Sandplain Soils Research Articles

The phytotoxicity of soil-applied herbicides is enhanced in the first-year post strategic deep tillage

The sandplain soils of WA are inherently fragile with surface layers that are very low in organic matter and clay content. The advent of minimum- and no-till farming has seen the increase in frequency and intensity of cropping on these soils. However, a combination of soil physio-chemical constraints and agronomic issues remain a challenge to the sustainability of cropping systems on them. These constraints include sub-soil compaction, soil water repellence, sub soil acidity and herbicide resistant weeds. Strategic deep tillage such, as soil inversion and deep soil mixing, have been shown to ameliorate these multiple constraints and dramatically increase crop production. For WA soils, an increase in herbicide usage is correlated with a decrease in regular tillage, and how the two interact is imperfectly understood. As a result, current herbicide strategies and rates are designed to perform optimally in a minimum tillage environment. Two field experiments were established to compare crop damage from a range of commonly used pre-emergent herbicides when grown in soil that remained under minimum tillage, was deep mixed or inverted. These trials demonstrated that both strategic tillage methods significantly changed the soil surface composition that would be expected to directly affect the bioavailability of some herbicides. Two commonly used herbicides, Metribuzin and Diuron, detrimentally impacted crop performance following tillage in both trials. These same treatments reduced yield by a greater extent on both the soil inversion and deep mixing treatments (p < 0.001). No other herbicides, when applied at either label or triple label rates, significantly impacted yield on any of the soil treatments. There was a substantial crop production benefit from strategic deep tillage at Esperance but not at Geraldton. These results reflect that the influence of deep tillage on the toxicity of herbicides is highly dependent upon soil properties and rainfall.

Biochar and Compost Increase Crop Yields but the Effect is Short Term on Sandplain Soils of Western Australia

Sandplain soils on the south coast of Western Australia have low inherent fertility, which is mainly due to poor nutrient retention caused by insufficient clay and organic colloidal material. Previous research has shown the benefits in nutrient levels and retention from adding clay to sandplain soils; however, there is almost no information on the addition of organic amendments. A field experiment was established at the Esperance Downs Research Station, Western Australian, in May 2010, to assess the effects of wheat straw (WS) and chicken manure (CM) biochars and compost with and without phosphorus (P) addition on soil properties and crop production over five growing seasons. The five seasons alternated between winter and summer crops. The CM and WS biochar and compost treatments significantly increased crop yields and P uptake in 3, 2 and 1 of the five seasons, respectively. The yield increases (P « 0.05) were no more than 8%. By the end of the third season, no differences in crop yields were found that could be attributed to the organic amendments. The addition of P increased crop yields in each winter cropping season. Phosphorus addition explained more than 30% of the variation in crop yields. Despite marginal P levels and summer drought conditions, arbuscular mycorrhizal root colonisation was not affected by the organic amendments. There were no significant interactions between the organic amendments and P addition in terms of crop yields, P uptake or P uptake efficiency. We conclude that much of the effect of the organic amendments was due to direct nutrient addition which dissipated over time.

Managing South Coast Sandplain Soils to Yield Potential

Soil Use and ManagementVolume 27, Issue 2 p. 281-281 Book review Managing South Coast Sandplain Soils to Yield Potential T. Batey, T. BateySearch for more papers by this author T. Batey, T. BateySearch for more papers by this author First published: 23 May 2011 https://doi.org/10.1111/j.1475-2743.2011.00332.xRead the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume27, Issue2June 2011Pages 281-281 RelatedInformation

Claying and deep ripping can increase crop yields and profits on water repellent sands with marginal fertility in southern Western Australia

