NITROGEN FERTILIZATION OF LAND CONTINUOUSLY CROPPED TO CORN (Zea mays L.)
Three field trials were conducted to determine if and how response of corn (Zea mays L.) to applied N changes during continuous production. Nitrogen was broadcast at rates of 0, 56, 112, 168, 224 and 336 kg/ha each year for 10 yr. Rates of N in excess of 168 kg/ha significantly reduced emergence at the Fox site; no effect occurred elsewhere. Applied N had no effect upon seedling weight, decreased the interval from seeding to silking, and increased grain and stover yields at all sites. The most profitable rates of N for grain production throughout the study were 85 and 110 kg/ha at the Conestogo and Fox sites, respectively. At the Chinguacousy site, there was a significant year by N rate interaction with grain yield declining by 5600 kg/ha over 10 yr in the 0-kg-N/ha treatment. A model developed by multiple regression analysis (R2 = 0.71) for this site predicted that the most profitable rates of N application were 38, 178, and 213 kg/ha in years 1, 5, and 10, respectively. Applied N decreased ear moisture content at harvest and increased lodging at all sites. Key words: Zea mays L., N fertilization, year by N interaction