Nitrogen and carbon release during decomposition of roots and shoots of leguminous green manure crops

In Nordic conditions, soils are frozen during winter, affecting the decomposition rates of crop residues. Hence, the decomposition rates of above- and underground biomass and the dynamics of the N and C released into the soil were studied in trials focused on green manure crops. The decomposition of the residue and N release from the residue varied among the five species of legume tested. There was a marked difference in decomposition rates between shoots and roots, which may also be explained by the differences in the chemical composition of the residue. The shoot residue decomposes rapidly and it serves as a source of N for the subsequent crop. The root residue decomposes more slowly and this had a positive effect in a crop rotation in the second year. The green manure crops play an important role in managing N for organic crop production. Through efficient utilization of symbiotically fixed N by legumes in green manure, it is possible to achieve higher yields of subsequent crops.