Cover crops and optimal N management reduce nitrate leaching to background levels in grass-clover—barley rotations on sandy soil
摘要
Cultivation of temporary grasslands prior to the arable phase in mixed crop rotations is accompanied by mineralization of soil organic matter and release of nitrogen (N). Depending on the grass-clover ley fertilizer history and management in the arable phase this may lead to considerable nitrate leaching. To determine the legacy effect of the ley phase, an on-farm experiment was carried out at two contrasting sites covering two years. The experiment comprised grass-clover leys with increasing rates of N fertilizer (0–480 kg available N ha−1), either mineral fertilizer alone or in combination with a basic application of cattle slurry. The legacy effect of fertilizer management was studied in two consecutive years of spring cereal cropping. This paper reports results from the arable phase and summarizes nitrate leaching across the entire four-year grassland/arable rotation. In the first season after the ley, the use of a cover crop, Italian ryegrass undersown in the spring barley efficiently reduced nitrate leaching to 4–18 kg N ha−1 compared to 59–79 kg N ha−1 without a cover crop, corresponding to a 70–95% reduction in nitrate leaching. Across the two sites, the implementation of optimal fertilization practices during the grass-clover phase and a highly effective cover crop strategy in the follow-on crops resulted in nitrate concentrations being reduced to levels of 2.0–3.5 mg NO3-N l−1, which are very low for agricultural systems. Thus, mixed ley-arable rotations, which include cover crops and with good fertilization practices can meet nitrate leaching requirements even in areas with significant restrictions on nitrogen load to aquifers.