Walter Anderson

Responses of soil properties and grain yields to deep ripping and gypsum application in a compacted loamy sand soil contrasted with a sandy clay loam soil in Western Australia

In the low rainfall, cropping area of Western Australia, massive soil structure due to machinery traffic is common on a range of soil types and is a major obstacle to crop yield improvement. Yield increases on compacted soils have been poor in the last decade compared with those on other soils. An experiment was conducted over 4 years (1997–2000) on a loamy sand soil with massive subsoil structure using a factorial combination of soil ripping to 0.4 m (DR), and application of commercial grade gypsum at 2.5 t/ha (G) to address the soil compaction problem. Complete nutrients, based on soil test each year, were applied to all treatments and regarded as the control treatment. All crop residues were retained after harvest and returned to the soil. The experiment was conducted in a wheat–grain legume (chickpea in 1998, field pea in 2000) rotation at Tammin in Western Australia. The purpose of the experiment was to assess possible improvements in soil properties and grain yields that may result from deep soil disturbance and application of an aggregating agent such as gypsum on a loamy sand soil in a low rainfall cropping system. Soil water infiltration rate, soil strength, porosity, water-stable aggregates, exchangeable Ca and Mg, cation exchange capacity, and grain yields were measured. The results of this experiment on a loamy sand soil are compared and contrasted with those from a similar experiment on another common soil type in the low rainfall zone, a sandy clay loam soil (reported earlier by MA Hamza and WK Anderson). Grain yields were increased slightly more on the loamy sand soil at Tammin than on the sandy clay loam soil at Merredin due to deep ripping and gypsum application, even though the corresponding improvements in soil parameters were not as great on the loamy sand soil. The yield increases of wheat and legumes due to gypsum treatment were significantly lower on both soil types than those due to the combination of gypsum and ripping, whereas ripping alone without gypsum produced a yield decrease in the third and subsequent years after treatment. The main treatment effects on yield were additive, as significant interactions between the treatments on yield were seldom found. Deep ripping and gypsum application (DRG) resulted in the greatest improvement in the soil physical properties as indicated by crop growth on both soil types. The DRG treatment increased soil water infiltration rate by about 90% on the loamy sand soil but by more than 130% on the sandy clay loam soil 4 years after the application of the treatments. Strength and porosity of the topsoil were decreased much more on the sandy clay loam soil. Summer rain stored in the soil prior to seeding was increased almost 3 times in both soils. The increase in water-stable aggregates was only 8% in the loamy sand soil but 46% on the sandy clay loam soil. Cation exchange capacity and exchangeable calcium were also increased more on the clayey than on the sandy soil by the use of DRG. Economic analysis of the yield improvements showed that the DRG treatment produced significantly higher profit than the G or DR treatments alone on both soil types, but was slightly greater on the loamy sand soil type. The combination of soil ripping and gypsum application in the presence of complete nutrients and annual return of crop residues to the soil had somewhat different effects on the soil physical properties and grain yields at a loamy sand soil site compared with the sandy clay loam soil site. However, the effect in both cases was favourable and is suggested to improve crop grain yield and soil physical fertility on both commonly occurring soil types in the low rainfall, cropping zone of Western Australia.

Improving soil physical fertility and crop yield on a clay soil in Western Australia

In the low rainfall area of Western Australia, clay soils with massive soil structure form a major part of the area sown to wheat. Yield increases on such soils have been poor in the last decade compared with those on other soil types. An experiment was conducted over 4 years (1997–2000) using a factorial combination of soil ripping to 0.4 m, application of commercial grade gypsum at 2.5 t/ha, and addition of complete nutrients based on soil test each year. All crop residues were retained after harvest and returned to the soil. The experiment was conducted in a wheat–field pea rotation at Merredin, WA. Soil water infiltration rate, soil strength, bulk density, water-stable aggregates, cation exchange capacity, and wheat yields were measured. Grain yields of wheat and field peas were increased by deep ripping, the addition of gypsum, or the addition of complete nutrients in some years. The main treatment effects on yield were additive, as significant interactions between the treatments on yield were seldom found. However, all the main treatments also significantly improved many of the soil physical properties related to crop growth. In 2000, 4 years after the treatments were applied, soil water infiltration rate was increased by more than 200%, strength of the topsoil decreased by around 1600 kPa, and soil bulk density decreased by 20%. Gypsum application increased water-stable aggregates, but soil mixing caused by deep ripping reduced them. The combination of soil ripping and gypsum application in the presence of complete nutrients and annual return of crop residues to the soil is suggested to improve crop grain yield and soil physical fertility on a range of Western Australian soils.

