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Fluid Journal : Late Spring 2013
13 The Fluid Journal Late Spring 2013 treatment also had the highest level of residual soil NO3-N in late November 2009 (Table 2), which probably accounts for the slightly higher N2O emissions during the non-crop period. Nitrification was probably the dominant pathway of soil N2O loss from applied N fertilizer from this ST, irrigated system based on WFPS being generally <70% both years, except for a short period in early 2010 when WFPS was 80% before N fertilization. The slightly elevated level of residual soil NO3-N at the end of the growing season with the ESNssb Table 2. Residual soil NO3-N in four soil depth increments after corn harvest in 2009 and 2010 and averages over years (no significant interaction between N treatment and years) Sampling Date N treatment* Soil depth 0-15.2 cm 0-30.5 cm 0-61.0 cm 0-91.5 cm kg NO3-N ha-1 25 Nov. 2009 (DOY** 329) Urea 9.1a*** 29.3bc 53.1bc 88.3ab ESNssb 10.6a 62.9a 121.7a 152.0a ESN 11.1a 37.3ab 66.5b 83.9b SuperU 5.1a 15.0bc 34.3bc 52.6bc UAN 6.2a 19.4bc 40.6bc 83.0b UAN+Nf 5.2a 15.0bc 27.3bc 39.8bc UAN+AP 4.6a 13.4bc 27.7bc 57.8bc Blank 2.8a 8.4bc 13.9c 16.3c Check 2.0a 6.2c 11.7c 14.6c 2 Nov. 2010 (DOY 306) Urea 10.2a 19.4a 28.9a 39.1a ESNssb 36.0a 53.4a 64.4a 73.6a ESN 14.6a 24.6a 34.5a 39.8a SuperU 14.1a 32.8a 53.1a 66.1a UAN 14.7a 26.02a 35.7a 44.2a UAN+Nf 18.1a 30.2a 42.2a 50.2a UAN+AP 17.3a 28.1a 40.9a 55.5a Blank 5.4a 9.2a 12.7a 15.9a Check 6.1a 9.6a 14.0a 16.2a Avg. 2009 and 2010 Urea 9.7b 24.3b 41.0b 63.7ab ESNssb 22,6a 63.4a 101.6a 118.7a ESN 13.7ab 29.5ab 49.0ab 63.4ab SuperU 9.6b 23.9b 43.7b 59.4b UAN 10.4ab 22.7b 38.2b 63.6ab UAN+Nf 11.6ab 22.6b 34.7b 45.0b UAN+AP 10.9ab 20.7b 34.3b 56.5b Blank 4,1c 8.8c 13.3c 16.1c Check 4.1c 7.9c 12.9c 15.4c *ESNssb = ESN subsurface band; ESN = polymer-coated urea; SuperU = stabilized granular urea; UAN = urea ammonium nitrate; UAN+Nf= UAN with Nfusion+AP = UAN with AgrotainPlus. **DOY = day of year *** Values within columns followed by the same lower case letter are not significantly different at probability level = 0.05 treatment is consistent with observations by others who have reported slightly elevated residual soil N with polymer- coated urea than with conventional urea. Cumulative daily N2O-N fluxes during the corn growing season are shown in Figure 6 for 2009 and Figure 7 for 2010. A rapid rise in cumulative daily flux levels for urea and UAN was very apparent both years following N application, with SuperU, UAN+Nfusion, and UAN+AgrotainPlus also showing rapid rises in cumulative N2O emissions immediately following N application in 2010. Cumulative growing season emissions were greater in 2010 than 2009 for all N treatments, except for urea, which was similar both years but followed similar relative emission patterns both years. The rise in cumulative daily N2O-N flux was slower for all enhanced efficiency N sources than for urea and UAN both years. The delayed release of N2O-N from ESN until about mid-June was very prominent in 2010. The N2O emissions from the blank (no N applied) treatments that had received 202 kg N ha-1 in previous years was very similar to that from the check treatment that had not had any N applied since 1999. The residual soil NO3-N (Table 3) in the 0- to 15.2-, 0- to 30.5-, and 0- to 61- cm depths was significantly greater in the N source plot area where the blank treatment resided than in the check treatment located in an adjacent plot. Although the residual soil NO3-N was greater in the blank plot area than in the check plot area before corn planting, we did not observe a significant difference (Table 4) in the growing season N2O emissions between the blank and check treatments. A critical soil NO3-N concentration of 5 mg NO3-N kg-1 has been reported in the literature below which N2O emissions may be much reduced, even at high levels of WFPS. In this study, the difference in NO3-N levels between the check and blank treatments in the 0- to 15.2-cm soil depth had disappeared by 20 May 2010 (DOY 140). A soil NO3-N concentration of 5 mg NO3-N kg-1 would equate to 11 kg NO3-N ha-1 in this study, with the blank and check treatments generally having lower NO3-N levels than 11 kg NO3-N ha-1 during the growing season. This may help explain why there was little difference in N2O emissions between the blank and check during the growing season. This observation between the blank and check treatments was observed both years. This would tend to indicate in our system that the fresh application of N fertilizer was stimulating microbial activity and the nitrification process resulting in N2O loss from the N fertilizer applied. The fact that WFPS (Figure 3) was generally <70% most of the growing season would support the theory that nitrification is the main pathway of N2O loss at this location. Nitrous oxide emissions for the two growing seasons (5 May to 29 September 2009 and 6 May to 29 September 2010) are reported in Table 4, with a significant N source x year interaction. This interaction
Early Spring 2013