SOIL GROUPS OF NEW ZEALAND

Part 8

RECENT SOILS

New Zealand Society of Soil Science 1985

SOIL GROUPS OF NEW ZEALAND

PARTS

RECENT SOILS

Edited by W.C. Rijkse

NEW ZEALAND SOCIETY OF SOIL SCIENCE 1985

Bibliographic reference: Rijkse, W.C. (Ed.) 1985: Soil Groups of New Zealand. Part 8, Recent soils.

New Zealand Society of Soil Science, Lower Hutt, New Zealand. 44 p.

Typing: Tessa Roach Draughting: Carolyn Powell

This volume has been compiled from both published and unpublished information. Authors must be consulted before papers are cited in other publications.

PREFACE

In the August 1983 issue of New Zealand Soil News (31: 4), P.J. Tonkin out-lined a new policy for the production of further volumes of 'Soil Groups of New Zealand'. This policy relied heavily on voluntary contributions, with authors offering articles in response to relevant notices placed in N.Z. Soil News. A notice soliciting articles for a volume on 'Recent Soils' was placed in the February 1984 issue of Soil News, with a deadline for the receipt of these articles later set at 1 September 1984; this was subsequently extended to 30 April 1985. The articles presented in this volume - Part 8 'Recent Soils' - reflects the response by mem-bers to the call for material. Unfortunately coverage is not complete - particu-larly with respect to distribution.

Recent soils in the New Zealand Genetic Classification cover a wide range of soils occurring in almost all parts of New Zealand. They include, first of all, recent alluvial soils (approximately 800 OOO ha) which, if protected from flood-ing, include the most valuable and versatile soils in the country. Recent soils also include the gleyed recent soils of low-lying parts of flood plains, well drained to poorly drained colluvial soils, rejuvenating soils on unstable slopes and those of recent deposits of aeolian or pyroclastic origin.

Council would particularly like to thank the editor - W.C. Rijkse - and all those who have contributed articles. We hope the issue makes a worthwhile contribution to our knowledge of New Zealand soils.

As advances in soil science over recent years have overtaken production of the Soil Group series, this will be the last issue in the series to be published.

R. Lee Vice-President, NZSSS September 1985

. CONTENTS

Classification W. C. Rijkse ..................... ............................................................................................................... 7 Distribution and Properties

North Auckland and Waikato G.E. Orbell .................................................................................................... 8 Bay of Plenty and Poverty Bay W.C. Rijkse ................................................................................................. 8 Manawatu and Wanganui Regions R.H. Wilde ............................................................................................ 9 Canterbury T.H. Webb and CM. Bennett ................................................................................................... 15

Chemistry P.L. Searle ...................................................................................................................................... .. 1 7 Physical properties M. W. Gradwell ..... ............................................................................................................. 22 Sand and Clay Mineralogy J.S. Whitton .......................................................................................................... 25 Biology G. W. Yeates .......................................................................................................................................... 29 Land Use Capability and Land Use R.T. Salter ............................................................................................. 32 Bibliography J.E. Davin ..................................................................................................................................... 39

7

CLASSIFICATION

W.C. Rijkse, N.Z. Soil

Recent soils in New Zealand are derived from a range of parent materials that are deposited in dif-ferent ways. These soils are formed from alluvium, colluvium, pyroclastic material, wind-blown sand or loess.

To be classified as recent soils they must firstly have some form of active accumulation or reju-venation, and secondly they have an AC or ABwC horizon nomenclature. In many cases their youth-fulness is further expressed in buried A horizons, thin or very thin topsoils with low % C which decreases irregularly with depth.

In the N.Z. Genetic Classification, recent soils are called azonal, meaning soils without distinct genetic horizons, and the fo1lowing are distinguished: Recent soils from

alluvium }{rapidly, colluvium moderately wind-blown sand or slowly loess accumulating

Gleyed recent soils from alluvium colluvium

}{

rapidly, moderately or slowly accumulating

Recent soils from volcanic ash

Saline gleyed recent soils

D.S.I.R .. Rotorna

One of the problems with this classification occurs when a fresh deposit is one event only and no further deposition occurs as, for example, soils derived from Tarawera Ash or Rotomahana Mud, or other soils out of accumulation influence. Such soils have all the characteristics of recent soils except active accumulation and at some stage, must become a yellow-brown pumice soil, or a yellow-brown earth.

The definition of diagnostic horizons in Soil Taxonomy (Soil Survey Staff 1975) have been use-ful to some degree and the future development of the classification of recent soils may well be influ-enced by the definitions of Entisols in Soil Tax-onomy. A first step of reclassifying recent soils has been made by Cutler (1983) where recent soils are split into neosols, regosols and lapidisols. The neo-sols form the bulk of the recent soils, the lapidisols include the stony recent soils and the regosols are those on recent loess, coastal sand or pyroclastic deposits. This type of division seems a good basis on which to build a more advanced genetic classification.

SoilJaxonomy iiicludes most of the recent soils in the order of Entisols with suborders Aquents, Arents, Psamments, Fluvents and Orthents. Recent pyroclastic deposits such as Tarawera or Ngauru-hoe soils were originally classed in the Inceptisols suborder of Vitrandepts, but they would now be classified in the proposed Andisol order.

8

DISTRIBUTION AND PROPERTIES

NORTH AUCKLAND AND WAIKATO

G.E. Orbell, N.Z. Soil Bureau, D.S.I.R., Hamilton

The North Auckland and Waikato regions are conspicuous for their lack of Recent Soils. These regions do not seem to have suffered any wide-spread major environmental changes in recent times, which have been sufficient to produce large quantities of erosion material to act as parent material for extensive areas of recent soils. Rivers in the region do not have wide flood plains, and any eroded material tends to be transported straight out to sea rather than being deposited by overbank flooding. Where accumulation of alluvium has taken place on restricted flood plains it is fre-quently fine grained and occurs in the lowest parts of the landscape, where it gives rise to Gley soils rather than Recent soils.

One exception to the lack of recent material is the relatively recent eruption of Rangitoto Island in the Waitemata Harbour, which has supplied young volcanic debris for soil formation over_ a moderate area on offshore islands.

On the North Auckland Peninsular two series of recent soils are recognised: Whakapara series from alluvium derived from sedimentary rocks and Mangakahia series from alluvium derived mainly from doleritic and andesitic rocks.

These two series occur as narrow strips of free-draining flats bordering rivers and streams. The soils are deep and loamy and of high fertility. Pro-files are not markedly well developed and most of the properties of these soils result from the nature

and conditions of accumulation of the alluvium. With poorer drainage these soils grade into the northern Gley soils.

Within _the So~th Auckland-Waikato-King Country region, restncted areas of recent soils are again found as narrow strips of free draining soils bordering rivers and streams. In this case the allu. vium is generally derived from rhyolitic and andes. itic tephras originally mixed with alluvium derived from a wide variety of sedimentary rocks. Again; the soils are deep and loamy and of high fertility .•

Because of their narrow sinuous occurrence the recent alluvial soils of these regions are difficult to' farm as separate entities and are generally farmed; in conjunction with surrounding soils of often lower; fertility. In some cases, especially in narrow vallevs 1 in the King Country, they are the only flat lmid' available for hay production and supplementary cropping. Because the recent soils from alluvium occur in the lowest part of the landscape, in narrow valley _situations they are often the coldest soils in the region and hence are perhaps not as versatile as may be expected.

The Recent soils from volcanic tephra, asso-ciated with Rangitoto Island, are little known and of restricted importance. They are found on Rangi-toto, Motutapu and Rakino Islands. They show little profile development and have coarse textures. Many areas are bouldery and areas of basalt flows are included.

BAY OF PLENTY AND POVERTY BAY

W.C. Rijkse, N.Z. Soil Bureau, D.S.I.R., Rotorna

Recent soils are widespread in the Bay of Plenty and Poverty Bay. Those derived from alluvium occur on low terrace systems along major rivers which widen near the coast. The river terraces occur at two levels; one adjacent to the river which floods frequently if not protected by a stop bank system; and a slightly higher level where flooding is infre-quent or rare.

Soils that occur on low river fiats accumulate rapidly. They have A-C profiles with shallow top-

soils low in organic carbon which decreases irregu-larly down the profile where buried topsoils are common.

Soils that occur on the second river flat level have A-Bw-C profiles. Accumulation is often rare enough to overthicken the topsoil only. Recent soils derived from pyroclastic materials are concentrated around or near Mount Tarawera and the central volcanic plateau.

BAY OF PLENTY

Rangitaiki series are the excessively to well drained. rapidly accumulating soils that occur on the Rangitaiki Plains. Galatea Basin and in Opo-tiki. Their parent material, as for all recent soils in eastern Bay of Plenty, is derived from greyv.1acke and tephra eroded out of the upper catchments of the main rivers. In gleyed recent soils on the same level, such as Kukumoa series in Opotiki. traces of Tarawera Ash were detected to 70 to 100 cm depth, indicating considerable accumulation in the last l 00 years.

Small, former back-swamp areas of soils occur on the low river fiats where they are wide as in Opotiki and the Rangitaiki Plains (Amokura series, Awakaponga series). Further inland, in the Taupo Region, the recent soils adjacent to the river beds are derived from coarse pumiceous alluvium (Huka series) with local additions of greywacke (Te Ran-giita series). Soils on the second river fiat level usu-ally display a drainage sequence where well drained recent soils occur closest to the river bed (Opouriao series, Orini soils) grading from imperfectly drained soils (Otara series) to poorly drained recent soils (Apanui series, Waioeka series) of former back-swamps often influenced by seepage from adjacent hill country or higher terrace systems.

