Agricultural intensification has increased crop yields, but at high economic and environmental cost. Harnessing ecosystem services of naturally occurring organisms is a cheaper but under-appreciated approach, because the functional roles of organisms are not linked to crop yields, especially outside the northern temperate zone. Ecosystem services in soil come from earthworms in these cooler and wetter latitudes; what may fulfill their functional role in agriculture in warmer and drier habitats, where they are absent, is unproven. Here we show in a field experiment that ants and termites increase wheat yield by 36% from increased soil water infiltration due to their tunnels and improved soil nitrogen. Our results suggest that ants and termites have similar functional roles to earthworms, and that they may provide valuable ecosystem services in dryland agriculture, which may become increasingly important for agricultural sustainability in arid climates.

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Abstract. Water-repellent ('non-wetting') soils are a major constraint to agricultural production in southern and south-west Australia, affecting >10 Mha of arable sandy soils. The major symptom is dry patches of surface soil, even after substantial rainfall, directly affecting agricultural production through uneven crop and pasture germination, and reduced nutrient availability. In addition, staggered weed germination impedes effective weed control, and delayed crop and pasture germination increases the risk of wind erosion. Water repellency is caused by waxy organic compounds derived from the breakdown of organic matter mostly of plant origin. It is more prevalent in soils with a sandy surface texture; their low particle surface area : volume ratio means that a smaller amount of waxy organic compounds can effectively cover a greater proportion of the particle surface area than in a fine-textured soil. Water repellency commonly occurs in sandy duplex soils (Sodosols and Chromosols) and deep sandy soils (Tenosols) but can also occur in Calcarosols, Kurosols and Podosols that have a sandy surface texture. Severity of water repellency has intensified in some areas with the adoption of no-till farming, which leads to the accumulation of soil organic matter (and hence waxy compounds) at the soil surface. Growers have also noticed worsening repellency after 'dry' or early sowing when break-of-season rains have been unreliable.Management strategies for water repellency fall into three categories: (i) amelioration, the properties of surface soils are changed; (ii) mitigation, water repellency is managed to allow crop and pasture production; (iii) avoidance, severely affected or poorly producing areas are removed from annual production and sown to perennial forage. Amelioration techniques include claying, deep cultivation with tools such as rotary spaders, or one-off soil inversion with mouldboard ploughs. These techniques can be expensive, but produce substantial, long-lasting benefits. However, they carry significant environmental risks if not adopted correctly. Mitigation strategies include furrow-seeding, application of wetting agents (surfactants), no-till with stubble retention, on-row seeding, and stimulating natural microbial degradation of waxy compounds. These are much cheaper than amelioration strategies, but have smaller and sometimes inconsistent impacts on crop production. For any given farm, economic analysis suggests that small patches of water repellency might best be ameliorated, but large areas should be treated initially with mitigation strategies. Further research is required to determine the long-term impacts of cultivation treatments, seeding systems and chemical and biological amendments on the expression and management of water repellency in an agricultural context.

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Improving the water-limited yield of dryland crops and farming systems has been an underpinning objective of research within the Australian grains industry since the concept was defined in the 1970s. Recent slowing in productivity growth has stimulated a search for new sources of improvement, but few previous research investments have been targeted on a national scale. In 2008, the Australian grains industry established the 5-year, AU$17.6 million, Water Use Efficiency (WUE) Initiative, which challenged growers and researchers to lift WUE of grain-based production systems by 10%. Sixteen regional grower research teams distributed across southern Australia (300–700 mm annual rainfall) proposed a range of agronomic management strategies to improve water-limited productivity. A coordinating project involving a team of agronomists, plant physiologists, soil scientists and system modellers was funded to provide consistent understanding and benchmarking of water-limited yield, experimental advice and assistance, integrating system science and modelling, and to play an integration and communication role. The 16 diverse regional project activities were organised into four themes related to the type of innovation pursued (integrating break-crops, managing summer fallows, managing in-season water-use, managing variable and constraining soils), and the important interactions between these at the farm-scale were explored and emphasised. At annual meetings, the teams compared the impacts of various management strategies across different regions, and the interactions from management combinations. Simulation studies provided predictions of both a priori outcomes that were tested experimentally and extrapolation of results across sites, seasons and up to the whole-farm scale. We demonstrated experimentally that potential exists to improve water productivity at paddock scale by levels well above the 10% target by better summer weed control (37–140%), inclusion of break crops (16–83%), earlier sowing of appropriate varieties (21–33%) and matching N supply to soil type (91% on deep sands). Capturing synergies from combinations of pre- and in-crop management could increase wheat yield at farm scale by 11–47%, and significant on-farm validation and adoption of some innovations has occurred during the Initiative. An ex post economic analysis of the Initiative estimated a benefit : cost ratio of 3.7 : 1, and an internal return on investment of 18.5%. We briefly review the structure and operation of the initiative and summarise some of the key strategies that emerged to improve WUE at paddock and farm-scale.

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Artificial water-repellent sands were prepared in the laboratory from acid-washed sand and either cetyl alcohol or organics extracted from a natural water-repellent sand. Added clays (at 0.5% w/w) had no effect when gently mixed with a natural and the two artificial water-repellent sands. After a wetting and drying cycle, kaolinite reduced repellency to a low level in the natural sand and the artificial sand with extracted organics, but montmorillonite was not effective. Na+-saturated clays were generally more effective than Ca2+-saturated clays. In the cetyl alcohol sand, montmorillonite was more effective than kaolinite. Neither artificial sand was a perfect model of the natural system, although the extracted organic model was far superior. Kaolinite did not strongly adsorb hydrophobic molecules, but was effective because it was able to cover the hydrophobic sand surface. Application of kaolinite clay to a water-repellent sand appears promising.

Rising watertables and dryland salinity in southern Australia are due to excess groundwater recharge after the replacement of native vegetation by annual crops and pastures. The inclusion of perennial plants into agricultural systems has been proposed as a possible method of recharge reduction, through the creation of a buffer (extra water storage capacity generated by the perennial in comparison with an annual crop or pasture). However, the role of perennial phases under conditions of highly episodic leakage is not well understood. In this paper, a simple Leakage/Buffer Model (LeBuM) was developed to determine the effect of perennial phases on long-term average annual leakage, incorporating episodic events. Mechanistic modelling studies on contrasting soil types were used to demonstrate that leakage for any given May–December period was directly related to soil water storage at 1 May. From this finding, it follows that leakage from a phase rotation can be calculated if the size of the buffer, and the leakage quantity in the absence of a buffer, are known for each stage of the rotation. LeBuM uses a long-term sequence of leakage values in the absence of a buffer as input, and the maximum buffer size, its rate of development, and the length of perennial and annual phases are specified as parameters. LeBuM was applied to leakage data modelled for 5 contrasting soil types over 100 years at 24 sites in the Western Australian wheatbelt. Phase rotations on duplex, waterlogging duplex, or loamy sand soils reduced leakage by >90% for regions with <380 mm annual rainfall, but were less effective in wetter regions and on deep sands or acid loamy sands. Nevertheless, phase rotations if adopted widely could delay the onset of salinity by as much as several decades.