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Context: Australia is renowned for its climate variation, featuring years with drought and years with floods, which result in significant production and profit variability. Accordingly, to maximise profitability, dryland farming systems need to be dynamically managed in response to unfolding weather conditions. Aims: The aim of this study is to identify and quantify optimal tactical livestock management for different weather-years. Methods: This study employed a whole-farm optimisation model to analyse a representative mixed enterprise farm located in the Great Southern region of Western Australia. Using this model, we investigated the economic significance of five key livestock management tactics. These included timing of sheep sales, pasture-area adjustments, rotational grazing, crop grazing and sheep nutrition adjustments. Key results: The results showed that, on the modelled dryland mixed-enterprise farm in the Great Southern region of Western Australia, short-term adjustments to the overall farm strategy in response to unfolding weather conditions increased expected profit by approximately 16%. Each tactic boosted profit by between A$7704 and A$53,171. However, we outline several complexities that farmers must consider when implementing tactics. Conclusions: The financial gains from short-term tactical management highlighted their importance and farmers' need to develop and apply those skills. The tactical skills promote business resilience and adaptability in the face of climate uncertainties. Implications: The study highlighted the economic value of dynamic livestock management in response to climate variations, offering farmers in the Great Southern region the means to underpin profitable and sustainable farm practices. Under Australia's renowned climate variation, it is profitable for farmer to implement short-term tactical management adjustments in response to the unfolding weather conditions. This paper has identified and quantified optimal tactical livestock management for different weather-years for a mixed-farming system in the Great Southern region of Western Australia. [ABSTRACT FROM AUTHOR]

Conventional dryland cropping systems are characterised by low crop diversity and frequent fallows. This has significant impacts on soil microbes that underpin soil function. Diversifying crop rotations can potentially counter these effects; however, limited data exists on the impacts of diversified crop rotations on soil microbes in drylands. Using phylogenetic marker gene sequencing, we characterised soil microbial diversity in conventional and diversified dryland crop rotations in subtropical Australia. This included winter and summer dominant rotations. Conventional systems were cereal-dominant with a crop-fallow rotation. Diversified systems included greater crop diversity, double crops, cover crops, and a multi-year ley pasture. In summer rotations with increased crop diversity and cover crops, bacterial and fungal richness increased, and distinct communities were formed compared to fallow land. Often, these community shifts were associated with greater soil organic carbon (SOC) and nitrogen. All winter rotations had distinct fungal communities and ley pasture resulted in greater fungal diversity compared to other rotations. No effects of the winter rotations were evident on bacterial communities. Our results show that diversification of dryland crop rotations leads to significant shifts in soil microbial communities in both winter and summer cropping systems. Both summer and winter rotations incorporating cover crops and ley pasture had greater soil respiration and nitrogen, indicating increases in soil fertility. These rotations may offer an alternative to conventional crop-fallow rotations to counter ongoing declines in soil health. [ABSTRACT FROM AUTHOR]

Context: Rotations in rainfed farming systems of southwest Australia have shifted towards intensified cropping and it is necessary to reassess soilborne pathogens and plant parasitic nematodes within this context. Aims: We tested the hypothesis that these recent changes in rotations and agronomy have altered the efficacy with which rotations reduce the incidence of common root pathogens and plant parasitic nematodes. Methods: We tracked changes in common pathogen DNA in soil and the incidence and severity of crop root damage in 184 paddocks, over 6 years from 2010 to 2015, and related this to farmer practices. Key results: Overall, severe root damage was rare, with 72% of plant samples showing no damage or only a trace and only 1% severely damaged. We found that the reduction of paddocks in pasture and resultant very low weed populations, combined with early sowing, reduced persistence of pathogens and nematode pests. But some aspects of crop management had the opposite effect: high rates of herbicide, increased frequency of cereals and canola at the expense of lupin and increased N fertiliser use. Conclusions: Current agronomic practices and the frequency of non-host crops in rotations appear to be effective in controlling common root pathogens and plant parasitic nematodes. But the aspects of agronomic management that increased populations of pathogens should be applied cautiously. Implications: Studies such as this that link multiple productivity constraints, such as pathogens and nematode pests, weeds and nutrients, to management practices are important to understand the sustainability of current or proposed production methods. Current agronomic practices and rotations appear to be effective in controlling common root pathogens and plant parasitic nematodes in southwest Australian dryland cropping systems. But recent changes in rotations and agronomy have altered pathogen and plant parasitic nematode dynamics. We found low weed populations and early sowing reduced persistence of pathogens studied, but use of high rates of herbicide, increased frequency of cereals and canola at the expense of lupin and increased N fertiliser use had the opposite effect. [ABSTRACT FROM AUTHOR]

