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Keywords:

  • anthropogenic activity;
  • emission inventory;
  • reactive gases;
  • rural catchment

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

To evaluate the atmospheric load of reactive gaseous nitrogen in the fast-developing Eastern China region, we compiled inventories of nitrous oxide (N2O), nitrogen oxide (NOx) and ammonia (NH3) emissions from a typical rural catchment in Jiangsu province, China, situated at the lower reach of the Yangtze River. We considered emissions from synthetic N fertilizer, human and livestock excreta, decomposition of crop residue returned to cropland and residue burning, soil background and household energy consumption. The results showed that, for the 45.5 km2 catchment, the annual reactive gaseous emission was 279 ton N, of which 7% was N2O, 16% was NOx and 77% was NH3. Synthetic N fertilizer application was the dominant source of N2O and NH3 emissions and crop residue burning was the dominant source of NOx emission. Sixty-seven percent of the total reactive gaseous N was emitted from croplands, but on a per unit area basis, NOx and NH3 emissions in residential areas were higher than in croplands, probably as a result of household crop residue burning and extensive human and livestock excreta management systems. Emission per capita was estimated to be 18.2 kg N year−1 in the rural catchment, and emission per unit area was 56.9 kg N ha−1year−1 for NH3 + NOx, which supports the observed high atmospheric N deposition in the catchment. Apparently, efficient use of N fertilizer and biological utilization of crop straw are important measures to reduce reactive gases emissions in this rural catchment.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Modern agricultural activities have a great impact on the global atmospheric environment. It has been estimated that approximately 81% of nitrous oxide (N2O), 35% of nitrogen oxides (NOx, NO + NO2) and 85% of ammonia (NH3) originate from agricultural activities (Krafenbauer and Wriessning 1995). N2O is a potent greenhouse gas and also participates in the destruction of stratospheric ozone (Crutzen 1970). NOx contributes to the build-up of tropospheric ozone and is a precursor of nitric acid for acid rain (Crutzen 1979). NH3 is the only natural alkaline gas in the air and it influences the pH of aerosols, cloudwater and rainfall. Moreover, NH3 is an important contributor to ammoniated aerosols (Brasseur et al. 1999). Excessive reactive N may result in eutrophication of water bodies, soil acidification and changes in biodiversity (Galloway and Cowling 2002).

The lower reach of the Yangtze River, located in Eastern China, has long been one of the most densely populated agricultural regions and is legendary in China for its many centuries of productive rice-based agriculture (Wu et al. 2009). It has also been a fast-developing economic region over the past three decades. With the increased standard of living in rural areas, farmers have had increasing access to chemical fertilizer and high-quality fuel (e.g. LPG, coal). Crop residue that was traditionally used as organic fertilizer is now largely burned in the fields. Anthropogenic reactive N has far exceeded the bio-fixed N in natural terrestrial ecosystems in this region (Xing and Zhu 2002). In addition, this area is considered to be a hot spot area of N deposition (Galloway et al. 2004). Therefore, environmental problems such as air and water pollution are becoming a major concern.

Emission inventories provide crucial information for designing effective emission control strategies. Over the past two decades, concerns about N2O, NOx and NH3 emissions have been raised in China. Xing and Yan (1999) and Lu et al. (2006) used different methods to estimate N2O emission from agricultural fields. Li and Lin (2000) compared the emissions of N2O, NOx and NH3 from fuel combustion, industrial processes and agricultural sectors. Yan et al. (2003) estimated the emissions of N2O, NOx and NH3 from croplands in East, South-East and South Asia. Most of these earlier studies, however, have focused on the emission of one or more gases at regional or national levels. In such large-scale estimations, activity data are usually obtained from official statistics, which have often been questioned because of administrative interference with the generation of the statistical data. Inventories compiled using first-hand activity data for a typical area may provide more insight into the ongoing situation. In addition, emission estimates made on a per capita or per unit area basis may be more suitable for comparison among different regions or systems.

The purpose of the present study was to: (1) understand the contribution of anthropogenic activity to the reactive N emissions in a typical rural catchment in Eastern China, (2) identify major contributors to the reactive N emissions, (3) quantify the per capita and per unit reactive gaseous emissions. In contrast to previous inventory studies, the present study was supported by household investigations and experimental monitoring.

