Growth, nitrogen fixation, and nutrient uptake of hairy vetch as a cover crop in a subtropical region

Hairy vetch (Vicia villosa), as a winter cover crop, can be used to suppress weeds in subtropical regions, as well as temperate regions. Information on the potential biomass growth of hairy vetch for weed control and nutrient accumulation is not available in subtropical regions. Hairy vetch was sown in November 2004, and October, November, and December 2005. The wide-ranging cultivation period of hairy vetch indicated that it could be used in various cropping systems. It showed a higher biomass and nutrient accumulation when grown in subtropical Okinawa, Japan. Moreover, the biomass, and fixed carbon and magnesium (Mg) uptake in the above-ground parts of hairy vetch were found to be the highest in late May, with the highest nitrogen (N), potassium, and calcium uptake in mid-April and phosphorus (P) uptake in late March. Meanwhile, in the underground parts of the plant, they were highest in early May, except for the P and Mg uptake, which were highest in mid-April. According to the sowing date, the biomass and nutrient uptake of hairy vetch that was harvested in February were higher when sown in October. Similarly, when harvested in March, the biomass and nutrient uptake were higher when sown in October or November. In April, they were higher when sown in November or December. Hairy vetch has the potential to effectively suppress weeds in the winter and the spring seasons related to its sufficient biomass during the growing seasons. However, both the sowing and harvesting times of hairy vetch should be considered with reference to the cropping system; the subsequent crop will be sown to meet the N requirement.