Response of No‐Till Corn to Nitrogen Source, Rate, and Time of Application

A 3‐yr N‐source study was conducted on a site where urea was known to be less effective than NH 4 NO 3 (AN) for no‐till corn ( Zea mays L.) production. The purpose of the study was to compare two urea‐containing N sources thought to have lower N loss potential than AN and urea at two rates and times of application. Sources evaluated were urea, AN, Tennessee Valley Authority (TVA) experimental urea nitric phosphate (UNP) and TVA experimental urea ammonium phosphate (UAP). The soil was a Pope (coarse‐loamy, mixed, mesic Fluventic Dystrochrept), which is an acid soil with a C.E.C. of 12.1 cmol/kg and organic matter content of 3.7%. Nitrogen rates of 80 and 160 lb/acre were broadcast either at planting or 4 to 5 wk after planting. Experimental design was a randomized block with three replications. Results showed that AN and the TVA experimental materials performed comparably and that both were better than urea in grain yield and N content of total dry matter. Urea performed as well as the other sources in total dry matter accumulation. Delayed application of N increased grain yields from all N sources when compared with application at planting.