Materials and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Study site

The study catchment is located in Jurong, 40 km south-east of Nanjing city, Jiangsu province, China (32°01′N, 119°13′E), with an annual mean temperature of 15°C and annual mean precipitation of 1,050 mm (monitored results for the year 2007–2008 by the automatic weather station [Vantage Pro Plus; Davis Instrument Corporation, San Francisco, CA, USA] installed in the catchment). The total area of the catchment is 45.5 km2, of which 31.2% is paddy fields, 22.8% is uplands, 9.3% is tea garden and forest land, 27.5% is construction and roads, and the remainder is covered by water bodies. The total residential population is 18,092 (data from local statistical office). It is a typical rice-based agricultural catchment. The major soil type is paddy soil developed from Quaternary losses. Rice, cotton, maize and soybean are planted in the summer season, and wheat and oil rape are planted in the winter season. Rice–wheat and cotton–oil rape are the major annual cropping rotations in the paddy fields and upland fields, respectively. In conventional farming practice, synthetic compound fertilizer and urea are the major N nutrient sources for the croplands, and are usually applied at a rate of 500–600 kg N ha−1 year−1 to summer and winter crops.

There is no industry or intensive livestock farming in the catchment. A small number of livestock are raised for self-consumption. Agricultural activity is the dominant source of N contamination.

Source of the agricultural activity data

Nitrogen-related agricultural activity data were obtained through household investigation. A questionnaire table was designed to include items such as cultivation and type of crops, fertilization rate, crop yield, fate of crop residue, livestock population, and management of human and animal excreta. Approximately 600 households in the catchment were investigated in 2007 and 2008.

Household fossil fuel consumption was not surveyed in the catchment. Instead, we adopted the per capita consumption of fossil fuel energy obtained through a survey in a neighboring county that has a similar economic development level to the catchment (Wang et al. 2002).

Methodology for estimating N 2 O, NO x and NH 3 emissions

Emission of N2O was estimated principally by following the 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas Emission Inventories (hereafter referred to as the 2006 IPCC Guidelines). The emission sources considered include soil background emissions, synthetic N fertilizers (FSN, kg N), managed human and livestock excreta (FMON, kg N), organic N applied as fertilizer (FON, kg N), N from crop residue returned to croplands (above-ground and below-ground) (FCR, kg N), crop residue burning in situ (FRB, kg N), household residue consumption (FHRB, kg N) for cooking and animal feeding, as well as household fossil fuel energy consumption (FHE, TJ) for cooking and animal feeding. Biological N fixation was removed as a direct source of N2O emission in the 2006 IPCC Guidelines because of the lack of evidence of significant emissions arising from the fixation process itself (Rochette and Janzen 2005). There is no organic soil (FOS) or significant land-use changes (FSOM) in the study catchment and thus FOS and FSOM were not considered in the present study. The number of grazing animals in the catchment is negligible, thus urine and dung N deposited on pasture, range and paddock by grazing animals were not counted. As a result, the total N2O emission from the catchment in a year was estimated as:

  • image

where EFFIELD (kg N2O-N kg−1 N) is the N2O emission factor for N applied to soils (synthetic nitrogen fertilizer, organic nitrogen fertilizer and crop residue N returned to soil), EFMON, EFRB and EFHRB (kg N2O-N kg−1 N) are the N2O emission factors for N in managed human and livestock excreta, N in crop residue burned in situ and N in crop residue burned as household fuel, respectively, EFHE is the N2O emission factor for household fossil fuel energy consumption (kg N2O-N TJ−1) and EFBK is the background emission factor (kg N2O-N ha−1) on an area basis for croplands. Area is the total area of croplands in the catchment (ha).

The total consumption of synthetic nitrogen fertilizer (FSN) was calculated from the N application rates and areas of different crops, both were obtained through household surveys. The values are shown in Table 1.

