Maximizing the nitrogen efficiency of a prototype mixed crop-livestock farm in The Netherlands

Abstract This paper describes the year-over-year improvement of the nitrogen (N) efficiency in a prototype mixed farm system through the implementation of a coherent set of ecotechnological adjustments. This farm, the former APMinderhoudhoeve, was located on a marine clay loam soil in Oostelijk Flevoland, the Netherlands, reclaimed from the sea in the late 1950s. The designed farm structure was representative for the Dutch soil-bound agriculture in the late 1990s in terms of food crops’ choice and average level of milk production per ha of farmland. Key management strategies were the inclusion of grass-clover leys in the 7-year crop rotation, restricted grazing of the dairy herd and protein-poor and fibre-rich cattle diets including cereal straw. The farm components animal-manure-soil-crop were analysed in-depth in order to evaluate N flows and soil organic matter (SOM) dynamics at the farm system level, covering a period of six years. In its final experimental state, farm N use efficiency, expressed as the proportion of purchased crop fertilizers and cattle feed that was sold as exported products (crops, milk and cattle), was as high as 73%, Besides, total environmental losses were as low as 42 kg N ha −1 yr −1 . A scenario analysis revealed that these losses could be further minimized to 30 kg N ha −1 yr −1 in the stabilization phase, of which one-third as leached nitrate and a somewhat higher fraction as volatilized ammonia. The remaining losses represented mainly denitrified harmless N 2 from the stored animal slurry and farmyard manure. Soil N accumulated at an average rate of 89 kg N ha −1 yr −1 , whereas SOM showed a positive trend but with fluctuations from year to year which were negatively related to the annual rainfall amount. Despite the lowered protein content in the cow diets, average annual milk production increased from 8100 tot 8700 kg cow −1 . This could be mainly ascribed to a lower cow replacement rate due to less animal health problems, leading to an increased average lactation number of the dairy herd. Overall, the obtained environmental side effects on the prototype farm in its final experimental state were already below the targets set by the European Union with respect to the Nitrate Directive for the year 2020. It is concluded that when the best ecotechnological means are combined in a balanced mixed farm system a multiple win situation is attained in terms of food production capacity, cattle health and environmental quality.