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Fluid Journal : Fluid Journal 1993-1995
Spring 1994 differences in losses among the three source/methods beyond seven days after application. Excluding outlier plots In two of the fertilizer treatments (urea-three replications, UAN-two replications), the total amount of ammonia trapped in one of the three replications was significantly greater than the other two. Using the Q test, it was shown that there was greater than 80 percent probability that these two replications were outlier plots. By eliminating these outlier plots in these two N source/method treatments, the least significant difference for the total amount of ammonia N volatilized dropped from 6.5 to 1.0 lbs/A. This also resulted in significant differences among all three treatments in the total amount of N volatilized (Figure 2). If the outlier plots are excluded from the average, total ammonia volatiliza- tion lost from urea dropped to 25.9 lbs/A and dribbled UAN dropped to 13.1 lbs/A. Loss from urea was 21.6 percent of the 120 lbs/A applied. Loss from UAN was only 10.9 percent. Again, the most significant difference in losses among the three source/methods occurred during the first seven days after application. Stress hurts During the 1993 trials, rainfall in April was excessive with over eight inches- twice the normal. May, June, July, and August were very dry with approximately two inches of rain per month-roughly half the average for May, June, and July, and two-thirds the average for August. Thus, stress caused by dryness and varying depth to bedrock were responsible for the low and varying yields as seen in Figure 3. Weed competition was also severe because of the ineffectiveness of herbi- cides. Dribbled UAN again exceeded all other source/methods, this time in yield returned. Precision counts Ammonia samplers were placed in the center of the 50-meter (164-foot) diameter plots. One background sampler was placed at the edge of each of the three treatment fields, at least 100 meters from the nearest urea- containing treatment. Soils in all fields were Hublersburg silt loams. Fields had been in no-till for at least two years. Available P and K levels and soil pH were in the optimum range. Nitrogen fertilizer was applied at the rate of 120 lbs/A on May 12 when corn plants were one to two inches tall. Soil surface covered with crop residue when treatments were applied ranged from 60 to 80 percent. Dr. Fox is professor of Soil Science and Piekielek is research support assistant at Penn State University. !
Fluid Journal 1996-1998