Recent soils from volcanic ash are Tarawera series from basaltic scoria and Rotomahana series from hydrothermally altered volcanic ash. Both soils are a result of a one event deposit and there-fore are not truly recent soils except for their youth-fulness. Ngauruhoe soils do accumulate fresh ash during minor eruptions of Mount Ruapehu or Mount Ngauruhoe. The soils are included in the recent soils if the layer of recent volcanic ash is 20 cm thick or more.

9

POVERTY BAY

The largest areas of recent alluvial soils are in the Gisborne Plains. Tolaga Bay and in the Waiapu Valley near Ruatoria. Alluvium deposited by the Waiapu River and its tributaries contains a greater proportion of greywacke compared vvith those in Gisborne or Tolaga Bay when the alluvium is derived from sandstone, siltstone and mudstone with some tephra. Soil series have therefore been named differently.

Waipoa series are the rapidly accumulating, well drained soils of the low river flats in Gisborne and Tolaga Bay. In the Waiapu Valley these are rep-resented by the well drained Waiapu series and the poorly drained Waihoata series.

Soils that accumulate slowly are the well drained Matawhero series and the imperfectly drained Makaraka series in Gisborne and the well drained Matahiia series and the poorly drained Puhunga series in the Waiapu Valley. A third level of soils occurs on the Gisborne Plains that floods rarely. They are represented by the well drained Waihiere series and the poorly drained Makauri and Kaiti series. Such soils also occur in Waiapu Valley (Hikuwai series and Papawera series). The soils that flood rarely and show no clear signs of accumula-tion should not be classed as recent soils. This pre-sents no problem with poorly or imperfectly drained soils which are simply classed as gley soils, but the well drained soils of the levees tend to be still classed as recent soils, although in the old technical classification neo-fulvic has been used for Hikuwai series (Rijkse 1976).

MANAWATU AND \VANGANUI REGIONS

R.H. Wilde, N.Z. Soil Bureau, D.S.I.R., Palmerston North

~ecent soils of the Manawatu and Wanganui regions have been investigated, mapped and de~bed during the past two decades. Most of this onginal soil survey work is published (Campbell 1977a, 1979; Cowie 1974, 1978; Cowie & Hall 1965; CoWie & Rijkse 1977; Cowie et al. 1967; Rijkse 1977; Wilde 1976) and is readily available.

Some unpublished work on recent soils has been C~rr:ied out in the Wanganui and south Taranaki districts (Wilde 1979) and to make this work more readily available it is reported here.

Wilde (1976) briefly outlined the distribution of six soil series formed from Holocene alluvium occurring in Waitotara County immediately adja-cent to Wanganui City. Wilde (1979) enlarged this study and mapped soils from Holocene alluvium south-west to Patea. This present study describes more fully soils of the larger valleys incised into the marine terraces and adjacent hilly and steep land and relates their differences to ages and composi-tion of parent materials.

The climate of the Wanganui-south Taranaki region is subhumid '.Vith a mean annual rainfall ranging from about 900 mm at Wanganui City to about 1200 mm in the more northern and western parts of the survey area. The wettest month is June and the driest is March. The prevailing wind along this coast is westerly with most windrun occurring during late spring and early summer (N.Z. Mete-orological Service 1973, 1983).

The geology of the Wanganui-south Taranaki coastal region consists of a flight of gently sloping uplifted Pleistocene marine terraces cut in lower Pleistocene and upper Tertiary sedimentary rocks and covered successively with beach deposits, dunesands, loess and volcanic ash. The marine ter-races have been extensively dissected by a number of moderately large rivers and streams producing interfluves bordered by valleys, the floors of which comprise floodplains and low terraces of Holocene age. Alluvial fans from side streams have flooded onto some of these terraces.

Recent soils occur on the floodplains, low ter-races and fans where the alluvium is quartzo-feld-spathic and derived from erosion of the surrounding early Pleistocene and late Tertiary (mainly marine) sedimentary rocks. Associated older zonal soils from rhyolitic and andesitic Holocene alluvium occur on the older and higher of the low terraces. Soils are separated on the basis of age, internal soil drainage and composition of parent materials. All soils formed from Holocene alluvium in the region are described here, including yellow-brown pumice soils and yellow-brown loams formed from the vol-canic alluvium. Where classifications differ from those of recent soils a note is given in the text. With the exception of Putiki and Kai-iwi soils all soils have been previously mapped and described in the Manawatu Region (Cowie 1974, 1978; Cowie & Hall 1965; Cowie et al. 1967; Cowie & Rijkse 1977; Rijkse 1977). Putiki soils were first described in the Wanganui district by N.Z. Soil Bureau (1954) as part of the Waipunga Set, and later by Campbell (l 977a).

Traditionally, recent soils and associated older soils in the Wanganui-south Taranaki region have been used for pastoral farming supplemented with cropping, together with a minor amount of market gardening and orcharding. However, during the past five years or so the more freely draining recent soils, including the Putiki soils from pumice alluvium, have become popular among developers for the establishment of orchard crops such as kiwifruit.

A legend showing all the soils formed from Hol-ocene alluvium in the Wanganui-south Taranaki region is as follows:

10

Soils of the Roodplams and Low Terraces From rapidly accumulating quartzo-feldspath' alluvium

Excessively drained Rangitikei soils

From slowly accumulating quartzo-feldspath· alluvium

Well drained Manawatu soils

Imperfectly to poorly drained Kairanga soils

From non-accumulating quartzo-feldspathi alluvium

Well drained Karapoti soils

Poorly drained Te Arakura soils

From rhyolitic pumice alluvium Well to excessively drained

Putiki soils From andesitic alluvium

Moderately well drained Kai-iwi soils

Soils of the Fans From quartzo-feldspathic alluvium

Imperfectly to poorly drained Ohakea soils

Rangitikei soils

Rangitikei soils are rapidly accumulating, we drained soils occurring on the present floodplain They are situated between elevations of 5 and 60 and are flooded at least once every ten years.

Rangitikei soils characteristically show greyis brown, loamy sand textured A horizons, over oli or light olive brown C horizons, in turn resting o a thin, brown, buried A horizon, over buried horizons. Textures are sandy throughout. They d. fer from the other soils derived from Holoce alluvium by shov.ing coarser textures, les development of soil horizons, and flood laye · within the profile. The weak development Rangitikei soils is consistent with their extrem youthfulness.

Poorly drained equivalents of Rangitikei soil (named Parewanui soils in the Manawatu Region are not mapped in the Wanganui-Waitotara di trict. They are of minor occurrence only, their area being too small to map separately, and they ar included with the Kairanga soils.

'.'iana~atu soils

Manawatu soils are slowly accumulating. well drained soils occurring on the first terrace level above the present floodplains, between elevations of 5 and 60 m. They would be within the range of flood waters about once every 30 years. Their topography shows a gently undulating microrelief superimposed on very gently sloping terraces.

Manawatu soils characteristically show dark grey or black, sandy textured A horizons, with moder-ately or strongly developed structure; over brown-ish, sandy textured and friable B horizons, with weakly to moderately developed coarse blocky and subangular blocky structure. These rest on light yel-lowish brown or olive C horizons, sometimes silty textured and showing slightly impeded drainage, with friable to firm consistence, and weakly to moderately developed structure.

Differences between Manawatu soils and the Kai-iwi, Karapoti and Putiki soils described later are consistent with differing ages and composition of parent materials. Manawatu soils differ from Kair-anga soils by showing yellower colours within B horizons, with fewer mottles and colour patterns, owing to the better natural drainage of Manawatu soils; and from Rangitikei soils by showing thicker A horizons, better development of B horizon mor-phology, and fewer flood layers, owing to the greater age and development of Manawatu soils.

Kairanga soils

Kairanga soils are slowly accumulating, imper-fectly to poorly drained soils occurring on the same terrace level as Manawatu soils and also between elevations of 5 and 60 m. Like Manawatu soils, they would be within the range of flood waters about once every 30 years. Their topography shows a very gently undulating microrelief superimposed on very gently sloping terraces.

Kairanga soils characteristically show dark grey-ish brown or greyish brown, friable, silt loam tex-tured A horizons with moderately developed structure, and distinct iron staining around root channels; over grey, olive grey, and olive, friable to firm clay loams and heavy silt loams, with moder-ately developed blocky structure and abundant dis-tinct reddish brown mottles.

Putiki soils

.Putiki soils are non-accumulating, well drained s?ils from rhyolitic alluvium (Taupo Pumice Allu-vmm) occurring between elevations of 10 and 30 m Within the valley of the Wanganui River. Their topography is near level to gently sloping. They are classified as yellow-brown pumice soils.

Putiki soils characteristically show dark greyish b~own to black, loamy sand textured A horizons high in organic matter, with friable consistence and shoWing moderately developed structure; over pale Yellow or yellowish brown, loose to very friable, PUmiceous sands with weakly developed structure; 0 n Pale pumiceous sands. Putiki soils are very dis-

l l

tinctive on the low terraces by shO\ving pumice fragments throughout B horizons. coarser textures. generally darker A horizons with poorer developed structure. and paler subsoil colours at depth.

Ohakea soils

Ohakea soils are imperfectly to poorly drained soils occurring on alluvial fans that have flowed out from side streams on to the low terraces at eleva-tion~ between 15 and 65 m. They show very gently slopmg to gently sloping topography. They are classified as gleyed yellow-grey earths.

