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Fluid Journal : Late Spring 2013
11 The Fluid Journal Late Spring 2013 N2O Fluxes increased within days following the application of all N sources, except for ESN, which had a delayed release of N2O in 2009 (Figure 4) and 2010 (Figure 5). N2O fluxes were highest the first 30 days following N fertilization with urea and UAN when WFPS was highest and then declined to near background levels in ~45 days. Similarly, N2O-N fluxes from Super U increased within days following application but were of a smaller magnitude than for urea and UAN, then decreasing to background levels in ~45 days both years. This trend corresponds to the trend of soil NO3N levels being lower for Super U in 2010 in the 0- to 15.2- and 0- to 30.5-cm soil depths during June than urea and all UAN treatments (Table 1). Also, N2O-N flux peaks resulting from UAN +Nfusion and UAN +AgrotainPlus application occurred within days of application but were of a much smaller magnitude than those observed for UAN alone, even though the measured soil NO3-N levels were similar to UAN (Table 1). Nitrous oxide fluxes from surface banded ESN and ESN subsurface banded (ESNssb) followed a different pattern, remaining low until mid-June when N2O-N fluxes started to increase both years (Figures 4 and 5). In 2010, the soil NO3 levels for the ESN treatments were generally less than for the other N sources during the early part of the growing season following N application. On 29 July, the ESNssb treatment had higher soil NO3-N levels than the other treatments (Table 1). The N2O flux peaks from the ESN treatments during the growing season were greater in 2010 (Figure 5) than in 2009 (Figure 4), possibly due to a faster release of the urea N from the polymer-coated granule because of higher soil temperatures in 2010 than in 2009 (Figure 1). The N2O peaks from ESN application tended to be higher than those from the other N sources during mid-June through August but tended to be smaller and of shorter duration than the peaks observed just after urea or UAN application. The late- applied to the corn crop with a growing season total (precipitation + irrigation) of 656 mm. Annual precipitation totaled 273 mm in 2010, with a May through October corn growing season total of 129 mm. In 2010, the corn received 396 mm of irrigation water, with a growing season total (precipitation + irrigation) of 525 mm. Water-filled pore space (WFPS) ranged from ~65 to 80% from early May to mid- June in 2009 (Figure 3). In 2010, WFPS ranged from ~72 to ~82% in May, then declined to a low of ~50% during June and stabilized between 60 and 70% during the rest of the growing season. During the winter months, WFPS declined to a low of ~35% in December 2009 to February 2010. The WFPS tended to increase following precipitation and irrigation events (Figure 2) and averaged 67.8 and 65.1% during the 2009 and 2010 growing seasons (May to September), respectively. Table 1. Soil NO3-N levels in three depth increments from May 20 to July 29, 2010 from the N source treatments (significant N treatment x sampling day interaction teraction). N treatment* 20-May 3-Jun 16-Jun 30-Jun 15-Jul 29-Jul DOY140** DOY 154 DOY 167 DOY 181 DOY 196 DOY 210 0-15.2 cm soil depth, kg NO3-N ha-1 Urea 9.6a*** 31.2a 24.2abcd 25.1bc 7.1a 4.8bc ESNssb 11.7a 13.3bc 11.6 cd 14.2cd 9.5a 26.7a ESN 6.3a 11.4c 8.6d 11.9cd 6.1a 8.2b SuperU 8.8a 17.5bc 18.2bcd 17.9bcd 15.0a 4.9bc UAN 8.3a 33,5a 33.9ab 28.9ab 21.0a 8,8b UAN+Nf 7.8a 37.2a 41.1a 30.7ab 16.4a 6.1bc UAN+AP 9.2a 24.6ab 30.0abc 40.7a 16.7a 6.3bc Blank 8.8a 11.4c 7.1d 6.2d 3.7a 4.3bc Check 7.2a 9.9c 8.0d 5.6d 3.3a 3.5c 0-30.5 cm soil depth, kg NO3-N ha-1 Urea 20.5a 40.9ab 44.3ab 42.5ab 12.0a 10.3b ESNssb 22.2a 21.0cd 22.1bcd 21.3cd 13.9a 31.7a ESN 13.9a 19.1d 17.9cd 18.3d 9.2a 11.8b SuperU 18.8a 27.1cd 31.4ab 29.1bcd 20.6a 8.8b UAN 19.8a 43.3ab 52.1a 38.5abc 28.5a 15.2ab UAN+Nf 17.8a 47.4a 52.7a 44.3ab 22.2a 10.3b UAN+AP 20.8a 33.7bc 42.5ab 50.2a 20.4a 9.7b Blank 20.4a 18.8d 16.1d 12.0d 6.6a 7.5b Check 15.2a 18.3d 16.7cd 11.5d 6.7a 7.6b 0-61.0 cm soil depth, kgNO kg NO3-N ha-1 Urea 39.8a 57.3ab 65.6ab 70.6a 25.3bcd 25.0a ESNssb 44.7a 36.6de 38.2bcd 39.1bcd 26.1bcd 37.5a ESN 27.6a 34.4cde 33.3cd 35.4cd 18.6bcd 16.0a SuperU 32.9a 43.6bcd 49.7abc 52.8abc 35.0ab 14.3a UAN 37.9a 60.3a 72.5a 58.6ab 45.4a 24.2a UAN+Nf 40.4a 66.6a 69.9a 70.1a 36.3ab 16.0a UAN+AP 44.4a 51.7abc 59.6ab 69.3a 31.6abc 14.0a Blank 44.1a 34.0de 31.3cd 27.7d 14.7cd 11.2a Check 26.2a 28.1e 26.6d 21.3d 12.3d 12.4a * ESNssb = ESN subsurface band; ESN = polymer-coated urea; SuperU = stabilized granular urea; UAN = urea-ammonium nitrate; UAN+Nf = UAN with Nfusion; UAN+AP = UAN with AgrotainPlus. ** DOY, day of year. *** Values within a column followed by the same lower-case letter are not significantly different at the probability level = 0.05. "Corn grain yields were not different among N sources but greater than treatments with no N applied"
Early Spring 2013