Rotations and associated management practices in rainfed farming systems of southwest Australia have shifted towards intensified cropping. Survey data from 184 fields spanning 14 Mha of southwest Australia were used to document water use efficiency (WUE) and water-limited yield potential (WLYP) of commercial crops and crop sequences and identify biophysical variables influencing WUE. WUE achieved in commercial wheat crops was 10.7 kg grain/ha.mm. Using a boundary function Ywl = 25 × (WU − 45), farmers achieved 54% of WLYP. Climate variables affected WUE more than management and biotic variates, the highest latitude region having WUE of 9.0 kg grain/ha.mm, compared to 11.8 kg grain/ha.mm for regions further south. Increased soil nitrogen and nitrogen fertiliser increased WUE, as did sowing earlier; in keeping with farmers in southern Australia sowing crops earlier and trebling fertiliser nitrogen usage since 1990. Wheat yield and WUE increased a small amount after break crop or pasture (12.5 kg grain/ha.mm) compared to wheat grown after wheat (11.2 kg grain/ha.mm), due to good weed and root pathogen control, and high fertiliser nitrogen application. However, WUE of wheat declined to 8.4 kg grain/ha.mm when more than three wheat crops were grown in succession. Farmers continue to improve WUE with increased inputs and new technologies replacing some traditional functions of break crops and pasture. However, break crops and pastures are still required within the rotation to maintain WUE and break effects need to be measured over several years. High water use efficiency was associated with low levels of weed, disease and high fertliser nitrogen inputs in Western Australia's rainfed cropping systems. The yield benefit to wheat sown immediately after break crops or pasture was low, because of low levels of biophysical constraints. However, water use efficiency of wheat declined when three wheat crops were grown in succession. This highlights the need for continued research into the integration of break crops and pastures into wheat dominated rotations. [ABSTRACT FROM AUTHOR]

Sowing with conventional airseeders and seed drills results in random placement of seed along the row, causing variable interplant competition. Precision planting improves the uniformity of seed placement, minimising interplant competition, with the potential to improve yields. While precision planting has been used widely in summer cropping its benefits to yield in winter crops has not been well documented. Our hypothesis was that precision planting will improve yields by reducing the degree of interplant competition in crop stands. The objectives of the work were to (a) quantify the benefits to yield of improvements in uniformity in plant spacing in canola and some grain legume crops, (b) examine how crop stand uniformity affects responses to variation in plant density and (c) identify the stage of development which are most sensitive to improvements in interplant competition. Twenty field experiments were conducted with canola (11 experiments) and different grain legume crops (nine experiments) over three years in southern and western Australia. In each experiment crops were sown at between three and six densities with either a conventional seeder or a precision planter. Crop establishment, variation in interplant distance, crop biomass, grain yield and yield components were measured. Analyses of responses in biomass and yield per plant were also used to assess effects on interplant competition. Precision planting did not improve seedling establishment but consistently improved stand uniformity. Yields were increased by precision planting in 11 experiments, with greater effects observed in canola. In the remaining experiments, yields were similar. Average yield benefits were 6 % in canola, 2 % in lentil, 9 % in faba bean and 13 % in a single experiment with lupin, which represented average yield increases 80–100 kg/ha with maximum increases of 300 kg/ha in canola and 600 kg/ha in faba bean. Increases in yield from precision planting were related to improvements in growth after flowering and early podding and were influenced by rainfall in spring. Canola showed less variation in yield to variation in plant density than grain legumes. Responses to plant density in growth per plant suggested precision planting improved a plant's ability to use available space, resulting in a higher yield at the same density compared to conventionally-sown crops. Precision planting increased crop stand uniformity and has the potential to improve yields of dryland winter crops, but results are seasonally-dependent. The work highlighted the value of improved crop stand uniformity to yield independently of variation in crop establishment. It provides evidence that precision planting has the potential to improve yields of canola and some grain legumes in dryland farming systems, but the environmental conditions under which the greatest benefit will be achieved need to be defined. • Uniform plant spacing reduces interplant competition. • Improving crop uniformity by precision planting improved grain yields by about 9 %. • Yield increases were observed in canola and pulse crops. • More uniform spacing reduced interplant competition at flowering and podding. [ABSTRACT FROM AUTHOR]

Low-fertility soils and frequent droughts are typical characteristics of rainfed wheat production methods, which create an unfavourable environment for long-term crop growth. In this work, the water balance and nitrogen (N) dynamics in soils under rainfed wheat agriculture at low (219 mm, Pygery) and medium (392 mm, Yeelanna) rainfall sites in south Australia were assessed over the course of two seasons using a processed-based biophysical numerical model. The model was calibrated, validated, and the water and nitrogen consumption efficiency of wheat were calculated using estimated evapotranspiration components and data on N partitioning. The predicted water balance components for the two sites differed significantly from one another. At the low rainfall site, more than 40% to 50% of the rainfall was absorbed by plants. On the other hand, leaching losses at the medium rainfall site (Yeelanna) of up to 25% of seasonal precipitation show a large volume of water eluding the root zone. Ammonia-nitrogen (NH4-N) contributed little to plant nutrition, according to the model-predicted N partitioning, and its content in the soil stayed below 2 ppm for the majority of the crop season, with the exception of the period right after NH4-N-based fertiliser application. The majority of N uptake during both seasons at both locations was facilitated by nitrate-nitrogen (NO3-N). The primary causes of the N losses from the soil at the medium rainfall location (3.5-20.5 kg ha-1 ) were NO3-N leaching (NL) and NH4-N volatilization (Nv) below the crop root zone. Climate, water availability, and N dynamics in the soil all contributed to the extreme variability in water productivity (8-40 kg ha-1 mm-1 ) and N usage efficiency (31-41 kg kg-1 ). These findings imply that managing N applications to maximise wheat output and reduce N losses in rainfed agriculture can be accomplished by combining water balance and N modelling. [ABSTRACT FROM AUTHOR]

