Increasing demand for food and agricultural products

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1 TECHNICAL REPORTS: ATMOSPHERIC POLLUTANTS AND TRACE GASES Atmospheric Emissions of Nitrous Oxide, Methane, and Carbon Dioxide from Different Nitrogen Fertilizers K. R. Sistani,* M. Jn-Baptiste, N. Lovanh, and K. L. Cook Alternative N fertilizers that produce low greenhouse gas (GHG) emissions from soil are needed to reduce the impacts of agricultural practices on global warming potential (GWP). We quantified and compared growing season fluxes of N 2 O, CH 4, and CO 2 resulting from applications of different N fertilizer sources, urea (U), urea-ammonium nitrate (UAN), ammonium nitrate (NH 4 ), poultry litter, and commercially available, enhanced-efficiency N fertilizers as follows: polymer-coated urea (ESN), SuperU, UAN + AgrotainPlus, and poultry litter + AgrotainPlus in a no-till corn (Zea mays L.) production system. Greenhouse gas fluxes were measured during two growing seasons using static, vented chambers. The ESN delayed the N 2 O flux peak by 3 to 4 wk compared with other N sources. No significant differences were observed in N 2 O emissions among the enhanced-efficiency and traditional inorganic N sources, except for ESN in Cumulative growing season N 2 O emission from poultry litter was significantly greater than from inorganic N sources. The N 2 O loss (2-yr average) as a percentage of N applied ranged from 0.69% for SuperU to 4.5% for poultry litter. The CH 4 C and CO 2 C emissions were impacted by environmental factors, such as temperature and moisture, more than the N source. There was no significant difference in corn yield among all N sources in both years. Site specifics and climate conditions may be responsible for the differences among the results of this study and some of the previously published studies. Our results demonstrate that N fertilizer source and climate conditions need consideration when selecting N sources to reduce GHG emissions. Copyright 2011 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. J. Environ. Qual. 40: (2011) doi: /jeq Posted online 4 Oct Received 7 June *Corresponding author (karamat.sistani@ars.usda.gov). ASA, CSSA, SSSA 5585 Guilford Rd., Madison, WI USA Increasing demand for food and agricultural products directly relates to increased greenhouse gas (GHG) emissions, particularly for the three primary gases associated with agriculture nitrous oxide (N 2 O), carbon dioxide (CO 2 ), and methane (CH 4 ) (Follett et al., 2005). The atmospheric concentrations of these gases have increased significantly and are projected to continue to do so according to the report by the Intergovernmental Panel on Climate Change (IPCC, 1996). The total GHG emission for the United States in 2004 was estimated as 84.6% from CO 2, 7.9% from CH 4, 5.5% from N 2 O, and 2% from other sources (USEPA, 2005). A mole of CO 2, CH 4, and N 2 O is defined to have a global warming potential (GWP) of?1, 21, and 300, respectively. Therefore, even though non-co 2 GHGs represent only a small percentage of the GHG mixture, they can make a sizable contribution to the total GWP (Robertson and Grace, 2004). Agriculture is responsible for 7.7 Tg of CH 4 or 2% of the total GHG emissions in the United States, derived mainly from animal production and manure handling and storage. Soils are considered to be sources and sinks for many GHGs. For example, the net balance of CH 4 flux depends on two processes methanogenesis (production by microorganisms under anaerobic conditions) and methanotrophy (consumption by microorganisms) in the soil (LeMer and Roger, 2001). Preventing the emission of one molecule of CH 4 or N 2 O has the same effect as sequestering?20 and 300 molecules of CO 2, respectively. Preindustrial levels of atmospheric CO 2 concentration were estimated at 290 to 295 ppm (μg L 1 ) (Bolin et al., 1979). However, it is predicted that the CO 2 concentration could reach 500 ppm (μg L 1 ) by the end of the 21st century (IPCC, 1996). Nitrogen is one of the most important nutrients required for the survival of all living organisms and it is ubiquitous in the environment. Commercial inorganic N fertilizers and organic N sources, such as animal manure, stimulate N losses mainly in the form of N 2 O and volatilization through