Nitrogen management on experimental dairy farm 'De Marke'; farming system, objectives and results

In the sandy regions of the Netherlands, high nutrient surpluses from dairy farming harm the environment. Government policy aims at reducing nutrient losses to acceptable levels. To explore possibilities and to generate sufficient and accurate information for dairy farmers to reduce surpluses, research was carried out at the experimental dairy farm 'De Marke'. The objective of 'De Marke' is to design and operate a suitable farming system that meets strict environmental standards, taking into account societal objectives with respect to animal welfare, nature and landscape, and economic viability. A dairy farm is characterized as a system with soil, crop, herd and manure as components. Results of animal nutrition, crop yields and nitrogen (N) flows for the period 1993-1998 indicated that intensive farms could attain a N surplus of 158 kg ha-1. So compared with a 'current average' farm in the middle of the 1990s with the same milk production level (N surplus of 408 kg ha-1 a reduction of 62% in N surplus was realized. At 'De Marke', especially the input of purchased feed and chemical fertilizer was much lower. The most important characteristic of the farming system 'De Marke' was the realization of very high N utilization efficiencies in animal nutrition and crop production, allowing a similar milk production but at a much lower input level. With an ammonia volatilization level of 20 kg N ha-1 - which is much lower than the 64 kg ha-1 on the 'current average' farm - the target of 30 kg N ha-1 was attained. Total crop yields (pasture grass, grass silage and silage maize) at 'De Marke' were lower than expected. With a realized N surplus of 156 kg N ha-1 the target of 128 kg N ha-1 (including deposition and symbiotic fixation) was not yet attained