Exchange Fluxes of NOX, NH3, and N2O from Typical Wheat, Paddy

Chapter 4

Downloaded by SUFFOLK UNIV on January 19, 2018 | http://pubs.acs.org Publication Date (Web): October 11, 2011 | doi: 10.1021/bk-2011-1072.ch004

Exchange Fluxes of NOX, NH3, and N2O from Typical Wheat, Paddy, and Maize Fields in the Yangtze River Delta and North China Plain Yuanyuan Zhang, Shuangxi Fang, Junfeng Liu, and Yujing Mu* Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China *E-mail: [email protected]

The exchange fluxes of NOX, NH3 and N2O between two typical agricultural fields and the atmosphere were investigated in the Yangtze River Delta (YRD) and North China Plain (NCP). The average fluxes of NO and NH3 from the wheat field in the YRD were 79 and -5.1 ng N m-2 s-1, and from the paddy field were 3.7 and 34.8 ng N m-2 s-1, respectively. The fertilize-induced emission factors (EFs) as NO-N and NH3-N from the wheat field were 2.3% and 1%, and from the paddy field were 0.09% and 3.5%, respectively. Remarkable yearly variation of N2O emissions from the investigated NCP maize field was observed, with average fluxes of 72.1 ng N m-2 s-1 in 2008 and 30 ng N m-2 s-1 in 2009 and with EFs of 3.78% in 2008 and 1.08% in 2009. The average NO and NH3 fluxes from the maize field in 2009 were 36.5 ng N m-2 s-1 and 94.0 ng N m-2 s-1, respectively. Based on the molar ratios of NO/N2O, the emissions of NOX and N2O from the maize field were mainly ascribed to nitrification processes. Returning wheat straw back into the maize field could significantly reduce NOX and NH3 emissions.

Introduction Agricultural fields have been recognized as an important source of atmospheric nitrous oxide (N2O), nitrogen oxide (NOX) and ammonia (NH3) gas emission. These gases play an important role in regional and global environments (1). N2O is involved in the depletion of stratospheric ozone (O3) and consequently © 2011 American Chemical Society Guo et al.; Understanding Greenhouse Gas Emissions from Agricultural Management ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


the ozone layer (2–4). NOX are major precursors of tropospheric oxidants and have important contributions to tropospheric O3 and acid deposition (5). NH3, the only alkaline gas in the atmosphere (6), regulates atmospheric acidity (7), contributes to atmospheric aerosols and adds to soil acidification (8). The gaseous emission of N2O, NOX and NH3 from agricultural fields are mainly from nitrogen fertilization (1, 9–13). In the global budgets, estimated emission from agricultural soils ranged 0.11-6.3 Tg N yr-1 for N2O (14, 15) and 4-21 Tg N yr-1 for NO (16–19). NH3 from agricultural fields was estimated to be ~23% of its global emission (10). The large uncertainty estimations are mainly due to the spatial-temporal variations of different plant, soil, and microbial environments. To reduce the uncertainties, more sampling sites and long term field measurements are needed. The North China Plain (NCP) is one of the most important grain production regions in China. It accounts for 23% of Chinese cropland area while providing 39% of the total food in China (20). The Yangtze River Delta (YRD, Southeast of China) also accounts for a large proportion of total grain production in China. For example, the YRD produced 20% of total Chinese wheat harvest which accounted for 5% of the total Chinese grain production in 1990 (21). To meet increasing food demands, there has been a sharp increase in the use of nitrogen (N) fertilizers in China. Chinese fertilizer use accounts for more than a quarter of total N consumption in the world (22). According to Chinese statistical information (23), the current annual chemical fertilizer application rate (~866 kg ha-1 yr-1) has increased more than three fold since 1980. In order to estimate the impact of agricultural activities on N cycling, it is essential to investigate the soil surface-atmospheric exchanges of N gases above different agricultural fields. Although some works on this topic have been completed in these regions of China (24–29), additional studies on the exchange of NOX and NH3 between agricultural fields in the YRD and NCP regions of China and the atmosphere are required to further the current understanding. Although most of the completed studies focused on N2O emission (20, 29–38), the large differences of fertilizer-induced N2O-N emission factors (EFs, ranging from 0.006% to 1.94%) and average fluxes (ranging from 4.21 to 74.6 ng N m-2 s-1) indicate that further field measurements are still needed. In this study, the exchange fluxes of NOX, NH3 and N2O between two typical Chinese agricultural fields and the atmosphere were investigated in the YRD in 2004 and in the NCP during 2008-2009. The influencing factors, the gas emission rates, and N fertilizer loss rates to N2O, NOX and NH3 were determined.

