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The effect of the nitrogen (N) supply from hairy vetch, grown as winter green manure, on white cabbage was investigated in field trials performed on an organic farm in north-west Germany over two years. Hairy vetch was either used as green manure or harvested. One of two bare soil fallow treatments was supplied with hairy vetch shoot mass to serve as a reference. In 2002 and 2003, hairy vetch and weeds accumulated 136 and 178 kg ha−1 of shoot N and yielded 3.79 and 4.721 ha−1, respectively. After ploughing and planting white cabbage (Brassica oleracea L. convar, capitata var: capitata f. alba) at the beginning of June, the amount of soil mineral N (SMN) in the topsoil layer was investigated biweekly for about 6–8 weeks until canopy. In 2002, a maximum of 121 kg SMN ha−1 for the green manure hairy vetch treatment was reached within 2 weeks, whereas in 2003 a maximum of only 60 kg SMN ha−1 was observed, due to an exceptionally dry and warm season. In 2002, white cabbage shoot yielded an average 4.4 ...