Ohakea soils characteristically show dark, heavy textured A horizons with moderately to strongly d~veloped structure, over pale, heavy textured, sticky and plastic B horizons, with moderately developed structure and abundant yellowish brown or reddish brown mottles. Ohakea soils in the Wanganui district generally show only poorly developed clay coatings and an absence of concre-tions, probably as a result of their relative youth-fulness, compared for example with the older Marton soils occurring on the intermediate and high terraces. Ohakea soils differ from other recent soils by showing more olive colours, more mottles, greater stickiness and plasticity and better develop-ment of clay coatings in subsoils.

Karapoti soils

~rapoti soils are non-accumulating, well dramed and moderately well drained soils occur-ring on the terrace immediately above the (Ara-moho) terrace formed in Taupo Pumice Alluvium between elevations of 10 and 75 m. They are beyond the range of present day floodwaters. Their topography shows a very gently undulating mic-rore~ief superimposed on near level to very gently slopmg terraces.

Karapoti soils characteristically show very dark grey or black, friable, sandy loam or silt loam tex-tured A horizons v.i.th moderately developed struc-ture, over yellov.i.sh brown friable to firm B horizons with moderately to strongly developed structure and patchy clay coatings (the less freely draining Karapoti soils showing mottling), over sandy and silty textured C horizons.

Karapoti soils are older and more developed than other soils formed from quartzo-feldspathic allu-vium on low terraces. Consequently thev show thicker and darker A horizons with better de~eloped structure, and finer textured B horizons with firmer consistence and better development of structure and of clay coatings.

Karapoti soils differ from Kai-iwi soils described next by showing paler B horizon colours and firmer moist and stickier wet consistence throughout all horizons; and from Putiki soils by showing darker B horizon colours, more olive C horizon colours, and finer texture and better development of struc-ture throughout all horizons. Differences between Karapoti and Putiki soils result mainly from parent material differences and partly from age differences.

Kai-iVli soils

Kai-iwi soils are moderately well drained soils occurring on the highest Holocene terrace between elnations of 25 and 90 m. Thev have formed from andesitic alluvium derived as ~ product of erosion of andesitic ash and loess cover beds occurring on adjacent intermediate and high terraces. Their topography is a fiat to gently undulating microrelief superimposed on the gently sloping terraces. They are classified as yellow-brown loams.

They characteristically show dark, friable A horizons generally with silt loam texture, and moderately or strongly developed structure; over yellowish brown and dark yellowish brown, friable to firm B horizons with moderately and strongly developed subangular blocky structures and many well developed clay coatings; on mottled, yellowish brown, heavy textured C horizons with well developed clay coatings and many to abundant mottles.

Kai-iwi soils have darker yellowish brown colours in B and C horizons than do the other soils from Holocene alluvium, as well as a slippery and smeary consistence attributed to amorphous alu-minium and iron oxides. These properties result from Kai-iwi soils having formed from andesitic parent materials.

CHEMISTRY

The chemistry of soils formed from Holocene alluvium is summarised in Tables 1 and 2.

Rangitikei soils are very weakly leached soils showing near neutral pH, and are well supplied with bases. pH increases slightly with depth; % organic carbon (C) and total nitrogen (N) are both very low in A horizons and C/N ratio is low, P soluble in 0.5 M H2S04 is medium to high throughout the pro-file, and % P retention is very low. Cation exchange capacity (CEC) and total exchangeable bases (TEB) are very low and low throughout the profile, reflect-ing the sandy nature of the parent materials; base saturation is very high throughout; exchangeable Ca is low and moderate, and exchangeable Mg is low through the profile; exchangeable K and Na are both very low, and potassium reserves are medium to high. Tamm Al and Fe are both very low through the profile.

Manawatu soils are weakly leached soils show-ing slightly acid to near neutral pH, high Truog P, and are well supplied with bases. The pH increases slightly down the profile; C and N are both medium in the A horizon and C/N ratio is low; Truog P, and P soluble in 0.5 M H2S04 are very high in the topsoil, with the latter decreasing with depth; P retention is low throughout the profile; CEC and TEB are moderate in the A horizon decreasing with depth to low in B and C horizons; base saturation is very high in the A and AB horizons, dropping to high in the B and C horizons; exchangeable Ca is high in the A horizon, dropping to medium and

12

low in the B and C horizons; exchangeable Mg . medium throughout the profile; exchangeable l( very low in the A and B horizons, increasing t medium in the C horizon. Potassium reserves high; exchangeable Na values are generally very lo Tamm Al is very low and Tamm Fe is low throu out the profile.

Ohakea soils are weakly leached soils Wi moderate to slightly acid pH throughout the pr file, increasing slightly with depth. C and N vaJu are medium in the A horizon and C/N ratio is I to medium in the A horizon. P retention, CEC TEB values range from moderate to low thro out the profile, and base saturation ranges from 1 to high. Exchangeable K and Na values tend to very low and low respectively, whereas exchan able Ca and Mg tend to range from low to medi Potassium reserves are medium. Tamm Al valu are low and very low, and Tamm Fe values medium.

Well drained Karapoti soils show from moder ately acid to slightly acid pH throughout the pr file, the pH increasing slightly with depth; C an N values and C/N ratio are all medium in the horizon; Truog P, and P soluble in 0.5 M H2S04 both high in the A horizon and decrease with dep P retention is moderate in the A horizon and lo in the subsoil; CEC, TEB, base saturatio exchangeable Ca and exchangeable Mg ~e medium in A horizons and low in subso· exchangeable Na values are low to very low in horizons; exchangeable K is very high in the horizon, medium in the B horizon and high in C horizon. Potassium reserves are medium in topsoil and high in the C horizon; Tamm Al values are low throughout the profile and Tamm Fe values are medium.

Imperfectly drained Karapoti soils are moder~ ately leached soils showing moderately acid to near neutral pH; C and N values are both medium in the A horizon and C/N ratio is low, P soluble in 0.5 M H2S04 is high in the A horizon, dropping to medium lower in the profile; P retention is moder· ate in the A and B horizons, dropping to low values deeper in the profile. CEC decreases with depth from high in the A horizon to low in the C horizon; TEB is medium in the A horizon, dropping to low in the B and C horizons; base saturation is gener· ally medium throughout the profile. Exchangeable Ca is medium in the A horizon, dropping to low in the B and C horizons; exchangeable Mg is medium and low throughout, increasing with exchangeable K ranges from very high to decreasing with depth; potassium reserves are high, and exchangeable Na values are all low.

The chemistry of soils from andesitic is in marked contrast with that for the soils frolll quartzo-feldspathic alluvium. The more drained Kai-iwi soils are weakly leached soils near neutral pH. C is medium and N is high in horizons; C/N ratio is low. P retention ranges frolll moderate to high throughout the profile, and Al is high whereas Tamm Fe is medium in A

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16

Table 1 Environmental parameters distinguishing recent soil sets formed from alluvium in Canterbury. Areas of soils are from Long (1966).

Soil set Name .4.rea No. (ha)

95 W aimakariri 44 OOO 95a W aimakariri 68 OOO

shallow 95b Kaiapoi 15 OOO 95d Willowbridge 6 500

98d W aimangarara 80 98e Barry 2 500

99 Tasman 65 500

have olive brown or light olive brown subsoils which are thin (10-20 cm) but distinct in sandy materials and thicker but less distinct in silty materials. The soil pattern is generally quite vari-able with deep, shallow and stony profiles with varying textures intermingling in a mosaic of soil types reflecting the former braided river pattern. Surface topography is usually undulating, with channels and terrace scarps being more pro-nounced on the younger surfaces. Deeper profiles commonly overlie older surfaces and have well develeped topsoils, 20-30 cm thick (Cox 1978). Topsoil depth generally decreases with total soil depth and stony soils commonly have less than 15 cm of topsoil.

Recent soils associated with smaller rivers are generally deeper and have less texture variation within their profiles than have similar aged soils associated with larger rivers. Sandy profiles occur on the levees of the small rivers and these merge into siltier soils with increasing distance from the rivers. Small rivers near the coast, such as the Heathcote and Avon Rivers, have a catena of soils perpendicular to the river. Sandy well drained soils on the levees pass into silty imperfectly drained soils (Kaiapoi set) then into clayey poorly drained soils (Taitapu set) away from the rivers.

Younger soils with sub-humid climate have high to very high base saturation, varying to medium values in stony profiles. Older soils with sub-humid climate have medium values in topsoils which commonly rise slightly with depth. Only a few recent soils with a humid climate have been ana-lysed and these have low base saturation values.

Cation exchange capacity values are generally medium in topsoil horizons and decrease sharply to low or very low values in subsoil horizons. Organic matter levels are low, particularly where soils are shallow and stony. Available phosphorus levels are high except under humid climate where available phosphorus is medium to low.

Altitude Rainfall Parent (m) (mm) material

< 330 500-900 greywacke

.. c: 0

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The bulk of the values are in the low-medium range indicating that decomposition of organic ma Her takes place fairly readily, which is usual for iitter from vegetation growing on fertile soils. Higher values, indicating organic matter in a rawer state. occur in soils that have higher moisture regimes which retard organic matter decomposi-tion, with the maximum values occurring in the

120

100

80

60

40

20

18

saline gleyed recent soils (Muriwai silt loam, 9826). Some subsoil horizons have low values can occur if inorganic nitrogen compounds present (i.e. by fixation of ammonium ions micaceous clay minerals). However, when amounts of both carbon and nitrogen are at limits of detection, as occurs in some of these there is also a possibility of a high error in the calculated ratio.

