Nitrate leaching from silage maize is more related to biomass N concentration at harvest time than inclusion of undersown cover crops
摘要
Leaching of nitrate from the rootzone constitutes a considerable environmental risk in maize cropping. We performed eight field trials in Denmark over three growing seasons to study the effects of undersown cover crops on nitrate leaching from silage maize during and after the maize growing season. Cover crop species were perennial ryegrass, tall fescue, cocksfoot or chicory. Dry matter yield, nitrogen (N) concentration in harvested maize biomass, and nitrate leaching from May to next March were measured. Nitrate leaching from maize without cover crops differed considerably between trials (39–260 kg N ha−1), with a mean of 111 kg N ha−1. Generally, a very limited effect of cover crops on nitrate leaching from maize was found, with a significant reduction (75 kg ha−1) only in one treatment (chicory) in one trial. The experiments demonstrated that nitrate leaching can be high in maize cropping, and that under wet, temperate conditions there is a risk of nitrate leaching from maize both during and after the growing season, which undersown cover crops could not effectively prevent. Across all trials and all treatments, nitrate leaching increased significantly and non-linearly with N concentration in the harvested maize biomass, whereas maize dry matter yield decreased, i.e. higher N concentration in the biomass appears to indicate increased risk of leaching without providing any yield benefit. Hence, N supply to maize should be optimized, aiming at reduced nitrate leaching while meeting appropriate levels of biomass N concentration and maintaining yields.