DRY BEAN RESPONSES TO NITROGEN-FERTILIZER IN 2 TILLAGE AND RESIDUE MANAGEMENT-SYSTEMS

Few data currently exist concerning dry bean (Phaseolus vulgaris L.) production systems in which minimum tillage techniques and cover crops are integrated with reduced reliance on chemical inputs. For this reason, we conducted a 2-yr held experiment in central Maine to compare bean growth, N status, and seed yield in two tillage and residue management systems: conventional planting into a tilled seedbed and two herbicide applications vs. no-tillage planting into a rye (Secale cereale L.) cover crop and a single herbicide application. Nitrogen fertilizer was applied at 0, 45, 90 and 135 kg N ha(-1) to both systems. In 1990, a year characterized by wet early-season conditions, bean seed yield was 26% lower in the no-tillage-rye mulch system than the conventional system, and increased linearly with N fertilizer rate in both systems. In contrast, in 1991, when early-season rainfall was near normal, yield of the no-tillage-rye mulch system was 23% lower than that of the conventional system without N fertilizer, but increased quadratically to equal yield of the conventional system when N was applied. In both years, seed yield was significantly correlated with early and midseason leaf N concentration and late-season leaf area index. Weed growth was greater in the no-tillage-rye mulch system than the conventional system in 1990 but equally low in both systems in 1991, when an additional cultivation was performed. Because the no-tillage-rye mulch system we examined may reduce bean growth, N status, and yield, we recommend that other management strategies be pursued. Use of legume green manures as N sources in temperate bean production systems merits attention.