Nitrogen requirements of fresh-market tomatoes on hairy vetch and black polyethylene mulch

A 3-year experiment was conducted to determine the optimum fertilizer N requirements of fresh-market tomato (Lycopersicon esculentum Mill.) 'Sunbeam' grown on a hairy vetch (Vicia villosa Roth.) or black polyethylene mulch. In 1993 and 1994, four rates of fertilizer N (0, 56, 112, and 168 kg.ha(-1)) as water-soluble NH4NO3 were applied in 14 equal applications through the trickle irrigation system starting 1 week after planting. Four additional rates (224, 280, 336, and 392 kg.ha(-1)) were applied in 1995 to assess the plant response to supra-optimal levels of N. Hairy vetch produced 3.3-4.5 t.ha(-1) of aboveground biomass and a total N content of 126-169 kg.ha(-1) in the above-ground biomass. Leaf N content at 7 weeks after transplanting of tomatoes correlated positively with yield from black polyethylene but did not correlate with yield from the hairy vetch plots where leaf N content was optimal at all N rates. Predicted tomato yields were higher for the hairy vetch than for the black polyethylene treatment at all applied N rates in all years. Tomatoes grown in black polyethylene required N at 130 to 144 kg.ha(-1) to achieve yields equivalent to those grown following unfertilized hairy vetch. Tomato yield increased in response to applied N in both mulches in all 3 years; optimum N rates of 89 and 190 kg.ha(-1) in hairy vetch and black polyethylene, respectively, were predicted by a linear plateau model, and 124 and 295 kg.ha(-1) by a quadratic plateau model. The linear plateau model is recommended because it would allow less N to become available for runoff and leaching.