Recovery of slurry mitrogen in grass-clover mixtures

The percentage recovery of fertilizer nitrogen (cattle slurry and ammonium nitrate) in the harvested herbage of grass-clover mixtures, cocksfoot (Dactylis glomerata L.), perennial rye-grass (Lolium perenne L.)and white clover (Trifolium repens L.) were investigated. The mean amount of N in the yield of grass-clover mixtures (five cuts per year), which were fertilized with 150 kg slurry N ha-1 and year-1 , was 318 kg N ha-1 and year-1. Depending on the proportion of clover, 41 to 55 % (average: 47 %) of this harvested amount of N was derived from biological nitrogen fixation. The amount of N supplied by the soil and the atmosphere represented 33 % of the yielded N. The uptake of the slurry N contributed to 20 % of the total N, which corresponded to an apparent recovery of the slurry N of 41 %. The apparent recovery of the mineral fertilizer N was similar to the recovery of the slurry N. In grass monocultures the recovery of slurry N was slightly lower and of mineral fertilizer N higher than in grass-clover mixtures.