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Fluid Journal : Fluid Journal 2005-2007
EARLY SPRING 2007 Fluid Journal 21 Glacial Sites Total till Loess Outwash Number 321411 7 N responsive 28149 5 Preplant yield = Split yield 16 7 7 2 Preplant yield < Split yield 8 4 1 3 Preplant yield > Split yield 4 3 1 0 seemed to recover completely. In addition, rainfall later in the season did not appear adequate to move sufficient N into the active root zone to overcome the early-season deficiency. These results lend credence to the suggestion that N banded at 20 to 30 lbs/A close to the row in starter may provide sufficient N for critical early-season growth until sidedressed N can be applied. Continuous corn Experiments were conducted in southeastern Minnesota from 1987 through 1997 to determine optimum N application method for continuous corn. An experiment on a Port Byron silt loam soil in Olmsted County from 1987 to 1990 provided information on N efficiency and water quality in addition to corn production (Figure 1).Yields were optimized when N was applied at 150 lbs/A. Highest yield and N efficiency and lowest nitrate-N concentration in the soil water at a 5-foot depth in September 1990 were obtained with the spring preplant treatment. Fall or split application of N did not improve corn yield and N efficiency, but did increase the potential for greater leaching losses of nitrate. Similarly, using excess N (225 lbs/A) did not increase yields with corn on medium- and fine- textured soils in southern Minnesota. Preplant vs. split Experiments comparing spring preplant N with split N application for corn were conducted at 32 sites in southern Minnesota from 1989 to 1992. The sites were located on 14 fine-textured glacial-till soils, 11 medium-textured loess soils, and 7 coarse-textured, outwash (sandy) soils. Previous crops at these sites included primarily soybeans but also corn, oats, and rye. Yield differences between the preplant and split application strategies are summarized in Table 1. Corn grain yield responded to N at 28 of the 32 sites (88%). Preplant application was equal to split application at 16 of the 28 responding sites (58%). Split application was superior to preplant application at 8 sites (28%). In all cases, excessive growing season rainfall and/or sandy soils occurred where split N application out-yielded preplant application. Preplant application was superior to split application at 4 sites (14%). The disadvantage for split application generally occurred on the glacial- till soils when above-normal, early- season rainfall was accompanied by insufficient uptake. A portion of the N applied midway between the corn rows apparently remained positionally unavailable. Rainfall Examples of how rainfall affected corn yield response to method of application on fine-textured soils in south central Minnesota are shown in Table 2. Soybeans were the previous crop on both sites. The first year, at a site in Waseca County where May/ September rainfall was 56 percent above normal, yields were increased an average of 11 bu/A by the split- applied treatments. It is likely that a significant portion of the broadcast preplant-applied N was denitrified in this wet year. In the second year, at a site in Blue Earth County where rainfall was only 16 percent above normal, yields were decreased an average of 11 bu/A by the split-applied treatments. Under these conditions, some N- deficiency symptoms were visible at the time of the sidedress application (12-inch tall corn). Apparently the initial 30-lb/A preplant broadcast rate was insufficient to sustain an adequate supply of N to the plant early in the season. The plants never Time of application Year Preplant 12-inch corn 1991 1992 N rate (lbs/A) bu/A 0 0 84 107 30 0 129 132 60 0 143 144 30 30 161 141 90 0 158 156 30 60 157 137 120 0 165 164 30 90 182 153 Advantage for split = +11 -11
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