Nitrogen use efficiency on dairy farms with different grazing systems in northwestern Germany

Agricultural production is often accompanied by nitrogen (N) losses causing negative environmental effects. In order to assess dairy farms ' N management, appropriate indicators based on robust farm data need to be addressed. This study investigated N balance and N use efficiency (NUE) as a function of grazing intensity on specialized dairy farms in northwestern Germany. For that, 30 farms were grouped according to pasture management from full grazing to zero grazing: >10 h in group 1, 6 to 10 h in group 2, <6 h in group 3, and group 4 without pasture access. Based on multiple farm data, substance flow analysis was carried out. Subsequently, the data were analyzed according to the relevant indicators N surplus and NUE on feed-, field- and farm-level. The results revealed N surpluses on all farms, with the average N surplus tending to decrease from 259 to 179 kg N ha(-1), and farm-NUE to increase from 40 to 50 %, from full grazing to zero grazing management systems. There were considerable differences between the N balances calculated in this study and those reported by farms as part of statutory net N soil surface balance reporting under the German regulatory law. In conclusion, the N indicators were suitable to compare farm performance among and within different dairy farming systems. When comparing indicator values there is a need to consider the methodology applied, the system boundaries set, and the origin and quality of data used.