Dynamics of nitrogen derived from hairy vetch applied as cover crop in tomato production in plastic house

Fresh market tomatoes (Solanum lycopersicum L.) are mainly grown in plastic house in Japan and usually a large amount of nitrogen fertilizer was applied for getting high yield. One of the ways to establish an organic system, no chemical N fertilizer, is the use of cover crops. The application effect of a legume cover crop, hairy vetch (Vicia villosa R., HV), on N dynamics in fresh market tomatoes, 'House Momotaro', was investigated using the ¹⁵N-labeling method in 2011 and 2012. Before transplanting of tomato, the ¹⁵N-labeled HV (1.319 mg N pot^-1, 260 kg N ha^-1), and chemical N fertilizers were incorporated into the soil. Tomato seedlings were transplanted into a 1/2000 a Wagner pot with 0 and 240 kg ha^-1 of N application (N0HV and N240HV) in plastic house early June, 2011. Only 240 kg ha^-1 of N fertilizer was applied in conventional plot. There was no significant difference in fruit yield among the plots. In organic plot, N0HV, total N uptake in tomato plant was smaller than that in N240HV, however, the rate of N uptake derived from HV to total N uptake in tomato plants (%Ndfhv) in N0HV (37.1%) was larger than that in N240HV (24.8%) at 12 weeks after transplant. Nitrogen use efficiency from HV-derived N (NUE; N uptake derived from HV in tomato/amount of N applied in HV) was 44.4% in N240HV and 49.4% in N0HV. About half of HV-N including organic and inorganic type remained in the soil. Tomato was cultivated in the soil used 2011 with unlabelled HV and N fertilizer in 2012. There was no difference in the uptake amount of N derived from HV applied in 2011 (HV₂₀₁₁) into tomato between N240HV and N0HV, 57.7 mg plant^-1 on average, so nitrogen use efficiency (NUE) derived from HV₂₀₁₁ was 4.4% on average 2012. It was recognized HV could be available for not only short-term N source, but also long-term N source.