Dairy farm production strategy and nitrogen surplus

Summary

Via public legislation minimum standards for the utilization of manure have been introduced as an obligatory part of fertilization planning. And many Danish livestock farmers have improved the utilization of manure during the last five to ten years. There is, however, still not consensus concerning the question of whether the results are sufficient to reduce the loss of nitrogen to ground water and the Danish marine environment to acceptable levels.
In an analysis of 30 dairy farms Halberg et al. (1995) showed a variation in N surplus between 88 and 387 kg/ha depending on stocking rate and management. At ca. 1.4 livestock units1) per ha there was a difference between 250 and 116kg N/ha farm level surplus. It was concluded that differences between farms with comparable stocking rates were more dependent on differences in crop rotation and fertilization strategy than on animal feeding levels and production. There is, however, a need for a better understanding of the relations between different feeding and crop cultivation strategies both from a management and a regulations point of view.
We therefore find it interesting to study the possibilities for reducing dairy farm N-loss and how they can be exploited in commercial farming. We take the perspective of the farm and will show the need to understand the interdependencies in the production system and between the production system and -the different functions of- the management system. For this purpose we suggest a method called systemic modelling (Sørensen & Kristensen, 1992) where empirical findings from farms studies and experimental knowledge together form the basis for the development of computer models. This paper will
- present modelled results concerning the possibilities for a reduction in dairy farm N loss and on the basis of this and earlier empirical findings,
- discuss some important aspects of farm nitrogen balances (stocking rate, feeding strategy, fertilization strategy, management style),
- demonstrate the need for an integrated model that can handle interdependencies between crop and livestock production, and
- discuss the importance of these recognitions when considering regulation of farm N losses.