RIDGE PLANTING FOR ROW CROPS ON A POORLY DRAINED SOIL .2. ANHYDROUS AMMONIA AND UAN MANAGEMENT FOR MAIZE FOLLOWING SOYBEAN

A three year study was conducted over the period 1985-1987 to determine the effects of anhydrous ammonia and urea-ammonium nitrate solution (UAN) application methods on yield of ridge-planted maize (Zea mays L.) following soybean (Glycine max L. Merr.) on a Hoytville silty clay (Mollic Ochraqualfs). Nitrogen was applied to maize at a rate of 168 kg N ha-1 as injected anhydrous ammonia, or UAN broadcast or dribbled on the soil surface at various times. Anhydrous ammonia produced the highest average yield (9.1 Mg ha-1) over the study period. Treatments in which UAN was broadcast, or applied by split application (sidedress on the ridge), produced yields equivalent to those produced by ammonia in some years, but averaging 0.6 Mg ha-1 less than those produced by ammonia over three years. Treatments in which all UAN was applied by dribbling at planting produced average yields lower than did these three systems. Average ear leaf N concentrations showed differences similar to those seen in grain yields. Results indicated that the method of N application can affect yield of ridge-planted maize, and it appears that N management should be evaluated critically when designing such systems. © 1990.