All-arable organic farming systems, especially when they are working without organic fertilizer, are often in challenge with their nutrient management to fulfill the requirements of crops. In this context one of the main issues is to mitigate nutrient losses. Here the use of catch crops may one strategy to counteract against this. We hypothesized that under the climate conditions of north-west Germany winter hard catch crops are more suitable to reduce nitrogen (N) losses than catch crops killed by frost, here especially with cereals or legumes as previous crop. In a field experiment in 2015/16 we tested 3 different catch crops (grown in pure stand and in mixture with legumes) after peas and triticale for their nitrogen loss paths over the winter period. Soil mineral N content (0-90 cm) was determined before and after winter. Nitrous oxide (N2O) emissions were measured weekly. Nitrate (NO3) concentrations in leachate were analyzed once a week (Oct-Mar).The results show that corn legumes as pre crop have the highest N-loss potential over winter. In comparison, catch crops demonstrate a good reduction of nitrogen losses pathways like NO3 in leachate or gaseous N2O emissions. In particular significant lower nitrate losses via leaching were recorded after corn as pre crop. In comparison winter killed white mustard showed
significant higher NO3 and N2O losses over winter. Undersown catch crops showed the highest potential to mitigate N-losses
