Nitrogen from hairy vetch (Vicia villosa Roth) as winter green manure for white cabbage in organic horticulture

Summary

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 reference. In 2002 and 2003, hairy vetch and weeds accumulated 136 and 178 kg ha-1 of shoot N and yielded 3.79 and 4.72 t ha-1, respectively.
After ploughing and planting white cabbage (Brassica oleracea L. convar. capitata var. capitata f. alba) for sauerkraut production at the beginning of June, the amount of soil mineral N (SMN) of the topsoil layer was biweekly investigated until canopy for about 6 - 8 weeks. In 2002, already within 2 weeks a maximum of 121 kg SMN ha-1 for the green manure hairy vetch treatment was reached, 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 t DM ha-1 (range 3.9 - 5.1 t ha-1 DM) and had accumulated on average 153 kg N ha-1 (range 129 - 178 kg N ha-1). Mean fresh matter yield (FM) of a single head was only 1.2 kg (range 1.1 - 1.3 kg head-1) due to severe pest damage. In the following year, the mean head yield was 5.1 kg FM (range 3.4 - 6.4 kg) and head yield per hectare was 5.8 t DM (range 4.6 - 7.5 t DM ha-1) with a mean head N uptake of 182 kg ha-1 (range 136 - 237 kg N ha-1).
The relationship between the weighted arithmetic daily mean of SMN for the first 6 - 8 weeks after the hairy vetch harvest date and the N uptake of cabbage at two sampling dates was significant, as were most correlations between presented core parameters. Although N of hairy vetch used as green manure calculatively recovered on average only about 27% in cabbage shoot N at final harvest, a balanced field N budget can be ensured by using the green manure legume hairy vetch as a basic N source for a subsequent white cabbage cash crop.