Sandplain soils on the south coast of Western Australia have multiple limitations to crop production that include water repellence, low water and nutrient retention, subsoil acidity, and high soil strength. Crops on sandplain soils achieve, on average, almost 85% of their rainfall-limited yield potential; however, where there are multiple limitations the corresponding value is often &lt;50% in any given year. Previous research has shown the value of applying clay-rich subsoil (‘claying’) to ameliorate water repellent soils and improve nutrient retention. Other studies have shown that deep ripping is effective in reducing compaction in sandplain soils. This paper quantifies the effects of 5 subsoil clay rates (0, 50, 100, 200, and 300 t/ha), with and without deep ripping to 0.5m, on soil properties, crop growth, and profitability in a replicated field experiment. Crop yields were increased by 0.3–0.6 t/ha as result of added clay. The clay content of the surface soil required to alleviate water repellence and achieve the highest yield increases was 3–6% in soils with ~1% organic carbon. Longer term effects of claying included increased soil organic carbon by 0.2%, pH by 0.6 units, potassium by 47 mg/kg, soil strength by 250 kPa, and cation exchange capacity by 1.3 cmolc/kg to a depth of 0.1 m. However, changes in plant-available water (mm/m) were inconsistent between the clay treatments. Deep ripping to 0.5 m increased crop yields by 0.1–0.5 t/ha. These crop yield responses were still evident 3 years after the ripping treatment had been applied. Soil strength measurements indicate that re-compaction of the ripped treatments had occurred to a depth of 0.2 m in the second year following ripping. Crop responses to claying and deep ripping were additive. Claying and deep ripping, while almost doubling yields, achieved only 50–70% of the rainfall-limited yield potential on these marginally fertile soils. The highest clay rates (&gt;3–6%) had cumulative discounted cash returns $AU100–200/ha higher than the unclayed ‘control’ treatment and $300/ha higher than the lowest clay rates. For most of the clay treatments, deep ripping increased discounted returns between 2005 and 2007 by $80–120/ha.

Increased Concentration of Molybdenum in Sown Wheat Seed Decreases Grain Yield Responses to Applied Molybdenum Fertilizer in Naturally Acidic Sandplain Soils

ABSTRACT Spring wheat (Triticum aestivum L.) is the major crop in southwestern Australia where 75% of the 18 million hectares comprise sandy duplex and deep sandy soils, including uniform yellow sandplain soils. Some of the sandplain soils in the lower rainfall (< 350 mm annual average) eastern region are naturally very acidic (soil pH, as measured in 1:5 soil:0.01 M calcium chloride, 3.7–4.5) in soil horizons explored by wheat roots so molybdenum (Mo) deficiency and aluminium (Al) toxicity adversely affects grain production of wheat. Liming is not an economic option to ameliorate Mo deficiency and Al toxicity in these soils because uneconomical large amounts are required. However, despite Al toxicity, applying Mo fertilizer produces profitable grain yield. The fertilizer also increases Mo concentration in grain, and if this grain was used to sow the next crop, it may reduce the amount of Mo fertilizer required by the subsequent crop. To test this hypothesis we grew wheat in an experiment on naturally acidic sandplain soil (pH 4.5) when either 0 or 160 g/ha fertilizer Mo was applied. The grain harvested at the end of the growing season had Mo concentrations of 0.07 mg/kg when no Mo was applied (low Mo seed) and 0.27 mg/kg when Mo was applied (high Mo seed). In two further field experiments on naturally acidic sandplain soil (pH 4.3 and 4.4) we sowed low and high Mo seed of the same size (36.4 ± 0.2 mg per seed) when 4 rates of Mo fertilizer (0, 35, 70, and 140 g/ha Mo) was applied to soil. Grain yield responses to the Mo fertilizer were 59% for low Mo seed and 55 g/ha fertilizer Mo was required to produce 90% of the maximum grain yield. Corresponding values for high Mo seed were 15% response and 15 g/ha fertilizer Mo. Rather than sowing wheat seed harvested from acidic soils to sow wheat crops on the acidic sandplain soils, we instead recommend seed harvested from alkaline soils with larger concentrations of Mo in the seed be used reducing the rate of fertilizer Mo required for that crop. The concentration of Mo in the youngest emerged leaf blades (YEB) that was related to 90% of the maximum grain yield (critical prognostic tissue test value for grain production) was about 0.08–0.09 mg/kg at tillering (Gs24) and at emergence of wheat heads (Gs59).

