Manipulation pasture grass growth by nitrogen fertilization

In two field trials on a sown and a permanent pasture the possibilities of influencing grass growth of pastures through seasonal distribution of mineral nitrogen (N) fertilization was studied over four years in the region Bern-Solothurn. In the four treatments, the annual fertilizer application of 150 kg N in the form of ammonium nitrate was distributed as follows: evenly distributed over the whole growing season or higher doses in spring, summer or autumn. Three of the four experimental years were characterized by pronounced dryness periods during summer which lead to a considerable decrease of dry matter growth and annual yields of only 10-11 t/ha. In spite of this, the seasonal distribution of grass growth could be substantially modified through the seasonal distribution of N fertilization. It was possible to shift approximately 10% of the total annual yield from spring to late summer and autumn. The seasonal distribution of the N fertilizer did not significantly influence the total annual yield. On average the N fertilization increased the total annual pasture yield by 27%, as compared to the unfertilized control treatment. On average over all experimental sites, years and treatments the N effect was 16.3 kg DM per kilo N. The results imply that a tactical distribution of N fertilization may be helpful to harmonize pasture growth and feed requirements. Particularly on pastures with less than 25% clover, tactical distribution of N fertilization can help to simplify pasture management through a more even growth rate, especially with higher doses in summer.