Leaching and crop uptake of N, P and K from organic and conventional cropping systems on a clay soil

In this study, three types of cropping systems with different nutrient management strategies were studied on a clay soil with the aim of comparing leaching of N, P and K and obtaining knowledge on nutrient budgets. A conventional cropping system with cereals and application of mineral fertilizers (CON) was compared with two organic cropping systems, one without animal manure in which green manure crops were used for N supply (OGM) and one where animal manure (cattle slurry) was applied (OAM). Leaching and crop uptake of N, P and K, and soil mineral N were measured in pipe‐drained plots over a 6‐year period. The mean annual leaching loads of N were moderate and did not differ significantly ( P  > 0.05) between treatments; 13 kg N ha −1 in CON, 11 kg N ha −1 in OGM and 7.4 kg N ha −1 in OAM. Average annual P leaching showed greater variation than N leaching and was significantly greater in OGM (0.81 kg ha −1  year −1 ) than in CON (0.36 kg ha −1 ) and OAM (0.41 kg ha −1 ). For all cropping systems, removal in harvested crops was the most important export of nutrients from the field and constituted between 80 and 94% of total N outputs (harvested and leached N). Yields of cereals in the organic systems were considerably less (15–50%) than in the CON system, leading to a less efficient use of N than in the conventional system.