Strategien zur Verbesserung der N-Ausnutzung im ökologisch wirtschaftenden Futterbaubetrieb

Abstract

Organic forage and mixed farms often do not utilize their grassland to its full potential. In mixed farms this affects the arable farming as well. By intensifying grassland production (more clover, more cuts), N leaching might be reduced and N efficiency increased at the farm level. We conducted an experiment with organic crop rotations on a sandy soil in northwest Germany. The idea was to compare the N efficiency of two ways of supplying N to arable crops: nitrogen was supplied by arable legumes (red clover, field beans) or by farmyard manure (FYM). Within this concept, manure was assumed to be produced from permanent grassland of differing management intensity via feeding to housed cattle. Maize, triticale and spring barley were the N receiving plants in the rotations. Nitrogen was analyzed in manures, harvested biomass, soil (total N, soil mineral N) and as nitrate in leaching water during winter by applying the suction cup method. With higher clover contents, N produced in harvested biomass in permanent grassland increased from 80 kg N ha-1 to 130 kg N ha-1 while nitrate leaching was reduced from 12 to 8 kg N ha-1. Nitrate leaching from crop rotations that received manure or had grass-cover ley amounted to 54 kg N ha-1 year-1, but N losses increased to 61 kg N ha-1 year-1 in rotations with field beans. Generally, N leaching would have been smaller if cover crops had been cultivated as well as is common practice in organic farming. When, by calculation, the effects of extensive grassland and rotations with field beans or grass-clover ley were combined and compared with the combination of intensive grassland and rotations with farmyard manure, the advantages of intensifying grassland became apparent: related to N yields, N leaching losses of rotations with FYM were 0.12–0.19 kg N per kg N yield but 0.20–0.40 kg N per kg N yield for rotations with grass-clover leys or field beans. It seems that by in creasing productivity in permanent grassland through higher clover contents and cutting four times, N efficiency in organic farming can be improved. This will lead to higher N yields, less N leaching and open the opportunity to grow more maize when the proportion of arable legumes can be reduced.