Residual value of molybdenum for wheat production on naturally acidic soils of Western Australia

Naturally acidic sandplain soils in the lower rainfall (&lt;350 mm annual average) eastern region of the agricultural areas of south-western Australia are deficient in molybdenum (Mo) for grain production of wheat. Liming soils ameliorates Mo deficiency, but it is not an economic option for these soils because they are naturally acidic at soil depths commonly explored by wheat roots. Consequently, Mo fertiliser, usually as Mo trioxide, needs to be applied to wheat on these soils. The residual value of the Mo fertiliser for these soils was not known, so was measured using grain yield of wheat in 2 long-term field experiments. The Mo fertiliser treatments were applied once only in different years to plots not treated with Mo in a previous year. In both experiments, the residual value of the fertiliser was measured in 1993. Thus, it was possible to determine the effectiveness of the fertiliser applied once only 1–11 years previously (previous Mo) relative to freshly applied (current) Mo applied in 1993. At both sites, a continuous decline in the effectiveness of previous Mo relative to current Mo was related to time of Mo–soil contact. In experiment 1, the effectiveness of previous Mo relative to current Mo decreased by about 40, 50, 60 and 70% when applied 2, 5, 7 and 11 years previously. In experiment 2, on a more acidic soil with a larger capacity to sorb Mo, the relative effectiveness of previous Mo decreased by about 60 and 80% for Mo applied 2 and 6 years previously. The concentration of Mo measured in youngest emerged leaf blades was related to 90% of the maximum shoot yield at the time of sampling (diagnostic critical tissue test value) and to 90% of the maximum grain yield (prognostic critical tissue test value). Irrespective of the growth stage of wheat, both critical diagnostic and prognostic values were about 0.07 mg Mo/kg. The concentration of Mo in grain that was related to 90% of the maximum grain yield was 0.02 mg/kg. The reapplication of Mo fertiliser to naturally acidic sands can be made with knowledge of the residual value and use of tissue testing for Mo, particularly when sampled at early growth stages of wheat.

Lupin: the largest grain legume crop in Western Australia, its adaptation and improvement through plant breeding

Between 500 000 and 1 000 000 tonnes of narrow-leafed lupins (Lupinus angustifolius L.) are produced in Western Australia each year. It has become the predominant grain legume in Western Australian agriculture because it is peculiarly well adapted to acid sandy soils and the Mediterranean climate of south-western Australia. It has a deep root system and root growth is not reduced in mildly acid soils, which allows it to fully exploit the water and nutrients in the deep acid sandplain soils that cover much of the agricultural areas of Western Australia. It copes with seasonal drought through drought escape and dehydration postponement. Drought escape is lupin’s main adaptation to drought, and has been strengthened by plant breeders over the past 40 years by removal of the vernalisation requirement for flowering, and further selection for earlier flowering and maturity. Lupin postpones dehydration by several mechanisms. Its deep root system allows it to draw on water from deep in the soil profile. Lupin stomata close to reduce crop water demand at a higher leaf water potential than wheat, but photosynthetic rates are higher when well watered. It has been proposed that stomata close in response to roots sensing receding soil moisture, possibly at a critical water potential at the root surface. This is an adaptation to sandy soils, which hold a greater proportion of their water at high matric potentials than loamy or clayey soils, since the crop needs to moderate its water use while there is still sufficient soil water left to complete its life cycle. Lupin has limited capacity for osmotic adjustment, and does not tolerate dehydration as well as other crops such as wheat or chickpea. Plant breeding has increased the yield potential of lupin in the main lupin growing areas of Western Australia by 2–3 fold since the first adapted cultivar was released in 1967. This has been due largely to selecting earlier flowering and maturing cultivars, but also to improved pod set and retention, resistance to Phomopsis leptostromiformis (Kühn) Bubák, and more rapid seed filling. We propose a model for reproductive development in lupin where vegetative growth is terminated in response to receding soil moisture and followed by a period in which all assimilate is devoted to seed filling. This should allow lupin to adjust its developmental pattern in response to seasonal conditions to something like the optimum that mathematical optimal control theory would choose for that season. This is the type of pattern that has evolved in lupin, and the task of future plant breeders will be to fine-tune it to better suit the environment in the lupin growing areas of Western Australia.

