996. Automated analysis of light-element stable isotopes by isotope ratio mass spectrometry. p. 1-46. In T.W. Boutton, S. Yamasaki (Eds.) Mass spectrometry of soils. Marcel Dekker, New York, U.S.A.

Barry, G.A., P. Bloesch, E.A. Gardner, and G.E. Rayment. 1998. Re-use of sewage biosolids on canelands. Proc. Aust. Soc. Cane Technol. 20, 69-75.

Beattie, J.A., and R.H. Gunn. 1988. Field operations of soil and land resource surveys. p. 113-134. In R.H. Gunn, J.A. Beattie, R.E. Reid, and R.H.M. van de Graaff (Eds.) Australian soil and land survey handbook - Guidelines for conducting surveys. Inkata Press, Melbourne, Australia.

Bristow, K.L., K.R.J. Smettem, P.J. Ross, E.J. Ford, C.H. Roth, and K. Verburg. 1999. Obtaining hydraulic properties for soil water balance models: Some pedotransfer functions for tropical Australia. p. 1103-1119. In: M. Th. Van Genuchten, F.J. Leij, and L. Wu (Eds.) Characterization and measurement of the hydraulic properties of unsaturated porous media, Part 2. Proc. Int. Workshop on characterisation and measurement of hydraulic properties of unsaturated porous media, 22-24 October 1997, Riverside, California, U.S.A.

Brooks, R.H. and A.T. Corey. 1964. Hydraulic properties of porous media. Hydrol. Pap. No. 3. Civ. Eng. Dep., Colorado State Univ., Fort Collins, U.S.A.

Brooks, R.H. and A.T. Corey. 1966. Properties of porous media affecting fluid flow. J. Irrig. Drain. Div. Am. Soc. Civil Eng. 92 (IR2), 555-560.

Campbell, G.S. 1974. A simple method for determining unsaturated conductivity from moisture retention data. Soil Sci. 117, 311-314.

Campbell, G.S. 1985. Soil physics with BASIC. Elsevier, New York, U.S.A.

Coughlan, K.J., D. McGarry, R.J. Loch, B.J. Bridge, and G.D. Smith. 1991. The measurement of soil structure - some practical initiatives. Aust. J. Soil. Res. 29, 869-889.

Coventry, R.J. and D.E.R. Fett. 1979. A pipette and sieve method of particle-size analysis and some observations on its efficacy. CSIRO Division of Soils Divisional Report No. 38.

Gee, G. W. and J.W. Bauder. 1986. Particle-size analysis. p. 383-411. In A. Klute (Ed.) Methods of Soil Analysis Part I, Physical and Mineralogical Methods. American Society of Agronomy Monograph No 9, Madison, Wisconsin, U.S.A.

Heanes, D.L. 1984. Determination of total organic-C in soils by an improved chromic acid digestion and spectrophotometric procedure. Commun. Soil Sci. Plant Anal. 15, 1191-1213.

Hillel, D. 1982. Introduction to soil physics. Academic Press, Inc. San Diego, U.S.A.

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Isbell, R.F. 1996. The Australian soil classification. CSIRO, Melbourne, Australia.

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7. Appendices

7.1 List of Tables

Table 1: Experimental sites in Gooburrum – Moore Park area of Bundaberg (24.8°S, 152.3°E)............... 5

Table 2: Methods used for chemical analysis by DNR................................................................................ 9

Table 3: Profile description of the Oakwood soil at the FRA site (by T.E. Donnollan, DNR). ................ 13

Table 4: Particle size distribution of the Oakwood soil at the FRA site (Townsville analysis). ............... 14

Table 5: Total carbon of selected soil samples of the Oakwood soil at the FRA site. .............................. 15

Table 6: Soil pH at the final soil sampling (November 1996) of the cropping trial at the FRA site......... 15

Table 7: Bulk density of the Oakwood soil obtained from in situ samples in the soil pits at the FRA site. ...................................................................................................................................... 15

Table 8: Bulk density of the Oakwood soil obtained from soil samples taken during the first season of the cropping trial at the FRA site (FRA1)............................................................................... 16

Table 9: Bulk density of the Oakwood soil obtained from soil cores taken as part of the small scale bromide leaching experiments at the FRA and WIL sites and the best estimate “field average”. ...................................................................................................................................... 17

Table 10: Water retention data for the Oakwood soil at the FRA site. Values represent average volumetric water contents (four replicate measurements, standard deviations are given in parentheses). ................................................................................................................................ 20

Table 11: Smoothed Brooks-Corey parameters (Eq. 1) for the Oakwood soil at the FRA site. .................. 21

Table 12: Near-saturated hydraulic conductivity (cm/h) of the Oakwood soil obtained from disk permeameter readings at the FRA site......................................................................................... 22

