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Fluid Journal : Fluid Journal 2005-2007
22 Fluid Journal EARLY SPRING 2007 or N efficiency but increased nitrate leaching potential. Another study in Olmsted County compared various combinations of preplant and sidedress applications of N from 1992 to 1997. In these wetter than normal years, the 7-year average yield was 2 to 5 bu/A higher with split applications compared to a single preplant application. Applying a single sidedress application at the V6 to V7 stage reduced grain yield slightly. Cor n after soybeans A 7-year study (1987 to 1993) was conducted on a Canisteo clay loam (pH 7.6) to determine the effect of fall, spring preplant, and split applications of N on corn yield, N recovery in the grain, and leaching loss of nitrate into tile lines. The split application treatment consisted of 40 percent of N applied during preplant and 60 percent sidedress at the V8 stage. N rate was 135 lbs/A for all treatments. Seven-year yield average and N recovery were highest for the split application (145 bu/A), intermediate for spring preplant and fall N plus nitrapyrin (N-Serve) treatments (139 bu/A), and lowest when N was applied late in October without N-Serve (131 bu/A). The greatest response to split N tended to occur in the wet years (1990 to 1993). Nitrate losses in subsurface tile drainage water, averaged across the four corn/soybean cycles, were greatest for fall N without N-Serve, intermediate for split N application, and least for fall N + N-Serve and spring preplant treatments. Nitrate losses in the soybean year following corn tended to be slightly greater for the spring and split application treatments, compared to the fall treatments. A study on a Webster clay loam Figure 1. Continuous corn yields as affected by time, rate, and method of application, Olmsted County, 1987-90. Check 75 150 150 150 225 N - lbs/A Spring Preplant Spring Preplant Fall Yield bu/A 170 155 140 125 100 95 80 1/2 Spring-1/2 SD at V6 Spring Preplant Time of application and source of N Fall AA* Preplant Planting, Sidedress, Yield N recovery UAN UAN bu/A % None None None None 118 w/N-S, 100 167 63 w/N-S, 80 Dribble, 20 154 48 w/N-S, 80 Coulter, 20 169 60 w/N-S, 60 Dribble, 40 155 46 w/N-S, 60 Coulter, 40 169 56 AA, 100 164 60 AA w/N-S 165 59 Urea bdct incorp. 165 63 UAN bdct incorp. 163 59 Dribble, 40 Coulter, 60 175 65 Broadcast, 40 Coulter, 60 177 73 *w/N-S = with N-Serve
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