Corn Production as Affected by Nitrogen Application Timing and Tillage

Utilizing conservation tillage practices and increasing fertilizer N use efficiency for corn (Zea mays L.) are necessary for optimizing growers' profits and for minimizing loss of sediment and nutrients to the environment. A 3-yr study was conducted on a Nicollet clay loam (fine loamy, mixed, mesic, Aquic Hapludoll)-Webster clay loam (fine loamy, mixed, super active, Typic Endoquoll) soil complex in southern Minnesota to determine the effects of four tillage systems (no tillage, strip tillage, one-pass field cultivate, and chisel plow) and two N application times on corn production following soybean [Glycine max (L.) Merr.]. Anhydrous ammonia was applied at 123 kg N ha-1 either in late October when soil temperatures at 15 cm were generally below 10°C or in April before planting. Tillage system had a statistically significant effect on corn production but showed no interaction with the N timing treatments. Maximum differences among tillage systems were 4.3% for grain yield, 5.1% for silage yield, and 8.6% for total N uptake. In 1 yr, when April and May were wet and warm, grain yield and total N uptake were reduced 20 and 27%, respectively, with fall N. Apparent N recovery was reduced from 87% for spring N to 45% for fall N. Corn production was not affected by time of N application in the other 2 yr. Relative leaf chlorophyll, measured by a SPAD meter at the V10, R1, and R3 growth stages, was highly correlated to relative corn grain yield, and could be used as a diagnostic tool at the V10 stage to determine sidedress N needs under non-irrigated conditions. Because the risk of N loss is greater with fall N application, N should be applied in the spring on these soils to minimize risk and optimize profitability regardless of tillage system.