Residual effects of repeated catch crops on spring barley yield and nitrate leaching

Growing catch crops in autumn after the main crop is known to reduce nitrate leaching and improve soil fertility. Residual effects of growing catch crops repeatedly for several years on the grain yield and grain nitrogen (N) of the following main crop, and nitrate leaching are less known. We conducted field experiments with spring barley and catch crops, including an herbicide treated bare treatment, from 2015 to 2022 at two sites in Denmark, differing in soil type and climatic conditions. The spring barley was fertilized at four N levels (0–150 % of the recommended amount). The residual effect of the repeated catch crops was measured in 2021 for barley grain yield and grain N, and for nitrate leaching in the percolation periods of 2020–21 and 2021–22. During the repeated catch crop periods the average aboveground biomass N ranged between 20 and 61 kg N ha −1 yr −1 . A residual effect of the repeated catch crops on grain yield and grain N was only observed in unfertilized barley. Catch crops significantly reduced nitrate leaching compared to the bare soil, with a reduction of 38–91 % per percolation period. After discontinuing the catch crops, there was no residual effect on nitrate leaching. Repeated catch crops for four percolation periods did not have measurable residual effects on the following main crop, nor on nitrate leaching after their discontinuation. More research is needed on N immobilization and mineralization processes, and the factors that influence them to better understand the residual effects of catch crops.