Performance and environmental effects of forage production on sandy soils. II. Impact of defoliation system and nitrogen input on nitrate leaching losses.

A field experiment was conducted over a 4-year period to determine NO3 leaching losses from grassland on a freely draining sandy soil. The experiment consisted of all combinations of five defoliation systems; cutting-only (CO), rotational grazing (GO), mixed systems with one (MSI) or two silage cuts (MSII) plus subsequent rotational grazing, and simulated grazing (SG), four mineral nitrogen (N) application rates (0, 100, 200, and 300 kg N ha−1 year−1), and two slurry levels (0 and 20 m3 slurry ha−1 year−1). Due to the high N return by grazing animals, leaching losses in the rotational grazing systems generally were associated with NO3-N concentrations which exceeded the EU limit for drinking water. NO3 leaching losses in a rotational grazing system could be reduced by lowering the N fertilizer intensity and the inclusion of one or two silage cuts in spring. However, even in the unfertilized mixed systems, N fixation by white clover exceeded the amounts of N removed via animal products, which resulted in NO3-N concentrations well above the EU limit for drinking water. In terms of leaching losses, the cutting-only system was the most advantageous treatment. NO3 leaching losses on grassland could be predicted by the amount of soil mineral N at the end of the growing season and by the N surplus calculated from N balances at the field scale. From the results obtained a revised nitrogen fertilization policy and a reduced grazing intensity by integrating silage cuts are suggested. [ABSTRACT FROM AUTHOR]