Improvement of the value of green manure via mixed hairy vetch and barley cultivation in temperate paddy soil

Abstract

Legume hairy vetch and non-legume barley mixtures are broadly cultivated to improve the value of cover crops in mono-rice paddies. Nevertheless, the effects of mixing conditions of the two cover crops on biomass and nutrient productivities and on the yield characteristics of subsequent rice crops have not been well studied. To evaluate the effects of mix-seeding legume and non-legume cover crops on the value of green manure in paddy soil, barley and hairy vetch were sown at the rice harvesting stage as pure crops at the recommended rates (180kgha−1 of barley, B100; 90kgha−1 of hairy vetch, V100), and as mixtures, in which the two cover crops were mix-seeded with varying seed ratios according to the replacement principle. The mixed seeding of the two crops significantly increased the cover crop biomass and nutrient productivities compared with the single barley and hairy vetch cultivation. Biomass productivity linearly increased with increasing barley seeding level, but it was not affected by the hairy vetch seeding rate. The total N content of the barley biomass clearly increased as the proportion of the total biomass accounted for by hairy vetch was increased, and this significantly improved the value of the green manure of cover crop biomass. In contrast, the total N content of the hairy vetch biomass was not affected by changes in the barley proportion. Biomass produced in the pure barley seeding could not produce the nutrients required by the recommended chemical fertilization level (N–P2O5–K2O=90–45–57kgha−1) for rice, but the biomass increase caused by mixed seeding of the two cover crops resulted in enough nutrients to satisfy the recommended fertilization level. The highest biomass and nutrient yields were observed for the mixed seeding of barley and hairy vetch at 25 and 75% (B75V25) of their respective recommended seeding rates. This increased nutrient input stimulated the rice plant growth and significantly improved the rice yields. The highest yields were achieved with the B75V25 treatment. In conclusion, mixed seeding of legume hairy vetch and non-legume barley could be a very useful agronomic practice for increasing the cover crop biomass and its nutrient productivity and to improve the productivity of subsequent rice crops in temperate rice paddies.