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Take home message Shorter season, faster maturing crops can leave residual surface water from unutilised late season rain and/or residual deep water due to shallower roots and quicker maturity Legumes such as lentils, fababeans, field pea, and chickpea often leave 20-40 mm extra residual soil water compared to canola and winter cereals Higher residual water may not remain at sowing of next crop – fallow efficiency differences between crops and seasons can influence this – e.g. low cover after legumes For summer crops, mungbean typically leaves 20mm more residual water than sorghum/maize while cotton leaves 20mm less (i.e. mungbean > sorghum/maize > cotton) Early-sown, slower maturing crops (e.g. early sown winter crops) can dry the profile deeper (>2m) and utilise deep stored soil to support higher yield in dry springs. The legacy of drier soil may warrant changes to crop sequence and management to avoid yield penalties Extra residual water at sowing can increase grain yield of subsequent crops when water is limited during the critical period for yield determination so the marginal WUE (i.e. extra yield per mm of extra soil water available) can be very high (>60kg/ha/mm) As the value of the residual water is seasonally dependent, understanding how management (crop choice, sowing dates, N management) can be adjusted to capture value from such legacies across a sequence of crops is the goal of current farming systems research.

Take home messages • Previous trials have shown cover crops can increase stored fallow water and improve crop performance and returns in northern farming systems • A cover crop in a long fallow (14 months) in a dry season allowed improved ground cover with no net deficit in soil water. The extra ground cover improved the opportunity to deep plant wheat. • A cover crop in a short fallow had a water cost that translated to a yield penalty. • When the sorghum stopped growing in dry conditions it continued to use water, for no biomass (or cover) increase when it wasn’t sprayed out.

Take home message • While summer crops offer rotational options in the farming system, choose the correct crop to match your available soil water and crop history • Sorghum is a reliable performer often exceeding other options in terms of $ returned per mm used • Cotton and maize require higher water availability and produce less reliable WUE ($/mm). However, cotton has legacy impacts on water availability for subsequent crops that should be considered • Mungbean can produce higher $/mm in low water availability situations (<200 mm of rain + soil water). Repeated sowings of mungbeans are likely to induce yield reductions due to disease • Sorghum crops sown with > 150 mm of plant available water will maximise crop WUE and profitability. Every extra mm at sowing could be worth as much as $35-70 extra return/ha • Higher density sorghum crops may provide greater crop competition against weeds and potential upside yield benefits in good season. We have seen limited legacy benefits (e.g. improved ground cover) or costs (e.g. greater soil water/nutrient extraction) for soil water or nutrient availability.

Low groundcover increases risk of soil erosion and reduces fallow efficiency. To remedy this cover crops can be grown to increase groundcover, but does the increased ground cover improve fallow water accumulation enough to recover the water used to grow the cover crop? To answer this, cover crops were planted into a long fallow following skip row sorghum, and sprayed out prior to growing wheat. The main cover crop was White French millet, which had different termination timings imposed. Other crops included sorghum, lablab and a mixed species (millet, lablab and tillage radish), which were all sprayed out at the same time as the mid-terminated millet. By planting of the subsequent wheat crop, all cover crop treatments, except the lablab, had recovered the water they used prior to termination, with some accumulating more plant available water (PAW) than the control. Increased ground-cover improved establishment of the wheat and all cover crop treatments had higher grain yield than the bare control in a drier than average season. These results confirm a crop can be grown and sprayed out to improve ground cover in a long fallow, without having a net negative effect on PAW, with yield benefits in the following crop in excess of what can be explained by increased soil water.