Potential N-losses in three scenarios for conversion to organic farming in a local area of Denmark

Techniques are needed to investigate whether different strategies for conversion to organic farming might help to reduce N-losses. In this study, an N-balance technique was applied in a local area of Denmark; 25% of this area was designated as environmentally sensitive with special interests to protect groundwater quality. Three scenarios, where 25% of the local area was converted to organic farming, were compared to the present situation with conventional farming. The first two scenarios were conversion to organic dairy and pig production, respectively. The third scenario was conversion of the whole area with special interests in clean groundwater to organic farming, self-sufficient in fodder and fertiliser. Scenario 1 resulted in a lower N-surplus on the dairy farms, but the reduction was too small in order to significantly reduce the N-surplus in either the whole local area or within the area with special interests in clean groundwater. Scenario 2 resulted in an analogous result. In Scenario 3, the N-surplus was reduced significantly within the area with special interests in clean groundwater, but not within the whole local area. The N-surplus reduction from conversion to organic farming was divided into an extensification and a management effect. The extensification effect meant that the lower livestock density in the organic scenarios resulted in lower N-surpluses, due to an exponential relationship between livestock density and N-surplus. The management effect was primarily caused by lower net imports of fodder and fertilisers to the organic farms and the following higher self-sufficiency in fodder. In addition, the distribution of animal manure between the organic farms was more uniform than between the conventional farms and because of the exponential relationship between livestock density and N-surplus, this caused a lower average N-loss potential. We conclude that organic farming can help to reduce potential N-losses in environmentally sensitive areas, but only if the conversion is designed with respect to that aim and takes account of the spatial distribution of farm types present.