biochemical processes of nitrification (aerobic) and denitrification (anaerobic) (Mosier et al., 2006; Halvorson et al., 2008; Snyder et al., 2009). Eghball (2002) and Edmeades (2003) also reported that animal manure application to soil as an alternative plant nutrient may be very beneficial; however, manure addition to soil may increase the production of GHG emissions (Chang et al., 1998; Hayakawa, et. al., 2009; Sistani et. al., 2010). Of all the USDA ARS, 230 Bennett Ln., Bowling Green, KY Contribution from USDA ARS, Bowling Green, KY. Trade names and company names are included for the benefit of the reader and do not imply any endorsement or preferential treatment of the product by the authors or USDA ARS. Assigned to Associate Editor Martin H. Chantigny. Abbreviations: DOY, day of year; ESN, polymer-coated urea; GHG, greenhouse gas; GWP, global warming potential; UAN, urea ammonium nitrate; WFPS, water-filled pore space. 1797

2 sources of global warming potential in cropping systems, none are more poorly quantified than N 2 O production. This represents a big knowledge gap regarding the role of N 2 O in global warming, considering the fact that its GWP is?300 times greater than that of CO 2 in agricultural systems (Robertson and Grace, 2004). Nitrous oxide is oxidized in the stratosphere to form other nitrogen oxides (NO x ) that participate in photochemical processes that destroy atmospheric ozone (Duxbury, 1994). Human-induced emission of N 2 O is presently increasing by?150 Tg N yr 1 to provide food and energy for the growing world population (Mosier et al., 2002). Commercially available enhanced-efficiency N fertilizers, such as those containing nitrification inhibitors, urease inhibitors, and slow-release fertilizers, can potentially increase N-use efficiency by crops and reduce N losses. The USEPA (2009) reported that?67% of the total U.S. N 2 O emissions are credited to agriculture. Recent reports indicate that N sources may impact N-use efficiency and N loss as N 2 O (Delgado and Mosier, 1996; Bolan et al., 2004; Akiyama et al., 2010; Halvorson et al., 2010a,b; Venterea et al., 2005, 2010). Although several researchers have evaluated the impact of enhanced-efficiency N fertilizers on GHG (mainly N 2 O) emissions, there are still many questions regarding these products, such as their influence on all three major GHG emissions, including CO 2 and CH 4. The impact of combining urease inhibitors and nitrification inhibitors with animal manure (e.g., poultry litter) on GHG emissions is unknown. Therefore, the objective of this study was to quantify N 2 O, CH 4, and CO 2 emissions from application of several commonly used inorganic N fertilizers urea, urea-ammonium nitrate (UAN), ammonium nitrate (NH 4 ), and commercially available, enhanced-efficiency N fertilizer sources as follows: polymer-coated urea (ESN), SuperU, UAN + AgrotainPlus, plus poultry litter, and poultry litter + AgrotainPlus under no-till corn production (Super U and AgrotainPlus contain urease and nitrification inhibitors). Materials and Methods Field experiments were conducted in 2009 and 2010, in which corn was grown for grain on a Crider silt loam soil (fine-silty, mixed, active, mesic, Typic Paleudalfs) with 2 to 4% slope near Bowling Green, KY, USA ( N; W). The region has a temperate climate with a typical mean temperature of 14.5 C and rainfall of 1300 mm yr 1. This study was established as no-till under continuous corn production. The soil textural analysis was 3.1% sand, 65.3% silt, and 31.6% clay, soil organic matter 25 g kg 1, and ph 5.8. The average residual soil inorganic N measured in each spring before treatment applications were 8.2 mg kg 1 (NH 4 N) and 4.0 mg kg 1 ( N) in 2009; and 72.5 mg kg 1 (NH 4 N) and 3.4 mg kg 1 ( N) in We quantified and compared growing season fluxes of N 2 O, CH 4, and CO 2, resulting from application of 168 kg N ha 1 from six inorganic chemical N fertilizers and poultry litter (based on 55% N availability for plant uptake). The nine treatments evaluated in this study consisted of dry granular urea (46% N), liquid UAN (28% N), ammonium nitrate (NH 4 ) (34% N), ESN (44% N), SuperU (46% N), UAN + AgrotainPlus (28% N), poultry litter (3% N), poultry litter + AgrotainPlus (3% N), and a control treatment that received no