Emergy evaluation of three cropping systems in southwestern Australia

Wind erosion and rising water tables are serious threats to the ecological sustainability of annual plant-based farming systems on deep, infertile sandplain soils in southwestern Australia. In this study, an annual cropping system was compared with two novel perennial plant-based systems designed to address these threats in terms of their use of renewable indigenous resource, their use of non-renewable indigenous resources, their purchased inputs of energy and materials, and profitability. The farming systems were an annual lupin/wheat (Lupinus angustifolius L./Triticum aestivum L.) crop rotation, a plantation of the fodder tree tagasaste (Chamaecytisus proliferus L.) and an alley cropping system in which the lupin/wheat rotation was grown between spaced rows of tagasaste trees. Flows of energy and materials between the environment and the economy were identified for each farming system and the natural and human activity involved in generating inputs as goods or services then valued in terms of the equivalent amount of solar energy required for their production using the emergy method of Odum [Ecological and General Systems: An Introduction to Systems Ecology. University Press of Colorado, revised edition of Systems Ecology, 1983, Wiley, New York, 644 pp.; Environmental Accounting: Emergy and Environmental Decision Making. Wiley, New York, 370 pp.]. The results showed that the two largest energy flows in the conventional lupin/wheat cropping system were wind erosion and purchased inputs of phosphate. The renewable component of production was 15% of total flows in the lupin/wheat system, 30% in the alley cropping system and 53% in the tagasaste plantation. The annual net income from the plantation system was nearly four times higher, and from alley cropping 45% higher, than from the lupin/wheat rotation. This analysis suggested that once the two agroforestry systems were fully established, the tagasaste plantation was the most efficient at transforming natural resources into goods and services and the most profitable, while the lupin/wheat system was the least energy efficient and the least profitable.

"Paradise" and "Cloverdowns": following natural systems

Two properties, "Paradise" and "Cloverdowns", are farmed by the Melvin family near Dowerin in the central wheatbelt of Western Australia (see Fig. 1, Hobbs 2003). The annual average rainfall is 350 mm and, before Europeans settled the area, it was well vegetated with perennial vegetation. The sandplain soils were dominated by mallees Eucalyptus spp., Kwongan or heath (predominantly Myrtaceae, Proteaceae and Leguminosae), and patches of York Gum E. loxophleba woodland. The heavier soils such as the brown sandy loams and red brown loams were clothed in woodland of Salmon Gum E. salmonophloia and York gum. The gravelly sands were covered by Tamma scrub which was dominated by sheoak Allocasuarina spp.

Ability of retained stubble to carry-over leaf diseases of wheat in rotation crops

Increasingly, wheat rotations on sand-plain soils in Western Australia are being managed with stubble retention practices for reasons of moisture and soil conservation. A major concern in stubble retention practices is an associated increase in risk from septoria nodorum blotch (Phaeosphaeria nodorum) and yellow spot (Pyrenophora tritici-repentis). These pathogens frequently occur together in the region and survive in crop surface residues. The amount of disease carry-over on stubble is an important determinant of the severity of leaf diseases during the entire crop season. To provide a rationale for wheat leaf disease management in stubble retention rotation systems the extent to which retained wheat stubble induces disease in rotated crops was investigated. The frequency with which wheat stubble, which had been retained through a 1-year rotation, induced significant disease in seedling wheat was low (14%) over the 4-year period of study. While disease carry-over from wheat stubble retention in rotations is possible, it appears to be uncommon. The small proportion (1–8%) of retained wheat stubble that remained after germination of the return wheat crop in typical Western Australian farming systems further indicates that in general retained wheat stubble is not a significant source of disease carry-over in rotation wheat crops in this environment.

A comparison of the adaptation of yellow lupin (Lupinus luteus L.) and narrow-leafed lupin (L. angustifolius L.) to acid sandplain soils in low rainfall agricultural areas of Western Australia