Crop yield must increase to keep pace with growing global demand. Past increases in crop production have rarely been attributable to an individual innovation but have occurred when technologies and practices combine to form improved farming systems. Inevitably this has involved synergy between genotypic and management improvements. We argue that research focused on developing synergistic systems that overcome clear production constraints will accelerate increases in yield. This offers the opportunity to better focus and multiply the impact of discipline-focused research. Here we use the rainfed grain production systems of south-eastern Australia as a case study of how transformational change in water productivity can be achieved with research focused on genotype × management synergies. In this region, rainfall is low and variable and has declined since 1990. Despite this, growers have maintained yields by implementing synergistic systems combining innovations in (i) soil water conservation, (ii) crop diversity, (iii) earlier sowing, and (iv) matching nitrogen fertilizer to water-limited demand. Further increases are emerging from synergies between genetic improvements to deliver flowering time stability, adjusted sowing times, and potential dual-purpose use. Collaboration between agronomists, physiologists, and crop breeders has led to development of commercial genotypes with stable flowering time that are in early phases of testing and adoption. [ABSTRACT FROM AUTHOR]

Evaluating the cost-effectiveness of GHG mitigation in the dryland agricultural sector is needed in terms of designing and implementing detailed and efficient mitigation programs, which is currently rarely covered by the literature. In this paper, we use a parametric directional distance approach to explore the farm-level abatement potential and cost (shadow value) of GHG for dryland farms in southwestern Australia. The study indicates that dryland agriculture could abate substantial GHG emissions and save agricultural inputs simultaneously. For the years 2006–2013, the average abatement potential ratios fluctuated between 17 and 33%, with a mean value of 21%. The mean shadow price of dryland agricultural GHG was $17.60 per tonne CO2-e in 2013 Australian dollars. In general, the analysis supports that reducing GHG in dryland agriculture is relatively cost-effective. [ABSTRACT FROM AUTHOR]

• Zero tillage is a philosophical ideal for soil conservation. • The ideal can be in conflict with the need to manage soil and agronomic constraints. • We measured the detriment caused by a single tillage and the subsequent recovery. • One tillage caused minor loss of wet aggregate stability and no effect on hydraulic conductivity. • Recovery time was generally 1–2 years but for one site-year exceeded 2 years. Occasional, strategically applied tillage within an otherwise no-till system conflicts with the philosophical ideal of zero disturbance of soil, yet is often needed to manage soil constraints, pests and weeds. This study reports the impacts of a single strategic tillage applied to long term no-till soils (10–16 years) with a scarifier or offset discs, compared with ongoing no-till, on soil conditions and crop growth over four seasons at three locations in southern New South Wales, Australia. The tillage occurred just prior to sowing in autumn and under different management conditions at each site. The effect of a single tillage on wet aggregate stability (WAS) ranged from 0 to 14% loss of macro-aggregates, and the recovery time was generally one or two years with the exception of one site-year. The effect of a single tillage on saturated hydraulic conductivity was not statistically significant. Crop establishment was decreased by tillage in some site-years but effects on crop dry matter and grain yield tended to be neutral or minor. In most cases, seasonal effects and crop sequence had a much larger effect on crop productivity than tillage. The results demonstrated that strategic use of tillage within an otherwise no-till system generated minor and short term impacts on soil conditions. Strategic tillage therefore provides a tool for more flexible management of soil, pest and weed constraints to ensure long term productivity and sustainability of dryland mixed farming systems in southern New South Wales, Australia. [ABSTRACT FROM AUTHOR]

Understanding the implications of replacing fallows with cover crops on plant-available water (PAW) and soil mineral nitrogen (N) and their carry-over effects on subsequent cash crops is critical for understanding their potential for ecological intensification in water-limited environments. We modelled the impacts of different cover crop functional types over historical climate to predict how climate variability influences soil water and N acquisition and subsequent availability to a maize crop in a dryland farming system of subtropical Australia. Following local validation of simulation models (APSIM) with 3-site-years of field data, 70 years of crop-fallow rotations were simulated comparing conventional fallow against a diverse range of cover crops comprising monocultures and mixtures of grass vs. legume vs. brassica. Cover crops consistently reduced soil water and mineral N at maize sowing compared to conventional fallow. In dry to normal precipitation years, this induced a maize yield penalty of up to − 18% relative to fallow, primarily due to reduced water availability. In wet years, increased in maize grain yield (+4%) was predicted following legume and grass-associated cover crop mixtures with concomitant reductions in N leaching and soil surface runoff of up to 40%. Cash crop yields following grass-cover crops were more stable and carried lower downside risks; multi-species (grass-legume-brassica) cover crop mixtures carried higher yield penalties and greater downside risks due to high biomass accumulation and high soil water extraction. These long-term predictions in water-limited environments indicate that increasing cover crop complexity by using mixtures with diverse functional traits can lead to a greater risk of yield losses and increased yield instability unless they are managed differently to monoculture cover crops. Therefore, for successful integration of cover crops into dryland agroecosystems, cover crops should be considered as a flexible choice grown under favourable precipitation and economic scenarios rather than for continuous fallow replacement. • Applied APSIM to assess potential dryland fallow replacement cover crop options. • Cover crops reduced yields by 12% relative to fallow in dry to normal years. • Predicted yield gains in wet years following fababean and multi-species mixture. • Dryland cover crops should be considered as an opportunistic practice. [ABSTRACT FROM AUTHOR]