chemical fertilizer or poultry litter. The ESN is a controlled-release, polymer-coated urea, with a registered trademark of Agrium Advanced Technologies, Loveland, CO. The ESN is permeable to water and gradually releases N during the growing season with faster release with increasing moisture and temperature. The SuperU is a registered trademark of Agrotain International, St. Louis, MO, which contains urease [N-(n-butyl)-thiophosphoric triamide] and nitrification (dicyandiamide) inhibitors that are uniformly distributed through the granule during the manufacturing process. The AgrotainPlus added to UAN and poultry litter is also a registered trademark of Agrotain International and contains the same urease and nitrification inhibitor as SuperU. AgrotainPlus was mixed with poultry litter (0.5 g kg 1 poultry litter) and UAN (9.5 g L 1 ) before application. The application rate for the AgrotainPlus was suggested by the manufacturer (Agrotain International). Corn (DeKalb Roundup Ready/Bacillus thuringiensis [RR/ BT]) was planted (76-cm row spacing) in 3.1 m by 6.1 m plots on 27 Apr. (day of year [DOY] 117) 2009, and 20 May (DOY 140) Nitrogen treatments were applied 4 d after corn seeding: 1 May 2009 (DOY 124) and 24 May 2010 (DOY 141). All N treatments, except UAN and UAN+AgrotainPlus, were surface broadcasted by hand without incorporation. The UAN and UAN+AgrotainPlus were applied with a six-nozzle, handheld boom attached to a CO 2 -pressurized backpack sprayer. Nitrogen treatments were applied on the same plots each year after corn planting. Corn was harvested as grain in September by handpicking the two center rows of each plot for a harvest area of 1.5 m by 6.1 m. The experimental design was a randomized complete block with three replications. Greenhouse gas emissions were measured during the growing seasons using static, vented chambers (Livingston and Hutchinson, 1995) and a gas chromatograph analyzer. Measurement of N 2 O, CO 2, and CH 4 fluxes were made from 4 May (DOY 124) to 22 Sept (DOY 265), and 21 May (DOY 141) to 24 Sept. (DOY 267) 2010, following the same procedures reported by Mosier et al. (2006). Measurements were generally made two to three times per week during the growing seasons, midmorning of each sampling day. The chambers used were made of aluminum and measured 10 cm tall. At each flux measurement time, the chambers were placed in a water channel on fixed anchors (38 cm wide and 102 cm long). After treatment applications, one anchor was forced into the ground to a depth of 15 cm in each plot such that they were flush with the soil surface. Anchors were installed each year 1 to 3 d before beginning measurements and were not removed until fall. The anchors were placed such that the 102-cm length was parallel to the corn rows. Plants emerging inside the measurement area were removed. Duplicate flux measurement sites were included within each replicate of each treatment plot for a total of six gas measurements per treatment each sampling date. Air samples (40 ml) from inside the chambers were collected by syringe at 0, 15, and 30 min after the chambers were seated on the anchors. The air samples were injected into 20-mL evacuated vials that were sealed with gray butyl rubber septa. Samples were analyzed with a gas chromatograph (CP-3800, Varion, Inc., Palo Alto, CA) equipped with a thermoconductivity detector, flame ionization detector, and electron capture detector for quantification of CO 2, CH 4, and N 2 O, respectively. Quality control standards were analyzed every 25 samples during the analysis of unknowns. Fluxes were calculated for each gas from the linear or nonlinear 1798 Journal of Environmental Quality Volume 40 November December 2011