Almost the entire lupin industry of Western Australia is based on the single species Lupinus angustifolius L. (narrow-leafed lupin), which is very well adapted to coarse-textured, mildly acid soils. However, L. angustifolius is not well suited to the strongly acid sand plain soils along the low rainfall fringe of Western Australia’s agricultural areas, and alternative grain legume species may be preferable. These soils, known locally as wodjil soils, have very low nutrient contents, often high levels of extractable Al in the subsoil, and are common in areas where severe brown spot and root rot disease is caused byPleiochaeta setosa. Yellow lupin, Lupinus luteus L., may be a better species on these soils. This paper describes a series of trials comparing the grain yields of narrow-leafed lupin and yellow lupin on a range of soils in the agricultural areas of Western Australia. These trials were sown on a range of dates and in a range of rotational backgrounds between 1995 and 1998. With current cultivars, narrow-leafed lupin clearly has higher yield potential than yellow lupin when soil-extractable [Al] at a depth of 15–25 cm (measured in a 1 :5 extract of soil in 0.01 M CaCl2) is &lt;10 mg/kg. When extractable [Al] at this depth is greater, yellow lupin can produce greater yields than narrow-leafed lupin, depending on other environmental characteristics, especially when extractable [Al] exceeds 28 mg/kg, but its yield advantage is often small. Yellow lupin is less sensitive to delayed sowing than narrow-leafed lupin, and more tolerant of brown spot, but narrow-leafed lupin is more responsive to good seasonal conditions and less sensitive to frost. We conclude that yellow lupin has a place in Western Australian farming systems on soils with &gt;10 mg/kg extractable [Al] where these soils are in close lupin rotations, in areas where brown spot is severe, or in low rainfall areas where narrow-leafed lupin yield potential does not often exceed 1 t/ha on these soils. However, yellow lupin has had relatively little breeding effort in Australia and its place will remain precarious until better adapted, higher yielding cultivars become available.

DESIGNING MIMICS FROM INCOMPLETE DATA SETS : SALMON GUM WOODLAND AND HEATHLAND ECOSYSTEMS IN SOUTH WEST AUSTRALIA

In this article we assess the potential for developing mimics in situations where detailed data on the ecophysiology and ecosystem function of the native ecosystem are not available. We examine two ecosystems in south western Australia, and draw together available information on these. We discuss woodlands dominated by Eucalyptus salmonophloia, which formerly covered much of the valley bottom land in the Western Australian wheatbelt, and kwongan or heath which occurs on sandplain soils at the top of the landscape. From both of these we derive possible mimics which utilise aspects of the native vegetation which we hypothesise contributed to ecosystem function and resilience, but which still allow the production of a harvestable agricultural product. We conclude that situations for which we have adequate ecological knowledge from which to develop sound mimics are likely to be rare. We hence have to be prepared to make best-bet estimates and use these to develop experimental mimic systems.

Effectiveness of different methods of applying superphosphate for lupins grown on sandplain soils

In 3 experiments in 1991 on very sandy soils near Eradu, Western Australia, the effectiveness of superphosphate for producing lupin (Lupinus angustifolius L.) seed (grain), was measured for fertiliser applied at 0-73 kg P/ha to the soil surface just before sowing (topdressed), or banded with the seed, or 8 cm below the seed while sowing 5 cm deep. At all sites, banding phosphorus (P) below or with the seed was equally effective as applying P to the soil surface. In a fourth experiment, on a very sandy soil near Badgingarra, Western Australia, levels of P (0-547 kg P/ha) as superphosphate, had been applied once only from 3 to 7 years previously (1985-89). The P applied in previous years was found to have leached. In 1992, superphosphate (0, 9, 18 and 36 kg P/ha) was applied across all the original plots. Fertiliser was either applied to the soil surface just before sowing lupins, or banded with the seed at 5 cm depth or at 8 cm below the seed. Grain yields from banding P below the seed exceeded those where P was topdressed when &lt;250 kg P/ha had been applied in previous years, or where the Colwell soil-test P for the 10-20 cm depth was &lt;10-15 mg P/g soil. When &gt;250 kg P/ha had been applied in previous years, sufficient P had leached well below the seed, so there was little response to P and no advantage in placing freshly applied P below the seed when sowing. A possible explanation for the different results at Eradu and Badgingarra is provided.

Desert-aeolian origin of late Cenozoic regolith in arid and semi-arid Southwestern Australia

Using a sedimentary geology approach, the late Cenozoic regolith of Southwestern Australia is interpreted as basement saprock and saprolite unconformably overlain by sequences of continental sedimentary deposits. The sedimentary deposits which overlie saprock and saprolite are allochthonous, variously altered, and mainly, partly to wholly, desert-aeolian sediments. They include: aeolian and fluvial sandy clayrock facies (e.g. deposits which resemble the pallid and mottled zones of weathered Precambrian bedrock of the traditional “laterite profile”); altered aeolian sand and sandy dust facies (e.g. “hardpan”, lower parts of “duplex soils”, red sandy silt-claystone and calcrete valley fills); altered sandy duststones (e.g. “bauxite”, “laterite” and “ferricrete” of the traditional “laterite profile”); and bioturbated aeolian sand-sheets (e.g. “sandplain soils”, “lateritic sandplains” of the traditional “laterite profile”, and upper parts of “duplex soils”). The allochthonous and desert-aeolian views proposed here differ fundamentally from the traditional residual, colluvial, and erosional views. Consequently there is a need for both traditional and alternative views to be critically appraised from the perspective of sedimentary geology.

