Model calculations for the reduction of N-losses and nutrient surplus in dairy grassland farms

Dairy production in grassland often leads to surplus of nutrients and N-los ses. The concept 'nutrient-margin' with the aim of a settled balance rests on the assumption that nutrient imports either as fertilizers or concentrat es take place in the same range as nutrients leave the grassland farm by me ans of products (milk and meat) exclusively produced from basal grassland f eed. As part of this concept in this publication nutrient surplus and N-los ses are calculated using different casestudies in grassland farms with perm anent housing. The presented calculations apply for intensive milk producti on with high and low milk yield fi om basal grassland feed and for normal o r reduced concentrated crude protein in used concentrates; common and modem slurry techniques were taken into consideration. The study comes up with the following results: (1) A grassland farm with 1, 6 cows ha(-1) and a milk yield of almost 8.000 kg milk per cow can reach a settled N-balance (= 0 kg N ha(-1)) and a reduction of nutrient surplus of 68 kg N, 15 kg P, 41 kg K und 3 kg Mg ha(-1) under the condition that a 3.0 00 kg milk yield achieved through basal grassland feed and large imports of concentrates is replaced by a 5.000 kg milk yield from basal grassland fee d and an amount of used concentrates which has been calculated through N-ex port. (2) The reduction of N-surplus in the grassland farm does not remarka bly decrease the N-losses. (3) The use of low-emission slurry techniques re duces the N-losses up to 40 % compared to the surface application technique . (4) The reduction of N in concentrates from 16 % to 12 % crude protein on ly decreases the N-losses about 14 %. It has to be noted that the grassland farm with a low milk yield from basal grassland feed by use of N-reduced c oncentrates and an aimed N-balance of 0 kg N ha(-1) produces higher P- and K-surplus than the farm with high milk yield fi om basal grassland feed.