3 (Hutchinson and Mosier, 1981) increase in concentration (selected according to the emission pattern) in the chamber headspace with time as suggested by Livingston and Hutchinson (1995). To calculate the cumulative growing season fluxes, estimates of daily N 2 O, CO 2, and CH 4 emissions between sampling days were calculated using a linear interpolation between adjacent sampling dates. Volumetric soil water content (0- to 15-cm depth) and soil temperature (15-cm depth) were monitored at each gas sampling event using 5TM soil moisture and temperature probes (Decagon Devices Inc., Pullman, WA). Water-filled pore space (WFPS) was calculated according to the soil bulk density (measured by core method) at 0- to 15-cm depth and a particle density of 2.65 Mg m 3 (Linn and Doran, 1984). Precipitation data were collected from a nearby (1 km) weather station (Western Kentucky University Research Farm) during the growing seasons. Differences in growing season cumulative GHG emissions among N treatments and years were determined by analysis of variance using PROC GLM procedure (SAS Institute, 2001). Blocks were considered as random factor and year as repeated measurement. All statistical comparisons were made at α = 0.05 probability level using Fisher s protected least significant difference to separate treatment means. Results and Discussion Environmental Factors Figures 1 and 2 show air and soil temperatures, WFPS, and daily growing season precipitation in the 0- to 15-cm soil depth at the GHG sampling dates in 2009 and 2010, respectively. In 2009, total precipitation during corn growing season (May October) was 835 mm, which was 189 mm more than 2010 (646 mm). Soil temperature followed the air temperature pattern, with lower than 20 C in early May followed by a high of 26 C in early July and then stayed lower than 25 C the rest of the sampling period in In 2010, soil temperature was higher than 2009 during the first 3 wk after N applications (Fig. 1, 2). The WFPS is a practical index of soil aeration, which greatly impacts the activities of aerobic or anaerobic microorganisms with regard to nitrification or denitrification following N application. In both years during the early sampling dates (May and June), WFPS was more than 60%, whereas during midseason (July August), WFPS was less than 60% (Fig. 1, 2). Average WFPS during the sampling periods were 66% and 45% for 2009 and 2010, respectively. Nitrous Oxide Fluxes Since the interaction between N source and year for all three gases was significant, results are presented separately by year. Environmental factors, such as precipitation and temperature, may have caused the significant interaction. The average precipitation and air temperature for the 10 d following treatment applications were 55.1 mm and 17.0 C for 2009, whereas they were 16 mm and 24.2 C for Daily N 2 O fluxes increased rapidly following the application of all N treatments (except ESN), particularly poultry litter, NH 4, and UAN in 2009 (Fig. 3), and poultry litter Fig. 1. Soil temperature and water-filled pore space in 0- to 15-cm soil depth, air temperature, and rainfall collected daily during the growing season of DOY = day of year. in 2010 (Fig. 4). Nitrous oxide fluxes were highest the first 25 d following N fertilization for most of the treatments, except ESN (2009), and then declined to near background levels in?45 d. The N 2 O flux from ESN was delayed by 2 wk and then increased to maximum in?45 d after application in 2009 (Fig. 3). Except for poultry litter, the daily fluxes of N 2 O were smaller in magnitude in 2010 than The smaller N 2 O fluxes may be attributed to lower WFPS in 2010 than 2009 (Fig. 1, 2) in the first 45 d after treatment application. This suggests that soil condition may have been anaerobic and dominated by denitrification processes in The daily fluxes of N 2 O were greatest for poultry litter, followed by NH 4, UAN, and ESN in Sistani et al.: Nitrous Oxide, Methane, Carbon Dioxide Emissions from N Fertilizers 1799

4 Fig. 2. Soil temperature and water-filled pore space in 0- to 15-cm soil depth, air temperature, and rainfall collected daily during the growing season of DOY = day of year. both 2009 and The loss of N 2 O from poultry litter was consistently greater in both years. We speculate that N 2 O was lost during the process of mineralization of N in litter since most of the litter N is in organic or NH 4 N forms. Chantigny et al. (2010) reported greater N 2 O emissions from liquid swine manure application to a loamy soil. They suggested that apart from WFPS, C availability likely had more influence on N 2 O emissions from the loam soil. Hence, this may have contributed to the high N 2 O emissions from poultry litter compared with inorganic N fertilizers in this study since poultry litter contains a high level of available C, which could stimulate microbial activities. Hayakawa