Nitrate leaching in maize after cultivation of differently managed grass-clover leys on coarse sand in Denmark

Abstract

When grass-clover leys have been ploughed nitrate leaching may increase. However, management of leys before or after ploughing may affect the leaching risk. We examined the effect of cultivating a six year ley, which the last two years had been treated differently (grazing only; spring cut followed by grazing, and spring and autumn cuts with grazing during the summer season only) on nitrate leaching in maize with/without a catch crop (per. ryegrass) and with/without slurry application (135kg total-Nha⁻¹). An unfertilized barley harvested for silage with a catch crop of Italian ryegrass was used as reference. Shortening the grazing season in the grass-clover ley phase did not affect leaching after ploughing. In the following maize, the use of a perennial ryegrass catch crop in a high-yielding maize crop was not able to reduce nitrate leaching significantly, although leaching and maize yield tended to be lower with the catch crop. In unfertilized treatments both maize yields and nitrate leaching were significantly lower compared with treatments with slurry application. The unfertilized barley undersown with Italian ryegrass reduced leaching much more than unfertilized maize with perennial ryegrass as an undersown catch crop, despite yields of barley and ryegrass being less than half of the dry matter yields of unfertilized maize. The experiment illustrates that growing maize after ploughing of grass-clover leys without environmental consequences is difficult.