Median= 11.00

Mean=12.23

Std Dev.= 4.32

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Middle of in~rval

Figure 3 Carbon/nitrogen ratio

Cation exchange capacity (Ammonium acetate, pH 7) (Fig. 4)

Most values are low to medium, which is expected for soils that are weakly weathered and usually have low amounts of organic matter. Where high to very high values occur, these are in hori-zons that have high organic matter contents (i.e. gley recent soils) or in the subsoils of some of the older recent soils (e.g. Invermay deep silty clay loam, SB 9727) which have higher amounts of clay ( > 40%).

100

80

Median= 14.10

60 Mean=15.87

Ski Dev.=10.87

40

20

o......_-::--4-=-..__..._-L-J.---..l1...--'-....1...-L~L-..1==-....1..--1

0 5 JO 15 20 25 30 35 40 45 50 55 60 65

Middle of interval me.0 k

Figure 4 Cation exchange capacity

Base saturation % (Ammonium acetate, pH 7) (Fig. 5)

The base saturation of most of the horizons is high and a considerable number are fully base satu-ratecL which is expected for soils that are weakly leached because of their relative youth. Some recent soils, however, that are subjected to high rainfalls do have low base saturation values (e.g. Karamea heavy silt loam, SB 9435).

120

100

.. g 80 ·~

i! .. ~ 60 0

20

Median= 76.00

Mean= 73.77

Skl Dev.= 23.75

OL-C:::::::L~.L--L--L--l~L......L.....1...--L~L-J

0 10 20 30 -40 50 60 70 80 90 100

Middle of inlerval 0k

Figure 5 Base saturation

.. r::: .j

Tota.I phosphorus (Fig. 6)

AJthough there is a considerable spread of values indicative of a wide variation in the total P con-tents of the parent materials. the majority of the horizons have a medium rating. Where high to very high values occur they often result from a consider-able contribution from organic forms of phospho-rus and are usually associated with topsoil organic matter. One topsoil has an extremely high total phosphorus value (630 mg % P), which is a result of a 15 year history of fowl manure additions!

l 40

Median= 64.00

Mean=70.79

Std Dev.=43.81 .. .. ..c 0

0 20 0 z

19

10 20 30 40 50 60 70 80 90 100 110120130140>150

Middle of inlerval mg 0 k

Figure 6 Total phosphorus

0.5 M H 2S04 soluble phosphorus (Fig. 7)

The distribution trend for this form of extract-able phosphorus is similar to that for total phos-phorus. In these soils it is usual for virtually all the inorganic phosphorus to be soluble in 0.5 MH2S04, and this indicates that most of this form of phos-phorus is present in primary forms, and confirms the weakly weathered nature of these soils.

100

.. c: 0 . .,. "" 60 Median=34.00 c: .. .. Mean=38.63

..Q 0

0 40 Sid Dev.=34.56

0 2:

20

Phosphate retention (Fig. 8)

The majority of P retention values are low to very low. which is indicative of!ow abilitv to retain anions. This is to be expected because of low clav contents and moderately acid pH values. High values occur in some soils that have high clay con-tents and high acid oxalate soluble iron in the sub-soil, particularly in some gley recent soils (e.g. Opiki humic silt loam, SB 9929). Very high values occur in a few soils derived from andesitic alluvium or ash (Hangatahua sandy loam, SB 9318) which have appreciable amounts of amorphous material present.

120

100

.. 80 Median= 25.00 c:

0 ..,. Mean=29.25 "' c: ..

60 Std Dev.=19.76 "' ..c 0

0 0 z 40

20

0 .......... -'-~l--..&.-....L.--l.~.L--'--L----'~-== 0 10 20 30 40 50 60 70 80 90 100

Middle of inlerval "k

Figure 8 Phosphate retention

Phosphate extractable snlphate (Fig. 9)

The values for this property are generally low to very low for the majority of soils, and are similar to the trend shown for phosphate retention, thus confirming the low anion adsorption characteristics for these soils. High values occur in some soils that have high amounts of amorphous material, and exceptionally high values up to 2000 µg/ml occur in a saline gleyed recent soil (Muriwai silt loam, SB 9826) reflecting the influence of seawater on this

o soil. 0 10 20 30 40 50 60 70 80 90 100 110120 130 140

Middle of inlerval mg 0.li

Figure 7 0.5 M H,SO, soluble phosphorus

160

140

120

.. c: 100 _g

Median= 7.00

Mean=34.00

Sid Dev.=153.87 .. c: c ~ 80 0

0 6-0 z

.. c: 0 ·.;::; .. > «; ..

.Cl 0

0 0 z

40

20

ou..---11...-..1-...J--L~L-..l.--L-I.--'""'-"'-~

0 10 20 30 40 50 60 70 80 90>100

M icldle of interval ppm

Figure 9 Phosphate extractable sulphate

Reserve potassium and magnesium (Figs. 10, 11)

These soils exhibit a wide range of values for these properties and reflect the wide range of parent materials represented. For reserve potassium over 70% of the horizons analysed have ratings of high, and over half have very high values, indicating that most of the soils have high amounts ofweatherable potassium reserves. A similar trend occurs for reserve magnesium with over 60% of the horizons having high values and 30% having very high values. Once again this reflects the weakly weath-ered nature of these soils.

60 Median= 0.53

Mean=0.46

40 Sid Dev.=0.21

20

01....1:==L-...L..-L--l.~..l-...L-L--l.~.i:::=

o.o 0.1 0.2 o.3 o.4 o.5 o.6 0.1 0.0 0.9

Middle of inlerval me.0 :,

Figure 10 Reserve potassium

20

.. c: 40 -~

Median= 20.00

Mean= 25.95

S~ Dev.= 33.60

"' 2: tl l! 20 0

0 0 z

.. c: 0 ... .. c: @ ID

.Cl 0

0 0 z

O!-l~-'--'--L--1~.L.-L-L-1.__jL_~==~--~..LI 0 5 10 15 20 25 30 35 40 45 50 55 60

~iddle of interval me.0 b

Figure 11 Resen:e magnesium

Add oxalate extractable aluminium, iron and silicon (Figs. 12, 13, 14)

The trend is for low values for all these extract. able elements for these soils. There are exceptio where medium iron values occur in soils that ha B horizon development (e.g. soils of Taieri plain and where high to very high values for Al and occur in soils that have horizons influenced b andesitic ash (Rotomahana shallow sandy loam, S 9486).

200

180

160

140

120

100

80

60 Median= 0.14

Mean=0.23

40 Sid Dev.= 0.31

20

Middle. of inlerval 0 J,

Figure 12 Acid oxalate extractable aluminium

21

so

.. 60 Median= 0.46 c

j Mean=0.56 Ill

z: Sid Dev.= 0.42 fl 40 fl

.Cl 0

0 0 20 %

oL-L--1~.L-..1--L--1~1...-.J.--'--L~1...-..1.--L.-1.~L-.l

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 >1.4

Middle of inl!erval 0 t,

Figure 13 Acid oxalate extractable iron

SUMMARY

The soil chemistry confirms the immature nature of recent soils. The soils are in the main weakly leaching and consequently have moderately acid pH values, very high base saturation, and there is no appreciable organic matter buildup or translocation within the profile. The soils have high natural reserves of magnesium, potassium and phosphorus and this together with low anion retention prop-erties and low acid oxalate extractable aluminium, iron and silicon values is in line with their weakly weathered nature.

ACKNOWLEDGMENTS

The author is grateful to Mr M. W. Gourley, Sci-entific Services Section, N.Z. Soil Bureau, D.S.I.R., for help with accessing data from the data base and to Dr J. Reynolds, Applied Mathematics Division, D.S.I.R., for help in producing the histograms.

200

180

160

140

.. c: 120 0 . .,, "' 2: !ll II 100 .Cl 0

Median=0.05 0 0 8-0 Mean=0.09 z

Sid Dev.= 0.15

60

40

20

M icldle of inl!erval 0 fo

Figure 14 Acid oxalate extractable silicon

PHYSICAL PROPERTIES

M.W. Gradwell, N.Z. Soil Bureau, D.S.I.R., Lower Hutt

Pedologically speaking, recent soils include . a wide range of materials deposited too short a time ago for substantial modification to have occurred. Materials as diverse as coastal sand dunes, peats, Rotomahana mud, Ngauruhoe sand and Tarawera gravel fall within this group. If, however, we con-fine our study to areas of substantial economic importance to agriculture, the study may be nar-rowed to recent soils on alluvium in river valleys. Even within this range there is greater diversity than in many other soil groups, particularly in texture, and some of this variation occurs within short dis-tances. Sampling for physical studies on recent soils has not been carried out as systematically as on the main zonal groups, so what follows is based on a limited number of river flats, mainly those of the Manawatu, the Taieri and the Heretaunga Plains, for which measurements happen to have been made. The data from these areas have been studied and compared with those from zonal and intra-zonal soils in the hope that they will provide a rea-sonably representative overview of the recent soils on alluvium.

COMPACTNESS OF RECENT SOILS

The compactness of the soils has been assessed in terms of the 'packing density' of Hodgson (1974). This quantity equals

Dry bulk density + 0.009 clay content(%) It provides an estimate of compactness that is

not biased by texture. Packing densities less than 1.40 are regarded as 'low' and those greater than 1.75 as 'high'. 'Medium' densities are those between these limits. A count of 115 profile sampling points for which results are available yielded 45 'low' values of packing density, 67 'medium' values and only 3 'high' values. It seems that only occasional horizons in the alluvium have attained any great compactness, in line with the short time available since their deposition. The recent soils should, therefore, offer little impediment to the spread of roots. Soils of low or moderate compaction may also accommodate appreciable volumes of air or of plant-available water. The extent to which these volumes are actually present in the recent soils may be ascertained by studying measurements of large pores and of available water capacity respectively.

