Performance and environmental effects of forage production on sandy soils.: V.: Impact of grass understorey, slurry application and mineral N fertilizer on nitrate leaching under maize for silage

A field experiment with maize for silage was conducted to assess the effects of mineral nitrogen (N) fertilizer application rates (0, 50, 100, 150 kg ha(-1)), slurry application rates (0, 20, 40 m(3) ha(-1)) and the use of an understorey with perennial ryegrass on nitrate (NO3)- leaching losses. Leachate was collected using ceramic suction cups. Soil mineral N (SMN) was determined to a depth of 90 cm at the end of the growing season. Higher levels of N supply with mineral fertilizer or slurry resulted in higher leaching losses. The grass understorey significantly reduced the losses. The amount of N lost to the groundwater was positively related to SMN at the end of the growing season, with leaching losses representing less than 0.45 of SMN on average. Leaching. losses were positively related to the N surplus, which was calculated from the difference between N input (N from fertilizer, slurry and atmospheric deposition) and N output (N removed with maize herbage mass and bound in the understorey biomass in spring). in view of the large variation in weather conditions between the experimental years, it is suggested that for the sandy soils in this experiment N-leaching losses under maize can be estimated satisfactorily from SMN and the calculated N surplus.