The inorganic nitrogen fertilizer equivalency of hairy vetch (Vicia villosa Roth) as a winter green manure in Kanto and Tohoku district, Japan

ABSTRACT It is well known that legume green manure (GM) supplies nitrogen (N) to succeeding crops. However, in Japan, there are few experimental field studies that have quantitatively evaluated the effect of GM on the N supply. To estimate the inorganic N fertilizer equivalency of GM for the succeeding corn crop, two field experiments were conducted in 2012 at Morioka, Tohoku district (cool climate region) and in 2014 at Nasushiobara, Kanto district (warm temperate region). Each experiment had a split-plot design with a factorial arrangement of two cropping systems, hairy vetch [HV; Vicia villosa Roth] GM and conventional cultivation, with four N fertilizer treatments (0, 75, 150, and 225 kg N ha−1). In both sites, GM increased the N uptake and, as a result, the shoot yield of the succeeding forage (silage) corn. The apparent N recovery rates of HV shoot were 64% at Morioka and 24% at Nasushiobara. The inorganic N fertilizer equivalency rates of HV shoot were 82% at Morioka and 104% at Nasushiobara. In conclusion, by introducing HV as a GM, we can reduce the amount of inorganic N fertilizer applied to the succeeding corn crop with the same amount as at least 80% of N uptake in HV shoot.