Table 1.   Parameters for estimating nitrous oxide (N2O), nitrogen oxide (NOx) and ammonia (NH3) emissions from synthetic N fertilizer and N in crop residue
CropTotal area (ha)Synthetic N fertilizer application rate (kg N ha−1)Yield (kg ha−1)Above-ground residue/seed ratioBelow-ground residue/above-ground residue ratioNitrogen content in above-ground residue (kg N kg biomass−1)N content in below-ground residue (kg N kg biomass−1)§Ratio of biomass burning in situ (%)Ratio of biomass burning as household fuel (%)Cf
  1. Investigated results from the present study. Values from the China Fertilizer Information Web (http://www.natesc.gov.cn/sfb/). §Values from the Intergovernmental Panel on Climate Change (2006). Cf is the combustion factor from the Intergovernmental Panel on Climate Change (2006). ††Experimental results from the present study. ‡‡Values from Yan et al. (1999).

Rice1,4223297,2540.9††0.160.010††0.00853220.8
Cotton5162282,3902.0‡‡0.150.0120.0081990.83
Maize2291674,2481.0††0.220.0059††0.00776120.8
Soybean200181,7791.0‡‡0.010.0210.0080100
Oil rape9732272,4522.2††0.150.0067††0.0089910.83
Wheat7122124,7701.1††0.230.0056††0.0099070.9
Tea5041.7

The amounts of managed human and livestock excreta (FMON) and organic N applied as fertilizer (FON) were calculated as follows:

  • image

where N(T) is the number of head of livestock species T in the catchment; Nex(T) is the annual average N excretion (kg N animal−1year−1); FraclossMS is the fraction of managed manure N loss in the manure management system (%). In the 2006 IPCC Guidelines, human excreta were not included in the calculation of FMON and FON. However, human excreta have long been used as organic fertilizer in China. It was estimated that 33% of human excreta was used as organic fertilizer (Xing and Yan 1999). Therefore, we included human excreta as a source of organic fertilizer. The parameters required for calculating FMON are shown in Table 2.

Table 2.   Parameters for estimating nitrous oxide (N2O), nitrogen oxide (NOx) and ammonia (NH3) emissions from human and livestock excreta
Human or animalPopulationNitrogen excreta rate (kg N year−1 head−1 of human or animal)FraclossMS (%)§
  1. Investigated results from the present study. Values from Xing and Yan (1999). §FraclossMS is the amount of managed manure nitrogen loss in the different manure management systems; values from the Intergovernmental Panel on Climate Change (2006). This number is the corrected adult population from the permanent population using a factor of 0.85 reported by Zhu (1997).

Human15,378567
Poultry35,5030.355
Swine3,443848
Non-dairy cattle4004250
Sheep239715

FCR, FRB and FHRB were estimated from the total amount of above-ground crop residue N and its fate (the proportion of crop residue that is returned to the soil, burned in situ and burned as fuel). The below-ground crop residue was also included in the FCR as recommended by the 2006 IPCC Guidelines. The total amount of above-ground crop residue N was estimated from the crop yield, the above-ground residue/yield ratio and the N content in the above-ground crop residue. The below-ground crop residue N was estimated from the crop yield, the above-ground residue/yield ratio, the below-ground residue/above-ground residue ratio and the N content in the below-ground residue (IPCC 2006). For FRB, the total amount of crop residue N burned in situ should be multiplied by the corresponding combustion factor of each crop owing to incomplete burning in the field. Residue/yield ratios and N contents in crop residues were measured for the major crops (rice, maize, wheat and oil rape), with 10 samples for each crop in the catchment. The parameters for the other crops were adopted from the literature. The data used in the calculation are shown in Table 1.

The FHE was calculated according to the permanent population and the annual consumption of fossil fuel energy per capita (852 MJ coal and 505 MJ LPG per capita) adopted from the report of Wang et al. (2002).

Because NOx and NH3 emissions share the same sources as N2O, the estimation method was the same as that for N2O.

