Our first hypothesis, that the use of catch crops can considerably reduce N losses in comparison with fallow during the winter period was not confirmed. Under the conditions of the field experiments, catch crops had only small impacts on the N balance of the whole crop rotation and, in particular, catch crop use did not always reduce N losses. This is a remarkable result, considering that cauliflower was selected as the main crop, which is particularly prone to N balance surpluses and hence offers a great potential for the effective reduction of N losses by catch crops.
This result can presumably be in part explained by gaseous N losses from cauliflower crop residues. Future investigations should therefore also focus on measures to reduce gaseous N losses from fresh crop residues. The weather conditions strongly affected the N balances of the crop rotations and caused great variability of the results between experimental years. This supported our second hypothesis that effects of different crop rotation on the N balance can only be assessed in long-term trials.