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Fluid Journal : Fluid Journal 1993-1995
2 Fluid Journal Summer 1994 from 29 to 43 percent by reducing N rate from 100 percent of optimum to 40 percent. However, in reducing N rate to 40 per-cent of optimum, grain yield would be reduced from 159 to 139 bu/A or a 20-bu/A yield loss (Table 1). This would be unacceptable to a producer from a profitability standpoint, even though N rate could be reduced from 150 to 60 lbs/A. Thus, if regulations forced such an event, producers would obviously have to raise their grain prices to maintain profitability. This would ultimately be felt at the dinner table. The more desirable alternative to head this off is to fine-tune all the tools we have available for increasing N-use efficiency. Improving prediction of N needs, which includes mineralization, is a good place to begin. Better synchronization of applications to the times of plant need, where grain yield is maximized in relation to N uptake, is another area needing work. Frequent N application keeps N in the surface of the soil where water and nitrogen are being used. New plant sensing techniques and soil nitrate-N monitoring will probably lead the way to improved N-use efficiency in the future. Shallow depth Nitrogen uptake is associated with water uptake. Under the irrigation used in this study, which maintained optimum moisture in the top one to two feet of soil, N efficiency of nitrates found below two feet appeared to be quite low. At the optimum N rate, the crop in the studies had 150 lbs/A of N fertilizer, 72 lbs/A of soil N, and 75 to 100 lbs/A of mineralizable N available at the beginning of each year. Dr. Sander is extension soils specialist at the University of Nebraska. 0 100 120 140 160 10.7 bu 9.6 8.1 6.9 5.5 4.1 2.8 1.4 Optimum N Rate = 150lbs N/A Maximum Yield = 167bu/A Applied N (lbs/A) Corn Grain Yield (bu/A) 50 100 150 200 Mean of 10 irrigated Corn Sites, 1988-90 Table 1. Effect on applied N on irrigated corn yield across ten locations in Nebraska, 1988-90. Table 2. Corn grain N-use efficiency of applied N, based on 0.9 lbs of N per bushel from ten irrigated experiments in Nebraska, 1988-90. 20 100 90 80 70 60 50 40 Percent of Optimum N Rate ($2.50/bu Corn, $0.15/LbN) Rate 25 30 35 40 45 Corn Grain
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