the impact of extreme drought and climate change on the ... · nyngan hay griffith approx. westerly...

Proceedings of the 25th Annual Conference of The Grassland Society of NSW 75

IntroductionClimatic warming during the next century (IPCC 2007) is considered to be one of the primary threats currently facing global terrestrial biodiversity (Thomas et al. 2004). One of the key drivers of population and ecosystem change under global warming is likely to be an increase in the frequency and severity of droughts, heatwaves and floods (Meehl et al. 2000), since extreme climatic events are known to drive rapid demographic and distributional changes in plant populations and ecosystems (e.g., Breshears et al. 2005). Changes in ecosystem structure and function driven by such events are therefore likely to pose a major challenge for ecologists and land managers in coming decades, and new adaptive management strategies will be required to ensure adequate conservation of biodiversity and the maintenance of productive grassland systems.

Spatial heterogeneity and ecosystem resilienceRecently, it has been suggested that an ecoregional approach (Saxon 2003) to biodiversity

The impact of extreme drought and climate change on the demography of plains grass populations in central New South Wales

R.C. Godfree1, B.J. Lepschi2 and M.D. Carnegie3

1 CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601 2Australian National Herbarium, Centre for Plant Biodiversity Research,

GPO Box 1600, Canberra, ACT 2601 3 The Lake Cowal Foundation, PO Box 138, West Wyalong, NSW 2671

[email protected]

Abstract: Over the coming century, climate change is expected to increase the frequency and severity of extreme meteorological events both in Australia and around the world. This presents a major threat to biodiversity and sustainable agriculture, as plant populations will increasingly face abiotic stresses that lie beyond their physiological tolerances. However, it has recently been suggested that biodiversity losses under climate change could be mitigated by the inclusion of spatially heterogeneous habitats within the reserve system. In this paper we test this hypothesis using the results of a study conducted in central New South Wales between 2006 and 2008, in which we quantified the resilience and resistance of populations of plains grass (Austrostipa aristiglumis) to unprecedented drought conditions. We show that small-scale topographic variability generated significant habitat-level differences in drought survival and post-drought recovery of A.aristiglumis, and that populations growing in mesic, low-lying habitats are likely to be persistent even under future climate change scenarios. We conclude that native grass species would likely benefit from the inclusion of spatially heterogeneous landscapes within conservation reserves.

conservation may be the most effective means of producing climate change-resilient (“climate-ready”) ecosystems. This strategy involves the protection of spatially heterogeneous habitats within local and landscape-level conservation reserves or farming systems, which in turn allows plant populations to move to habitat refugia when faced with a changing climate. Capturing variation in micrometeorological and soil conditions via local topography in this way is thought to enhance both the resilience of plant species and populations to disturbance and stress (van de Koppel & Rietkerk 2004).

Currently, however, the effectiveness of this strategy for generating systems that are sufficiently resilient to withstand climate change is unknown for most plant species and plant functional groups. Few studies have determined how local variation in habitat quality enhances the resilience of plant populations to extreme climatic events, and we remain unable to predict the response of most plant species to global warming. In this paper we report on the impact of extreme drought on populations of the keystone native Australian perennial grass

Proceedings of the 25th Annual Conference of The Grassland Society of NSW76

Study site

flatgully

creekbedterrace

slope

a)

b)

4 m

Wyalong

Nyngan

Hay

Griffith

approx. westerly limit of A. aristiglumis

Figure 1. Location and topography of the study site. a) location of study site 30 km east of Wyalong, NSW. The approximate westerly limit of A. aristiglumis in NSW is indicated by the dashed line. b) basic topography of the study site.

0

200

400

600

800

1000

1889 20091950

2006

Year

Tota

l pre

cipi

tatio

n (m

m)

Figure 2. Annual rainfall recorded at Wyalong Post Office 1889–2009. The dashed line indicates the long-term average while the solid line indicates the 10-year running mean.


species Austrostipa aristiglumis (plains grass) in central NSW, and discuss the likely role that spatial variability will play in maintaining resilient grassland populations over the longer term.

The study systemOur work was conducted in a 34 hectare study site located approximately 30 km east of West Wyalong, NSW (S 33° 50.9′, E 147° 33.6′; Fig. 1a). The study site contains a range of habitat types dominated by A. aristiglumis (Fig. 1b), including steeper north-and south-facing slopes, terraces, small gullies and flats, the latter of which are most extensive. The site has low relief, with larger creekbeds lying 3–4 m below the surrounding flats. Grazing pressure at the site is minimal.

Between 2006 and 2008 the study site experienced extreme drought, with 2006, 2007 and 2008 all ranking among the driest 10% of years on record (records since 1889; Fig. 2). Overall, 2006 was the driest year in the instrumental record (180 mm, 65% below normal; Fig. 2), with considerably less rainfall than the next driest year (225 mm in 2002). Annual mean temperatures were also at or near record highs in 2006–2008, resulting in record low monthly and annual atmospheric

water balances at the study site during this period.

Impact on demography of A. aristiglumis

The unprecedented drought conditions experienced between 2006 and 2008 resulted in dramatic changes in the size and structure of A. aristiglumis populations in all of the primary habitats investigated at the study site. Repeated surveys of A. aristiglumis populations over the study period showed that the most acute period of drought (July 2006 to December 2007) caused the death of 40% to 98% of all adult tussocks, with the highest mortality rates occurring on steeper sloping terrain (98%) and on the spatially extensive A. aristiglumis flats habitat (96%), despite the fact that prior to drought the density of A. aristiglumis tussocks was highest on flats (Table 1). In contrast, tussock mortality in low-lying gully and terrace habitats was lower (40–75%), most likely due to a higher overall soil moisture content. These data clearly show that the resistance (i.e., the ability to resist change) of A. aristiglumis populations to extreme drought is strongly influenced by local variation in topography, with low-lying mesic habitats providing drought refugia for adult tussock plants.

1Several minor habitats contributing 29% of the total area are not shown. Slopes refer to north-facing slopes.2Density of adult tussock plants >1 year old.3Percentage mortality over the period July 2006 – Dec 20074Time until <1% of the population remains under recurring extreme drought (based on July 2006–July 2007 drought conditions).

Habitat type

Flat Terrace Slope Gully

Slope (degrees) 1.0 2.3 11.2 1.5

Area (% of total) 48 12 6 5

Density (m-2)2

July 2006 3.7 3.2 0.3 2.8

Dec 2007 0.2 1.9 0.0 0.7

July 2008 1.4 3.9 0.1 5.2

Drought mortality (%)3 96 40 98 75

Persistence time (yr)4 3 13.5 2.5 6

Table 1. Demography of A. aristiglumis populations in four key topo-edaphic habitat types based on data collected during the extreme drought period of July 2006 – July 2008.


Follow-up surveys conducted in July 2008 show that significant recovery of adult A. aristiglumis populations had occurred in all habitats, following widespread recruitment from the seedbank in autumn and winter 2007. Indeed, by July 2008 the density of adult A. aristiglumis tussocks exceeded the pre-drought density in both terrace and gully habitats (Table 1), mainly due to very high seedling recruitment rates in these environments. In contrast, populations declined overall on slopes and flats between 2006 and 2008, with virtual extirpation occurring on sloping terrain (Table 1). Consequently, the resilience of A. aristiglumis populations (the ability to return to a prior state following disturbance) was also higher in terrace and gully habitats.

Matrix-based population models constructed using life history data collected over the course of the study provide further indication that A. aristiglumis populations growing in mesic habitats at the study site are more likely to persist under chronic drought than populations in dry habitats. Population projections based on life history data collected between July 2006 and June 2007 indicate that A. aristiglumis populations in mesic habitats would persist for 6–14 years even under recurring, extreme drought, before declining to <1% of their pre-drought size (Table 1). This compares with 2–3 years in drier slope and flat habitats, where persistence is mainly a function of the longevity of the seedbank.

