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

Few data currently exist concerning dry bean (Phaseolus vulgaris L.) p roduction systems in which minimum tillage techniques and cover crops are integrated with reduced reliance on chemical inputs. For this reas on, we conducted a 2-yr held experiment in central Maine to compare be an growth, N status, and seed yield in two tillage and residue managem ent systems: conventional planting into a tilled seedbed and two herbi cide 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, yi eld 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 midseaso n leaf N concentration and late-season leaf area index. Weed growth wa s greater in the no-tillage-rye mulch system than the conventional sys tem in 1990 but equally low in both systems in 1991, when an additiona l cultivation was performed. Because the no-tillage-rye mulch system w e examined may reduce bean growth, N status, and yield, we recommend t hat other management strategies be pursued. Use of legume green manure s as N sources in temperate bean production systems merits attention.