LARGE PORE CONTENTS

'Large pores' are here defined as pores dra' by a tension of 50 cm of water. The subsoils of recent soils showed as wide a range of large p contents as are found in New Zealand soils as whole. Of 95 samples tested 22 had under 5% large pores by volume Oow range), 28 had from to 10% (medium range) and 45 had more than 1 of large pores by volume. Though vertical va tions in individual profiles could be appreciable, was rare for samples in the low and high ranges be found in the same profile. That is, whole pro tended to either good or bad drainage as meas by this test. There was a tendency for the small contents of large pores to be found in the dee subsoils, at depths between 60 and 100 cm. S ples of Kairanga silt loam and of some soils on t Taieri Plains had small volumes of large pores the deeper subsoils. Samples of Manawatu a Templeton silt loams and of the soils of the taunga Plains, on the other hand, appeared to tain many large pores to the deepest layers samp As the content of large pores is a measure of inherent properties of the horizon tested, a m lowering of the water table by drainage will not c appreciable water from layers scoring low in regard. In view of the great diversity of the I pore contents of recent soils quoted above, it wo be desirable for measurements to be made on · vidual soils or soil phases in areas where the ext of the outflow to be obtained by drainage is question.

PLANT-AVAILABLE WATER

The available-water capacities of recent soils al include some very high and some very low val but the overall impression is of a good capacity store water. Mean values for the 22 recent s mentioned above have been calculated from horizon means of individual profiles and compa with the results for 7 groups ofzonal and intrazo soils given by Gradwell (1976, Table 4). The ov all mean capacities of the zonal and intrazonal so are set out in Table 1, together with the figures fi recent soils.

It can be seen that the subsoil horizons of rec soils have exceptionally good capacities for sto plant-available water. As the greater part of

fable 1 Mean capacities of groups of soils for storing plant-available water (percent of soil volume).

Groups of soils

Recent soils Zona.l and intrazonal soils

Mean available-water capacity of A horizons

20.8 21.8

Mean available-water capacity of

B and C horizons

17.9 12.J

~ater within .the re~ch of plant roots is usually held m the subsoil honzons it seems that at least the deeper recent soils should have a favourable water economy. Another point arising from Table 1 is the exceptional lack of differentiation between A hori-zons and B and C horizons in recent soils. Every one of the seven groups of zonal or intrazonal soils showed an excess of topsoil over subsoil water capacity of at least 7% of soil volume.

.These comments apply to deep, stone-free recent so~s. Where gravel contents are appreciable, or the soils are shallow over gravel or sand, the incidence

23

of drought will be greater. These profile variations are comparatively common amongst recent soils. The effect of gravel in the soils may be safely enough taken as a mere dilution of their ability to store water, e.g. a soil phase containing 20% of gravel by volume is taken as having an available-water capacity 20% less than that of the gravel-free phase. The effect of shallow depth over gravel or sand is more complex. The substitution of a gravel or coarse sand with little storage for water for the deeper part of the rooting zone must reduce the water supply of the profile, but this is partly com-pensated by the greater amounts of water held after drainage, in the upper horizons where the~e sit above coarse material. Oothier et al. (l 977a) have illustrated this for Manawatu silt loam. When the rate of drainage ofthis soil had slowed to 1 mm/day the water tension immediately over the top of the sand was about 35 cm of water, considerably less than what is found at normal field capacity and this tension increased by only 1 cm of wat~r per cm of height above the interface. For loams over-lying gravel or a coarser sand than is found under the Manawatu silt loam, the equilibrium tension would be even less and the amount of water held in the profile for subsequent extraction by plants correspondingly greater.

ACKNOWLEDGMENTS

Mr N.R. Kendall ofN.Z. Soil Bureau Analytical Section provided the greater part of the test results used in this review.

SAND AND CL.\ Y :\UNER.\LOGY

J.S. Whitton, ~.z. Soil Bureau, D.S.I.R .• Lower Hutt

Recent soils are soils formed on parent materials recently put in place, or still accumulating, from one of three processes: ( 1) alluviation. (2) aeolian (loess) deposition, and (3) volcanic eruption. Recent soils have therefore had little time to undergo changes due to soil-forming processes, and their mineralogy is primarily a reflection of parent material mineralogy rather than soil process.

Of the three processes, alluviation is by far the most important both in terms of extent and economic value of the soils.

These three processes of formation give rise to three distinct kinds of recent soil parent materials.

(a) A well mixed uniform parent material (1) from a single source i.e. greywacke, e.g. Waimakariri, Waikanui, Eyre and Templeton soils formed on the Waimakariri river flood plain (Table 1), or (2) from several sources i.e. greywacke, mud-stone, rhyolitic and andesitic volcanic ashes, e.g. Hastings, Twyford and upper part of the Pako-whai soil from the Heretaunga Plains (Table 1).

(b) A layered parent material in which two or more distinctly different materials from different origins are sequentially laid down by alluviation, aeolian or eruptive events. Examples are Pako-whai, Hastings (SB 9754, not given in Table 1 but similar to Pakowhai SB 9763) and Ngatar-awa soils of mixed alluvium over rhyolitic ash (Table I), or Takarangi soil from the Bay of Plenty, basalt scoria ash over peat over rhyolitic ash (Table 1), and Kamaka soil from the West Coast, sandstone and mudstone alluvium over limestone alluvium (Table 1).

(c) Besides mixing materials, the alluvial process can separate and concentrate particular compo-nents to form on alluvium enriched in one par-ticular component e.g. Paki Paki soils of the Heretaunga Plains which are almost pure vol-canic glass (Table 1), and Waimaku soil enriched in heavy minerals.

In recent soils from alluvium of uniform com-position (a(l) and a(2) above) different mineral compositions can occur depending on texture, e.g. in the Taieri Plains, Janefield, Mosgiel and Dukes soils occur in which the sandier J anefield soils have sand fractions higher in quartz and feldspar and lower in mica and chlorite than the clay-rich Dukes soil (Table l ). The clay fractions follow a similar trend with the sandier Janefield clays having higher quan.z, feldspar and interstratified clay minerals and low mica and smectite contents compared to the higher mica and smectite contents of the Dukes soil. !his pattern is also evident in the Heretaunga Plains if sandier Hastings and Twyford soils are compared With the clay-rich Mangateretere soils.

Generally clay fractions of recent soils contain high amounts of clay minerals which are easily altered by weathering e.g. mica/illite. chlorite and volcanic glass. This is because in the processes of formation of recent soils (alluviation, aeolian or eruptive events) physical breakdown and sorting often occurs, but there is little opportunity for chemical alteration or weathering. However, in some recent soils there is a relative abundance of kaolin group minerals and other strongly weath-ered and resistant minerals. In these soils the kaolin group minerals etc. are the products of previous weathering cycles rather than a result of in situ weathering of the recent soil. Examples are:

(a) The soils of the Taieri Plains, where the kaolin content of these soils is most likely related to earlier weathering cycles in the Central Otago region as shown by Churchman (1978).

(b) Rotomahana soil, where hydrothermal alter-ation of the lake bottom sediments prior to erup-tion resulted in a high smectite and kaolin content of the clays.

(c) Waiwhetu soil, which is formed on alluvium derived from Taita hill soils which are them-selves formed on strongly weathered greywackes.

In Table 2 the average sand and clay composi-tions of recent soils, and the range of values over which these components vary, is given for four areas of New Zealand. From the Table it can be seen that the Canterbury soils are remarkably uniform as shown by the narrow range of values over which each component of sand and clay varies. This is in strong contrast to the soils from Heretaunga Plains and the Bay of Plenty where the sand and clay com-ponents vary widely. This emphasises the simple one component nature and thorough mixing of the Canterbury greywacke alluvium, as compared to the various origins of materials, layering effects, frac-tionation and size grading in the alluvium of the Heretaunga Plains.

The consequent effect on the mineralogy of recent soils for these two areas is that the recent soils of one area have a single uniform mixed mineral com-position whereas the other area has a variety of both mixed mineral assemblages and specific single component enrichments.

From all of the above a general conclusion can be drawn that the mineralogy of recent soils com-prises either a uniform mixed mineral assemblage or a specific mineral enrichment depending on the origin, and number of parent materials, method of deposition, and particle size.

Table 1 Sand and clay composition of Recent Soils

Lab. no.

Hastings SB9817 A

c G

Twyford SB9755 C

E G

Pakowhai SB9763 B

D F H

Mangateretere SB9698 C

E G

Ngatarawa SB9762 B

D F

Paki Paki SB9816 A

D F I

Rangataiki SB9856 A

c E

Takarangi SB9830 A

B ct D E

Janefield SB9772 A

B c

Mosgiel SB9774

Dukes SB9777 A

B c D

Waimakariri SB9746 BC

DE FG

Waikanui SB975J B

c D E

Eyre SB9749 BC

DE FG

Templeton SB9771 B

c D G

Waimaku SB9906 A

c E

Kamaka SB9769 B

D E F H K

Rotomahana SB9581 B

D G

Waiwhetu SB8201 A

B D

Q

37 43 40

55 53 55

51 47 52

5

55 48 48

39 50 58

5 2

v >

0

<

0 >

::2 u

-or-oo

o-oo -- -or---..o - N

o-or---N

or-o-.....

t.r".INNf"'I

0 r- """' "!tN("I"')~

gg I I

X"1" X"1"

I I I I 00

V'lN .,., r-c!, ...!. I I

N r--NN

6 I 6 ...!,

NOO '° N- le!, I I NI"'>

'

.-\ grassed orchard on Karapoti silt loam con-tained 35 nematode genera including the plant feeding genera Prarrlenchus. Helicotylenchus. Her-erodera and Hemicycliophora (Egunjobi l 968a). Pratylenchus populations were higher in grass roots than in apple roots (Egunjobi l 968b).