Prospects for A. aristiglumis under climate changeOver the coming century much of south-eastern Australia is expected to become significantly warmer and drier, particularly in winter and spring (Hennessy et al. 2004); by 2070 the study region could see a 2–5% decline in annual rainfall, a 2–4% increase in potential evapotranspiration, and a 1–2°C increase in annual temperature (see www.climatechangeinaustralia.gov.au). These changes would result in the climate of the study area approximating that currently experienced by Nyngan, NSW, which lies 260 km to the north. Interestingly, at Nyngan, and at comparable locations to the west of Wyalong with similar atmospheric water balances (e.g.,

Hay and Griffith, NSW; Fig 1a), A. aristiglumis has only a scattered distribution in mesic habitats along rivers. This distributional range, along with the demographic data discussed above, suggests that drying and warming of the climate over the next century would increasingly restrict A. aristiglumis to local topoedaphic riverine refugia, where resilience of populations to drought is highest. This appears to be true even in regions near Wyalong that lie near the centre of the species distribution.

The contraction of A. aristiglumis towards small-scale refugia under a warming and drying climate would pose significant challenges for land managers. From a conservation perspective, A. aristiglumis is a keystone species in a range of endangered native grasslands in south-eastern Australia (DEWHA 2010) and its decline would significantly alter the composition and structure of these communities. While our data indicate that, even under climate change, viable populations would continue to exist in mesic habitats, these comprise only a small fraction of the landscape (<20% at our study site) and so the continued existence of widespread A. aristiglumis-dominated grassland ecosystems in south-eastern Australia appears uncertain.

Finally, A. aristiglumis is also an important forage pasture species over much the western slopes of NSW, particularly on self-mulching vertosols (McKenzie et al. 2004). Our data suggest that in drier parts of its range, adaptation to future climate change may necessitate the establishment of more drought-tolerant ecotypes, or even the replacement of A. aristiglumis with more drought tolerant species. Future work will focus on the ability of A. aristiglumis and other native grassland species to adapt to climate change through expression of phenotypic plasticity or micro-evolution for stress tolerance.

ConclusionsThe results of our work support the hypothesis that local topographic variation generates variation in the resilience and resistance of native grass populations to extreme drought. Indeed, even topographic relief of only 3 to 4 m can produce significant variation in drought survival, seedling recruitment rates and the


overall drought persistence of A. aristiglumis populations. We are therefore confident that A. aristiglumis, and probably other native grass species as well, would benefit from an ecoregionally-based conservation and management strategy for climate adaptation based on the inclusion of spatially heterogeneous landscapes within conservation reserves.

AcknowledgementsWe would like to thank Kim Block for access to the field site.

ReferencesBreshears, DD, Cobb, NS & Rich, PM. (2005) Regional

vegetation die-off in response to global-change-type drought. Proceedings of the National Academy of Sciences 102, 15144–15148

DEWHA, (Department of the Environment, Water, Heritage and the Arts) (2010) Natural grasslands on basalt and fine-textured alluvial plains of northern New South Wales and southern Queensland in Community and Species Profile and Threats Database, Department of the Environment, Water, Heritage and the Arts, Canberra. Available from: http//www. environment.gov.au/sprat

Hennessy, K, Page, C, McInnes, K, Jones, R, Bathols, J, Collins, D & Jones, D (2004) Climate change in NSW. Part 1: past climate variability and projected changes in average climate. CSIRO (Commonwealth Scientific and Industrial Research Organisation) consultancy report for the New South Wales Greenhouse Office. Climate Impact Group, CSIRO Atmospheric Research, Aspendale

IPCC, (Intergovernmental Panel on Climate Change) (2007) Climate change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the IPCC. Cambridge University Press, Cambridge, UK.

McKenzie, N, Jacquier, D, Isbell, R & Brown, K (2004) Australian soils and landscapes. (CSIRO Publishing, Collingwood, Victoria, Australia).

Meehl, GA, Zwiers, F, Evans, J, Knutson, T, Mearns, L & Whetton, P (2000) Trends in extreme weather and climate events: issues related to modeling extremes in projections of future climate change. Bulletin of the American Meteorological Society 81, 427–436.

Saxon, EC (2003) Adapting ecoregional plans to anticipate the impact of climate change. In: Drafting a conservation blueprint: a practitioner’s guide to planning biodiversity (Ed. Groves CR) pp. 319–344. (Island Press, Washington, DC).

Thomas, CD, Cameron, A & Green, RE (2004) Extinction risk from climate change. Nature 427, 145–148.

van de Koppel, J & Rietkerk, M (2004) Spatial interactions and resilience in arid ecosystems. The American Naturalist 163,113–121.


IntroductionUltimately the nutritive value of the diet of grazing animals depends on what they eat, and determination of the nutritive value of the diet of grazing ruminants is still one of the major challenges of grazing scientists and managers, especially when the grazing environment is highly diverse, as is the case for the Australian grasslands and rangelands. In these environments the pastures are heterogeneous and, frequently, the plant assortment is highly complex.

Faecal analyses are effective methods for compiling information about the diets of animals. Sample collections are easy and fast to carry out and unlimited in the number of samples collected, which is ideal for grassland and rangeland environments. Faecal fractions such as faecal fibre, lignin and nitrogen (N) or faecal near infrared spectroscopy (fNIRS) have been used to predict the quality of the diet of grazing animals. Vera (1973) and Hodgman et al. (1996) showed the potential of faecal fibre fractions to predict digestibility and energy contents of ruminant diets. Faecal N has been found to be closely associated with dietary N (Holecheck et al. 1982; Mubanga et al. 1985), organic matter digestibility (OMD, Boval et al.

Determining the quality of diets of grazing animals

G.L. KrebsA, M.B.P. Kumara MahipalaB, P. McCaffertyC, and K. DodsC

AE.H. Graham Centre for Agricultural Innovation, School of Animal and Veterinary Sciences, Charles Sturt University, Wagga Wagga, NSW, 2678; [email protected]

BSchool of Agriculture and Environment, Curtin University of Technology, GPO Box U1987, Perth, WA, 6845.

CChemCentre, PO Box 1250, Bentley Delivery Centre, WA 6983. [email protected]

Abstract: Predicting growth rates or determining the needs for supplementary feeding of grazing animals requires knowledge of the nutritive value of the diet the animals are consuming. Faecal analyses are non-invasive and effective methods for compiling information about the diets of animals. In this study the usefulness of faecal chemistry and near infrared spectroscopy (fNIRS), either used individually or in combination to predict the quality of mixed diets fed to sheep, was investigated. Faecal nitrogen, ash, neutral detergent fibre and lignin contents can be successfully used to predict the metabolisable energy content and the organic matter digestibility of the diet as well as the type of rumen fermentation (in terms of short chain fatty acids) whilst fNIRS calibration equations can be successfully used to predict the crude protein, total phenolic and total tannins contents of mixed diets consumed by sheep.

2003) and metabolisable energy (ME) content (Kamler & Homolka, 2005) of typical (grass/legume) ruminant diets. However, faecal N is less useful for predicting the quality of diets containing forages high in soluble phenolics and tannins (as is typical of many plants found in rangeland grazing environments). Condensed tannins (CT) bind to fibre and protein in the ruminant digestive tract (Degan et al. 1995; Makkar et al. 1995), increasing the excretion of faecal N and fibre (Ben Salem et al. 2005; Kaitho et al. 1998; Krebs et al. 2007). The increased faecal N values may misleadingly suggest diets are high in protein.

Faecal NIRS equations have been used to predict various nutritional parameters of mixed diets fed to ruminants (Boval et al. 2004; Landau et al. 2004; Landau et al. 2008; Li et al. 2007). Each livestock species is unique in its digestive physiology (Huston et al. 1986) and, therefore, fNIRS equations derived for one livestock species may not be applicable for another, essentially due to spectral differences. Generally, fNIRS requires calibration equations to be developed for each of the diet types under consideration. However, Decruyenaere et al. (2009) derived a fNIRS calibration to predict in vivo organic


matter digestibility (OMD) of sheep diets containing a wide range of temperate forages.

In this study the usefulness of faecal chemistry and fNIRS, either used individually or in combination to predict the quality of mixed diets fed to sheep was investigated.

