Impact of crop type and sequence on soil water accumulation and use in farming systems

Abstract

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 profitabilityIn 2015 seven farming systems experiments were established from Central Queensland to Central NSW. Soil water, nitrogen and pathogens were regularly monitored along with crop biomass, grain yield and variable costs, as measures of system performance. A baseline cropping system, representing current commercial practice was established and tested against other systems with higher and lower crop intensity, higher crop diversity, greater inclusion of legumes in the rotation and higher fertiliser inputs. A key driver of northern farming system productivity and profitability is soil water accumulation during fallows periods for use by subsequent crops. We found that winter cereals and sorghum had the highest fallow efficiency (median 0.26), ahead of chickpeas (0.14) and canola (0.19). Short (4-8 months) and long (9-18 months) fallows following wheat had similar fallow efficiency, however lower fallow efficiency was recorded for sorghum stubble with longer fallows (0.33 vs 0.22) Changing cropping intensity had the greatest impact on fallow efficiencies, with increases in Higher intensity systems (0.37) and decreases in Lower intensity systems (0.16) relative to the Baseline (0.22). Varying fallow length has shown increased grain yield and water-use-efficiency for longer fallows, however rainfall use efficiency and gross margin/mm has favoured a 4-6 month fallow. Profitability favours a moderate intensity, with 0.8-1 crops/year providing the greatest return per mm of rainfall. Introduction 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. Fallow water is stored and used as a buffer for more reliable grain production in highly variable rainfall patterns. Fallow efficiency (FE) (i.e. the proportion of rainfall that accumulates in the soil profile) is critical, and is influenced by ground cover levels, seasonality or timing of rainfall events, the length of the fallow and the amount of water in the soil profile. While accumulating more soil water prior to sowing a crop is always preferable, this often requires longer fallow periods, meaning there are additional costs for maintaining that fallow and the number of crops grown declines. In this study we analyse the data from a series of farming systems experiments across seven locations (Emerald, Pampas, Billa Billa, Mungundi, Narrabri, Spring Ridge and Trangie) over four years to explore the question; 'how much does the farming system (i.e. mix of crops and their frequency) and different crops influence the accumulation and utilisation of water?'