Ski pp and Christensen ( 1983) included Kara-poti, Kairanga, Harihari and Templeton soils in their survey of organisms invading white clover roots; they found Pratylenchus in the first two soils but the two negative samples are not conclusive. Most root damage observed in their survey could be attributed to endoparasitic nematodes (Heter-odera, Pratylenchus, Meloidogyne).

PASTURE INSECTS

Grass grub populations were reduced by 80% in Rotomahana shallow sandy loam and by 88% in two yellow-brown pumice soils, following broad-cast application of lindane in spring (Lauren et al. 1982). In all soils, drilled application gave poorer control ( 41-70%). Recent alluvial soils at Flock House, on which blue-green luceme aphid and pea aphid populations were studied (Kain et al. 1979), remained above wilting point through summer, and the aphid populations were not suppressed as they were on older soils at Takapau, Masterton and Hawera where there were severe droughts; this rela-tively moist regime at Flock House seems unusual in relation to other recent soils.

Initial work on insecticidal control of porina in Canterbury included trials on Barrhill soil (Uprit-chard 1970). Techniques such as deep-ploughing, mob-stocking, rolling and cultivar changes to com-bat insect pests have been advocated for the region by French (1976). The effects of animal treading on Manawatu and Kairanga soils have been summar-ised by Brown and Evans (1973).

Natural infestation by the bacteria Hafnia alvei in grass grub in 23 paddocks in Ashburton was assessed by Trought et al. ( 1982). Some sites were on Templeton or Mayfield soils, but no effect of soil group on infection is apparent in their results. Subsequent application of H. a!vei, or the nema-todes Neoaplectana glaseri and Heterorhabditis bacteriophora, gave some promising control of grass grub in experimental plots (Jackson & Trought 1982).

In assessing the release of insecticides, Udy (1977) found that granules retained more diazinon, ethoprophos and fensulfothion on Templeton silt loam than the average for the eight soils investi-gated. However, diffusion of ungranulated material through moist Templeton soil was above average. Adsorption of all three insecticides was relatively low, the order agreeing with the level of organic matter, cation exchange capacity and nitrogen in these soils.

30

YI:RTEBR\ TES

The areas of inte::isive cropping and honicultu on recent alluvial soils in Hawke's Bay provict the sites for the ecological study of starlings {Mo 1980) and rooks (Purchas 1980). While no soil fac was invoked. the suitability of these soils for er ping provides conditions for the development pest populations at a range of trophic levels. It m be coincidence that the main rook populations New Zealand are both in areas with significant are of recent soils - Hawke's Bay and Canterbury.

In studying the bird problem at Christchurc International Airport, which is sited on Selwyn Waimakariri soils, ~ioeed (1976) found black-b' gulls, starlings and magpies fed on a variety insects, earthworms, arachnids, and, to a les extent, seeds; these birds were opportunistic fee ers dependent on temporarily abundant food su plies. Black-backed gulls fed exclusively earthworms. The soil fauna was clearly an imp tant factor in the bird problem. Good control Coleoptera and Lumbricidae was obtained wit isobenzan, fensulfothion and diazinon (Moe 1975).

PASTURE PRODUCTIVITY

Pasture herbage production is the pri development role of many areas of recent so· (Table 1 ). While often apparently limited by m agement and by climatic constraints, production · also strongly influenced by biological processes · the soil. Roots pw.,ide the plant's intimate conta with soil water, nutrients, and the microbial pr cesses which may be indicative of potential pr ductivity (Jenkinson & Ladd 1981, Ross et al. 1982

Table 1 Annual pasture herbage production and nitrogen fixation on some recent alluvial soils (n = years of measurement).

Soil t D.M./ha kg Nfha n Reference

Recent alluvial 11.7 n.d. 27 Radcliffe complex (Gisborne) and Sinclair

(I 975) Rangitikei loamy 6.3 n.d. 6 Radcliffe sand (1976) Wingatui silt 10.4 n.d. 11 Round-Turne loam et al. (1976) Kairanga silt loam 11.4. 212, 2 Oark et al. + fine sandy loam 16.1 243 (1979) Manawatu fine 12.6. 184. 2 Brock and sandy loam 12.8 232 Hoglund

(1979)

Seasonal root production of ryegrass. white clover and cocksfoot in Karapoti brov.n sandv loam has been reported (Caradus & Evans 1977). and both yertical rooting patterns and water extraction for this soil have been described (Evans 1978). While there are no comparative data for other New Zealand soils. the balance for different swards between roots in the upper nutrient-rich horizons and the deeper horizons in which moisture is the main resource was clearly important. Genotypic effects, which were found to be important in deter-mining white clover rooting patterns in Kairanga silt loam (C1radus 1977), apply equally to other soils.

Agronomic trials such as those of Sears (1953), Sears and Evans (1953) and Sears et al. (1953) on

31

Manawatu silt loam and a recent alluvial soil at Gore. Manawatu fine sandy loam (Harris 1973). and the recent gley K.:iiranga silt loam (Pineiro & Harris I 978a.b) have ~n supplemented by a body of data on nitrogen fixation (Table !), nitrification acti\itv (Steele et al. 1980). and response to nitrogen fe;-tiliser (Ball et al. 1978). In these developed pas-tures, there appears to be no simple relation bern·een nitrogen fixation and soil type, or soil carbon or carbon/nitrogen ratio (Hoglund et al. 1979).

The feature of recent soils most affecting the pat-tern ~nd intensity of their biological activity is their medmm to coarse texture. Given adequate depth of solum, they are suitable for cropping and effluent disposal. Their drainage, however, may be rapid and lead to droughtiness.

32

LA~D t;SE CAPABILITY A.'JD LA~D t:SE

R.T. Salter, \Yater and Soils Directorate, \1inistry of \Yorks and Development, Wellington

INTRODUCTION

Recent soils are widely distributed throughout New Zealand, and are a valuable component of our soil resources. Many of these soils are highly ver-satile and they comprise much of our present inten-sive cropping and horticultural land. Current trends towards intensification of land use will result in these soils being used increasingly for arable agriculture.

This paper contains an analysis of the distribu-tion, land use capability and land use of recent soils based on the New Zealand Land Resource Inven-tory (NZLRI) (NWASCO 1975-1979). Soils were mapped as one of the five inventory factors of NZLRI (the others being vegetation, erosion, slope and rock type). Productivity data for both pastoral agriculture and forestry have also been incorpo-rated into the NZLRI by indexation to land use capability units (Page 1981; Anon 1981).

Using all available soil survey information, complete NZLRI coverage was carried out at a scale of 1:63 360. The method of applying soil maps at differing scales to the inventory is described by Hawley and Leamy (1980):- Although soils data from all available soil surveys were used, all soil units have been correlated to soil sets mapped in the

Table 1 Land use capability classes as used in the NZLRI

*GENER.\L PASTOR.\L & CROPPING PRODUCTION FORESTRY "GENER~L

CLASS SUT ABILITY SUITABILITY SUITABILITY

High II

III Medium

IV Low

v

VI L:nsuitable

VII

VIII

High

Medium

Low

Unsuitable

Multiple use land

Pastoral forestry land

Catchment protection land

*LUC Classes IV-VII which have wetness as the major limitation and those units in very low rainfall areas or those occurring on shallow soils are normally not suited to production forestry.

(NWASCO 1979)

general survey of the soils of North and So Islands (N.Z. Soil Bureau 1954, I 968a). This vides simplified summary data suitable for natio analyses and was used in this study.

DISTRIBUTION

The distribution of recent soils is shown in ures l and 2. In the North Island, recent s formed from volcanic materials are distributed follows.

In the Bay of Plenty, Tarawera Ash and Lap' and Rotomahana Mud are the parent materials significant areas of these soils. Ngauruhoe s derived from andesitic eruptions are widely tributed around the Tongariro Volcanic Centre. Burrell and Tahurangi recent soils are recorded Mount Egmont, having developed on recent and itic lapilli and ash eruptions. Small areas of rece soils from volcanic materials also occur near Re roa as a result of hydrothermal alteration of voJ: canic materials.

The distribution of recent soils from alluvium· strongly related to the location of river chann and their flood plains. Hence, in the North Islan the major areas of recent soils occur in the Wai-rarapa, Hawke's Bay, Gisborne and Manawatl! Regions, and in the South Island large areas are present in Canterbury, Southland, Marlborough and Nelson. Coarse-textured recent soils are mainly recorded in Westland and in the high country o the Southern Alps. Some recent soils are al derived from v.indblown sand; in the main these are located in coastal areas subject to strong winds, such as along the west coast of the lower North Island. A few recent soils are also mapped on Ioess accumulating sites near Eastern South Island rivers, e.g. Barrhill and Kowai soils on the south bank o the Rakaia River.

LAND USE CAP ABILITY OF RECENT SOILS

The land use capability (LUC) classification integrates the five physical factors recorded in the NZLRI inventory together with other factors such as climate, altitude, land management, etc.

The LUC classification identifies and groups land "'ith similar characteristics and the same physical capacity for sustained production (NW ASCO 1979).

The LUC classification is a hierarchical system of assessment with three levels: the class, subclass, and unit. The LUC class expresses the total degree of limitations to use as outlined in Table l.

33

Fig. 1 N(JRTH ISLRNO RECENT

.... • ' A-....

