Influence of cover crops and inorganic nitrogen fertilization on tomato and snap bean production and soil nitrate distribution

Commercial vegetable production depends almost solely on inorganic fertilizers. In an era of environmental sensitivity, enrichment of soils with green manures and cover crops may reduce the dependence on these fertilizers while maintaining and enhancing crop yields. The objectives of this research were to determine (1) if supplemental nitrogen (N) at 60 or 120 kg · ha⁻¹ following winter cover crops of wheat (Triticum aestivum L.) or crimson clover (Trifolium incarnatum L.) affect yield of tomato (Lycopersicon esculentum Mill.) and snap bean (Phaseolus vulgaris L.) grown in rotation; and (2) the distribution and retention of soil nitrates in the soil profile as affected by N fertilization and cover cropping. ‘Mountain Pride’ fresh market tomato and ‘Strike’ snap bean were grown in rotation for four years. Clover and wheat cover crops increased total marketable yield of ‘Mountain Pride’ tomato in one out of four years. Total marketable tomato yield increased as fertilizer N increased to 60 kg · ha⁻¹ in two out of four years and with 120 kg · ha⁻¹ in one out of four years. N did not interact with cover crops to affect yield. ‘Strike’ snap bean marketable yield summed over all years was 60% lower in clover plots compared with fallow. Total marketable snap bean yield increased with 60 kg N · ha⁻¹ in one out of three years but was unresponsive to N in two out of three years. Soil nitrates to 1.2 m depth were higher after clover and wheat than after fallow. Nitrate level was highest in soil with clover and 120 kg N · ha^−1. In all cover crop or fallow plots, as fertilizer N application levels increased, the soil nitrates also increased. Cover crops or fertilizer N application did not increase the retention of residual nitrates in the 1.2 m soil profile depth after four years of cropping.