WINTER ANNUAL GRASS-LEGUME BICULTURES FOR EFFICIENT NITROGEN MANAGEMENT IN NO-TILL CORN

Winter annual cover crops may be an effective tool for managing inorga nic N in the sandy soils of the Atlantic Coastal Plain when summer dro ughts can result in relatively high residual fertilizer N levels. A fi eld experiment was conducted from 1992 to 1994 on a Norfolk loamy sand to determine the effect of (1) previous corn fertilizer N rate (150 o r 300 kg ha(-1)) on dry matter (DM) and N accumulation in rye, crimson clover, and hairy vetch monocultures and respective rye-legume bicult ures; (2) the respective cover crops on residual soil inorganic N leve ls; and (3) cover crops on corn grain yield. Compared to the preplant corn N rate of 150 kg ha(-1), the 300 kg N ha(-1) rate resulted in gre ater profile soil inorganic N contents on subsequent sampling dates in both years. Concomitant with these greater residual soil N levels wer e increases in cover crop DM and N accumulation compared with low resi dual soil N levels. Averaged over 2 year, cover crop DM accumulation b y April was in the order of rye > rye-vetch = rye-crimson clover > hai ry vetch > crimson clover. The corresponding cover crop N content rank ing was hairy vetch > rye-hairy vetch > crimson clover = rye-crimson c lover > rye. Before corn planting in Apr, rye monoculture reduced soil inorganic N content an average of 62% in 1993 and 37% in 1994 compare d to legume monocultures. Soil inorganic N content under the rye-legum e bicultures was reduced an average of 44% and 15% for the same dates. Inadequate rainfall during both corn growing seasons resulted in poor corn yields (1.18 to 2.50 Mg ha(-1)) that were generally unaffected b y cover crop or prior N rate. The results from this study demonstrated the ability of rye and rye-legume bicultures to scavenge residual soi l inorganic N following a summer corn crop, thereby minimizing the lea ching of N from the plant resting zone. (C) 1997 Elsevier Science B.V.