Nitrate leaching and energy efficiency of stockless arable systems compared with mixed farming and a non-organic system on fertile soils in Northern Germany

Kurzfassung

Previous 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 farming 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 non-organic, two organic all-arable crop rotations and a typical rotation of a mixed organic farm was carried out over a three-year period at a highly productive site in Northern Germany. Comparing the all-arable crop rotations, the 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 percent lower energy efficiency than a comparable conventional. In the present study, the higher N inputs and higher N surplus in 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 potential yields, higher energy efficiency and lower nitrate leaching in the organic mixed farming system. Management of the grass/clover (mulching versus feeding) had the strongest influence on nitrate leaching and energy efficiency in the organic systems. The decision to undertake stockless instead of mixed organic farming should not only be based on economic reasons, but also take the important aspects of energy and nitrogen efficiency into account.