KILL DATE OF VETCH, RYE, AND A VETCH-RYE MIXTURE .2. SOIL-MOISTURE AND CORN YIELD

Spring cover crop kill date effects on N and water availability to sub sequent no-till corn (Zea mays L.) have not been studied. This 2-yr st udy was conducted in 1990 and 1991 at Coastal Plain and Piedmont locat ions in Maryland to evaluate soil moisture and corn responses to three cover crop kill dates, three corn planting dates, and four fertilizer N (PN) rates following cover crops of hairy vetch (Vicia villosa Roth ), cereal rye (Secale cereale L.), and vetch-rye mixture. No-cover che cks were included for each corn planting date. Corn yield ranged from 0.8 to 13.3 Mg ha(-1) in 1990,and from 3.9 to 12.6 Mg ha(-1) in 1991. Corn grain yield without FN was greatest following vetch or vetch-rye mixture. Late April or early May kill dates consistently resulted in g reater corn yield than earlier kill dates, probably due to differences in N availability and moisture conservation. Cover crops killed late did not deplete surface soil moisture. The economic FN rate reflected N contributions and moisture conservation by each cover crop. At the C oastal Plain location, economic FN rates were 30 to 76 kg ha(-1) for c orn following vetch, 65 to 193 kg ha(-1) following vetch-rye mixture, 161 to 247 kg ha(-1) following rye, and 201 kg ha(-1) following no cov er crop. Similar rankings were observed for the Piedmont location, but maximum yield was lower following rye, and lower FN rates were requir ed to attain that yield. Summer soil water conservation by cover crop residues was more important than spring moisture depletion by growing cover crops in determining final corn yield.