Table 13: Profile description of the Otoo sandy variant soil at the SCH site; (a) first soil pit, and (b) second soil pit (by K.J. Smith, CSIRO Tropical Agriculture)..................................................... 24

Table 14: Particle size distribution of the Otoo sandy variant soil at the SCH site (Townsville analysis). ...................................................................................................................................... 25

Table 15: Electrical conductivity (EC) of the Otoo sandy variant soil at the SCH site. ............................. 25

Table 16: Average pH at the SCH site (1992-1994). ................................................................................... 25

Table 17: Exchangeable cations of the Otoo sandy variant soil at the SCH site (3 locations).................... 26

Table 18: Bulk density of the Otoo sandy variant soil obtained from in situ samples in the soil pits at the SCH site. ............................................................................................................................ 26

Table 19: Bulk density of the Otoo sandy variant soil obtained from soil samples taken during the first season of the cropping trial at the SCH site (SCH1). Sampling positions af, bf, and i are explained in the text............................................................................................................... 27

Table 20: Bulk density of the Otoo sandy variant soil obtained from soil cores taken as part of the small scale bromide leaching experiments with the drip infiltrometer at the SCH site and the best estimate “field average”. ................................................................................................ 28

Table 21: Water retention data for the Otoo sandy variant soil at the SCH site. Values represent average volumetric water contents (six replicate measurements for the subplot 80 samples and four replicates for the samples from the two soil pits*, standard deviations are given in parentheses) ............................................................................................................................. 30

Table 22: Smoothed Brooks-Corey parameters (Eq. 1) for the Otoo sandy variant soil at the SCH site (subplot 80). .......................................................................................................................... 31


Table 23: Smoothed Brooks-Corey parameters (Eq. 1) for the Otoo sandy variant soil at the SCH site (soil pits). .............................................................................................................................. 31

Table 24: Near-saturated hydraulic conductivity (cm/h) of the Otoo sandy variant soil obtained from disk permeameter readings in subplot 80 of the cropping trial at the SCH site (values represent averages of eight replicates, standard deviations in parentheses)................................ 32

Table 25: Near-saturated hydraulic conductivity (cm/h) of the Otoo sandy variant soil obtained from disk permeameter readings in and around the two soil pits at the SCH site (values represent averages of eight replicates, standard deviations in parentheses)................................ 32

Table 26: Profile description of the Otoo soil at the PAO site (by P.R. Zund, DNR)................................. 33

Table 27: Particle size distribution of the Otoo soil at the PAO site (Townsville analysis). ...................... 33

Table 28: Bulk density of the Otoo soil obtained from in situ samples near the soil surface at the PAO site....................................................................................................................................... 34

Table 29: Bulk density of the Otoo soil obtained from soil cores taken as part of the bromide leaching experiments at the PAO site and the best estimate “field average”. ............................. 35

Table 30: Water retention data for the Otoo soil at the PAO site. Values represent average volumetric water contents (four replicates, standard deviations in parentheses). ....................... 35

Table 31: Smoothed Brooks-Corey parameters (Eq. 1) for the Otoo soil at the PAO site. ......................... 35

Table 32: Near-saturated hydraulic conductivity (cm/h) of the Otoo soil obtained from disk permeameter readings at the PAO site (values represent averages of eight replicates, standard deviations in parentheses). ............................................................................................ 36

Table 33: Profile description of the Gooburrum soil at the SFF site (by P.R. Zund, DNR). ...................... 37

Table 34: Particle size distribution of the Gooburrum soil at the SFF site (Townsville analysis). ............. 38

Table 35: Particle size distribution of the Gooburrum soil at the SFF site (DNR analysis)........................ 38

Table 36: Organic carbon of the Gooburrum soil at the SFF site (Townsville analysis). ........................... 39

Table 37: Chemical analysis of the Gooburrum soil at the SFF site (method description in Table 2)........ 40

Table 38: Bulk density of the Gooburrum soil obtained from in situ samples in the soil pit at the SFF site. ....................................................................................................................................... 41

Table 39: Bulk density of the Gooburrum soil obtained from soil cores taken as part of the bromide leaching experiments at the SFF site and the best estimate “field average”. .............................. 41

Table 40: Water retention data for the Gooburrum soil at the SFF site. Values represent average volumetric water contents (four replicates, standard deviations in parentheses). ....................... 42

Table 41: Smoothed Brooks-Corey parameters (Eq. 1) for the Gooburrum soil at the SFF site. ................ 42

Table 42: Near-saturated hydraulic conductivity (cm/h) of the Gooburrum soil obtained from disk permeameter readings at the SFF site (values represent averages of eight replicates, standard deviations in parentheses). ............................................................................................ 43

Table 43: Profile description of the Alloway soil at the TOW site (by P.R. Zund, DNR).......................... 44

Table 44: Particle size distribution of the Alloway soil at the TOW site (Townsville analysis). ............... 44

