Influence of cover crop on water and nitrogen balances and cash crop yield in a temperate climate: A modelling approach using the STICS soil-crop model

Cover crops are crucial to diversify cropping systems into more agroecological systems by providing ecosystem services, such as reduction of nitrate leaching, provision of a green manure effect, and soil carbon storage. However, they can influence water drainage and nitrogen (N) or water availability for the succeeding crop, depending on their management and the climate. In this simulation study, we used the STICS model to predict the influence of cover crop species, date of sowing and termination, and cover crop residue management on N and water balances, and the yield and stress of the succeeding cash crop. We performed 25-year simulations for five contrasting sites in south-western France, which is a temperate region of Europe with dry summers. As expected, cover crops decreased nitrate leaching effectively but also decreased drainage by a mean of 5–40 mm. This decrease depended mainly on the sowing and termination dates, while the decrease in nitrate leaching varied greatly among sites and depended most on sowing date, followed by cover crop species and then termination date. Cover crops had little influence on soil water content in the upper 0.1 m of soil at sowing of the succeeding cash crop, but decreased soil water content of the total soil profile by 0–30 mm. Soil water content depended most on termination date, followed by species and then site. Total soil mineral N content (SNC) also decreased, by 5–40 kg N.ha−1, at the three driest sites and up to 10 kg N.ha−1 at the rainiest site. Termination date, the second-most influential factor on SNC, indicated that later termination resulted in lower SNC than that after bare soil. N uptake by the succeeding cash crop depended on species and termination date, and a legume cover crop and earlier termination date resulted in higher N uptake. The decrease in maize and sunflower yield was due mainly to changes in the N stress index during the vegetative phase for maize, and both vegetative and reproductive phases for sunflower. No water stress or increase in irrigation volumes was predicted or was correlated with yield changes, except at dry sites for the few years that experienced a severe drought in spring. While cover crops decreased nitrate leaching effectively, they decreased drainage and could induce N stress for the succeeding crop, particularly in dry regions. Including legumes in mixtures and adapting the termination date to local climate conditions could decrease or avoid these negative effects.