MethodData and faecal samples collected from five sheep digestibility trials using mixed (browse and grass) diets conducted during the period 2006–2008 were used for the study. In total, 40 experimental diets consisting of varying levels of (fresh) browses (Acacia saligna [saligna], Chamaecytisus palmensis [tagagaste], Atriplex amnicola [river saltbush], Atriplex nummularia [Oldman saltbush] and Rhagodia eremaea) and oaten (Avena sativa) chaff were fed to individually penned sheep at a daily forage DM intake equivalent to 2% of the body weight of the sheep.

Feed and faecal samples collected from each sheep were analysed for neutral detergent fibre (NDF), acid detergent fibre (ADF), lignin, ash and crude protein (CP) contents. Total phenolics (TP) and tannin (TT) contents and in vitro gas production of the feed samples were also measured, according to the procedures described by Makkar (2003). Organic matter digestibility (OMD), short chain fatty acid production (SCFA) and metabolisable energy (ME) content of the diets were determined using the net 24 h gas volume (GV), CP and ash contents (Getachew et al. 2002; Menke & Steingass 1988).

Feed and faecal data were pooled. Pearson correlation coefficients (r) among feed and faecal variables were estimated. The predictive regression models of dietary CP, TP, TT, OMD, SCFA, and ME were developed from faecal indices by a stepwise regression procedure. Faecal N, ash, lignin/NDF and lignin/ADF were specified independent variables. The stepwise regression procedure adds independent variables one by one to the model and proceeds towards increasing of the precision. The model was specified to retain those coefficient of independent variables significant at P<0.05

level. The significant (P<0.05) predictive model with the highest R2 and lowest residual standard deviation (RSD) was selected (i.e. best-fit predictive model). This model was then used to predict nutritional characteristics of diets included in a validation trial from respective faecal indices.

Ground faecal samples were scanned over the range 1100–2498 nm in 2 nm increments using a Foss 6500 NIR system. Results of dietary chemical analysis (CP, TP, TT), digestibility (DM digestibility, OMD, CP digestibility) and ME were used as reference values. Calibration equations were developed using version 1.04a of WinISI (II) software. The calibration relies on modified partial least squares (MPLS) procedure (Martens & Naes 1987). First order derivatives were used in the calibrations, with scatter correction. A global H (GH) factor of 3 was applied to eliminate outliers. GH, the standardised Mahalanobis distance, ascertains the degree of difference of the result in the data set – those with a GH of 3 or greater are eliminated, to retain the rigor and accuracy of the calibration data set. The precision of calibrations was evaluated by the coefficient of determination (R2

c) and standard error of calibration (SEC). The predictive ability of calibrations was internally evaluated by standard error of cross-validation (SECV) and standard error of prediction (SEP) (Landau et al. 2006; Stuth et al. 2003). The slope of the validation regression (Landau et al. 2006) and the ratio of the standard deviation of the original data to the SECV (RPD, Williams & Sobering 1993) were used to evaluate accuracy of calibrations. The fNIRS equations with R2

c and RPD greater than 0.80 and 3, respectively were considered as acceptable predictive equations (Williams 2004).

Results None of the investigated faecal chemical properties had strong (significant) correlation with dietary CP content. The best-fit regression models predicting dietary TT, TP and ME contents, OMD and SCFA from faecal(f) N, fash and flignin/fNDF had high R2 and low RSD (Table 1). However, the regressions between measured and predicted TP and TT contents


had positive intercepts (13.90 and 11.62, respectively; P<0.05) and low R2 (0.62 and 0.65, respectively). In addition, the slopes of these regressions were much lower than 1.0 (0.50 for TP and 0.61 for TT). Regressions between measured and predicted OMD, SCFA and ME contents did not have significant intercepts and both the slope and R2 of these regressions were close to 1.

Calibration and validation of the fNIRS prediction equations for chemical and functional nutritive attributes of the mixed (browse and grass) sheep diets are presented in Table 2. The R2

c was greater than 0.80 for all fNIRS calibrations. The SEC was close to the respective SECV. The slope of the validation regressions (i.e. predicted values against respective reference data) of chemical

attributes did not deviate from 1 while that of functional attributes (except SCFA) deviated from 1. The RPD of DMD and OMD was less than 3 but was greater than 3 for other (i.e. CP, TP, TT, PPC, P, CPD, IVOMD, ME, SCFA) calibrations.

DiscussionIf a predictive regression model is perfect, the validation regression will have an insignificant intercept, a slope of 1 and a R2 of 1. The positive (P<0.05) intercept recorded for validation regression for TP and TT indicated an over estimation of the variables by the predictive models. On the other hand, the considerably low slope (compared to a perfect prediction) indicated underestimation of the predicted value.

Diet characteristic Predictive regression model (P<0.05) Adjusted R2

RSD

Crude protein CP= 58.82729 + 107.83681(fLignin/fNDF) 0.21 2.15

Total phenolics TP = 2.2036 + 1.55408(fN) – 0.14331 (fAsh) + 32.22348 (fLignin/fNDF) 0.89 0.45

Total phenolics TT = –17.43746 + 1.36504 (fN) + 50.37654 (fLignin/fNDF) – 0.04475 (fAsh) 0.87 0.44

Organic matter digestibility

OMD = 814.55657 – 514.4869(fLignin/fcNDF) – 0.93196(fAsh) – 5.4971(fN) 0.78 3.45

Short chain fatty acids

SCFA = 1.64152 – 0.00256(fAsh) – 1.55683(fLignin/fNDF) – 0.01352 (fN) 0.78 0.01

Metabolisable energy

ME = 12.32323 – 8.25181(fLignin/fNDF) – 0.01522(fAsh) – 0.07933(fN) 0.78 0.05

f: faecal

Table 1. Best-fit regression models

Attribute Calibration statistics Validation statistics RPD

R2C R2

C R2CV SECV SEP Slope Bias

CP† 0.96 3.97 0.94 4.91 6.69 0.95 0.87 4.19

TP† 0.96 3.09 0.92 4.34 9.13 0.85 1.28 3.45

TT† 0.93 2.89 0.90 3.44 5.83 1.04 0.44 3.13

DMD† 0.83 21.6 0.79 24.3 40.7 0.74 3.23 2.18

CPD† 0.95 38.5 0.94 42.7 175.9 0.51 17.3 3.95

OMD† 0.85 21.6 0.80 25.0 46.6 0.65 5.11 2.21

ME†† 0.95 0.24 0.93 0.30 0.98 0.62 0.09 3.80

SCFA††† 0.94 0.05 0.92 0.06 0.12 0.80 –0.02 3.49

R2c, R

2 of calibration; SEC, Stranded error of calibration; R2cv: R

2 of cross validation; SECV: Stranded error of cross validation;

SEP: Stranded error of prediction; RPD: SD/SECV; †: g/kg DM; ††: MJ/kg DM; †††: mL/0.2 g DM

Table 2. fNIRS calibration performance of chemical and functional nutritive attributes of mixed (browse and grass) sheep diets


Such association is undesirable in a predictive equation (Draper & Smith 1981). Therefore, the validity of the predictive regression models of TP and TT is less. Insignificant intercept and slope close to 100% with very high R2 of validation regressions for OMD, SCFA and ME imply that the predictive models approached a highly accurate prediction. Therefore, the best-fit predictive regression models for OMD, SCFA production and ME derived from faecal chemical components will be useful in the field where sheep are consuming mixed diets.

Faecal NIRS calibrations developed to estimate dietary chemical attributes (CP, TP and TT) had excellent performance. The R2

c (0.93–0.98) and RPD (3.10–5.9) were well above the minimum acceptable levels for NIR calibrations (Stuth et al. 2003; Williams 2004). The slope of validation regressions being close to 1 (0.85–1.07) confirmed that the calibrations derived for dietary chemical attributes do not under- or over-estimate the true values. In addition, the estimates of SEC, SECV and SEP were small, and the difference between SEC and SECV was marginal.

The low RPD (<3) of DMD and OMD calibrations indicated low accuracy due to greater variability in predicted data compared to reference data (Williams 2004). Low slopes (0.51–0.65) of OMD and ME calibrations would seriously underestimate the respective predictions.

In conclusion, whilst neither method (faecal chemical composition or fNIRS) could be used exclusively to predict the nutritive value of the diet, combining both methodologies would be useful for application in the field. Faecal chemistry is appropriate for predicting the OMD and ME content whilst fNIRS can be used to predict the CP, TP and TT contents of mixed diets consumed by sheep.

