Out of season cover crops: seasonal and cumulative impacts on wheat yields and the cropping environment

Growing more crops on available resources and building the environmental credentials of the farm is a goal that most farmers share and they are actively investigating their options. Farming systems science needs to keep pace by evaluating new ideas with evidence and leading the public debate on best management practice. Farmers are becoming interested in growing cover crops between cereal crops, typically in summer, to improve ground cover, manage weeds and potentially increase soil carbon and health. This research investigated the effects of grass and legume cover crops on wheat crops. Cover crops did help protect the soil but often resulted in lower wheat yields, except in above average rainfall years. Cover crops primarily reduced the nitrogen available for wheat crops. Simulations indicated that after some years legume cover crops would release nitrogen and wheat yields would then be similar to current practices, potentially sustaining longer cropping phases. Through a review of the literature it was concluded that there is very little information available about the potentially beneficial and negative effects of summer cover crops on following crops in Australian growing conditions. A large field experiment was established to investigate the effects of different tactics to replace a no-till summer fallow with grass or legume summer cover crop before a wheat crop, over three years of cropping. The experiment was conducted in the Wellington district of Central NSW where there is a long term average annual rainfall (1889-2009) of 577mm. The strategies and ideas tested in this research have wide application for future studies to investigate the feasibility of intensified cropping in low rainfall environments.