Seasonal variations in soil mineral nitrogen and in the response of grassland to nitrogen fertilization

Grassland is intensively used in the Netherlands. According to the fertilizer recommendation, the optimum N supply for such grassland is 250 kg ha-1 yr-1 for well-drained peat soils and 400 kg ha-1 yr-1 for all other soils. Environmental problems, associated with N losses from intensively used grass­land, necessitate a refinement of the general recommendations. This, in turn, requires understanding of the dynamics of soil mineral nitrogen. This paper reports on (1) seasonal dynamics of soil mineral N and (2) seasonal variations in the response of cut swards to N. Results of grazed swards will be dealt with elsewhere (Oenema et al., in prep.).