Those not immediately involved in managing a dryland farm sustainably in a risky water-limited environment such as Australia may think a comparison with rocket science a bit of a stretch. But if the level of challenge, the importance to humanity, the long-term multidisciplinary team approach and planning required, and the level of uncertainty inherent in the pursuit are measures, then I think the comparison is warranted. The importance of the farming systems agronomy research that has supported agriculture and food security in Australia and globally since William Farrer's time perhaps receives less public attention than some other science areas such as genetics, genomics, or digital agriculture—indeed, agriculture is now literally "rocket science" as satellite-guided machines and sensors gather volumes of data about the soils, plants, and weather on farms at scales and speeds hitherto impossible. Yet despite spectacular advances in individual genetic or management technologies, few have been singularly transformational. Rather significant productivity improvements generally arise when a combination of technologies, often old and new are integrated and synergize in specific ways within a system—a process here termed incremental transformation. William Farrer himself was clearly aware of this fact, as this article shows, he placed as much importance on maintaining the fertility of the soil in which he grew wheat as on improving the wheat plant itself. This article first provides some background to Farrer and on his interests in Genotype × Environment × Management (G × E × M) interactions (though he certainly did not use that terminology). It then describes some examples from my own research teams, to demonstrate the ongoing impact that arises from research to capture synergies from new genetics and improved management in the pursuit of incremental transformation. [ABSTRACT FROM AUTHOR]

The rainfed cropland belt in Australia is of great importance to the world grain market but has the highest climate variability of all such regions globally. However, the spatial-temporal impacts of climate variability on crops during different crop growth stages across broadacre farming systems are largely unknown. This study aims to quantify the contributions of climate and Land Surface Temperature (LST) variations to the variability of the Enhanced Vegetation Index (EVI) by using remote sensing methods. The datasets were analyzed at an 8-day time-scale across the rainfed cropland of eastern Australia. First, we found that EVI values were more variable during the crop reproductive growth stages than at any other crop life stage within a calendar year, but nevertheless had the highest correlation with crop grain yield (t ha −1 ). Second, climate factors and LST during the crop reproductive growth stages showed the largest variability and followed a typical east-west gradient of rainfall and a north-south temperature gradient across the study area during the crop growing season. Last, we identified two critical 8-day periods, beginning on day of the year (DoY) 257 and 289, as the key ‘windows’ of crop growth variation that arose from the variability in climate and LST. Our results show that the sum of the variability of the climate components within these two 8-day ‘windows’ explained >88% of the variability in the EVI, with LST being the dominant factor. This study offers a fresh understanding of the spatial-temporal climate-crop relationships in rainfed cropland and can serve as an early warning system for agricultural adaptation in broadacre rainfed cropping practices in Australia and worldwide. [ABSTRACT FROM AUTHOR]

The paper examines how Murray-Darling Basin (MDB) farmers respond to water-related challenges such as induced by climate change and environmental policy. This is a critical and ongoing aspect of farming operations in Australia’s largest watershed. Using the 2013 Regional Wellbeing Survey data, we show that irrigators and dryland farmers adjust their production processes and business models using a wide range of strategies, with irrigators adopting more strategies than dryland farmers and investment-related strategies being the most prevalent form of adjustment. The extent of adjustment depends on farm characteristics: large, intensive-farming units, on-farm income-dependent and annual cropping farmers were more likely to adapt among irrigators. Irrigators also generally place more importance on water-related strategies than output- and input-related strategies. Amongst dryland farmers, hobby farming, non-intensive-farming and perennial cropping units were more likely to adjust than other dryland farms. These empirical findings inform the important debate about developing and targeting adequate policy support for structural adjustment of farming operations in the MDB. [ABSTRACT FROM PUBLISHER]

