Potential growth of hairy vetch as a winter legume cover crops in subtropical soil conditions

Soil acidity is one of the most serious causes of land degradation and limits crop production in subtropical agriculture. A number of legumes have adapted to P-limiting conditions, and the aim of the present study was to select an appropriate species for use as a winter legume cover crop under subtropical soil conditions in Okinawa, where P deficiency stems from soil acidification. Four vetch and four clover species were examined in pot trials. Of these, hairy vetch (Vicia villosa Roth) was found to be the most tolerant of P-limiting conditions. The shoot biomass of hairy vetch was also generally higher than that in the clover species when the P supply was non-limiting in the spring season. Hairy vetch was then compared in a pot trial with four clover species for an extended period of growth with adequate P supply. The N fixing activity of hairy vetch in the vegetative stage was 3.2-fold greater than that of the clover species. Nitrogen and P uptake in shoots and roots was significantly higher in hairy vetch than in the clover species in the vegetative and flowering stages. The C/N ratio in the shoots and roots of hairy vetch tended to be lower than that in the clover species. Shoot K uptake by hairy vetch was significantly higher in the vegetative stage than that in the clover species. In a field trial, shoot biomass and nutrient uptake of hairy vetch were similar on four different subtropical soils with pH values ranging from 5.7 to 7.5. Hairy vetch is an appropriate winter legume cover crop to improve subtropical soils by increasing organic matter and supplying nutrients to the subsequent crop.