et al. (2009) also reported that N 2 O emission rates from organic fertilizer treatments were larger than that from chemical fertilizer treatments, possibly because organic C stimulated denitrification. They measured the highest N 2 O flux from pelleted poultry manure after a rainfall following fertilization. Addition of AgrotainPlus to litter or UAN did not impact the quantity of N 2 O fluxes (Fig. 4). This is in contrast with Fig. 3. Daily N 2 O flux from day of year (DOY) 121 through 265 (2009) and DOY 141 through 266 (2010) of the growing seasons for the various N sources indicated. Nitrogen treatments were applied at rate of 168 kg N ha 1 on DOY 121 (2009) and DOY 141 (2010) without incorporation. results obtained by Halvorson et al. (2010a), perhaps because of differences such as rain-fed vs. irrigated, broadcast vs. band application, soil properties differences such as soil ph, soil texture, soil organic matter, and other environmental factors, such as air temperature and rainfall. Cumulative N 2 O fluxes for the growing seasons are shown in Fig. 5 for 2009 and Fig. 6 for Cumulative N 2 O flux values for 2009 tended to be greater for 2010 with 168 kg N ha 1 applied. The cumulative N 2 O fluxes were the same for Super U, UAN, and urea and were significantly smaller than ESN, NH 4, and poultry litter in 2009 (Fig. 5). The cumulative daily N 2 O flux values were smaller in 2010 compared with 2009, except for poultry litter (Fig. 6). We think that similar to daily fluxes of N 2 O, the cumulative fluxes were greatly influenced by environmental factors, such as soil temperature and soil moisture (WFPS). The significant rainfall precipitation the same day or the day after treatment applications may have helped urea become dissolved in the water and percolate into soil quickly, resulting in less N losses as N 2 O and volatilization, while neutralizing the advantage of SuperU, which contains urease inhibitor. Leaching of N to deeper soil sections may have also contributed to less N 2 O emission in the case of NH 4, UAN, and UAN+AgrotainPlus. In both years, the enhanced-efficiency N sources were not effective in reducing N 2 O-N flux compared with urea and UAN, but SuperU was less than NH 4 in However, other researchers, such as Halvorson et al. (2010a,b), have reported significant reduction of N 2 O-N fluxes credited to enhanced-efficiency N sources Journal of Environmental Quality Volume 40 November December 2011

5 Poultry litter produced the greatest growing season N 2 O-N emissions for both 2009 and However, warmer temperature, 24.2 C, average of the 10 d following litter application in 2010 in contrast to 17 C during the same time in 2009, may have caused greater emission in The higher temperature may have stimulated greater microbial activities and resulted in greater mineralization of organic N in the litter, resulting in greater losses in The percent N 2 O-N emission resulting from the application of N fertilizer or poultry litter was calculated for each treatment after correction for the N 2 O-N emission from control treatment (no N added). This was done by dividing the difference between N 2 O-N emissions from N-applied treatments and control by the quantity of N applied (fertilizer or poultry litter), then multiplying by 100 to obtain the percentage. The N 2 O-N emissions as a percentage of N applied (fertilizer or poultry litter) for the cumulative growing season were: Super U (0.91%), UAN (1.6%), ESN (2.6%), urea (1.2%), NH 4 (2.8%), and poultry litter (3.2%) for Except for poultry litter, the percentages were smaller in 2010 as follows: Super U (0.48%), UAN (0.36%), ESN (1.4%), urea (0.4%), NH 4 (0.6%), and poultry litter (5.8%). Compared with the default 1% Tier I methodology of IPCC (De Klein et al., 2006), which is used to estimate yearly N 2 O-N emissions from N fertilizer application, in our study, the average cumulative growing season N 2 O-N emissions from application of 1 kg N fertilizer (poultry litter not included) was greater in 2009 (1.8%) than 2010 (0.65%). However, many researchers have reported a range of 0.16 to 1.7% N 2 O emissions per kilogram of N applied as fertilizer (Adviento-Borbe et al., 2007; Rochette et al., 2008; Halvorson et al., 2010a). For example, Halvorson et al. (2010a) reported that N 2 O-N