Current forest industries in south-western Australia are based on regrowth natural eucalypt forests andPinusandEucalyptusspp. plantations, and restricted to areas with >600 mm y−1annual rainfall. Dryland farming systems have been developed across 20 million ha in a zone with 300–600 mm y−1annual rainfall and a Mediterranean climate. This zone is beset with land degradation problems, such as salinity and wind erosion, and there has been considerable effort in the last three decades to develop reforestation options to stabilise the landscapes. Traditional forestry approaches using pulp wood or sawlog production in this zone have been limited by unfavourable economics driven by modest tree growth rates, large transport costs to processing and export facilities, and high labour costs. Given that salinity results from a disruption of the landscape water balance, reforestation has represented a major component in attempts to tackle the problem. Issues with reforestation include (1) obtaining sufficient scale of activity to impact watershed water balances, (2) obtaining a hydrological response without displacing farm production and rural communities and (3) gaining payment for non-forest benefits. This paper reviews the approaches that have been used to integrate trees into the dryland farming (300–600 mm y−1annual rainfall) systems of south-western Australia, and have resulted in at least 113 286 ha of reforestation. These included both traditional (pine and eucalypt sawlogs) and new (sandalwood, biodiversity restoration and carbon mitigation through bioenergy and carbon sequestration) projects. Ongoing investment has centred on carbon sequestration as this represents one of the few profitable options for the management of dryland salinity in this region. Approaches developed in this region to encourage farmland reforestation will be applicable in other dryland regions, particularly with the interest in using the land-sector to meet climate mitigation targets. [ABSTRACT FROM AUTHOR]

Rainfed crops rely on two sources of water: stored soil water at sowing and seasonal rain. In strongly seasonal winter-rainfall environments, stored soil water at sowing is minor, and uncertain seasonal rainfall is a source of risk. In south-eastern Australia, under-fertilisation is a common outcome of nitrogen risk management with implications for wheat yield and mining of soil organic matter. Here we explore the use of carbon isotope composition (δ 13C) to capture the effects of crop water status on grain yield in a context of nitrogen top dressing. In the sampled environments, crops receive at least 50% of seasonal rainfall by stem elongation, and at least 70% of seasonal rainfall by flowering. In a sample of 1518 plots, yield varied from 0.07 to 9.96 t ha-1 and correlated with δ 13C measured with isotope ratio mass spectrometer (IRMS) at flowering (r = −0.76, p < 0.0001); this is consistent with the rainfall pattern and the physiology of the crop featuring a critical period for yield from 300 °Cd before to 100 °Cd after anthesis. In a sample of 135 plots, yield varied from 1.2 to 8.4 t ha-1 and correlated with δ 13C measured with IRMS at stem elongation (r = −0.56, p < 0.0001). Yield response to nitrogen, defined as the difference between yield in fertilised crops (50–200 kg N ha-1) and unfertilised controls, correlated with δ 13C measured with IRMS at stem elongation, except for late-sown crops. Mid-infrared spectroscopy (MIR) returned estimates of δ 13C that agreed with δ 13C measured with IRMS (calibration: R2 = 0.82, RMSE = 0.53‰, n = 833; validation: R2 = 0.70, RMSE = 0.75‰, n = 364). We conclude that a MIR based, high-throughput, affordable measurement of δ 13C could be scaled to guide nitrogen management of wheat in winter-rainfall environments. • In a sample of 1518 plots, yield varied from 0.07 to 9.96 tha-1 and correlated with δ 13C at flowering. • Yield response to nitrogen correlated with δ 13C at stem elongation, except for late-sown crops. • Mid-infrared spectroscopy is a cost-effective, high-throughput approach to estimate δ 13C for agronomic applications. [ABSTRACT FROM AUTHOR]

A genome-wide association study (GWAS) was performed in six environments to identify major or consistent alleles responsible for wheat yield traits in Australia and North China where rainfed farming system is adopted. A panel of 228 spring wheat varieties were genotyped by double digest restriction-site associated DNA genotyping-by-sequencing. A total of 223 significant marker-trait association (MTAs) and 46 candidate genes for large- or consistent-effect MTAs were identified. The results were compared with previous studies based on a mini-review of 23 GWAS analyses on wheat yield. A phenomenon seldom reported in previous studies was that MTAs responsible for the trait tended to cluster together at certain chromosome segments, and many candidate genes were in the form of gene clusters. Although linkage disequilibrium (LD) might contribute to the co-segregation of the regions, it also suggested that marker-assisted selection (MAS) or transgenic method targeting a single gene might not be as effective as MAS targeting a larger genomic region where all the genes or gene clusters underlying play important roles. • A mini review was conducted forGWAS outcomes on wheat yield-related traits, which had not been reported before. • GWAS analyses were carried out in six individual environments in Australia and North China. • A panel of 228 spring wheat varieties were genotyped by ddRAD sequencing. Forty-six candidate genes for major or consistent MTAs were identified. • Gene clusters and clustered MTAs responsible for yield were frequently identified in GWAS. [ABSTRACT FROM AUTHOR]