The role of management in yield improvement of the wheat crop—a review with special emphasis on Western Australia

Modern bread wheat (Triticum aestivum) has been well adapted for survival and production in water-limited environments since it was first domesticated in the Mediterranean basin at least 8000 years ago. Adaptation to various environments has been assisted through selection and cross-breeding for traits that contribute to high and stable yield since that time. Improvements in crop management aimed at improving yield and grain quality probably developed more slowly but the rate of change has accelerated in recent decades. Many studies have shown that the contribution to increased yield from improved management has been about double that from breeding. Both processes have proceeded in parallel, although possibly at different rates in some periods, and positive interactions between breeding and management have been responsible for greater improvements than by either process alone. In southern Australia, management of the wheat crop has focused on improvement of yield and grain quality over the last century. Adaptation has come to be equated with profitability and, recently, with long-term economic and biological viability of the production system. Early emphases on water conservation through the use of bare fallow, crop nutrition through the use of fertilisers, crop rotation with legumes, and mechanisation, have been replaced by, or supplemented with, extensive use of herbicides for weed management, reduced tillage, earlier sowing, retention of crop residues, and the use of ‘break’ crops, largely for management of root diseases. Yields from rainfed wheat crops in Western Australia have doubled since the late 1980s and water-use efficiency has also doubled. The percentage of the crop in Western Australia that qualifies for premium payments for quality has increased 3–4 fold since 1990. Both these trends have been underpinned by the gradual elimination or management of the factors that have been identified as limiting grain yield, grain quality, or long-term viability of the cropping system.

Variability of optimum sowing time for wheat yield in Western Australia

Sowing wheat (Triticum aestivum L.) at the right time is one of the most important means of maximising grain yieldindrylandagriculture.Objectivesofthisstudyweretounderstandthevariationinestimatesofoptimumsowingtimeas influenced by cultivar and environmental characteristics, and to assess the relative importance of location, season, sowing time, and cultivar factors in maximising grain yield in Western Australia. Twenty-seven cultivartime of sowing experimentswereconductedoverthreeseasons(2003-05)atarangeoflocations(annualrainfall300-450mm,lat.28-358S). Therewerefourtypesofcultivarsowingtimeresponses,namely,quadratic,lineardeclining, flat,andlinearincreasing, associated with opening rains before mid-May, opening rains after mid-May, low-yielding sites, and good spring rains, respectively.Regression-treeanalysisrevealedthatdifferencesamongcultivarsinTmax(sowingtimewhenmaximumgrain yieldwasachieved)weremuchlessintheeasternsites(mostlydrierseasons).AbiplotdifferentiatedcultivarsforTmaxacross the range of environments used, while the subset regression analysis specifically indicated an association of average temperature and growing-season rainfall with variation for Tmax of individual cultivars. The yield penalty for sowing before the optimum time in quadratic-type responses was clearly greater for shorter season cultivars but no clear relationship was apparent between maturity class of cultivars and the penalty for late sowing, possibly due to differential plasticity of cultivars for grain weight under harsh finishing conditions. The duration of the optimum sowing window at a given location was inversely proportional to the yield potential, implying that it is critical to sow at or close to the optimum time when the yield potential is high, most common when the season breaks early. Yield component analysisshowedthattherelativechangeingrainyieldoversowingdateswassignificantlycorrelatedwithrelativechangesin grain numbers/m 2 in the late May sowings but other yield components were also important in the early May experiments. Sowingtimeaccountedfor10%ofgrainyieldvariationcomparedwithcultivar(1%),whiletherestwasduetouncontrollable factors of location and season.

Small grain screenings in wheat: interactions of cultivars with season, site, and management practices

Small grains that pass through a 2-mm slotted screen (sievings or screenings) are one of the most important causes of price dockages of wheat in Australia because grain size variation greatly affects flour yield and commercial value. The aims of this study were to examine the effects of season, time of sowing, plant population, and applied nitrogen, and their interactions with cultivars, on small grain screenings. Twenty-one field experiments involving 16 new cultivars and elite crossbreds, and various management variables, were conducted in the medium (annual rainfall 325-450 mm) and low (annual rainfall grain number/area > grain number/head > grain yield. Cultivars differed in production of screenings in response to plant population, nitrogen fertiliser and sowing time. Harrismith was the most sensitive cultivar and Wyalkatchem was overall the most tolerant cultivar. Delayed seeding had the least effect on the screenings of cultivars Westonia, Carnamah, and Wyalkatchem. Carnamah was the most stable cultivar against higher levels of applied nitrogen, whereas Westonia required high plant numbers to contain screenings. It is concluded that cultivars can be classified according to specific sensitivities, and appropriate management practices may be suggested to growers.