KM 0 50 100 150 200 250 300 350 ~00 ~~--1~~--'~~__.J'-r-~~'--~-.-'--~~'--.---'~~--;-

M ILES 0 50 100 150 200 250

DATA FROM NWASCO NZ LANO RESOURCE INVENTORY USING LADEDA

34

Fig. 2 SOUTH ISLRNO RECENT SOILS

300 350 400 50 100 150 200 250 KM 0 I I I I ~

I I I

50 100 150 200 250 MILES 0

USING LADEOA ORTA FR(jM NWRSCCl NZ LAND RES(jLJACE INVENT(jRI

The subclass divides the land within each class according to the major kind of limitation to use. four subclasses are used: erodibility (e). wetness (w). soil limitation within the rooting zone (s). and cli-mate (c). The unit level of the classification groups together map units with similar physical charac-teristics. productive potential and management requirements. More detailed data on individual land use capability units and LUC classification regions can be obtained from NZLRI regional bulletins and extended legends.

LUC CLASSIFICATION

The distribution of recent soils by land use capa-bility class, as presented in Table 2, illustrates the varied productive potential of this soil group. This mainly reflects the wide variation in soil physical characteristics. The soils range from deep, fine tex-tured, highly productive soils to very stony, sand and boulder deposits of little productive value and best suited to catchment protection.

Over 17% of New Zealand's arable land (LUC Gasses I-IV) is derived from recent soils from allu-vium. This reflects the importance of these lowland flood plains and terraces of New Zealand's major rivers for agricultural uses. On the non-arable LUC Classes V-VUI land, coarse textured (sands, grav-els)_ river materials are recorded as well as recent volcanic materials of the North Island on rolling to steep slopes. However, these comprise only a small proportion of the country's non-arable land. Class I

The flat terraces of the Rangitaiki, Wairoa, Gis-borne and Heretaunga Plains, and the large areas of the Wairarapa and the Manawatu, comprise the majority of Oass I land with recent soils in the North Island. The soils of Class I land typically have deep profiles, good structure and high nutrient status.

35

In the South Island Class I soils are located on lowland flood plains and terraces. and are generally free draining. such as the Templeton soils in Can-terbury and the Waimea soils around Nelson. The Kaiapoi (Canterbury) and Mataura (Otago and South1and) soils have a slight wetness limitation after drainage and are classified as Class Iw (Table 3).

Class II

Oass II land "1

36

Table 3 Subclass limitations of Recent Soils :"forth Mand

LUC Erosion Wetness Soil Oimate class Al Vole Al Vole Al Vole Al Vole

I 27 600 17 200 II 3 700 142 200 2 800 25 200 4 700 III 2 500 3 300 160 700 I OOO 29 900 6 200 2 900 IV 600 7 200 26 700 200 27 800 10000 800 v 300 200 VI 6 600 80000 10600 400 16 200 100 2 900 vu 12 600 48 100 13 300 6 300 I 700 VIII 700 34 800 200 400 2 300 200 4 500

South Island

LUC Oass

I II III IV V-VI VII VIII

Erosion

14 400 27 500 4000 2 200 2 500

100

Values rounded to nearest 100 ha

from Tarawera Ash and Lapilli in the Bay of Plenty are often drought prone, as are soils such as Argyll sandy loam and Pakipaki coarse sandy loam occur-ring over gravels in the Wairarapa. These are all classed as ms.

In the South Island, recent soils on Class Ills land, such as the Eyre-Paparua soils, are generally shallow and stony with a reduced cropping versa-tility and an average stock carrying of 9 su/ba. Recent soils near the gorge areas of the Waimak-ariri and Rakaia Rivers, and adjacent to the river channels, are classed as Ille due to the potential for wind erosion when cultivated. These areas are often still accumulating windblown material, are gener-ally fertile, and have a present stock carrying capacity of 11 su/ba.

Oass IV

Class IV land with restricted cropping suitability occurs in Westland where high rainfall is the princi-pal climatic limitation to crop choices. These are, however, generally fertile soils with a high stock carrying capacity and forestry potential. There is also a large area of Class IV s land, generally flat flood plain areas, with shallow stony soils of medium to low fertility. Most of these have a potential for slight streambank and wind erosion.

Over 10 OOO ha of recent soils developed on Tar-awera Ash and Lapilli are Class IV s because of cropping limitations and difficulty in establishing pasture as a result of the coarse texture and fre-quent periods of drought. Forestry site index values are very high.

Wetness

11 600 16 700 8 900 4 OOO 2 500 1 200 I OOO

Soil

4 700 73 300

192 800 188 800

171 700 38 300 9 700

Climate

6 100 35 300 24 900 14 400

1 600 2400

400

Narrow flood plains-and river terraces wi recent alluvial soils varying in texture from coa sandy to bouldery are also classified as IV s Ian These occur in the Rangitikei and Manawatu Dis. tricts and in the Galatea Basin.

Class VI - VITI

Many of the recent soils (177 OOO ha) in the Sout Island are Class VI, i.e., non-arable. Those with soil limitation consist of the stony and boulde flood plains of the West Coast, and the very la areas of shallow and stony soils of Central Ota the W aitaki Basin and other dry eastern areas. T man and Matukituki are typical soils of this regio These generally have stock carrying capacities un present management of less than 1 su/ba, with fi estry site index values also being very low, at le than 20 m.

In the North Island, narrow river and lake mar gins with seasonally high watertables comprise t Class VIw land. These areas are unsuitable fi cropping and because of the wetness limitation~ ~ also unsuitable for forestry. Pastoral product1Vl is generally low with average stock carrying capa ities of 7-10 su/ba. Recent soils with a great flooding hazard and/or prolonged periods of in dation and waterlogging are classified as VIIw. r majority of the Class VIw and Vllw land is locat in Northland and in the Waikato and Haura lowlands.

Class VI land with an erosion limitation co prises soils derived dominantly from the volca materials, Rotomahana Mud and Tarawera Ash all

t,apilli. Composite recent soils on yellow-brov.11 pumice soils also have_ the same erosion limitation oimoderate sheet erosion. Exposure of bare ground rnust be minimised by careful management to reduce the erosion hazard.

There are large areas of Class VII and VIII land with recent soils derived from volcanic materials around the Tongariro Volcanic Centre and Mt Egmont. These are of limited productive value and those areas in the Central North Island are suscep-tible to extreme sheet and wind erosion. Some of the lower altitude Class VII areas, although being unsuitable for pastoral production, are suitable for forestry, with site index values in the range of 16-26 rn. The small area of Class VII land on Tar-awera Ash and Lapilli is well suited to exotic forest with generally high site index (27-39) values, but is unsuitable for pastoral production due to the problems of revegetation of exposed ground.

In the South Island, Class VII and VIII land with recent soils, comprising very stony and boulderv flood plains, is generally restricted to the West Coast and the high country. There are also minor areas of Oass VII and VIII land derived from dredge tailings with little productive use, although exotic afforestation may be a suitable land use in the future.

Table 4 Land use of Recent Soils (up to 1979)

L\ND USE

An analysis of present land use on recent soils is given in Table 4. This is derived from the vege-tation inventory factor recorded in the NZLRI. ~..\s this information was obtained between 1973 and 1979, the more _recent trends in land use change can~ot be ident~fied. This applies particularly to horticulture, which has developed mainlv at the expense of intensive grazing. ·

Horticulture only occupied 7700 ha of recent soils in New Zealand, although the current area used for horticulture is likely to be somewhat higher. 1':1any recen~ soils derived from alluvium are par-ticularly smtable for horticultural development because of their excellent physical characteristics and suitability for irrigation, and being generally locat~d close to river channels and groundwater supplies. In the North Island, horticulture is located ma~nly on Class le land with deep, fertile, well dramed soils, where water inputs can be better con-trolled and wetness does not restrict crop suitabil-ity or limit workability of the soils. These areas are loc~ted on t~e Gisb~rne, Wairoa and Heretaunga Plams. Horticulture 1s also located on significant areas of qa_ss ~w land in the Manawatu, Wairarapa and Ran~ti~e1,. where there is only a very slight wetness hffiltatlon after drainage.

Land Use LUC Oass (ha) % of that Land Use II III IV v VI VII VIII Total

NORTH ISLAND Horticulture 6100 200 100 Cropping 1 600 l 200 l 800 Mixed pasture 4 800 13 300 6200 crop

6400 46 4 600 74

24 400 50

Intensive 32 OOO 160 500 180 300 37 OOO grazing Extensive l 600 13 OOO 20200 grazing* Exotic forestry 100 l OOO 10000 Indigenous 100 l 800 I 700 forest

200 20 500 200 430 500 lO

30 500 24 200 13 600 103 100 4.5

31 600 25 100 67 700 12 16 700 7 200 5 300 33 100 1.5 300

Scrub!and 800 600 3 100 Undevelopedt 600 I 600 I 600

10 100 13 OOO 69 100 96 700 6.5 7 300 12 500 17 400 41 OOO 4.5

SOUTH ISLAND Horticulture 600 600 100 1300 25 Cropping 2 OOO 3 700 500 6200 32 Mixed pasture 8000 27 100 7 800 600 43 500 29 crop Intensive 11 700 107 600 226 700 130000 700 16 400 493 100 18 grazmg Extensive 200 700 17 200 67 700 2 900 116 700 10000 500 215 900 4 gi:azmga Exotic forestrv 100 800 l OOO l 800 600 9 600 13 900 9 Indigenous · forest 200 6 400 29 200 23 600 59 400 1.6 Scrubland 700 4400 12 OOO 5 300 22 400 2.4 Undevelopedt l 100 100 1 OOO 2400 3 700

; Includes tussock grasslands which are not grazed in all areas. v:cludes herbfields, sand dune associations and bare ground.

ues rounded to nearest l 00 ha.

