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Fluid Journal : Fluid Journal 2008-2009
Table 1. The response of durum, spring wheat, oat, and barley to different rates of N fertilizer. N rate (kg/ha Bu/A Durum Spring wheat Oat Barley 0 38.6 30.8 95.1 41.0 25 40.5 32.7 89.7 52.2 50 52.3 36.5 115.0 70.4 75 52.5 40.2 112.7 62.5 100 59.7 42.5 113.7 85.8 125 60.1 39.2 117.5 81.8 cv (%) 15.3 13.2 5.4 22.7 Contrasts p-values linear 0.0001 0.0022 0.0001 0.0003 quadratic Ns ns ns ns cubic Ns ns ns ns Linear Regression Y intercept 38.8 31.7 94.3 44.6 Slope 0.1889 0.0858 0.2077 0.3376 R2 0.92 0.79 0.68 0.85 N rate (kg/ha) Winter Wheat N rate (kg/ha) Canola 0 33.2 0 20.4 25 38.8 25 27.8 50 51.2 50 31.0 75 56.7 100 37.1 100 57.9 150 38.3 125 59.9 200 41.4 150 61.0 cv (%) 22.3 cv (%) 10.7 p-value <0.0001 p-value <0.0001 Y intercept 21.7 Y intercept 32.1 x2 -0.0006 X2 -0.0016 X 0.2064 X 0.4264 R2 0.98 R2 0.98 Table 2. The response of winter wheat and canola to different rates of N fertilizer on grain yield bu/A assessment of the proposed algorithms. The validation consisted of applying specific amounts of UAN at the 6- to 7-leaf stage in cereals and the mid-bolting stage of canola using rates determined by the algorithms. The results were then compared to actual N rate studies for each crop adjacent to the plot studies where the algorithms were tested. This was to verify how well the algorithms were able to predict the best N rate possible using the N response curves from the adjacent plots as a measure of precision or accuracy Yield responses Responses of durum, spring wheat, oat, and barley to N fertilizer rates were linear and overall response tended to be flat given the high values for the y-intercept (Table 1). The rate of yield increase per kg of N applied (bu/kg N) was 0.2, 0.1, 0.2, and 0.3 for durum, spring wheat, oat, and barley, respectively. With winter wheat and canola, the response to N was quadratic in nature and the optimum N rate was estimated as 133 and 172 kg N/ha, respectively (Table 2). The results for grain yield and grain protein regarding the evaluation of the optical sensor for refining N rates in durum, spring wheat, oat, and barley are presented in Tables 3 and 4. With spring wheat and oat, all N management treatments yielded the same and the sensor was able to reduce the N rates used by an average of 33 percent in spring wheat and 28 percent in oat (Table 3). With barley, the split application of N gave similar yields to FP and yielded more than the reduced N rate treatment (#4 in Table 3), indicating a response to post- emergent applications of UAN. Treatment #7 yielded less than treatment #3 (FP) where 50 percent of the recommended N rate was applied at seeding and the balance determined with the sensor. This was not observed in treatment #8 where 66 percent of the N was applied at seeding and the balance with the optical sensor. However, it should be noted that the N applied was 95 kg/ ha for treatment #8 vs. 64 kg/ha for treatment #7. More refinements are required for the barley algorithm. With durum, applying 50 percent of the recommended N rate at seeding and the balance in-crop yielded less than FP as well as when 66 percent of the N was applied at seeding, regardless of whether or not a uniform rate was used or a rate determined with GreenSeeker®. The results suggest that the level of starter N required for durum to maintain grain yields with post- emergent N applications is at least 66 percent of the targeted rate. The spring wheat algorithm was used for durum and this may have affected the results with the optical sensor. Although the N Rich (#2) and the FP (#3) treatments yielded the same, the yields were lower than N Rich for all other treatments. More refinements to N management in durum are required.
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