Table 45: Particle size distribution of the Alloway soil at the TOW site (DNR analysis). ......................... 45

Table 46: Organic carbon of the Alloway soil at the TOW site (Townsville analysis)............................... 45

Table 47: Chemical analysis of the Alloway soil at the TOW site (method description in Table 2). ......... 46

Table 48: Bulk density of the Alloway soil obtained from in situ samples in the soil pit at the TOW site................................................................................................................................................ 47


Table 49: Bulk density of the Alloway soil obtained from soil cores taken as part of the bromide leaching experiments at the TOW site and the best estimate “field average”............................. 47

Table 50: Water retention data for the Alloway soil at the TOW site. Values represent average volumetric water contents (four replicates, standard deviations in parentheses). ....................... 48

Table 51: Smoothed Brooks-Corey parameters (Eq. 1) for the Alloway soil at the TOW site. .................. 48

Table 52: Near-saturated hydraulic conductivity (cm/h) of the Alloway soil obtained from disk permeameter readings at the TOW site (values represent averages of eight replicates, standard deviations in parentheses). ............................................................................................ 49

Table 53: Profile description of the Moore Park soil at the FA1 site (by T.E. Donnollan, DNR). ............. 50

Table 54: Particle size distribution of the Moore Park soil at the FA1 site (Townsville analysis). ............ 51

Table 55: Particle size distribution of the Moore Park soil at the FA1 site (DNR analysis)....................... 51

Table 56: Organic carbon of the Moore Park soil at the FA1 site (Townsville analysis). .......................... 51

Table 57: Chemical analysis of the Moore Park soil at the FA1 site (method description in Table 2)....... 52

Table 58: Bulk density of the Moore Park soil obtained from in situ samples in the soil pit at the FA1 site........................................................................................................................................ 53

Table 59: Bulk density of the Moore Park soil obtained from soil cores taken as part of the bromide leaching experiments at the FA1 site and the best estimate “field average”............................... 53

Table 60: Water retention data for the Moore Park soil at the FA1 site. Values represent average volumetric water contents (four replicates, standard deviations in parentheses). ....................... 54

Table 61: Smoothed Brooks-Corey parameters (Eq. 1) for the Moore Park soil at the FA1 site. ............... 54

Table 62: Near-saturated hydraulic conductivity (cm/h) of the Moore Park soil obtained from disk permeameter readings at the FA1 site (values represent averages of eight replicates, standard deviations in parentheses). ............................................................................................ 55

Table 63: Profile description of the Fairymead soil at the FA2 site (by T.E. Donnollan, DNR). ............... 56

Table 64: Particle size distribution of the Fairymead soil at the FA2 site (Townsville analysis). .............. 57

Table 65: Particle size distribution of the Fairymead soil at the FA2 site (DNR analysis)......................... 57

Table 66: Organic carbon of the Fairymead soil at the FA2 site (Townsville analysis). ............................ 57

Table 67: Chemical analysis of the Fairymead soil at the FA2 site (method description in Table 2)......... 58

Table 68: Bulk density of the Fairymead soil obtained from in situ samples in the soil pit at the FA2 site................................................................................................................................................ 59

Table 69: Bulk density of the Fairymead soil obtained from soil cores taken as part of the bromide leaching experiments at the FA2 site and the best estimate “field average”............................... 59

Table 70: Water retention data for the Fairymead soil at the FA2 site. Values represent average volumetric water contents (four replicates, standard deviations in parentheses). ....................... 60

Table 71: Smoothed Brooks-Corey parameters (Eq. 1) for the Fairymead soil at the FA2 site. ................. 60

Table 72: Near-saturated hydraulic conductivity (cm/h) of the Fairymead soil obtained from disk permeameter readings at the FA2 site (values represent averages of eight replicates, standard deviations in parentheses). ............................................................................................ 61

Table 73: Profile description of the Flagstone soil at the EWA site (by T.E. Donnollan, DNR)................ 62

Table 74: Particle size distribution of the Flagstone soil at the EWA site (Townsville analysis). ............. 62

Table 75: Particle size distribution of the Flagstone soil at the EWA site (DNR analysis). ....................... 63

Table 76: Organic carbon of the Flagstone soil at the EWA site (Townsville analysis)............................. 63


Table 77: Chemical analysis of the Flagstone soil at the EWA site (method description in Table 2). ....... 64

Table 78: Bulk density of the Flagstone soil obtained from in situ samples in the soil pit at the EWA site................................................................................................................................................ 65

Table 79: Bulk density of the Flagstone soil obtained from soil cores taken as part of the bromide leaching experiments at the EWA site and the best estimate “field average”............................. 65

Table 80: Water retention data for the Flagstone soil at the EWA site. Values represent average volumetric water content values (four replicates, standard deviations in parentheses). ............. 66

