Hairy vetch becomes an alternative basal N fertilizer in low-input fresh-market tomato production in plastic high tunnel

Environment pollution is one of the major concerns in recent times. In order to establish low-input alternative production systems based on cover crops, the effectiveness of hairy vetch (Vicia villosa Roth; HV) incorporated as a basal nitrogen (N) fertilizer in fresh-market tomato production in plastic high tunnel was investigated in Sapporo, Japan. The treatments consisted of HV seeding rates (HV20, 20 kg ha^-1; HV50, 50 kg ha^-1) and ammonium sulfate (AS100, 100 kg ha^-1) applied as basal N fertilizers, and the control with no basal fertilizer. In all plots, 150 kg ha^-1 of N was added as topdressing slow-release N fertilizer (LPS100 41%-N) before transplanting. HV aboveground biomass (dry weight) was 5.85 t ha^-1 in HV20 and 7.19 t ha^-1 in HV50. Nitrate in petiole sap was found to be higher in HV20, HV50 and AS100 plots than in control plots throughout the cultivation period with the exception of the first 2 weeks after transplanting (WAT). The growth index (GI) was higher in HV20 (47971), HV50 (46285), and AS100 (43397) than in control (39847) at 7 WAT. Higher marketable yields were found in tomatoes grown in HV20 (68.7 t ha^-1), HV50 (69.1 t ha^-1) and AS100 (60.8 t ha^-1), compared with control (51.9 t ha^-1). The HV plots had greater soil organic nitrogen and soil carbon than AS100 and control after tomato production. From these results, the HV seeding rate of 20 kg ha^-1 will be enough to support the growth of tomato planted after HV production if HV grows smoothly in greenhouse.