Emission factors

The N2O emission factor from rice paddy was adopted from Zou et al. (2010). The N2O emission factor from upland was derived from equations in Lu et al. (2006) to take into account the effect of fertilization rate and precipitation. The NOx emission factors from all soils were adopted from Yan et al. (2003). Because NH3 emission often accounts for a significant proportion of applied synthetic fertilizer N, we measured NH3 emissions from synthetic N fertilizer applied to the four major crops in the catchment (rice, maize, wheat and oil rape) using the method reported by Dong et al. (2006). For each of the four crops, emission factors were measured on three farmlands for two crop seasons (2007–2009), replicated three times in every farmland. The applied N fertilizers were urea and compound fertilizer; at 210–310 kg N ha−1 for rice and 75–300 kg N ha−1 for upland crops. Average results are shown in (Fig. 1). For NH3 emissions from synthetic fertilizer applied to the other summer crops (soybean and cotton), we used the average emission factor measured from maize land over 2 years. Annual average NH3 emission factor from maize and oil rape lands was used for synthetic fertilizer applied to the tea land. The NOx and NH3 emission factors from biomass burning were reported to be related to the residue N content (Delmas et al. 1997). We corrected the emission factors of NOx and NH3 from Andreae and Merlet (2001) using the measured N contents in the crop residue. Other emission factors for various sources are shown in Table 3.

image

Figure 1.  Ammonia (NH3) volatilization during the growing seasons of the four predominant crops in the study rural catchment from July 2007 to June 2009.

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Table 3.   Emission factors of nitrous oxide (N2O), nitrogen oxide (NOx) and ammonia (NH3) from different sources used in the estimation
Emission factorSourceN2O (kg N2O-N kg−1 N)NOxa (kg NOx-N kg−1 N)NH3 (kg NH3-N kg−1 N)
  1. aThe amount of NOx emission was calculated as NO-N. bValue from Zou et al. (2010). cValues from Yan et al. (2003). dThis NH3 emission factor was obtained from the combined emission factors of NOx and NH3 reported in the Intergovernmental Panel on Climate Change (2006) Guidelines minus the NO emission factor from the corresponding sources reported by Yan et al. (2003). eValues from Lu et al. (2006). fExperimental results from the present study. gValues from Intergovernmental Panel on Climate Change (2006) Guidelines. hThis factor was the corrected factor according to the N content in the crop residue from the reported emission factor of Andreae and Merlet (2001). iValues from Geadah (1985).

EFFIELDSynthetic N fertilizer applied to rice paddies 0.0042b 0.0013c0.12d
0.17 in maize landsf
Synthetic N fertilizer applied to uplands0.02e0.0066c0.07 in rape landsf
0.03 in wheat landsf
Crop residue applied to rice paddies0.0042b0.0013c
Crop residue applied to uplands0.02e0.0066c
Human, swine, poultry and non-dairy cattle excreta applied to rice paddies0.0042b0.0013c0.2c
Human, swine, poultry and non-dairy cattle excreta applied to uplands0.02e0.0066c0.2c
Sheep excreta applied to rice paddies0.0042b0.0013c0.1c
Sheep excreta applied to uplands0.02e0.0066c0.1c
EFMONManaged excreta of human and swine0.01g0.0066c0.47d
Managed excreta of poultry0.01g0.0066c0.54d
Managed excreta of sheep0.01g0.0066c0.11d
Managed excreta of non-dairy cattle0.01g0.0066c0.44d
EFRBEFHRBResidue burning in situ and household residue burning0.07g0.219h0.2h
EFHEHousehold coal consumption (kg N T J−1)1.0g89.1d0.028i
Household liquefied petroleum gas consumption (kg N T J−1)0.06g69.1d
EFBKSoil background (kg N ha-1 year−1)1.56e0.57c1.5c

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

N 2 O, NO x and NH 3 emissions from different sources

Annual N2O, NOx and NH3 emissions resulting from synthetic N fertilizer application were estimated to be 12.6, 4.13 and 103 ton N, respectively (Fig. 2). NH3 was obviously the dominant gas emitted by N fertilizers, and NH3 emissions from rice paddies accounted for more than half of the total NH3 emissions from synthetic N fertilizer, owing to the high application rate. On average, NH3 emissions accounted for 10% of the total synthetic N applied to croplands in the catchment.

image

Figure 2.  Annual nitrous oxide (N2O), nitrogen oxide (NOx) and ammonia (NH3) emissions from different croplands caused by synthetic N fertilizer application in the study rural catchment.

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Annual N2O, NOx and NH3 emissions resulting from human and livestock excreta during management and after application as organic fertilizer to the fields were 1.99, 1.10 and 73.6 ton N, respectively (Table 4). The amount of NH3 emission was much greater than the emissions of N2O and NOx. Much more NH3 was emitted during the management process than after being applied to the soils. Owing to the small population of livestock, human excreta were the dominant source of NH3 emission.