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Ben Salem, L (2005) Effect of early experience and adaptation period on voluntary intake, digestion and growth in Barbarine lambs given tannin-containing (Acacia cyanophylla Lindl. foliage) or tannin-free (oaten hay) diets. Animal Feed Science and Technology 122, 59–77.

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• Increases pasture productivity.• Controls and suppresses problem grass and broadleaf weeds.• Manipulates pasture composition to allow growth of desirable

species (soft on clover, medic and lucerne).


IntroductionClimate variability is a major issue facing producers (Lodge et al. 2009a) as they try to maintain production from their feed base. The variability we have been experiencing in our climate over the last few years (e.g. Lodge and McCormick 2010b) is setting the scene for the future, and as an industry we need to have flexibility within our grazing systems to help meet the challenge. In the coming years, producers who are equipped to manage this variability and the predicted climate change (e.g. Cullen et al. 2009) will be better positioned. This variability can be managed, with flexibility within livestock enterprises and by utilising a range of forage sources that produce high quality feed at different times of the year under different environmental conditions. In northern New South Wales (NSW), native pastures play a significant role, as does lucerne, forage oats and more recently tropical perennial grass pastures.

Northern inland NSW has significant summer and winter rainfall, providing a unique and challenging environment for perennial pastures. Summer rainfall tends to be relatively ineffective as it falls as storms and is quickly lost through evapotranspiration due to high temperatures. In contrast, winter rainfall is more effective and useful for refilling the soil profile (Murphy et al. 2004, 2010). While this may make the area potentially suitable for both summer- and winter-growing pasture species, the challenge is for these species to survive hot summers and cold

Recent tropical perennial grass research and their potential role in maintaining production in a variable and changing climate

S.P. Boschma, G.M. Lodge, L.H. McCormick

Industry & Investment NSW, Primary Industries, 4 Marsden Park Rd, Calala NSW 2340 [email protected]

Abstract: Tropical perennial grass pastures have come under the spotlight for their capacity to respond quickly to summer rainfall and produce large quantities of herbage. These pasture traits are valuable in an area with a highly variable climate, but fertility and grazing management are essential to maintain the quality of a tropical grass pasture. This paper summarises some of the results from research conducted at Tamworth, NSW, the characteristics of sown tropical perennial grass-based pastures, their role in farming systems under future variable and/or changed climates, and some future research areas.

winters. To do this sown temperate perennial grasses need to be summer dormant (Boschma et al. 2009), while sown tropical perennial species need to be frost-tolerant (McCormick et al. 1998; Boschma et al. 2009). Recent studies conducted on the North-West Slopes of NSW have shown that the most persistent and productive pasture options available are tropical perennial grasses and lucerne (Boschma et al. 2009; Boschma et al. 2010).

Tropical grasses were first evaluated in northern NSW in the 1950s (Johnson 1952; Buckley 1959). Although their potential was recognised and their use recommended, limited seed availability and the pursuit of cropping resulted in low adoption. During the 1970s, species were evaluated on the North-West Plains (Watt 1976) and establishment methods investigated in the 1980s−1990s (Bowman 1990; Campbell et al. 1993). Widespread evaluation of grass species and cultivars was conducted during the 1990s at over 27 sites in an area from Forbes in central NSW to the Queensland border and west from Scone to Walgett (McCormick et al. 1998).

Despite tropical perennial grasses being available for 60 years, it is only in the last ~10 years that there has been widespread interest in these grasses and a rapid increase in the area sown. Estimates from commercial seed sales in NSW indicate that over 250,000 ha have been sown over the last 3 years (LH McCormick, pers. comm.). This interest was sparked by the ability of tropical perennial grass pastures to


respond to summer rainfall and produce large quantities of herbage in recent years which have been characterised by highly variable seasons (e.g. Boschma et al. 2009) and long dry periods with predominantly dry autumns (Lodge and McCormick 2010b).

In this paper, we outline some of the results from recent research at Tamworth, NSW, the characteristics of sown tropical perennial grass-based pastures, their role in our farming systems under future variable and/or changed climates, and some future research areas.

Characteristics of sown tropical perennial grass pastures

The seasons we have experienced over the last decade or so have highlighted the productivity and resilience of tropical perennial grasses. During this time, temperate perennial grasses

and annual legumes have often failed to persist or respond to intermittent rainfall events, and native pastures have been persistent, but not highly productive. In contrast, tropical grass pastures have responded quickly to summer rainfall producing large quantities of herbage, which has been invaluable, particularly when there has been a lack of follow-up rain. They have also shown good persistence under extended dry periods and a wide range of grazing management.

Tropical perennial grasses are adapted to a wide range of environments and soil types with different pH (Table 1). There is also a range in their tolerances for aluminium toxicity, inundation by flooding, and salinity. Pastures have been successfully established on a broad range of soils and environments throughout northern inland NSW including the Northern

Species and cultivar Light Medium Heavy

Sand, sandy loam;

pHCa <5.0–7.0

Clay loam, silty clay loam;

pHCa 5.0–7.0

Red/grey clay, black earth;

pHCa 6.0 –8.0

Digit grass (Digitaria eriantha ssp. eriantha ) cv. Premier

Forest bluegrass (Bothriochloa bladii ssp. glabra) cv. Swann

Rhodes grass (Chloris gayana)

cv. Pioneer

cv. Katambora

Buffel grass (Cenchrus ciliaris)

cv. America and Gayndah

cv. Biloela

Lovegrass (Eragrostis curvula type conferta) cv. Consol

Creeping bluegrass (Bothriochloa insculpta) cv. Bisset

Panic (Panicum coloratum var. makarikariense) cv. BambatsiA

Purple pigeon grass (Setaria incrassata) cv. InverellBC

Bluegrass (Dicanthium aristatum) cv. FlorenA

A Tolerant of flooding; B Tolerant of waterlogging; C Performs with higher nutrition;

Table 1. Tropical grass species and cultivars suitable for light, medium, heavy and saline soils in northern inland NSW (McCormick et al. 1998).


Tablelands at Bundarra, west of Guyra and near Woolbrook, at altitudes as high as 1000 m.

In inland NSW, tropical pastures grow during the warmest months of the year. Growth commences in spring as day temperatures rise and slows in late summer and autumn as overnight temperatures fall, ceasing when frosts commence, with little to nil growth in the winter period. Therefore, tropical perennial grasses can be productive for ~9 months of the year on the North and Central-West Plains, 7–8 months on the North-West Slopes and 5–6 months on the Northern Tablelands. They also have high water use efficiencies, with for example, Premier digit (Digitaria eriantha ssp. eriantha) and Katambora Rhodes (Chloris gayana) producing 32.4 and 22.3 kg dry matter (DM)/ha/mm of water, respectively, compared with 6.5 kg DM/ha/mm from a native pasture dominated by summer-growing grasses (Murphy et al. 2008a, Table 2).

Tropical grasses respond well to good nutrition, and grazing management is the key to maintaining forage quality. All grasses need nitrogen (N) to maximise herbage production and protein levels for optimum livestock performance. The nutritive value of tropical grasses is lower than that of temperate grasses at the same growth stage, but temperate and tropical grasses grow at different times of the year so direct comparisons are often irrelevant. When assessing the role of tropical grass pastures on your farm they should be compared with other summer-growing species such as forage sorghum, lucerne and native pastures dominated by summer-growing grasses.

Tropical grass pastures have several environmental benefits. These include the ability to maintain

high ground cover year-round, reducing runoff and soil erosion. Ground cover of at least 70% can be achieved within the establishment year (SR Murphy, unpublished data) and maintained by good grazing management. Once established, tropical grass pastures are effective at controlling weeds such as spiny burr grass (Cenchrus incertus or C. longispinus), blue heliotrope (Heliotropium amplexicaule), lippia (Phyla canescens) and galvanised burr (Sclerolaena birchii) (McCormick 2004). Tropical grasses produce large amounts of herbage and have large, fibrous root systems which may help improve soil carbon levels and soil structure, particularly on old, degraded cropping lands. They are also deep rooted (Murphy et al. 2008b, Table 2) so are effective in reducing water tables and ground water recharge in salinity prone areas (Lodge et al. 2010a).