loss as a percentage of N applied was 0.3% for urea, with all other N sources used in their study (e.g., UAN, Super U, ESN) having lower losses. Grain Yield In 2009 and 2010, there was a significant increase in corn grain yield with the application of 186 kg ha 1 when compared with control treatment. There was no significant difference in grain yield among all N sources in both years (Table 1). However, averaged across all N sources, corn grain yield (10.5 Mg ha 1 ) in 2009 was greater than average yield (7.9 Mg ha 1 ) in 2010 mainly due to higher precipitation and greater soil moisture in 2009 than This also may have caused the significant N source year interaction. Nitrous oxide emissions per unit of corn grain yield for all N sources are also presented in Table 1. Even though grain yield was the same among N sources in 2009, there were differences in the N 2 O fluxes per unit (Mg) of grain yield. However, in 2010, all N sources, except poultry litter, had similar N 2 O emissions per unit grain yield. These results demonstrate that N source and climate conditions are critical factors when selecting N sources to reduce GHG emissions. Fig. 4. Daily N 2 O flux from day of year (DOY) 21 through 265 (2009) and DOY 141 through DOY 266 (2010) of the growing seasons for the various N sources indicated. Nitrogen treatments were applied at rate of 168 kg N ha 1 on DOY 121 (2009) and 141 (2010) without incorporation. Methane and Carbon Dioxide Fluxes In both 2009 and 2010, the daily CH 4 emissions were highly variable, particularly in 2010 for all treatments (Fig. 7, 8). In 2010, there were many negative values for CH 4 fluxes at different sampling dates. However, the average growing season was negative only for UAN. It is not clear why the CH 4 had a negative emission value in 2010; however, we believe that soil moisture (WFPS) and temperature conditions had the most impact on CH 4 because the larger negative values coincide with WFPS much less than 30% for almost all treatments. Additionally, 2010 recorded 189 mm less precipitation than The negative values reflect the system s uptake of CH 4, meaning the consumption of CH 4 by aerobic methanotrophs exceeds the production of CH 4, which is via anaerobic methanogens. The cumulative growing season CH 4 C was greater in 2009 (SuperU, 43 g C ha 1 ; UAN, 59 g C ha 1 ; ESN, 39 g C ha 1 ; urea, 38 g C ha 1 ; NH 4, 21 g C ha 1 ; poultry litter, 75 g C ha 1 ; control, 67 g C ha 1 ) than 2010 (SuperU, 9 g C ha 1 ; UAN, 37 g C ha 1 ; ESN, 59 g C ha 1 ; urea, 40 g C ha 1 ; NH 4, 5 g C ha 1 ; poultry litter, 34 g C ha 1 ; control, 43 g C ha 1 ) for all N sources except ESN. Poultry litter produced the highest CO 2 flux early in the growing season (first 2 wk) in both years (Fig. 9, 10). Poultry litter treatment had significantly greater cumulative growing season CO 2 emissions than the rest of the treatments in both years (Fig. 5, 6). However, no significant difference was observed among other treatments, including control, except for Super U in The cumulative growing season CO 2 emission for different N sources in our study are greater than Sistani et al.: Nitrous Oxide, Methane, Carbon Dioxide Emissions from N Fertilizers 1801

6 Fig. 5. Cumulative CH 4, N 2 O, and CO 2 fluxes during 2009 growing season from day of year (DOY) 121 through DOY 265 for the N sources studied. Fig. 6. Cumulative CH 4, N 2 O, and CO 2 fluxes during 2010 growing season from day of year (DOY) 141 through DOY 266 for the N sources studied. Table 1. Corn grain yield, cumulative growing-season N 2 O-N emissions, and N 2 O-N emissions per unit (Mg) grain yield for each N source in 2009 and N Sources Corn grain yield N 2 O emissions N 2 O-N per unit of grain yield Mg ha 1 kg ha 1 kg N 2 O-N Mg yield 1 SuperU 11.32a 7.95a 2.85b 1.83bc 0.26c 0.25b UAN 10.29a 7.94a 3.94b 1.61bc 0.40abc 0.21b UAN+AgrotainPlus 10.44a 7.79a 3.90b 1.80bc 0.38b 0.24b ESN 9.76a 7.99a 5.69a 3.30b 0.63a 0.44b Urea 10.65a 7.80a 3.31b 1.70bc 0.31c 0.22b NH a 8.18a 5.97a 2.03bc 0.56ab 0.28b Poultry litter 10.63a 7.54a 5.81a 10.85a 0.56ab 1.44a Poultry litter+agrotainplus 10.25a 6.78ab 6.60a 8.90a 0.64a 1.31a Control 7.13b 5.52b 1.33c 1.01c 0.18c 0.18b Values for each year (column) followed by the same letters are not significantly different at 5% probability level. UAN = urea ammonium nitrate; ESN = polymer-coated urea Journal of Environmental Quality Volume 40 November December 2011

