Very high applications of nitrogen fertilizer on grassland and residual effects in the following season

At very high nitrogen applications (480 and more kg N ha^–1 yr^–1) in field trials on all-grass swards the amount of N applied exceeded the amount of N harvested. In the humid temperate climate of the Netherlands in the subsequent spring approximately 25, 40, and 50% of this excess nitrogen was recovered as accumulated mineral nitrogen in the 0–100 cm layer of sandy, clay and heavy clay soil, respectively. The effect of this excess nitrogen on growth during the subsequent season was measured through the increase in DM and N yield over a reference treatment. In this season all treatments received a uniform application (40 kg N ha^–1 cut^–1). Residual effects were absent on sandy soil but distinct on the clay soils. On the clay soils each accumulated kg soil mineral nitrogen produced 15 kg DM. Assuming a relatively small contribution of residual nitrogen carried over in stubble, roots and organic matter, the accumulated soil mineral nitrogen would seem to be as effective as applied fertilizer nitrogen.