Effect of different direct drilling and conventional sowing techniques on soil strength, root growth and grain yield of wheat on sandplain soils in Western Australia

Experiments were conducted to compare different direct drilling and conventional sowing techniques, and describe the effects of these techniques on soil strength, root growth and grain yield of wheat on sandplain soils in the northern wheat-belt of Western Australia. Soil strength was identified as a critical factor affecting root growth; increasing the depth of soil loosening beneath seeding depth with a modified direct drill reduced soil strength relative to that found in the traditional direct drill treatments, and increased rooting density beyond the 10 cm soil depth. As loosening depth increased, there were increases in both shoot growth and grain yields, and water use efficiency also improved. Maximizing the depth of soil disturbance by deep ripping after sowing resulted in the highest grain yields, but the time and cost penalties associated with this tillage operation are substantial and likely to deter its routine use. Modifying a direct drill to loosen soil beneath sowing depth therefore combined the advantages of conventional direct drilling (timeliness, moisture conservation and lower risk of erosion), with those obtained by sowing after cultivation (improved root growth and yield) without the yield penalties associated either with direct drilling or delayed sowing on these soils.

Increasing the depth of soil disturbance increases yields of direct drilled wheat on the sandplain soils of Western Australia

We evaluated on sandplain soils in the northern wheatbelt of Western Australia in 1990 and 1991 the effect on wheat yields (Triticum aestivum) of increasing the depth of soil disturbance (4-40 cm) while direct drilling. These sandplain soils are easily compacted and eroded by wind, but yields after direct drilling with tined implements are frequently poorer than yields after cultivation. Direct drilling with a tined seeder was compared with: (i) direct drilling with a modified seeder on which the front 3 rows of cultivating tines could be lowered relative to the rear 3 rows of seeding tines; and (ii) with direct drilling followed immediately by deep ripping. Progressively increasing the depth of disturbance reduced soil strength and generally increased grain yields of wheat. Effects on yield were more pronounced in the wetter year of 1991 on an experimental site that had not been previously ripped; responses of 32 kg/ha for each centimetre increase in depth of disturbance were recorded. The highest yields followed deep ripping (3429 kg/ha), and the lowest yields followed minimal soil disturbance using narrow (5 cm) seeding tines working to seeding depth only (2144 kg/ha). These results confirmed that it is possible to use a modified direct drilling technique (thus retaining the advantages of timely sowing after rainfall and lowered risk of wind erosion) and raise yields above those normally expected from direct drilling on these soils.

Amelioration of subsurface acidity in sandy soils in low rainfall regions .2. Changes to soil solution composition following the surface application of gypsum and lime

Two field trials were sampled to investigate the changes to soil solution chemical properties of a yellow sandplain soil with an acidic subsoil following the application of gypsum and lime to the soil surface in 1989. The soils were sandy textured and located in a region of low annual rainfall (300-350 mm). Soil was sampled annually to a depth of 1 m and changes in soil solution composition were estimated by extraction of the soil with 0.005 M KCl. Gypsum leaching caused calcium (Ca), sulfate (SO4) and the ionic strength to increase substantially in both topsoil and subsoil by the end of the first year. Continued leaching in the second year caused these properties to decrease by approximately one-half in the topsoil. Gypsum appeared to have minimal effect on pH or total Al (Al-T), although the amount of Al present as toxic monomeric Al decreased and the amount present as non-toxic AlSO+4 ion pairs increased. Magnesium (Mg) was displaced from the topsoil by gypsum and leached to a lower depth in the subsoil. In contrast, lime caused pH to increase and Al to decrease substantially in the topsoil, but relatively little change to any soil solution properties was observed in the subsoil. There was an indication that more lime may have leached in the presence of gypsum in the first year after application at one site. Wheat yields were best related to the soil acidity index Al-T/EC (where EC is electrical conductivity of a 1:5 soil:water extract), although the depth at which the relationship was strongest in the subsoil varied between sites. The ratio Al-T/EC was strongly correlated with the activity of monomeric Al species (i.e. the sum of the activities of Al3+, AlOH2+ and Al(OH)+2 in the soil solution. An increase in the concentration of sulfate in the subsoil solution (which increased the ionic strength, thereby decreasing the activity of Al3+, and also increased the amount of Al present as the AlSO+4 ion pair) was probably the most important factor decreasing Al toxicity to wheat. The results indicated that gypsum could be used to increase wheat growth in aluminium toxic subsoils in sandy soils of low rainfall regions and that a simple soil test could be used to predict responses.