Rainfall, sowing time, soil type, and cultivar influence optimum plant population for wheat in Western Australia

In this paper we analyse existing experimental data (grain yield and yield components) from seed rate experiments on wheat in Western Australia, with the aims of determining which factors most influence the optimum plant population, and advancing some practical guidelines for improving the choice of seed rate under rain-fed conditions. Experiments (32) were conducted in the rain-fed cropping zone of Western Australia between 1996 and 2001, using factorial combinations of wheat cultivars (3–25) and target plant populations (4 or 5). Some of them also contained treatments of nitrogen fertiliser (0 or 40 kg/ha of N) or sowing times (2). Each cultivar × plant population dataset (248) was considered to be a record for the sake of the subsequent analyses. Actual plant numbers were counted in each experiment and the optimum plant population was estimated when the slope of an inverse polynomial curve (choosing the most appropriate of the LDL and QDL models in GenStat) fitted to each record was 2.5 kg/ha of grain yield for each extra plant/m2. The optimum populations were initially grouped using a regression tree technique into groups with similar characteristics using pre-sowing rainfall, rainfall in the growing season, sowing date, and soil type. The variables cultivar and nitrogen fertiliser rate were later added to the regression tree analysis. Yield components available for most experiments were used as an aid to interpretation of the results. The optimum plant population varied from 35 to 175 plants/m2 and average grain yields varied from 0.42 to 3.91 t/ha. Rainfall in the growing season (sowing date to harvest date) provided the first split in the regression tree, but pre-sowing rainfall (January to sowing date), sowing date, and soil type further modified the optimum population. The addition of N fertiliser rate as a variable in the regression tree did not induce any different groupings of the optimum population sets, but cultivars were grouped into 4 response types according to pre- and post-sowing rainfall amounts. Where rainfall in the growing season was 291 mm. Increases in yield components in response to improved growing conditions above about 400 culms/m2, 300 ears/m2, 10 000 kernels/m2, and 600 g/m2 of dry matter at anthesis were not associated with higher optimum plant populations. In general, the optimum plant population increased at about 40 plants/m2 for each tonne of grain yield up to about 3.0 t/ha. The effect of cultivar on the optimum population appeared at yield levels above 2.5 t/ha, but was only detectable when the rainfall in the growing season exceeded 205 mm. Growing conditions and cultivars associated with lower weight per ear (due to fewer kernels and/or lower kernel weight) were associated with higher optimum plant population when the rainfall in the growing season exceeded 205 mm. It is suggested that farmers can make better estimates of the appropriate plant population (and hence can calculate seed rate) on the basis of pre-sowing rainfall (likely stored water), rainfall zone (probability of rainfall in the growing season), sowing date, soil type, and characteristics of individual cultivars where known.

The effects of soil type and seasonal rainfall on the optimum seed rate for wheat in Western Australia

Seventeen experiments were conducted in 1996, 1997 and 1998 in the central and northern wheatbelt of Western Australia, covering a range of soil types, seasonal rainfall, cultivars and sowing times. The objective of the experiments was to investigate how these factors affect the range of optimum seed rates derived from seeding rate experiments and, thus, to improve advice to farmers. Our results suggest that soil type and seasonal rainfall were the major factors influencing the differences in optimum seed rate. Regression tree methods were used to show that experiments in clay loam soils had higher optimum seed rates (52–76 kg/ha, depending on the cultivars used). In sandier soils, the optimum seed rate was lower (35–60 kg/ha, depending on cultivar and sowing time) but higher (67xa0kg/ha) at higher seasonal rainfall (>450 mm). We found some cultivars were grouped into consistent response patterns. Sowing time also influenced optimum seed rate; later sowing required higher seed rates, to maximise grain yield. A positive correlation was not observed between grain yield and optimum seed rate, possibly due to the narrow range of yields recorded in the experiments. Our data showed that the percentage of establishment fell off rapidly at higher seed rates. This implies that lower establishment percentages should be used when calculating the seed rates required to produce high plant populations in the field.