Abstract: Recurring water stresses are a major risk factor for rainfed maize cropping across the highly diverse agro-ecological environments of Queensland (Qld) and northern New South Wales (NNSW). Enhanced understanding of such agro-ecological diversity is necessary to more consistently sample target production environments for testing and targeting release of improved germplasm, and to improve the efficiency of the maize pre-breeding and breeding programs of Qld and New South Wales. Here, we used the Agricultural Production Systems Simulator (APSIM) – a well validated maize crop model to characterize the key distinctive water stress patterns and risk to production across the main maize growing regions of Qld and NNSW located between 15.8° and 31.5°S, and 144.5° and 151.8°E. APSIM was configured to simulate daily water supply demand ratios (SDRs) around anthesis as an indicator of the degree of water stress, and the final grain yield. Simulations were performed using daily climatic records during the period between 1890 and 2010 for 32 sites-soils in the target production regions. The runs were made assuming adequate nitrogen supply for mid-season maize hybrid Pioneer 3153. Hierarchical complete linkage analyses of the simulated yield resulted in five major clusters showing distinct probability distribution of the expected yields and geographic patterns. The drought stress patterns and their frequencies using SDRs were quantified using multivariate statistical methods. The identified stress patterns included no stress, mid-season (flowering) stress, and three terminal stresses differing in terms of severity. The combined frequency of flowering and terminal stresses was highest (82.9%), mainly in sites-soils combinations in the west of Qld and NNSW. Yield variability across the different sites-soils was significantly related to the variability in frequencies of water stresses. Frequencies of water stresses within each yield cluster tended to be similar, but different across clusters. Sites-soils falling within each yield cluster therefore could be treated as distinct maize production environments for testing and targeting newly developed maize cultivars and hybrids for adaptation to water stress patterns most common to those environments. [Copyright &y& Elsevier]

Abstract: To feed a growing world population in the coming decades, agriculture must strive to reduce the gap between the yields that are currently achieved by farmers (Ya) and those potentially attainable in rainfed farming systems (Yw). The first step towards reducing yield gaps (Yg) is to obtain realistic estimates of their magnitude and their spatial and temporal variability. In this paper we describe a new yield gap assessment framework. The framework uses statistical yield and cropping area data, remotely sensed data, cropping system simulation and GIS mapping to calculate wheat yield gaps at scales from 1.1km cells to regional. The framework includes ad hoc on-ground testing of the calculated yield gaps. This framework was applied to wheat in the Wimmera region of Victoria, Australia. Estimated Yg over the whole Wimmera region varied annually from 0.63 to 4.12Mgha−1with an average of 2.00Mgha−1. Expressed as a relative yield (Y %) the range was 26.3–77.9% with an average of 52.7%. Similarly large spatial variability was described in a Wimmera yield gap map. Such maps can be used to show where efforts to bridge the yield gap are likely to have the biggest impacts. Bridging the exploitable yield gap in the Wimmera region by increasing average Y % to 80% would increase average annual wheat production from 1.09Mtonnes to 1.65Mtonnes. Model estimates of Yw and Yg were compared with data from crop yield contests, experimental variety trials, and on-farm water use and yields. These alternative approaches agreed well with the modelling results, indicating that the proposed framework provided a robust and widely applicable method of determining yield gaps. Its successful implementation requires that: (1) Ya as well as the area and geospatial distribution of wheat cropping are well defined; (2) there is a crop model with proven performance in the local agro-ecological zone; (3) daily weather and soil data (such as PAWC) required by crop models are available throughout the area; and (4) local agronomic best practice is well defined. [Copyright &y& Elsevier]

Abstract: Frequent severe droughts can financially cripple dryland farm businesses and farmers need effective business strategies to survive. This study analysed the economic performance of 123 farms in a rainfed agricultural region of Australia from 2004 to 2009, a period that included severe droughts in 2006 and 2007. The business indicators examined were business equity, operating profit/ha, return on capital, and the debt to income ratio and the droughts altered these indicators for many of the farms surveyed. Over the study period the equity position of just over 60% of farms declined, although 55% of these had more than 80% equity in the business initially and were able to absorb a short term decline in equity caused by the drought. In addition, 9% of farms had levels of equity below 80% at the start of the investigation, but actually improved their equity position by the end of the study. Strong links were found between wheat yield and the business indicators. Mostly this was due to the crop dominant nature of the farm businesses where wheat was by far the main crop. However, farms that were able to capitalise on favourable conditions in other years were better placed to enhance or recover their financial position. Farms that cropped a higher proportion of their farm area were at an advantage. Structural indicators, including the percentage of area cropped, had a small but significant effect on the debt to income ratio, the return on capital and operating profit. Farm diversity also favourably lessened the debt to income ratio. Other factors, including farm size did not influence the outcome of any business indicator. Farms that remained resilient, despite the serious droughts were those that cropped more than 50% of their farm area, were prudent in their expenditure, maintained some enterprise diversity and often generated wheat yields in each year that were near the yield potential for that year. [Copyright &y& Elsevier]

