Nitrogen leaching from organic agriculture and conventinal crop rotations

Summary

The goal of our study is to investigate nitrogen leaching from organic agriculture, taking into account a complete organic rotation (6-9 years) and to compare the results with leaching from conventional systems. There are long time series on sub-root crop concentrations in conventional agriculture in the Seine Basin. These scored an average of 25 ± 4 mg N-NO3.l-1 (standard for drinking water is 11 mg N-NO3.l-1) in different types of soil, crops and climatic conditions. However, no data still exists for organic farming (OF) in this area. In 2012-2013, a total of eight practices of arable crops have been equipped with suction cups for all their rotations (5 in OF and 3 in CF), in three pedoclimatic situations, in order to determine concentrations and fluxes of nitrogen leached. In the conditions of the first step of our study, the average of sub-root concentrations in the organic rotations was 11 ± 6 mgN-NO3.l-1 (N=35) against 26 ± 9 mgN-NO3.l-1 (N=8) for the conventional ones. Organic farming in the north of France could therefore reduce by 60% the nitrogen leaching potential compared to conventional practices widely spread in the Ile-de-France Region and the Seine Basin.