In the South Island honiculture is recorded mainly on Class Is and Ils land.

Fletcher (1984) outlines the anticipated demand for horticultural crops and the expected competi-tion between honiculture and pastoral farming. For many areas of recent soils large changes are expected in Poveny Bay, Hawke's Bay, Nelson and Motueka as a result of kiwifruit plantings. Vegetable pro-duction is expected to require an additional 3000 ha over the next five years and this is likely to be located close to existing processing facilities in the Hawke's Bay, Poverty Bay, Manawatu and Can-terbury regions. Fletcher (1984) estimates that an additional 25 OOO ha of pastoral land is likely to be converted to horticultural uses by 1990. This is likely to occur particularly on LUC Class I and II land. With over 0.5 M ha in the North Island and 0.6 M ha in the South Island being recent soils suit-able for arable use (LUC Class I-IV land), there are likely to be significant changes in land use to horticulture and cropping.

Cropping is also identified as an important land use on recent soils. In the North Island the major crop is maize, whereas wheat and barley are the most important crops in the South Island. The category 'mixed pasture/cropping' is used for those areas where high producing improved pasture is the dominant vegetation and cropland is a secondary but significant proportion of the land use. Much of the mixed farming areaS-Of Canterbury and Otago on recent soils are recorded in this category. Classes Iw, Ilw and IIIw land in the North Island, and Classes Iw, Ils and Ills land in the South Island are the most important cropland classes.

With increasing profitability of cereal crops, this land use is expected to continue to expand in the future. Anticipated changes in the wheat industry will also mean that cropping will expand in the North Island, particularly in drier areas such as the Wairarapa, Hawke's Bay and Rangitikei, where recent soils currently in pasture would be expected to change to a cropping land use.

Intensive grazing as the predominant land use of recent soils, occurs on over 0.9 M ha. These areas are associated with the more versatile classes ofland and reflect the traditional pastoral land use pattern of much of the country. In the North Island the large areas with wetness limitations and without significant seasonal soil moisture deficits are well suited to pastoral production. Much of this land is presently used for dairy production in Northland, Waikato, Bay of Plenty and Manawatu regions. Productivity of these areas is often high, with pres-ent carrying capacities of up to 19 su/ha in the Bay of Plenty on Oass IIw and Us land.

In the South Island the large areas of intensive grazing are mainly located on the Class He, Us, IIIs and IV s land on the Canterbury Plains and Otago downlands. This area is predominantly under a dryland sheep and cattle grazing regime. However, irrigation has resulted in significant increases in

38

productivity. and changes to dairying have occu in some areas.

Extensive grazing land is characterised by un proved pasture in lowland areas and tussock gr land at higher altitudes. The North Island l Class VB and VIII land includes the tussock lands occurring around the Tongariro Vole Centre on recent Ngauruhoe soils.

The South Island extensive grazing land c prises large areas of Class IVs land with shon sock vegetation. Present stock carrying capaci on this class of land are generally very low, fr less than 1 to 5 sujha.

Only 9% of North Island and 2% of South Is recent soils are covered by exotic forestry. In North Island this is located mainly on Class I VIe and VIIe land where there are 35 OOO ha exotic forest on soils derived from Tarawera and Lapilli. Small areas are also located on uruhoe soils in the Karioi State Forest and on r soils from wind-blown sand in the Waitarere Santoft State Forests.

Most of the exotic forestry in the South Is! is for protection purposes on Class VIIIs land. covers 9600 ha. Small areas of Class IV s and land with exotic forestry cover make up remainder.

In the South Island most of the indigenous fo is recorded on Class VIs and VUs land in West and Fiordland. These stony and bouldery ft plains are coarse textured and flood prone. attempts at pastoral or forestry development been made to date. Unless drained and high ra of fertiliser applied, these areas are likely to rem under their present vegetation.

In the North Island the indigenous forest located in the same areas as the exotic plantati with the majority on Classes VIe and VUe on awera soils. Small areas are also associated Class VIIIe land on Mt Egmont. There are small patches of indigenous forest on Class IV VIw and VUw land in the Waikato.

CONCLUSION

Recent soils are presently dominated by int sive pastoral uses and comprise some of Zealand's most productive dairying, grazing cropping land. The high versatility of many of soils will result in their becoming increasi important for horticulture and cropping uses. M of the non-arable (LUC Class IV - VIII) land the North Island is derived from recent volca materials and has an exotic or indigenous for cover. The South Island Class IV - VIII land generally stony or bouldery and is used as ex~ sively grazed tussock grasslands or has an indt nous forest cover.

39

BIBLIOGR..\PHY

Compiled b.r Jewel E. Davin, N .z. Soil Bureau, DSIR. Lower Hutt

This bibliography includes all references used in the paoers of this volume on recent soils, whether or not they are about recent soils. Those references which do i:i

CO\\ !E. J.D .. RIJ!\.SE. W.C. 10;~ Soils of \lanawalU Count'. "lonh Island. '-iew Zealand. \" Z Sm! Suncr Rcp,•rr 30.

COX. J.E. I 062 Rc'1:Cnt soils of the eastern South Island. nonh of the Wanak1 R1,er. S. Z S,oi/ Sc11 s 196::: 115-123.

cox. J.E. 1978 Soils and ~griculture of pan Paparua County. S.Z. Soil Bureau Bullenn 34. l 28p.

CROSS. D. 1963 Soils and geology of some hydrothermal eruptions in the Waiotapu District. S.Z. Journal of Geology and Geophysics 6: 70-87.

CUTLEK E.J.B. 1983 "Soil Classification in New Zealand: A Review of Soil Clas-sification Systems and Proposals for a New Zealand Soil Classification" 2nd ed. Lincoln College. Depanment of Soil Science, Occasional Repon. 2. l 48p.

EDMOND, D.B. l 958a The influence of treading on pasture: a preliminary study. S.Z. Journal of Agricultural Research 1: 319-328.

EDMOND, D.B. l 958b Some effects of soil physical condition on ryegrass grow1h. S.Z. Journal of Agricultural Research 1: 652-659.

EDMOND. D.B. 1962 Effects of treading pasture in summer under different soil moisture levels. S.Z. Journal of Agricultural Research 5: 389-395.

EDMOND. D.B. ! 963 Effects of treading perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L) pastures in winter and summer at two moisture levels. S.Z. Journal of Agricultural Research 6: 265-276.

EGUNJOBL 0.A. l 968a An ecological study of some soil nematodes associated with apple trees in a New Zealand grassed orchard. S.Z. Journal of Agricultural Research l 1: 386-406.

EGVNJOBL 0.A. l968b A comparison of Pratylenchus spp. (Nematoda) population densities in grass and apple roots. S.Z. Journal of Agricultural Research 1/: 142-148.

EVANS. P.S. 1978 Plant root distribution and water use patterns of some pas-ture and crop species. _v.z. Journal of Agricultural Research 21: 261-265.

FIELDES, M.; WEATHERHEAD. A.V. 1966 Mineralogy of sand fractions of New Zealand soils. S.Z. Journal of Science 9: 1006-1021.

FITZGERA.LD. P. 1966 Soils of Heathcote County. Canterbury. N.Z. S.Z Soil Bureau Repon 1/1966. 33p.

FLETCHER. J.R. 1984 Pastoral land - horticulture and forestry as competing land uses. S. Z. Agricultural Science l 8: 164-16 7

FOX. J.P.: GIBBS. H.S.: MILNE. R.A. 1964 Soils and Agriculture of Kowai County, Canterbury. N.Z. S.Z. Soil Bureau Repon 4/1964. 53p.

FRENCH. RA. I 976 Farm management to control pasture pests. Proceedings of the NZ. Grasslands Association 37 (1975): !38-142.

FURKERT. R.J.; SMIDT. R.L WELLS. N. 1975 Mineralogy of topsails and subsoils from Camp Stream Catchment of the Waimakariri Valley. New Zealand. S.Z. Journal of Science 18: 277-287.

GIBBS. H.S. 1965 Soil Map ofWhareama Catchment, Wairarapa. New Zealand. Scale I: 126 720. S.Z. Soil Bureau .'vfap 4/1965.

40

GIBBS. H.S.; \1ERCER . .\D.; COLLIE. T.W. 1950 Soils and Agnculture of Westland. \l.Z. YZ. Soil B11reuu 8;,:.

R.\DCUFFE. J.E. J

YLl. TES. G .W. 1980 Populations of nematode genera in so ils under pas1ure. !II. \ 'e rtical distribut io n at ele '"cn si tes. .\" Z. Journal of .1gncultural Rl'sca rch _'_!: 11 ~- 1 2 8 .

YE.UES. G.W. 1981 Populations of nematode genera in soils under pasture. IV . Seasonal dvnamics at five North Island sites. S.Z. Jour,;al of .1gricultural Research ::4: 107-121.

YE . .\ TES. G.W. 198-l Vanat ion in so t! nematode d i,·ersitY under pasture "-"Ith and year. . Soil 8 1c'!ogi· .ind 81c•.:h('l111 stn- 16: 95- i O:' .

YEATES. G .W.: RIJKSE. W.C.: HAWKE. M.F. 1981 Soil nematodes in a Typic Vitrandept under forest fanni (Abstract). n P.8:' m ·soils v.ith Variable Charge Conference. Massev U versity. Palmerston North. New Zealand. 11-18 Febru n 1981. Programme and Abstracts." I 94p. a