Table 81: Smoothed Brooks-Corey parameters (Eq. 1) for the Flagstone soil at the EWA site. ................ 66

Table 82: Near-saturated hydraulic conductivity (cm/h) of the Flagstone soil from disk permeameter readings at the EWA site (values represent averages of eight replicates, standard deviations in parentheses)............................................................................................................ 67

7.2 List of Figures

Figure 1: Location of experimental sites and soils groups of the Gooburrum – Moore Park area of Bundaberg (derived from Gooburrum – Moore Park Soils 1: 50 000, 1998, P.R. Zund, T.E. Donnollan, and S.A. Irvine). .................................................................................................. 6

Figure 2: Brooks-Corey hydraulic property functions: (a) water retention curves, and (b) and (c) related hydraulic conductivity functions. Dashed curve in (c) is an example of an additional function to deal with “macroporosity”. ...................................................................... 11

Figure 3: Bryan Bridge and Denis Orange taking disk permeameter measurements in a pit at the SFF site. ....................................................................................................................................... 12

Figure 4: Photo of the Oakwood soil at the FRA site (photo by T.E. Donnollan)...................................... 14

Figure 5: Comparison of bulk density data for the Oakwood soil: (a) in situ bulk density vs. median bulk density for the first year of the cropping trial at the FRA site (FRA1), (b) bulk density obtained using various estimates for the FRA and WIL sites (note different depth scale). ........................................................................................................................................... 16

Figure 6: Effect of uncertainty in bulk density on the volumetric water content profiles in the drip experiments. For each of the two plots shown (Plot 1 top row and Plot 2 bottom row) three replicate profiles are given (curves connect data points at the mid points of sampled layers). ......................................................................................................................................... 18

Figure 7: Brooks-Corey fits of water retention data for the Oakwood soil at the FRA site. ...................... 19

Figure 8: Effect of structure (macroporosity) on the relation between near-saturated matric potential and hydraulic conductivity; (a) 0-5 cm and (b) 15-20 cm layers of the Oakwood soil at the FRA site. ..................................................................................................................... 22

Figure 9: Photo of the Otoo sandy variant soil at the SCH site; also shown the markings for the 20x20 cm blocks for the two dimensional sampling. .................................................................. 23

Figure 10: Comparison of bulk density data for the Otoo sandy variant soil at the SCH site: (a) in situ samples from the soil pits vs. average and median of samples taken during the SCH1 and SCH2 cropping seasons, (b) median bulk density of samples taken in the drip experiments.................................................................................................................................. 28

Figure 11: Brooks-Corey fits of water retention data for the Otoo sandy variant soil at the SCH site. ....... 29

Figure 12: Comparison of bulk density data for the Otoo soil at the PAO site; also shown is the best estimate “field average” of the Otoo soil at the SCH site. .......................................................... 34

Figure 13: Brooks-Corey fit of water retention data for the Otoo soil at the PAO site . .............................. 35


Figure 14: Photo of the Gooburrum soil at the SFF site (photo by P.R. Zund). ........................................... 38

Figure 15: Comparison of bulk density data for the Gooburrum soil at the SFF site. .................................. 41

Figure 16: Brooks-Corey fits of water retention data for the Gooburrum soil at the SFF site ..................... 42

Figure 17: Effect of structure (macroporosity) on the relation between near-saturation matric potential and hydraulic conductivity of the Gooburrum soil at the SFF site; (a) 10 cm and (b) 161 cm depth. ......................................................................................................................... 43

Figure 18: Photo of the Alloway soil at the TOW site (photo by P.R. Zund)............................................... 45

Figure 19: Comparison of bulk density data for the Alloway soil at the TOW site. .................................... 47

Figure 20: Brooks-Corey fits of water retention data for the Alloway soil at the TOW site........................ 48

Figure 21: Photo of the Moore Park soil at the FA1 site (photo by T.E. Donnollan)................................... 51

Figure 22: Comparison of bulk density data for the Moore Park soil at the FA1 site. ................................. 53

Figure 23: Brooks-Corey fits of water retention data for the Moore Park soil at the FA1 site ................... 54

Figure 24: Photo of the Fairymead soil at FA2 site (photo by T.E. Donnollan)........................................... 57

Figure 25: Comparison of bulk density data for the Fairymead soil at the FA2 site. ................................... 59

Figure 26: Brooks-Corey fits of water retention data for the Fairymead soil at the FA2 site. ..................... 60

Figure 27: Photo of the Flagstone soil at the EWA site (photo T.E. Donnollan). ........................................ 63

Figure 28: Comparison of bulk density data for the Flagstone soil at the EWA site.................................... 65

Figure 29: Brooks-Corey fits of water retention data for the Flagstone soil at the EWA site. ..................... 66

Figure 30: Comparison of selected water retention curves. .......................................................................... 69

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