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Fluid Journal : Fluid Journal 2002-2004
Fall 2004 Fluid Journal 2 The optimal N rate data in Figure 1 also show the variability among sites. University scientists usually set their recommendations slightly higher than the response data suggest. This cushions the farmer from risk of yield and profit loss under unforeseen conditions. In this case, an N recommendation of 120 lbs/A was actually more than was needed for optimal yields at 10 of 13 sites. Based on these yield responses to N in small-plot studies, the 120-lb N rate (recommended by the University of Minnesota for 150 to 174 bu/A corn grown on these soils) was enough to optimize yield and profit at 10 of 13 sites. In fact, the yield maximum at 7 of 13 sites was reached at an N rate of less than 90 lbs/A. Field-size strip studies. Spring or sidedress application was used at 10 sites and fall anhydrous ammonia plus N-Serve was used at 3. N was applied at rates of 0, 60, 90, 120, and 150 lbs/A at 10 sites and included 180 lbs/A at 3 sites. N was applied by the dealer or farmer in strips matching the applicator width (30 to 60 ft). Strip length ranged from about 400 to more than 1200 feet. At each field strip site, tillage, planting, pesticide application, and hybrid and planting rate selection were performed by the farmers. All yield data were collected by the farmer and/or consultant. EONR ranged from 55 to 169 lbs/A and averaged 100 lbs/A for the 13 field- size strip studies. YEONR was 151 bu/A. As with the small-plot studies, these field-size experiments demonstrate the Table 1. Corn yield, apparent N recovery by corn, economic return to fertilizer N and N-serve, and nitrate-N loss to subsurface drainage as affected by time of N application and N-Serve. Nitrate-N Grain N Economic loss in Treatment N-Serve yield recovery return drainage bu/A % $/A lb/A/inch Fall No 131 31 67 3.8 Fall Yes 139 37 78 3.1 Spring No 139 40 85 3.1 Split No 145 44 97 3.3 7-year avg. Figure 2. Effect of fertilizer N rate on average corn yield and EONR from 13 small plot field-size strip studies in Minnesota. site-to-site variability when finding an optimal N rate for corn. But in total, a 120-lb/A N rate was enough to optimize corn yield and profit at 11 of 13 sites. On 4 sites, yield and profit were maximized at N rates of 90 lbs/A and less. Small plots vs. field-size strip. Corn yields for N rates of 0, 60, 90, 120, and 150 lbs/A were pooled for all 13 small- plot studies to find the EONR for all 13 sites. The same yield pooling procedure was used for the field-size studies. Although the procedures were different for these two types of field studies, the results were remarkably similar (Figure 2). EONRs for the small plots and field size were 105 and 99 lbs/A of N, respectively. The YEONR was greater in the small plots (173 bu/A) than in the field-size strips (151 bu/A) due to very high yields in the small plots in southeastern Minnesota in 1989, 1998, and 1999 when field-size strip studies were not performed. This shows that plot size used in N rate calibration trials does not affect N fertilizer rate recommendations. Primary conclusions from these 26 site-years on-farm studies: EONRs averaged across small plots and field-size strips were 86 and 100 lbs/A, respectively. When yield data were pooled, EONRs were 105 and 99 lbs/A, respectively. Yields were 173 and 151 bu/A, respectively. Although yield variability among the sites was significant, it was not nearly as dramatic as the variability among EONRs across the sites. EONR ranged from 0 to 140 lbs/A in small plots and from 55 to 169 lbs/A in field-size strips. Plot size used in N rate calibration research did not affect N fertilizer rate recommendations. N rate recommended by the University of Minnesota achieves
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