Experimental Section Sampling Site in the YRD The sampling site was Shuangqiao farm (30º50’N, 120º42’E), about 10 km north of Jiaxing city, Zhejiang province, China. The farm consisted of an area of about 40 ha. The soil was classified as Typic Endoaquepts with NO3- -N of 4.29 mg kg-1, NH4+-N of 12.1 mg kg-1, total N of 1.9 g kg-1, and pH of 6.12 (in a 1:2.5 soil-to-water ratio). The experimental area was about 667 m2 (divided into two 52 Guo et al.; Understanding Greenhouse Gas Emissions from Agricultural Management ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


sampling plots) for investigating NOx and NH3 exchange fluxes from winter wheat in 2004. One plot (UC) was traditionally fertilized with urea and the other (UL) was fertilized by using a mixture of urea and lignin (lignin was from the sewage of paper production). It has been reported that N fertilizers with added lignin could increase the yield of crops (39). However, there are no studies that have examained the influence of lignin on the emission of NOx and NH3. A small area of bare soil in the UC plot was used as a control (CS). Prior to winter wheat sowing, both plots received 400 kg ha-1 compound fertilizer (N:P2O5:K2O = 20%:10%:10%) as basal fertilizer while urea (70 kg N ha-1) was applied to each plot on 29 February, 2004. All fertilizers were surface broadcast. In order to study the effect of lignin on the emissions of NOx and NH3, an aqueous solution of urea (105 kg N ha-1) was applied to the UC and CS plot before the tassel stage (8 April, 2004). The UL plot was fertilized with a mixture of urea and lignin (10/1, w/w). Seasonal variations of NOx and NH3 fluxes were measured between March 5 and June 1, 2004. Average sampling frequency was approximately 2 days between 12:00 to 16:00. The wheat was sown on 15 December 2003 and harvested on 28 May, 2004 (149th day). Rice was cultivated in the same experimental manner as wheat, and two treatments were included: conventionally fertilized (RF) and no fertilizer input (RN) plots. The rice was transplanted on July 6, 2004. Compound fertilizer (300 kg ha-1, N:P2O5:K2O = 20%:10%:10%) was applied as basal fertilizer to RF plot. On July 15 and August 30, 2004, urea was side-dressed to the RF plot at the rates of 69 and 51.7 kg N ha-1, respectively. The rice was harvested on October 30, 2004. Sampling Site in the NCP The field experiment was carried out in an agricultural field (38°71′N, 115°15′E) in Wangdu County, Hebei Province, China. The investigated crops were wheat (Triticum aestivum L.) and summer maize (Zea mays L.) under rotational cultivation. The field soil was classified as Aquic Inceptisol with a sandy loam texture. Soil pH (in a 1:2.5 soil-to-water ratio) was 8.1, the soil organic C was 8.34-9.43 g kg-1 and total N was 1.02-1.09 g kg-1. The annual mean rainfall is about 555 mm and annual mean temperature is about 12.3 °C. The highest and lowest monthly mean air temperatures are 26.5 °C in July and -4.1 °C in January. The experimental field with a total area of 68 m2 was divided into three 6.5×3.5 m2 plots, including control (CK, without crop, fertilization and irrigation), fertilizer N (NP) and wheat straw incorporated plus fertilizer N (SN) treatments. Maize was sown on 25 June, 2008, and 29 June, 2009. According to the cultivating methodology of local farmers, compound fertilizers (525 kg ha-1, N:P2O5:K2O = 17%:20%:8% in 2008 and 413 kg ha-1, N:P2O5:K2O = 24%:12%:6% in 2009) as basal fertilizer were evenly broadcasted onto the soil surface by hand after sowing for all plots. Another kind of compound fertilizer (375 kg ha-1, N:K2O = 22%:8%) was further applied to the NP and SN plots as supplementary fertilizer on 16 August, 2008, and urea (150 kg ha-1, N = 46.2%) as supplementary fertilizer was applied to the NP and SN plots on 1 August, 2009. Wheat straws (9.5 t ha-1 in 2008 and 4.3 t ha-1 in 2009, N = 0.48%) were evenly broadcast onto the soil 53 Guo et al.; Understanding Greenhouse Gas Emissions from Agricultural Management ACS Symposium Series; American Chemical Society: Washington, DC, 2011.

surface as basal fertilizer in the SN plot in both years. Flooding was initiated immediately after the application of supplementary fertilizer in 2008 and basal fertilizer in 2009. The field was not irrigated on 25 June, 2008, and 1 August, 2009, due to strong rain events with cumulative rainfall of ~25 mm. Maize was harvested in mid-October for both years.


Measurements of N2O, NOX and NH3 Fluxes For the winter wheat and paddy fields in the YRD, NOX and NH3 fluxes were measured by dynamic chambers and the concentrations of NOX and NH3 were measured by the national standard methods for environmental air pollution in China (39). N2O fluxes from the maize field in NCP were investigated by static chambers, and NOX and NH3 fluxes were measured by dynamic chambers. N2O concentration was measured by our improved GC-ECD method (about 0.1% CO2 in N2 was introduced into the ECD as makeup gas) and the concentrations of NOX and NH3 were measured by a chemiluminescent NH3 analyzer (Thermo Electron model 17i, USA). Detailed information about the chambers and flux measurements can be found in other published reports (40–44).

Results and Discussions NOX and NH3 Fluxes from the Winter Wheat and Paddy Field in the YRD Figure 1 shows the seasonal variations of NOX and NH3 fluxes from the winter wheat and paddy field in 2004. For NO, the average fluxes from the UC (urea only) plot were 79 and 3.7 ng N m2 s-1 for winter wheat and rice, respectively. The majority of NO was emitted during the winter wheat growing period. An exponential dependence of NO fluxes on soil temperature was observed during the main growing period of winter wheat (r = 0.76, UC, p

Exchange Fluxes of NOX, NH3, and N2O from Typical Wheat, Paddy

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