Tropical pastures in our farming systemsTropical perennial grass establishment

Establishing a tropical grass pasture requires planning and preparation. Weed control is essential for up to 2 years prior to sowing to reduce annual summer grasses (Lodge et al. 2010b). Choose a grass and cultivar suitable for the soil type in your paddock (McCormick et al. 1998, Table 1) and buy seed with good purity and germination (McCormick et al. 2009). Seed quality can be extremely variable so always ask for a copy of a recent certificate of seed analysis. Tropical grass seed is commonly bought as a mixture of species. This has the advantage of each species finding its niche in the paddock, but some grass seedlings are more competitive than others. For example, Katambora Rhodes grass is more competitive than both Premier digit and Bambatsi panic (Panicum coloratum

Species Soil drying (mm)

Herbage mass (kg DM/ha)

Water use index (kg DM/ha/mm)

Rooting depth (m)

Premier digit 137 16157 32.4 1.2

Katambora Rhodes grass 149 11516 22.3 1.6

Swann forest bluegrass 119 6893 13.7 1.4

Native grasses 39 2689 6.5 1.0

Table 2. Soil drying, herbage mass, water use index and rooting depth of 3 tropical grass species and a native grass pasture [dominated by Bunderra wallaby grass (Austrodanthonia bipartita), redgrass (Bothriochloa macra), bluegrass (Dichanthium sericeum) and windmill grass (Chloris truncata)] from September 2006−May 2007 (Murphy et al. 2008a, b).


var. makarikariense) and should not exceed 25% of the seed mix (Lodge et al. 2009b).

Tropical grasses should be sown in the warmer months of the year. In northern NSW, tropical grasses are best sown from November–January, although sowing in November increases the likelihood of sufficient rainfall to establish the pasture (Lodge and Harden 2009). Sowing after early February on the North-West Slopes and early-January on the Northern Tablelands should be avoided, as the risk of plant losses from frost increases. Late sowing can result in plant losses of up to 70% of some species when they are not well established (Lodge et al. 2010b). Tropical grass seed is generally small and needs to be sown shallow at ~10 mm depth. Sowing into cereal stubble may assist establishment in marginal years (MA Brennan, unpublished data) and it is important to have ~1 m of subsoil moisture (Lodge and McCormick 2010a) to promote early growth. Further information on establishing tropical grasses can be found on the Industry & Investment NSW website (www.dpi.nsw.gov.au/primefacts), and Lodge and McCormick (2010a) have provided tips for establishment.

Managing an established tropical grass pasture

Once established, tropical grass pastures are responsive to nutrition and management. To achieve the best value from a tropical pasture it needs to be treated as a high value crop and managed to its potential (McCormick 2004).

Tropical grass pastures are generally considered to be better suited to cattle, but they are also suitable for sheep – grazing management is the key.

Tropical grasses can have growth rates of ~170 kg DM/ha/day when there is good soil moisture and fertility. Without N, growth rates decline to ~35 kg DM/ha/day and growth ceases (<10 kg DM/ha/day) when available soil moisture is low (SP Boschma, unpublished data). As a general rule-of-thumb, for every kg of N applied, an additional 100 kg of herbage can be produced over a growing season. For example, at Tamworth unfertilised Premier digit produced 5000 kg DM/ha over the 2007–08 season,and 15000 kg DM/ha when fertilised with 100 kg N/ha.

One of the biggest challenges with tropical grass pastures is maintaining high feed quality. This can be achieved with good soil fertility and grazing management. Fertility can be improved by annual application of fertiliser, including N applied either as fertiliser or provided by a legume in the pasture. Good grazing management is required to maintain the pasture in a vegetative state, because once stem elongation commences the quality of the pasture decreases. This is because flowering plants have a higher proportion of stems, which have lower quality and a lower green leaf quality. Recent research at Tamworth has shown that crude protein and metabolisable energy levels of Premier digit defoliated every 2 weeks were higher than when defoliated every 6 weeks (Table 3). These studies also showed that the proportion of leaf after 2 weeks regrowth

Table 3. Crude protein (%) and metabolisable energy (MJ/kg DM) of green leaves of Premier digit unfertilised or fertilised with 100 kg/ha nitrogen during the growing season (SP Boschma, unpublished data).

Month 2-week regrowth 6-week regrowth

Unfertilised Fertilised Unfertilised Fertilised

Crude protein (%)

November 15.9 18.7 14.2 17.0

January 14.7 18.4 13.4 16.9

March 13.1 18.0 11.8 17.4

Metabolisable energy (MJ/kg DM)

November 9.5 9.6 9.1 8.6

January 9.1 9.5 9.2 9.5

March 7.1 7.7 7.2 7.3


was ~75%, but declined to ~30% after 6 weeks of regrowth (SP Boschma, unpublished data). Unfertilised tropical grass pastures can utilise soil N that results from mineralisation in winter, but this N is rapidly depleted, and so plant crude protein levels often decline. In contrast, when the pasture is fertilised with 100 kg N/ha, crude protein levels are maintained throughout the summer growing season (Table 3).

All grasses need adequate N to maximise protein levels for optimum livestock performance. Research has shown that if the crude protein content of tropical grasses falls below 6–8%, animal intake will be depressed because of a crude protein deficiency in the animal’s rumen (Minson 1990). Crude protein levels are lower when the pasture is unfertilised, allowed to flower or to accumulate large amounts of stem and dead material. Raising crude protein levels from 4.1 to 9.9%, increased dry matter intake of beef cattle from 4.3 to 7.7 kg/head/day. Similarly, when fed unfertilised tropical grass, cattle lost 0.22 kg/head/day, but when fed fertilised grass they gained 0.69 kg/head/day (Chapman and Kretschmer 1964). Recent work at Tamworth (e.g. Table 3) suggested that animal production from a tropical grass pasture may be limited by energy not protein. To more fully understand the role of these pastures in livestock production systems a better understanding of the role of different supplements throughout the year is required.

In the middle of summer, when there is good soil moisture, tropical pastures require high stock numbers and regular grazing to maintain them in a high quality, leafy stage of growth. For a tropical grass pasture growing at 100 kg DM/ha/day, for example, the stocking rates required to prevent the pasture from accumulating herbage would be ~100 lambs/ha (25 kg liveweight with an intake of ~1 kg DM/head/day) or 13 steers/ha (~300 kg liveweight, intake ~7.5 kg DM/head/day) (Bell 2006). Therefore, in the growing season, these pastures need to be either set stocked or rotationally grazed with only a couple of weeks rest, both at high stocking rates, to prevent the pastures from flowering and producing too much stem material.

High utilisation of tropical grass pastures may well require paddocks being subdivided into smaller areas which are easier and more flexible to manage. As an example, if a farm had 4 paddocks of tropical pastures, in spring these could be heavily grazed, but following summer rainfall pasture growth rates will be higher and so rest periods between grazings may need to be shortened and possibly only 2 paddocks grazed to keep the pasture vegetative and maintain quality. Alternative strategies for using excess forage could include; buying additional store stock to fatten; turning the excess feed into hay or silage; leaving the ungrazed paddocks to be used as a ‘standing haystack’ in winter with supplements; or a combination of these options. Some producers are adopting the coastal strategy of, slashing or mulching their tropical grass pastures to keep them in a leafy vegetative growth stage.

Legumes are the most sustainable means of providing N and lifting the overall quality of a pasture. Research on the North-West Slopes is currently investigating a range of annual and perennial legumes for use in tropical grass pastures (Boschma and Harris 2009). At Tamworth, the summer-growing perennial legumes lucerne (Medicago sativa), desmanthus (Desmanthus virgatus cv. Marc), round-leaf cassia (Chamaecrista rotundifolia cv. Wynn) and leucaena (Leucaena leucocephala ssp. glabrata cv. Tarramba) are showing potential (SP Boschma, unpublished data). At Bingara, Phoenix birdsfoot trefoil (Lotus corniculatus) a newly developed medium leaf, fine stem type that is high yielding in cool and warm season environments (Ayres et al. 2008) is also showing potential (CA Harris, unpublished data). Desmanthus, round-leaf cassia and leucaena are tropical legumes and their foliage is frosted in winter, but desmanthus and leucaena reshoot from plant crowns in spring. Round-leaf cassia plants are killed by severe frost, but following spring rainfall regenerate from seed set the previous year. Annual legumes are also being investigated, although dry autumns in the last few years have been unsuitable for establishment and regeneration of annual legumes (Lodge and McCormick 2010b). These studies will continue until June 2011.


