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.