YIELD AND NITROGEN REQUIREMENT OF NO-TILLAGE CORN AS INFLUENCED BY CULTURAL-PRACTICES

Nitrogen fertilizer use efficiency in corn (Zea mays L.) production could be improved if farmers adjusted N fertilizer rates for different yield potentials caused by variations in cultural practices. Fire studies were conducted in Ohio, three on Hoytville silty clay (fine, illitic, mesic Mollic Ochraqualf) and two on Riddles silt loam (fine-loamy, mixed mesic Typic Hapludalf), to assess the effects of planting date, plant population, N rate, and timing of N application on yield of two corn hybrids grown using no-tillage methods. Increasing plant population increased grain yield in only one of five site-year comparisons, but did not increase the amount of N required to produce maximum yield. Crop yield potential varied depending on site-gear, with maximum grain yield indicated by response functions ranging from 55 to 11.3 Mg ha(-1) for early-planted corn, and 30 to 10.1 Mg ha(-1) for late-planted corn. Nitrogen rates needed to achieve maximum yield varied from 0 to 205 kg N ha(-1) for early-planted corn and from 0 to 175 kg N ha(-1) for late-planted corn, depending on site-year. In most site-years, late-planted corn required less N to achieve maximum yield than early-planted corn. The reduction in N requirement averaged 60 kg N ha(-1) and was directly related to the magnitude of the yield reduction associated with delayed planting. Split applications of N generally produced yields equivalent to application of all N at planting. Split application fan offer many farmers a way to use lower N rates to compensate for delayed planting.