Role of tropical grass pastures in future environments of variable climatesRainfall variability and changed rainfall patterns, higher temperatures and higher levels of atmospheric carbon dioxide are likely to be features of future environments. At Barraba in northern NSW, for example, annual rainfall in the past 10 years (2000–09), has been below the long-term average (Lodge and McCormick 2010b), while rainfall received in December has been higher than average. This would have favoured the establishment and growth of tropical perennial grass pastures and to some extent may have ‘buffered’ the declines in production from annual legumes (e.g. subterranean clover and annual medics), forage oat and lucerne pastures in autumns that were markedly drier than average. This trend may continue in the future, with feed grown in summer increasingly being used to offset production declines in other seasons.

Similarly, climate change predictions for a site near Barraba (Cullen et al. 2009; Lodge et al. 2009a), indicated that by 2030 annual temperatures were likely to be 1.2oC higher (high-emissions scenario) and rainfall to remain unchanged compared with the baseline period of 1971–2000. By 2070, temperatures were predicted to be 2.7oC higher for a mid-emissions scenario and 4.4oC higher for a high-emissions scenario, but annual rainfall increases were only ~1.0% higher than the baseline period. However, at Barraba, the trend in the climate change projection data was for total annual rainfall to increase by up to 12% compared with the long-term mean and for rainfall in January–February to be higher (Lodge and McCormick 2010b). Other climate change models have indicated that rainfall in the future may increase in spring and decrease in autumn (Watterson et al. 2007). These changes in rainfall pattern, combined with the predicted temperature increases, would favour the establishment and growth of tropical species.

Future research for tropical grass pastures in NSWThe potential for tropical pastures in NSW is still largely untapped. Demand for red meat is predicted to increase, with greater quantities required for both the domestic and export

markets. To achieve this, livestock numbers will need to increase, as will the quantity and quality of pastures to feed them. In the summer dominant rainfall areas of northern NSW, tropical pastures have an important role on-farm in contributing to an improved supply of forage throughout the year.

Over the past few years there has been some discussion on the potential of tropical grass pastures in the more winter rainfall dominant areas of southern NSW, but their persistence and productivity in environments with less summer rainfall needs to be determined.

If the summer-growing perennial legumes that are showing promise in current studies continue to persist, then further research will be required to develop the best methods for their establishment and management in future environments.

Evaluation of 130 species/lines of perennial tropical grasses in northern NSW (Harris 2008) has identified elite lines of green panic (Megathyrsus maximus) that are more persistent than the commercial cultivars Gatton and Petrie green panic, which failed to persist for more than 3 to 4 years in the evaluation conducted by McCormick et al. (1998). Promising lines of Panicum coloratum and Rhodes grass have also been identified. These elite lines are currently being evaluated under grazing throughout northern NSW by Industry & Investment (Harris et al. 2009) and Heritage Seeds (W Swann, pers. comm.) and in Western Australia. Several legumes, such as desmanthus, round-leaf cassia and leucaena are also showing some potential for the North-West Slopes and are new to NSW. Further work will be needed to evaluate and incorporate them into future farming systems.

Strategies to utilise carryover herbage produced by tropical grass pastures in the summer-growing season will need to be developed for both current and future farming systems. Studies are needed to determine techniques for maximising vegetative growth in-season, as well as make use of excess herbage out-of-season by using supplements and fodder conservation of hay and silage.


Conclusion

Tropical perennial grass pastures have an important role in grazing systems in northern NSW, and this role is likely to increase given their resilience in our increasingly variable climate. In order for tropical grass pastures to provide quality forage for grazing animals, both high soil fertility and good grazing management are essential. While our knowledge of tropical grass pastures in northern NSW is increasing, further research needs to be conducted, including on suitable legumes and the use of supplementation, and to determine the potential of tropical grasses in southern NSW.

Acknowledgements

The research projects described in this paper were funded by Future Farm Industries Cooperative Research Centre (CRC) (formerly CRC for Plant-based Management of Dryland Salinity), Meat and Livestock Australia and Industry & Investment NSW.

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and Matador – new birdsfoot trefoil cultivars for permanent pasture applications in eastern Australia. In ‘Proceedings of the 23rd Annual Conference of The Grassland Society of NSW’. (Eds SP Boschma, LM Serafin and JF Ayres) pp. 107–109. (NSW Grassland Society Inc.: Orange)

Bell, AK, Ed. (2006) PROGRAZE ™ Manual. NSW Agriculture, Orange and Meat and Livestock Australia. Sixth edition 2003.

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Harris, CA (2008) New Panicum cultivars on the horizon for northern NSW. In ‘Proceedings of the 23rd Annual Conference of The Grassland Society of NSW’. (Eds SP Boschma, LM Serafin, JF Ayres) p. 114 (Grassland Society of NSW Inc.: Orange)

Harris, CA, Boschma, SP & Moore, G (2009) Developing a more productive, persistent panic grass cultivar. Tropical Grasslands 43, 269–270.

Johnson, A (1952) Sown pastures for Inverell, Moree and Boggabilla Districts. The Agricultural Gazette of NSW 63, 343–366, 410–414, 418.

Lodge, GM & Harden, S (2009) Effects of depth and time of sowing and over-wintering on tropical perennial grass seedling emergence in northern New South Wales. Crop & Pasture Science 60, 954−962.

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Lodge, GM, Brennan, MA, Harden S & Boschma, SP (2010a) Changes in soil water content under annual, perennial and shrub-based pastures in an intermittently dry, summer rainfall environment. Crop & Pasture Science 61, 331–342.

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Overview

As a family we have bought into the concept of a ‘WIN/WIN’ scenario when food and fibre production techniques are closely aligned to natural processes in the environment. The WIN for the environment (and the community) is a shift towards natural landscape function which can eliminate many agricultural issues such as erosion, salinity, loss of biodiversity, inefficient mineral cycling, over reliance on chemicals and over simplified soil producing over simplified food. The WIN for farmers is simplification of the production process reducing the reliance on herbicides, pesticides, synthetic fertilisers, expensive seed and energy which all lead to high break even points and the constant need to tweak and fight nature.

When a regenerative farmer is achieving production levels which match profit levels of high input systems they have an advantage by minimising the continual pressure to increase output just to break even.

Productivity gains are good but this should not be the only focus for agriculture into the future. At some point the economic and environmental costs of focussing on productivity in isolation will exceed the benefits.

Regenerative production systems provide an opportunity to break this cycle and in our view a worthy long term aspiration.

Good soil health for us !!

Our idea of healthy soil contains a mixture of plants and layers of decomposing litter. This leaf material will be broken down by a mixture of soil biology and patchy disturbances such as short duration high intensity grazing, establishment of an annual crop and even better a combination of both.

To achieve this we have chosen to let natural regeneration of plants occur on 80% of our

farming area. This has resulted in significant recruitment of native perennial grasses (mainly C4 grasses some C3 grasses and some forbs) in amongst the existing introduced plants such as phalaris, lucerne and clovers. To achieve this, we use a combination of Pasture Cropping, No Kill Cropping and Time Control Grazing which when done correctly, often simultaneously, will continue to promote natural regeneration while achieving production results. This is a WIN/ WIN situation.

We like the flexibility these techniques provide with the bias easily adjusted from season to season. For example in the last 7 years pasture cropping has ranged from 30% to 65% of total area with livestock and no kill cropping increasing and decreasing in response to seasonal and market conditions as well.