Abstract: The Australian Government has recommended that farmers move from cultivation-based dryland farming to reduced or zero tillage systems. The private benefits could include improvements in yields and a decrease in costs while the public benefits could include a reduction in greenhouse gas (GHG) emissions due to a diminution in the use of heavy machinery. The aim of this study is to estimate and compare total on-farm GHG emissions from conventional and zero tillage systems based on selected grain crop rotations in the Darling Downs region of Queensland, Australia. The value chain was identified, including all inputs, and emissions. In addition, studies of soil carbon sequestration and nitrous oxide emissions under the different cropping systems were reviewed. The value chain analysis revealed that the net effect on GHG emissions by switching to zero tillage is positive but relatively small. In addition though, the review of the sequestration studies suggests that there might be soil-based emissions that result from zero tillage that are being under-estimated. Therefore, zero tillage may not necessarily reduce overall GHG emissions. This could have major implication on current carbon credits offered from volunteer carbon markets for converting conventional tillage to reduced tillage system. [Copyright &y& Elsevier]

Grain yields of rainfed agriculture in Australia are often low and vary substantially from season to season. Assimilates stored prior to grain filling have been identified as important contributors to grain yield in such environments, but quantifying their benefit has been hampered by inadequate methods and large seasonal variability. APSIM-Nwheat is a crop system simulation model, consisting of modules that incorporate aspects of soil water, nitrogen (N), crop residues, crop growth and development. Model outputs were compared with detailed measurements of N fertilizer experiments on loamy soils at three locations in southern New South Wales, Australia. The field measurements allowed the routine for remobilization of assimilates stored prior to grain filling in the model to be tested for the first time and simulations showed close agreement with observed data. Analysing system components indicated that with increasing yield, both the observed and simulated absolute amount of remobilization generally increased while the relative contribution to grain yield decreased. The simulated relative contribution of assimilates stored prior to grain filling to grain yield also decreased with increasing availability of water after anthesis. The model, linked to long-term historical weather records was used to analyse yield benefits from assimilates stored prior to grain filling under rainfed conditions at a range of locations in the main wheat growing areas of Australia. Simulation results highlighted that in each of these locations assimilates stored prior to grain filling often contributed a significant proportion to grain yield. The simulated contribution of assimilates stored prior to grain filling to grain yield can amount to several tonnes per hectare, however, it varied substantially from 5–90% of grain yield depending on seasonal rainfall amount and distribution, N supply, crop growth and seasonal water use. High N application often reduced the proportion of water available after anthesis and decreased the relative contribution of remobilization to grain yield as long as grain yields increased, particularly on soils with greater water-holding capacity. Increasing the capacity or potential to accumulate pre-grain filling assimilates for later remobilization by 20% increased yields by a maximum of 12% in moderate seasons with terminal droughts, but had little effect in poor or very good seasons in which factors that affect the amount of carbohydrates stored rather than the storage capacity itself appeared to limit grain yield. These factors were, little growth due to water or N deficit in the weeks prior to and shortly after anthesis (when most of the assimilates accumulate for later remobilization), poor sink demand of grains due to low grain number as a result of little pre-anthesis growth or high photosynthetic rate during grain filling. Increasing the potential storage capacity for remobilization is expected to increase grain yield especially under conditions of terminal drought. [ABSTRACT FROM AUTHOR]

Grain yields of rainfed agriculture in Australia are often low and vary substantially from season to season. Assimilates stored prior to grain filling have been identified as important contributors to grain yield in such environments, but quantifying their benefit has been hampered by inadequate methods and large seasonal variability. APSIM-Nwheat is a crop system simulation model, consisting of modules that incorporate aspects of soil water, nitrogen (N), crop residues, crop growth and development. Model outputs were compared with detailed measurements of N fertilizer experiments on loamy soils at three locations in southern New South Wales, Australia. The field measurements allowed the routine for remobilization of assimilates stored prior to grain filling in the model to be tested for the first time and simulations showed close agreement with observed data. Analysing system components indicated that with increasing yield, both the observed and simulated absolute amount of remobilization generally increased while the relative contribution to grain yield decreased. The simulated relative contribution of assimilates stored prior to grain filling to grain yield also decreased with increasing availability of water after anthesis. The model, linked to long-term historical weather records was used to analyse yield benefits from assimilates stored prior to grain filling under rainfed conditions at a range of locations in the main wheat growing areas of Australia. Simulation results highlighted that in each of these locations assimilates stored prior to grain filling often contributed a significant proportion to grain yield. The simulated contribution of assimilates stored prior to grain filling to grain yield can amount to several tonnes per hectare, however, it varied substantially from 5–90% of grain yield depending on seasonal rainfall amount and distribution, N supply, crop growth and seasonal water use. High N application often reduced the proportion of water available after anthesis and decreased the relative contribution of remobilization to grain yield as long as grain yields increased, particularly on soils with greater water-holding capacity. Increasing the capacity or potential to accumulate pre-grain filling assimilates for later remobilization by 20% increased yields by a maximum of 12% in moderate seasons with terminal droughts, but had little effect in poor or very good seasons in which factors that affect the amount of carbohydrates stored rather than the storage capacity itself appeared to limit grain yield. These factors were, little growth due to water or N deficit in the weeks prior to and shortly after anthesis (when most of the assimilates accumulate for later remobilization), poor sink demand of grains due to low grain number as a result of little pre-anthesis growth or high photosynthetic rate during grain filling. Increasing the potential storage capacity for remobilization is expected to increase grain yield especially under conditions of terminal drought. [ABSTRACT FROM AUTHOR]

