Nutrient characteristics of four kinds of winter green manure and their influences on soil mineral nitrogen before incorporation

In order to replace the winter bare fallow with green manure crop in rice cropping system in South of Jiangsu province, the field experiment was carried out to investigate the growth and nutrient characteristics of hairy vetch (Vicia villosa Roth ), smooth vetch (Vicia villosa var.), milk vetch (Astragalus sinicus L.) and radish（Raphanus sativus L.） as winter green manure crops and their influences on soil mineral nitrogen before incorporation. The results showed that four kinds of green manure crops in our study all produced relatively high aboveground biomass and N, P, K nutrients accumulation, the fresh and dry biomass ranged from 24.8 t/ha to 30.7 t/ha and from 3.6 t/ha to 4.2 t/ha individually. No significant differences were found among different green manure crops. The nitrogen uptake ranged from 69.8 for radish to 136.4 kg/ha for hairy vetch. The phosphorus uptake ranged from 7.1 for radish to 11.3 kg/ha for milk vetch. The potassium uptake ranged from 117.6 for smooth vetch to 151.3 kg/ha for hairy vetch. Compared with bare fallow treatment, planting green manure crops decreased the mineral nitrogen content in plow layer soil to different extents (averagely decreased by 38.9 kg/ha). The decrease of soil mineral nitrogen content was related to significant decrease of soil nitrate nitrogen content. The soil ammonium nitrogen content had an increasing trend (averagely increased by 6.5 kg/ha). There were significant increases in ammonium nitrogen for hairy vetch and smooth vetch treatment compared with that in the bare fallow treatment. Four kinds of green manure crops in our study all suitable for planting as green manure crop in rice cropping system in South of Jiangsu province, and potentially reduced the loss risk of soil mineral nitrogen and supplied the nutrients for rice growth in the next season.