Each January we make a plan for each paddock for the year. In formulating the plan we look at the production history on each paddock (grazing and cropping), the plant mix, mineral cycling potential and then subjectively rank paddocks on their production potential. We then look at a good, average, bad gross margin scenario from different enterprise choices and allocate one of the options to each paddock. This process provides a framework for us all too fully discuss

Regeneration for profitable production

Angus and Lucy Maurice, Rick and Bren Maurice

“Gillinghall” and “Montauban”, Wellington NSW 2820


the options and hopefully generate good triple bottom line decisions for the year ahead. While the annual plant provides the basis for an initial budget, this can be adjusted to meet changes in seasonal conditions and markets with no cost and limited time required to actually switch from one production technique and type to another.

Diverse grassland provides the constant foundation, with choice of enterprise determined by multiple factors.

The only way we can truly achieve full flexibility in enterprise choice is by having multiple production techniques which operate on top of grasslands. To try and do this without grasslands is generally degrading, time consuming, costly and inflexible. Some examples of things we’ve tried are:

1. Pasture Crop Wheat, Barley, Cereal Rye, Oats, Mustard, Spelt

2. No Kill Oats, Barley, Cereal Rye, Clover, Millet, Lab Lab

3. Livestock Trading Lambs, Merino Ewes, Xbred Ewes, Steers, Heifers & Cows

4. Livestock Breeding 1st Cross Lambs, Dorper Lambs, Cows & Calves

Many of our paddocks have had one from each of the four choices all in the same year.

We have retained 20% of area as conventional no-till cropping with rotations of Wheat, Canola, Barley and Lupins. These paddocks are the most suited to continuous cropping and provide the best chance of high production results when the seasonal conditions allow. These paddocks have the highest cost base and carry the highest financial risk if there is a production failure, they also carry the highest ecological risk as the system is completely simplified and controlled by us. These areas also provides our own localised comparison with the regenerative techniques.

The transition is a long term process and this is OK.In the process of implementing regenerative techniques we have observed different production and regenerative results each year. We continue

to be attracted by the large upside of cropping gross margins so we have continuously pasture cropped some paddocks (with a herbicide) which is a frequent disturbance that can actually limit ecological advancement. We are still recruiting c4 perennials doing this but it is difficult to achieve maximum diversity (our idea of soil health) with 1 or 2 herbicide applications simplifying the ecology.

In a continuous pasture cropping situation we have the advantage of grazing income plus animal impact for soil health along with significant reductions in chemical inputs compared to conventional systems. However, with frequent herbicides we limit ecological advancement and partly move back towards the farming system of full control with the need to tweak a more likely outcome.

Reconciling the inner conflict that comes with targeted use of herbicides (and other disturbances) for short term production outcomes is an issue for us. With a stated long term goal of maximum bio-diversity, sometimes in Pasture Cropping we are using herbicides, synthetic fertilisers and non renewable energy to increase the yield of the crop at the expense of plant and biological diversity.

Disturbance sounds like a negative put it is a necessary positive!Having worked with Bruce Maynard and Colin Seis over the last 3 years we have learnt the disturbance is an important thing to understand for regenerative farmers. Disturbance can have a positive influence on production and ecology and the same type of disturbance can have a negative effect on both as well. The challenge is to use the right type at the right frequency to achieve WIN/ WIN results under the conditions we have on our own farms.

• We have had good ecological resultswith a one off Agrow Plow disturbance (2 foot spacing, lead coulters, minimal soil inversion) followed by No Kill Cropping and good grazing management.

• WehavehadgreatecologicalresultswithNoKill Cropping and good grazing management on their own.


• Wehavehadgoodproductionandecologicalresults with one off Agrow Plowing, pasture cropping with discs, herbicide and fertiliser.

• Wehavehadgoodproduction resultsbutpoor ecological results if the above is frequent.

Concluding commentsWe aim to find the right balance for our ecological and economic realities with a strong preference to retain all the enterprise options we currently have with the full removal of herbicides and pesticides as a frequent short term production disturbance. The ongoing goal will continue to be a farming system with minimal reliance on outside inputs with production levels delivering a return worthy of the effort and capital invested.

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IntroductionForage rapes (eg. cv Winfred) with the ability to re-grow following grazing have been widely adopted as a feed source for finishing lambs and feeding other livestock classes. Over a 2–3 month period, such forage rapes can produce high quality dry matter (2–6 t DM/ha). Traditionally they fit into summer dry environments utilising late spring moisture. In these environments the quality, and usually the quantity, of dry matter from rapes is superior to grass at this time. In NSW they are increasingly being sown in the autumn to provide large quantities of high quality winter feed. These forage systems are characterised by either a mid to late September sowing or an April sowing, with grazing commencing 80–100 days after sowing. Multiple grazing (2–3 events) are possible when moisture is available.

A large number of studies in New Zealand and overseas have indicated that the performance of lambs can vary with degree of utilisation of the crop and method of grazing (Armstrong et al. 1984). New Zealand data show that maximising animal production from summer leaf turnips requires a rotational system which optimises stocking rate and utilisation (Judson & Parris 2007).

The aim of this experiment was to investigate the effect of grazing intensity on liveweight gain of lambs eating a mid-height forage rape (cv. Winfred) to determine optimum grazing parameters.

Maximising productivity from Brassica crops

H.G Judson

PGG Wrightson Seeds, P.O Box 175 Lincoln, Christchurch 7640, New Zealand [email protected]

Abstract: Regrowth forage rape (Brassica napus) crops can be an important forage source for lambs, particularly in environments which are periodically dry. Lambs were grazed on regrowth from a rape crop over summer at four different allowances to determine grazing parameters for maximising lamb production. Maximum live weight gain per hectare was achieved at a daily allowance of 2.5 kg DM/head/day where lambs ate 60% of the crop and left a grazing residual of 1350 kg DM/ha. There was some evidence that grazing intensity affected regrowth ability.

Methods

Forage rape (cv Winfred) treated with 12 ml/kg Gaucho (Bayer Crop Sciences) was sown into a pre-irrigated, 1.5 ha trial area in spring (24th October) at a seeding rate of 4 kg/ha. Di-ammonium phosphate (DAP; 350 kg/ha) was broadcast prior to drilling. The area was fenced into 4 small paddocks (approx 0.3 ha) each representing a different grazing treatment. In each paddock, temporary fences were erected dividing the paddock into 5 weekly grazing breaks. In mid-January, mixed sex, cross-bred lambs (approximately 28 kg) were placed in each paddock after being weighed. Animals were randomly allocated to treatment groups and stocked at a rate that achieved a daily allowance of 1.0, 1.5, 2.0, or 3.5 kg DM/head/day (Table 1).Lambs were re-randomised before grazing the second rotation. Grazing ceased in late March, 148 days after sowing. The number of lambs in each break at the beginning of the experiment and at the beginning of each subsequent week was determined by;

Pre-grazing crop mass was determined by cutting 6 quadrats (each 0.25 m2) to ground level and drying a sub-sample to constant weight in an oven at 80°C. Post-grazing residuals were determined in the

No. of lambs = Pre-grazing crop mass (kg DM/ha) x break area (ha)

Allowance (kg DM/head/day) x 7 days


Allowance (kg DM/lamb/day)

Utilisation (%)

Residual (kg DM/ha)

Stocking rate (lambs/ha)

1.0 100 0 93

1.5 80 467 55

2.0 66 1003 51

3.5 40 2205 38

same way. The proportion of leaf, petiole and stem on plants was estimated by dissecting 10 plants in each plot prior to grazing and a further 10 plants in each plot after grazing in all treatments. Freshly harvested plants were weighed and subsequently dissected into leaf, petiole and stem. Sub-samples were dried to constant weight at 80°C to determine dry matter percentage.

Results and discussionDry matter production

Pre-grazing mass for the first grazing averaged 5100 kg DM/ha, which represented a crop at mid-thigh height. The mean regrowth across all treatments was 2000 kg DM/ha. There were large differences (1600 kg/ha) between treatments in total yield. Some of this difference may have been due to differences in fertility resulting from previous cropping rotations. Brassica yields are well known to respond to soil availability of both phosphate and nitrogen (de Ruiter et al. 2009). However, regrowth potential of the crop also appeared to be significantly affected by previous grazing intensity (Figure 1.).

