Integrating long fallow into wheat-based cropping systems in Western Australia: Spatial pattern of yield and economic responses

Abstract

CONTEXTLong fallow, once a common management practice in the low-rainfall of Mediterranean-type environments, may provide growers with an opportunity to switch cropping sequence and reduce the risk of yield and income losses during the recent drought period. However, such benefits are usually not uniform across a spatially variable environment. It is important to identify where long fallow would have a role in increasing crop yield and economic return. OBJECTIVETo examine the spatial pattern of yield and economic performance of integrating long fallow into a wheat cropping system in dryland Mediterranean environments of Western Australia. METHODSThe Agricultural Production Systems Simulator (APSIM) driven by 0.05° gridded climate over the dry period of 1990–2020 was used to simulate five rotations (fallow followed by one, two, three or four wheat crops, respectively) and continuous wheat. With offset simulations, simulated wheat yields, plant available water at sowing after a wheat crop or long fallow and N fertilizer requirement were compared and analysed for fallow-wheat and wheat-wheat. Wheat yields and economic returns were also calculated for each rotation and compared with continuous wheat. RESULTS AND CONCLUSIONSWheat yield and economic responses to long fallow showed clear geographic patterns that increased from the south-west to north-east across the wheatbelt, which could be explained by climate and soil conditions. Yield increase from fallow could be >6%, equivalent to 13% of economic increase, in the areas where growing season rainfall was <230 mm and the difference in plant available soil water at sowing between fallowed and continuously cropped soil was >30 mm. Although fallow resulted in overall reduction in crop production, integrating one fallow into a continuous wheat sequence every three or more years might achieve similar profit to continuous wheat for fields with weeds and diseases challenges in the north-eastern wheatbelt. SIGNIFICANCEThe results of yield and economic performance after fallow in the context of space and crop sequence provide a systematic analysis to map where and how fallow could be adopted into cropping systems.