• NUE was lower in grazed than in grain-only crops fertilized soon after grazing. • The reduction in NUE was partly due to low N demand by recently grazed crops. • Crop-N demand was increased by waiting two weeks for regrowth. Dual-purpose crops are grazed during the vegetative phase by cattle, goats and sheep in many dryland farming systems. After grazing, these crops continue to grow until maturity when they are harvested for grain. The process of grazing depletes crop nitrogen (N) content. Yield and grain protein concentration may therefore be more N-limited in grazed than in grain-only crops. This paper reviews 14 field experiments in south-eastern Australia, 12 of which were on farms, to measure the responses to N fertilizer by wheat, barley or canola crops defoliated by mowing or grazing with sheep. In five experimental comparisons of defoliated and grain-only crops, the average nitrogen use efficiency (NUE) of fertilizer N applied soon after defoliation, as is typically practiced, was 18 %, while NUE of grain-only crops fertilized at the same time and N-rate was 41 %. Applying N fertilizer to defoliated crops at this stage was usually unprofitable. In one experiment comparing responses of grazed and grain-only crops to time of N application post-grazing, a delay of two weeks after grazing increased yield of grain-only crops and NUE of both grazed and grain-only crops, compared with application soon after grazing. Our explanation of these results is the low N demand by small, defoliated crops and increased N demand as they regrew after defoliation. Additional evidence for the N-demand explanation came from a positive relationship between NUE of grazed crops and the yield of grain-only crops. The results suggest that delaying N application for two weeks after grazing and retaining more biomass after grazing can increase N demand, yield and NUE of grazed crops. [ABSTRACT FROM AUTHOR]

Modern rice varieties adapted to aerobic (dryland) conditions have expanded to new rice growing systems thanks to their plasticity in adapting to rainfed and irrigated conditions. This is important because, as water becomes scarce in paddy rice regions (as it is already in Australia), there will be a move towards tropical to subtropical dryland rainfed rice with attendant problems of drought and low temperature. To assess rice adaptability in the wet season of the semi-arid subtropical conditions of coastal central Queensland, field experiments were established for a late season (in January) planting in 2014 and early season planting in November 2015 with 13 varieties developed by Australian Agriculture Technologies (AAT) Ltd were seeded in a vertisol soil. This was to assess their adaptation to rainfed conditions and their response to strategic irrigation. Water scarcity and low temperature prior to and at flowering were important factors constraining yield. Early flowering varieties in the late season planting escaped the otherwise cold and drought stress during the reproductive stage and had higher yields. In the second year, earlier planting made possible with strategic irrigation avoided the low temperature constraint on yield, but without follow-up strategic irrigation, yields were still low. The average yield of varieties increased from 1.5 times (AAT 4) to 16.3 times (AAT 15) with strategic irrigation compared with rainfed yields averaged across years. The increase in yield with strategic irrigation was associated with a greater leaf area index, spikelet fertility, and instantaneous water use efficiency during flowering. Strategic irrigation concentrated roots in the top 15 cm, but differences in yield between varieties under rainfed conditions were not related to root properties. It is important to consider variations in flowering time, yield potential, and drought patterns when developing rice varieties for rainfed semi-arid tropical conditions, as well as when quantifying the benefits of strategic irrigation. [ABSTRACT FROM AUTHOR]

Subsoil alkalinity is a common issue in the alluvial cotton-growing valleys of northern New South Wales (NSW), Australia. Soil alkalinity can cause nutrient deficiencies and toxic effects, and inhibit rooting depth, which can have a detrimental impact on crop production. The depth at which a soil constraint is reached is important information for land managers, but it is difficult to measure or predict spatially. This study predicted the depth in which a pH (H2O) constraint (>9) was reached to a 1-cm vertical resolution to a 100-cm depth, on a 1070-hectare dryland cropping farm. Equal-area quadratic smoothing splines were used to resample vertical soil profile data, and a random forest (RF) model was used to produce the depth-to-soil pH constraint map. The RF model was accurate, with a Lin's Concordance Correlation Coefficient (LCCC) of 0.63–0.66, and a Root Mean Square Error (RMSE) of 0.47–0.51 when testing with leave-one-site-out cross-validation. Approximately 77% of the farm was found to be constrained by a strongly alkaline pH greater than 9 (H2O) somewhere within the top 100 cm of the soil profile. The relationship between the predicted depth-to-soil pH constraint map and cotton and grain (wheat, canola, and chickpea) yield monitor data was analyzed for individual fields. Results showed that yield increased when a soil pH constraint was deeper in the profile, with a good relationship for wheat, canola, and chickpea, and a weaker relationship for cotton. The overall results from this study suggest that the modelling approach is valuable in identifying the depth-to-soil pH constraint, and could be adopted for other important subsoil constraints, such as sodicity. The outputs are also a promising opportunity to understand crop yield variability, which could lead to improvements in management practices. [ABSTRACT FROM AUTHOR]