At generous allowances where grazing residuals were high (2200 kg DM/ha), regrowth was poor (300 kg DM/ha), compared to the regrowth from lower allowances where residuals were lower (1200–1500 kg DM/ha). As the effect of grazing intensity and pre-grazing mass were somewhat confounded, it is unclear whether poor regrowth is a symptom of high residuals and/or large first yield brassica crops. The effect of grazing intensity on regrowth requires further investigation, because it has serious implications for both optimal grazing management and cultivar selection.

Lamb liveweight gain

Daily allowance of forage rape had an effect on the average liveweight gain of lambs in this study (Figure 2). Lamb growth rate increased as daily allowances increased, from 59 g/day at a daily allowance of 1.0 kg DM/head/day, up to 316 g/day at a daily allowance of 3.5 kg DM/head/day. In this study, the maximum liveweight gain was achieved at an allowance equivalent to 10% of liveweight. This is in general agreement with

Table 1. The stocking rates employed to create a range of daily allowances, utilisation and grazing residuals.

0

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Reg

row

th y

eild

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DM

)

Figure 1. Effect of different daily allowances of brassica (kg DM/lamb/day) on dry matter (kg DM/ha) produced in the regrowth period.

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Figure 2. Effect of daily allowance of brassica (kg DM/lamb/day) on lamb liveweight gain per head (g/day) (O; solid line) and per hectare (kg/ha/day) (☐; broken line) compared with liveweight gain data from pastures (Thompson et al. 1979) (∆; solid line)


Armstrong et al., (1984) and Fitzgerald (1983) who suggested that allowance in excess of 7% of liveweight were necessary to maximise growth rate in lambs. It is possible that maximum liveweight gain could have been reached at allowances less than 3.5 kg DM/head/day but not detected in this study because there was not a treatment to generate a data point between 2 and 3.5 kg DM/head/day.

In all but the lowest allowance, lambs grew faster on the brassica crop than ryegrass when compared with previous data (Thompson et al. 1979). Brassicas generally contain a greater concentration of metabolisable energy than pasture, especially during summer. They also may contain higher concentrations of crude protein and may have a faster fractional degradation rate in the rumen, which generally leads to increases in intake.

In the present experiment, as allowance increased, lamb liveweight increased, most likely due to increases in intake. Allowances in excess of 2.5 kg DM/head/day had little effect on lamb liveweight gain because it is likely they had reached maximum intake. Allowances below 2.5 kg DM/head/day reduced liveweight gain, which maybe attributed to individual intake being limited as a result of increased inter-animal competition at higher stocking rates.

At low allowances (1.0 kg DM/lamb/day) liveweight gain per-hectare was low (5.5 kg/ha/day) because, despite high stocking rates (93

lambs/ha), mean liveweight gain per-lamb was low (59 g/day). At the highest allowance (3.5 kg DM/lamb/day) liveweight gain per-hectare was not maximised because, despite rapidly growing lambs (316 g/day), stocking rates were low (38 lambs/ha). Maximum liveweight gain per-hectare (approximately 14 kg/ha/day) would probably have been achieved at an allowance of around 2.5 kg DM/lamb/day, where lambs would have grown at close to maximum (300 g/day) with stocking rates of 47 lambs/ha. The tentative nature of this conclusion reflects the absence of data points between allowances of 2 and 3.5 kg DM/lamb/day. However, in earlier work on leaf turnip (Judson and Parris 2007) maximum liveweight gain per-hectare (12 kg/ha/day) was achieved at an allowance of 2–2.5 kg DM/lamb/day, which is comparable to the current data.

Utilisation

The effect of daily allowance on utilisation and post-grazing crop mass is shown in Figure 3. Increasing allowance reduced utilisation from 100% at an allowance of 1.0 kg DM/lamb/day to 40% at 3.5 kg DM/lamb/day. Post-grazing crop mass increased as allowance increased (from 0 kg DM/ha at an allowance of 1.0 kg DM/lamb/day to 2200 kg DM/ha at an allowance of 3.5 kg DM/lamb/day). According to the data in Figure 3, at an allowance of 2.5 kg DM/lamb/day, which probably maximised liveweight gain per-hectare, lambs would utilise 60% of the pre-grazing crop mass on a DM basis and leave on

0

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0 0.5 1 1.5 2 2.5 3 3.5 4

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-gra

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s (kg

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)

Figure 3. Effect of daily allowance on post-grazing crop residuals and percent utilization.


average 1350 kg DM/ha after grazing. As the lower stem has a significantly higher dry matter content compared with other parts of the plant a 60% utilisation of dry matter represents, from a practical point of view, lambs consuming all the leaf and petiole and eating a little more than half the height of the stem.

This data suggests that grazing management aimed at increasing utilisation of summer crop beyond 60% of dry matter would not optimise production of liveweight. Systems which currently utilise more than 60% of the crop by dry matter could increase productivity per-hectare by leaving a higher residual and increasing lamb liveweight gain.

Conclusions This data has shown that using regrowth forage rape brassica crops (eg. cv. Winfred) is likely to have a beneficial effect on lamb growth rates over and above pastures. However, maximising animal production from these crops requires careful management of daily allowance through stocking rate. An allowance of 2.5 kg DM/lamb/day, where only 60% of the crop (on a dry matter basis) is removed at grazing, appears to maximise liveweight gain per-hectare on mid-height (75cm) crops. Lower allowances (through higher

stocking rates) will limit lamb growth rate, while higher allowances (through lower stocking rates) will limit crop utilisation. There is some need to investigate further the relationship between crop yield, grazing intensity and potential for regrowth. This study suggests that rape crops may suffer from reduced regrowth where high residuals are left.

ReferencesArmstrong, RH, Maxwell, TJ & Sibbald, AR (1984) The rape

crop (Brassica napus): utilisation and effects on animal performance. In: Proceedings of Better Brassicas ‘84 Conference, St Andrews. (Eds. WH McFarlane-Smith and T Hodgkin). pp. 72–76. (Scottish Crop Research Institute).

De Ruiter, J, Wilson, D, Maley, S, Fletcher, A, Fraer, T, Scott, W, Berryman, S, Dumbleton, A & Nichol W (2009) ‘Management practices for forage brassicas’. Forage Brassica Development Group.

Fitzgerald, S (1983).The use of forage crops for store lamb fattening. In: “Sheep Production” (Ed. W Haresign). pp. 239–286. 35th Easter School in Agricultural Science, University of Nottingham. (Butterworths, London).

Judson, HG & Parris, MA (2007) Optimising lamb production on summer crops. Proceedings 37th Seminar, Society of Sheep and Beef Cattle Veterinarians, NZ Vet Association 29–35.

Thompson KF, McEwan JC, Risk WH (1979) Proceeding of the New Zealand Society of Animal Production 40, 92.


NSW Hay and Silage Feed Quality Competition 2010Following the success of the competition at last years conference producers across New South Wales were again invited to enter a Hay and Silage Feed Quality Competition with awards presented at the conference dinner.

The aim of this competition was to promote the benefits of high quality hay and silage to all farmers with emphasis on the importance of feed quality in animal production and how to achieve feed quality in conserved forages.

Awards were based on feed quality analysis results from the I&I NSW Feed Quality Service with emphasis on metabolisable energy and crude protein.

Results can be compared with guidelines provided in I&I NSW Silage Note 4 (www.dpi.nsw.gov.au) and TopFodder Successful Silage manual.

Awards compared hays and silages in each category ie. one award for each crop or pasture type, not separate awards for hay and silage.

Samples were representative and must have come from commercial lot size intended for feeding to animals. Minimum lot size 5 tonnes of product.

Samples were to be of forage (hay or silage) conserved and/or fed in 2009/2010

Categories for awards were: Sponsor

Overall winner best conserved hay or silage Integrated Packaging

Winter/temperate pasture New Holland

Summer/tropical pasture New Holland

Winter crop New Holland

Maize Pioneer Hi-Bred

Other summer crop New Holland

Lucerne New Holland

Other New Holland

$5,000 worth of prizesWe thank sponsors of these awards:

➢ NSW Feed Quality Service

the impact of extreme drought and climate change on the ... · nyngan hay griffith approx. westerly...

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