Amelioration of subsurface acidity in sandy soils in low rainfall regions .1. Responses of wheat and lupins to surface-applied gypsum and lime

Amelioration of subsoil acidity using gypsum (CaSO4.2H2O) or lime (CaCO3) was studied on sandy textured soils with low water holding capacity in a low rainfall environment. Field trials were established in 1989 at two sites on yellow sandplain soils to investigate whether different rates, sources and combinations of gypsum and lime application could be used to increase wheat and lupin yields. Gypsum increased wheat yields by up to 45% in the first two growing seasons whereas lime increased wheat yields by up to only 15% in the second season. The highest yields were generally recorded when gypsum and lime were applied together. The response of wheat to the various treatments varied both regionally and temporally and it is suggested that the inherent soil solution composition affected the magnitude and rapidity of wheat responses to gypsum. The rate of gypsum application affected the longevity of the wheat responses, with a low application rate (1 t ha-1) increasing yields for only one season. No differences in wheat yields were recorded between different sources of gypsum or application rates higher than 3 t ha-1. In contrast to wheat, lupin yields were substantially lower on gypsum-treated plots. The yield decline did not appear to be related to any simple nutritional factor and the gypsum effect was generally minimized when lime was added with the gypsum. The results indicated that lower rates of gypsum than used in previous subsoil amelioration studies were suitable for increasing wheat yields on sandy soils in low rainfall environments, and that gypsum should not be used if lupins are to be grown within at least 2 years of its application to the soil surface.

Distribution of potassium in the soil profile of a sandplain soil under pasture species

The influence of pasture species and pasture/crop rotations on the fate of K fertilizer in the soil profile of a sandplain soil was investigated. Results for Lupinus cosentinii, subterranean clover and a subterranean clover/wheat rotation are presented. Potassium was applied as KCl at six rates up to 150 kg K ha-1 for three years; bicarbonate-extractable K was measured at five depths in the profile (0–100 cm) for four years. The net change in available K in the top 100 cm of the profile (kg ha-1) was calculated. There was a gradual increase in K down the profile under all species with fertilizer application. The increase was largest for L. cosentinii, which also appeared to redistribute K from below 100 cm to the soil surface. The K residual value on this soil type was higher than expected with most of the fertilizer applied over three years being retained in the top 100 cm.

A comparison of different tillage-seeding systems: the interaction of tillage and time of sowing on sandplain soils in Western Australia

The effects of tillage-seeding method and 2 times of sowing on yields of wheat (Triticum aestivum) were examined on the sandplain soils in the northern wheatbelt of Western Australia. Four methods were compared: sowing after cultivation, sowing followed by deep ripping, direct drilling (i.e. single-pass seeding with a tined drill), sowing with a new cultivation depth modified drill (CDM) modified to cultivate up to 14 cm deep while sowing at 4 cm. Crops direct-drilled with the CDM produced more grain than crops established with conventional direct drilling or 'crops sown later using the cultivate-sow method and had similar yields to late-sown deep-ripped crops, where appropriate cultivars were used. Early sowing followed by deep ripping produced the highest grain yield. However, increasing the depth of soil disturbance while sowing early with the CDM in a 1-pass system resulted in a progressive increase in grain yield. When the cost of the extra ripping or cultivation operation is taken into account, early direct drilling with the CDM drill is likely to be more profitable than either conventional direct drilling or sowing with deep ripping or cultivation.