Nitrogen balances, nitrate leaching and energy efficiency of conventional and organic farming systems on fertile soils in northern Germany

Various studies based on either small-scale plot experiments or modelling approaches indicate a lower risk of nitrate leaching and a higher energy efficiency in organic than in conventional fanning systems. Because there is still a lack of data measured at the farm scale, which also take farm type and farming practices into account, a comparison between an N-intensive conventional and two organic all-arable crop rotations was carried out over a three-year period at a highly productive site in Northern Germany. Parallel a typical crop rotation representing an organic mixed farm was tested. Comparing the all-arable crop rotations, organic systems had 70% lower potential yields than the regional typical conventional crop rotation. In spite of 60% lower input of fossil energy, an N-intensive organic crop rotation showed 20% lower energy efficiency than a comparable conventional. In the present study, the higher N inputs and higher N surplus of the conventional system did not lead to significantly higher nitrate leaching than in the organic all-arable crop rotations. Comparison of an organic all-arable crop rotation with the corresponding mixed farming system showed significantly higher yields, higher energy efficiency and lower nitrate leaching in the organic mixed farming system. Management of grass/clover (mulching versus feeding) had the strongest influence on nitrate leaching in the organic systems. Because farm type and farming practices had a decisive impact on yields, nitrate leaching and energy efficiency, we conclude that a comprehensive assessment of land use systems at both the regional and the farm scale is needed to legitimize incentive payments for the adoption of organic farming standards.