Water use efficiency is improved by storing more water before planting

The efficiency of soil water accumulation during fallow periods, and the availability of that soil water for use by crops are key drivers of northern farming system productivity and profitability. In 2015 seven farming systems experiments were established from central Queensland to central New South Wales to answer the question; Can system performance be improved by modifying farming systems in the northern grains region? To assess this soil water dynamics were monitored under different farming systems, along with soil nitrogen, pathogens, crop biomass, grain yield and variable costs, as measures of system performance. Analysis of soil water accumulation during the fallows and its subsequent use by sorghum, wheat and chickpea crops, showed a cost to all crops for converting biomass to grain yield. This cost was least for chickpea (50 mm), followed by wheat (100 mm) and highest for sorghum (150 mm), and should be deducted from crop water use to calculate water-use-efficiency (WUE). The WUE was lowest for pulse crops (10 kg/mm), but sorghum and wheat returned the same WUE (17 kg/mm). Northern growers typically store plant-available-water (PAW) in the fallow as a buffer against variable quantity and timing of in-crop rainfall. Crops produced a better than average WUE when planted with at least 60 mm PAW in a high in-crop rainfall season, or 120 mm of PAW with low in-crop rainfall.