ABSTRACT The effects of summer cover crops on cash crop yields and soil health in semi‐arid cropping systems in southern Australia remain largely unexplored. A study was conducted in Western Australia to investigate cover crop impacts on soil carbon and nitrogen cycling, soil water, and mineral nitrogen (N) and cash crop yield. A range of monoculture and mixed‐species cover crops were grown over summer between a lupin hay crop (terminated in October) and a canola cash crop sown the following April, in addition to a chemical fallow control. Cover crops produced 50–1050 kg ha −1 and did not affect soil water or mineral N compared to the bare fallow control prior to sowing canola the following winter, 2022. As a result, there was no impact on canola yield. This lack of difference is consistent with high evaporative demand over summer in this climate and associated low fallow water use efficiency. Cover crops had no significant effect on soil health indicators – soil organic carbon (C), total N, C:N ratio, permanganate‐oxidisable C (POXC) and soil respiration – measured in early autumn prior to canola (cash crop) seeding. However, POXC and soil respiration increased by 50% in response to cash crop biomass production, while soil C:N increased over the cash crop growing season as soil N declined from peak canola biomass to harvest. The lack of impact of cover crops on soil function at the Western Australian site likely reflects low C inputs into the soil (cover crop biomass < 1 t ha −1 ). While the cover crops did not impact subsequent cash crop yields, the lack of impact on soil function and the costs associated with sowing cover crops need to be considered in any management decisions.
Gibson et al. (Sun,) studied this question.