Catch crops affect nitrogen dynamics in organic farming systems without livestock husbandry—Simulations with the DAISY model

This paper presents simulations of the soil–plant–atmosphere model DAISY based on an organic crop rotation with incorporation of different catch crops following pea as a leguminous cash crop. Special emphasis was placed on the simulation of nitrogen (N)-mineralisation/immobilisation and of soil microbial biomass N. The DAISY model was able to simulate soil mineral N and soil microbial biomass N after soil incorporation of catch crop plant residues to some extent only. Several processes need further attention and should be integrated into the DAISY model: (1) soil tillage induced mobilisation of organic material including considerable amounts of organic N; (2) winter killing of sensitive plant species and varieties; (3) decomposition of plant residues at the soil surface; (4) decomposition of easily decomposable plant residues at low temperatures, both with respect to the temperature modifier function and to the linkage of C and N turnover; (5) furthermore, reliable criteria for the subdivision of green plant residues into an easily decomposable pool and a more recalcitrant pool have to be developed.