摘要：The basic limiting factors for forage production on grasslands are insufficient available nitrogen (N) and harvest at advanced maturity stages. The aim of the present research was to determine the optimum quantity of N fertilizer, the possibility of mineral N fertilizer reduction by sowing the perennial legumes and the influence of N fertilization level and the stage of maturity at harvest on grassland yield and botanical composition. The investigation was carried out on sown grass-legume mixture in Zaprešić in 2002 and 2003. Four levels of N fertilization were applied on grassland (N35, N100, N150, N200 relating to 35, 100, 150 and 200 kg N ha-1 per year respectively) and cut at two stages of maturity (panicle emergence and panicle clear of leaf sheath of Dactylis glomerata as the dominant grass). The average dry matter (DM) yields in 2002 and 2003 were 7.52 t ha-1and 2.84 t ha-1 respectively. More than 100 kg N ha-1 had no significant effect on DM yield in 2002 while white clover proportion was significantly (P<0.01) reduced only at N200. Grass DM yield was the highest at N200 and N150 (7.25 and 7.12 t ha-1 respectively). Fertilizing treatment had no significant effect on relative grass proportions in DM yield (82.7% in average). Harvest at the stage of panicle clear of leaf sheath increased DM yield for 15% in comparison with the panicle emergence growth stage (6.98 t ha-1). Grass yield increased for 24% and the relative grass proportion for 7.5% at the stage of panicle clear of leaf sheath in comparison with the panicle emergence growth stage (5.58 t ha-1 and 79.94% respectively). The stage of growth at harvest had no significant effect on legume and forbs yield and their contribution to total DM yield in 2002. The highest DM yield in 2003 was determined at N200 (3.14 t ha-1) and the lowest at N35 (2.47 t ha-1). The increased N application led to increased grass and reduced legume contribution to the total DM yield. The highest grass contribution to DM yield determined at N200 (91.4%) was 14.6% higher in relation to N35 (79.76%). The highest legume contribution to DM yield was determined at N35 (11.75%) and at N100 (11.36%) while the lowest at N200 (4.14%).
关键词：nitrogen; stage of maturity; grassland; yield; botanical composition