7 Fig. 7. Daily CH 4 flux from day of year (DOY) 121 through 265 (2009) and DOY 141 through DOY 266 (2010) of the growing seasons for the various N sources indicated. Nitrogen treatments were applied at rate of 168 kg N ha 1 on DOY 121 (2009) and 141 (2010) without incorporation. Fig. 8. Daily CH 4 flux from day of year (DOY) 121 through 265 (2009) and DOY 141 through DOY 266 (2010) of the growing seasons for the various N sources indicated. Nitrogen treatments were applied at rate of 168 kg N ha 1 on DOY 121 (2009) and 141 (2010) without incorporation. Sistani et al.: Nitrous Oxide, Methane, Carbon Dioxide Emissions from N Fertilizers 1803

8 Fig. 9. Daily CO 2 flux from day of year (DOY) 121 through 265 (2009) and DOY 141 through 266 (2010) of the growing seasons for the various N sources indicated. Nitrogen treatments were applied at rate of 168 kg N ha 1 on DOY 121 (2009) and 141 (2010) without incorporation. Fig. 10. Daily CO 2 flux from day of year (DOY) 121 through 265 (2009) and DOY 141 through 266 (2010) of the growing seasons for the various N sources indicated. Nitrogen treatments were applied at rate of 168 kg N ha 1 on DOY 121 (2009) and 141 (2010) without incorporation Journal of Environmental Quality Volume 40 November December 2011

9 those reported by Halvorson et al. (2010a,b), potentially due to differences in cropping system, tillage management, and site-specific conditions, such as soil microbial community, soil texture, soil organic matter content, soil ph, growing season soil moisture, drainage conditions, and soil temperature. Conclusions Nitrous oxide fluxes resulting from urea, UAN, SuperU, and NH 4 applications peaked within the first 2 wk after application, but, N 2 O flux peaks from ESN occurred much later. Cumulative growing season N 2 O emissions were greater with poultry litter compared with the enhanced-efficiency fertilizers in both years. The sequence of N 2 O-N emission reductions for all treatments were as follows: SuperU = UAN = urea < ESN = NH 4 = poultry litter for 2009, and SU = UAN = ESN = urea = NH 4 < poultry litter for The CH 4 and CO 2 emissions were not impacted by N source but more by environmental factors, such as soil temperature and soil moisture. There was no significant difference in corn grain yield among all N sources in both years. However, averaged across all N sources, corn grain yield in 2009 was greater than The results of this study show that additional work is needed to further evaluate the potential of enhanced-efficiency N fertilizer sources in reducing N 2 O emissions in nonirrigated cropping systems in humid areas. Our study also indicates that selection of N source can be an important management practice for reducing N 2 O emissions to the environment. Acknowledgments The authors thank Jason Simmons and Marty Haley for their technical assistance in plot establishment, maintenance, and data collection. The authors also thank the International Plant Nutrition Institute s Foundation for Agronomic Research (with product and funding support from Agrium Inc., Calgary, AB, and Agrotain International, St. Louis, MO) for support of this project. This publication is also based on work supported by ARS under the Greenhouse Gas Reduction through Agricultural Carbon Enhancement network Project. References Adviento-Borbe, M.A.A., M.L. Haddix, D.L. Binder, D.T. Walters, and A. Dobermann Soil greenhouse gas fluxes and global warming potential in four high-yielding maize systems. Glob. Change Biol. 13: doi: /j x Akiyama, H., X. Yan, and K. Yagi Evaluation of effectiveness of enhanced-efficiency fertilizers as mitigation options for N 2 O and NO emissions from agricultural soils: Meta-analysis. Glob. Change Biol. 16: doi: /j x Bolan, N.S., S. Saggar, J.F. Luo, R. Bhandral, and J. Singh Gaseous emissions of nitrogen from grazed pastures: Processes, measurements and modeling, environmental implications, and mitigation. Adv. Agron. 84: doi: /s (04) Bolin, B., E.T. Degens, P. Duvigneaud, and S. Kempe The global biogeochemical carbon cycle. p In B. Bolin, E.T. Degens, S. Kempe, and P. Ketner (ed.) The global carbon cycle. 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