Addressing the yield gap in rainfed crops: a review

The problems and challenges of rapidly increasing world population, global climate change, shortages of water suitable for irrigation and degradation of agricultural land are increasing the demand to improve grain production from rainfed arable lands. Specific challenges include estimating the size and thus the value of the yield gap, identifying the factors limiting current average production and designing profitable remedial strategies for a range of agro-ecological regions. This review of the rainfall-limited potential yields and the gap between actual or average yields of cereal and legume crops and the rainfall-limited potential indicates that there is still substantial room to increase the average yield of crops in rainfed systems in both developed and developing regions. The review has indicated that (1) the size of the gap between average and potential yields varies according to the agro-ecological zone and the available technologies from about 0.5 to over 5xa0t/ha, leaving considerable scope for future yield improvement; (2) there is relatively less information applicable at the farm or field scale that assesses the spatial and temporal variability of the yield gap, the reasons for the gap and the possible methods to close the gap; (3) there is also limited information on the feasibility and profitability of applying various approaches to close the gap, including tactical and strategic management practices and plant breeding; (4) the evidence of the impact of the components of conservation agriculture on crop yields in a wide range of agro-ecological regions supports the adoption of zero tillage and crop rotation but is less clear in support of residue retention; (5) objective identification and testing of factors that limit production can lead to a rational sequence of amelioration that is specific to each agro-ecological or field situation and can close the yield gap in winter-dominant rainfall environments; and (6) farmer-participatory varietal selection, including breeding for specific adaptation can make a substantial contribution to closing the gap in a range of environments. A common observation from the reports reviewed here is that sustainable yield improvement will need to employ a range of methods that are appropriate to specific agro-ecological conditions—previous approaches based on single inputs, practices or genotypes can only be partial solutions.

Can increased nutrition raise cereal yields to the rainfall-limited potential in the high rainfall cropping zone of south Western Australia?

Average yield of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) in the high rainfall cropping zone (>750 mm) of south Western Australia from 1996 to 2001 was 2.5 t/ha. This is far below the water-limited potential yield (water losses of 110 mm, transpiration efficiency of 20 kg/ha.mm) of 6–8 t/ha. Nutrition of the cereal crops has been regarded as one constraint to reaching the potential yield, although grain yield increases (responses) under conventional management practices (a series of full cultivation operations) have been inconsistent. Three experiments, with a total of five trial sites conducted over two seasons, were carried out to test the response of wheat and barley to fertiliser applications of nitrogen (N), phosphorus (P), potassium (K), sulfur (S) and trace elements (TE). Various combinations of nutrients were applied. These ranged from no fertiliser (nil), to farmer practice (N at rates at 34–82 kg/ha, P at 3–17 kg/ha, K at 0–50 kg/ha and S at 4–11 kg/ha), to nutrients calculated to supply the needs of a 6–8 t/ha cereal crop (N, P, K, S, TE). The aim was to determine whether the supply of non-limiting levels of crop nutrients could raise yields to the potential yield as determined by seasonal rainfall. In the drier seasons experienced in 2001 and 2002 at Arthur River and Cranbrook, with growing season rainfall (May–November) up to about 350 mm, it was possible to raise grain yields to levels at or above the calculated rainfall-limited potential with increased nutrition (4.2 t/ha for barley and 4.5 t/ha for wheat). However, in the wetter environment of Boyup Brook in 2002, where seasonal rainfall was greater than 500 mm, extra nutrition by itself was not sufficient to reach the water-limited potential, even where the yields were increased from 3.5 to 5.2 t/ha for wheat and from 3.9 to 4.5 t/ha for barley. Further experimentation is required to clarify the factors limiting responses to nutrition when the growing season rainfall is greater than 500 mm and thus allow greater confidence in extrapolating these results in the high rainfall cropping zone of Western Australia. In wheat, the highest profits were obtained from the complete fertiliser strategy (N, P, K, S, TE). However, for barley, the greatest profits were not obtained with the highest grain yields and fertiliser strategies due to decreased grain quality.

Managing yield reductions from wide row spacing in wheat

Experiments were conducted to investigate row spacing effects on wheat yield and grain quality and the interactions between row spacing and cultivars, plant population density, nitrogen application rate, time of sowing, fertiliser placement and row spread from 2000 to 2002 in the south coast region of Western Australia. In the experiments that were conducted following pasture or lupins, wider row spacings of 240 and 360 mm consistently reduced wheat yield and increased grain protein and small grain screenings compared with a narrow row spacing of 180 mm. Average plant numbers were reduced in the wider rows in all experiments. This result, possibly related to increased competition for water as the seeds were placed closer together in the wide rows, may also have been related to reductions in wheat grain yield. The yield decline in wider rows was lowest for the long season cultivar Camm with a May sowing in 1 experiment and at the higher N rate in another experiment. The response of Camm at wider row spacings can be partially explained by its higher dry matter production as measured in 2000 and may also help to explain the observed advantage of Camm in suppressing weed growth at all row spacings. In 2002, the row spread (seed width within the row) was varied from normal 25 mm widths to 50 and 75 mm widths. Yield was increased at the widest row spacing (360 mm) by using the wider row spreads of 50 or 75 mm. Fertiliser placement methods significantly affected plant establishment but not grain yield. Grain quality (protein percentage, small grain screenings and hectolitre weight) was reduced in wider rows in some cases or unaffected in others. This research has demonstrated that yield reductions due to wide row spacing can be minimised by using a long season cultivar when sown in May, by using adequate N fertiliser and by increasing the spread of seed across the row.