Table 4.   Annual nitrous oxide (N2O), nitrogen oxide (NOx) and ammonia (NH3) emissions from human and livestock excreta
SourcesN2O (ton N)NOx (ton N)NH3 (ton N)Total
Managed human excreta0.7690.50736.437.7
Managed livestock excreta0.5670.37426.527.4
Fertilized human excreta0.3070.1005.085.48
Fertilized livestock excreta0.3500.1145.656.11
Total1.991.1073.676.7

The N2O, NOx and NH3 emissions from crop residues were estimated to be 1.79, 36.7 and 33.5 ton N year−1, respectively (Table 5). These emissions occurred in three processes, that is, field burning, burning for household energy and decomposition of above-ground and below-ground crop residue in the field. Irrespective of whether it was N2O, NOx or NH3, more than half of the emissions occurred during the field burning of crop residue, followed by residue burning for household energy.

Table 5.   Annual nitrous oxide (N2O), nitrogen oxide (NOx) and ammonia (NH3) emissions from crop residue burning in situ (FRB), household residue burning (FHRB) and crop residue returned to cropland (FCR)
SourcesN2O (ton N)NOx (ton N)NH3 (ton N)Total
FRB0.99723.521.546.0
FHRB0.36913.112.025.4
FCR0.4260.1400.566
Total1.7936.733.572.0

Reactive gas emissions from household fossil fuel energy consumption (including coal and LPG) were small, with annual N2O and NOx emissions of 0.01 and 1.70 ton N, respectively. NOx emission mainly occurred during household coal consumption.

Background emissions of N2O, NOx and NH3 were also considerable at 3.69, 1.35 and 3.55 ton N per year, respectively.

Total emissions of N 2 O, NO x and NH 3

Total N2O, NOx and NH3 emissions from the different sources are summarized in Fig. 3. The total annual N2O emission was estimated to be 20.1 ton N. Synthetic N fertilizer application was the largest contributor to N2O emissions, accounting for 63% of the total emissions. Soil background emission contributed 18% of the total emissions. N2O emission from the other sources (FMON, FON, FCR, FRB, FHRB and FHE) only accounted for 19% of the total emissions (Fig. 3).

image

Figure 3.  Contributions of soil background (FSB), synthetic fertilizer (FSN), managed human and livestock excreta (FMON), fertilized excreta (FON), crop residue returned to cropland (FCR), crop residue burning in situ (FRB), household residue burning (FHRB) and household fossil fuel energy consumption (FHE) to nitrous oxide (N2O), nitrogen oxide (NOx) and ammonia (NH3) emissions in the study rural catchment.

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For the total 45.0 ton of NOx-N emission, crop residue burning in situ (FRB) and in households (FHRB) was by far the dominant source. NOx emissions from crop residue burning in the fields and in households as biofuels accounted for 52 and 29%, respectively, of the total emissions. Synthetic N fertilizer application was responsible for 9% of the total NOx emission (Fig. 3).

The total annual NH3 emission was estimated to be 214 ton NH3-N. Similar to N2O emission, synthetic N fertilizer application was the largest source and accounted for 48% of the total emissions. Another important NH3 emission source was managed human and livestock excreta, which accounted for 29% of the total emissions. Emissions from residue burning in the field and residue burning for household energy comprised 10 and 6%, respectively, of the total emissions (Fig. 3).

The total reactive gaseous emissions in the catchment amounted to 279 ton N year−1 (Table 6). The emitted N2O, NOx and NH3 comprised 7, 16 and 77%, respectively. The averaged emissions per capita were 1.31 kg N2O-N, 2.93 kg NOx-N and 13.9 kg NH3-N, and the per unit area emissions were 4.42 kg N2O-N ha−1, 9.89 kg NOx-N ha−1 and 47.0 kg NH3-N ha−1, respectively, totaling 61.3 kg reactive gaseous N ha−1 year−1.

Table 6.   Comparison of nitrous oxide (N2O), nitrogen oxide (NOx) and ammonia (NH3) emissions in the field and residential areas in the study rural catchment
AreasItemsN2ONOxNH3Total
  1. Values in parentheses indicate the percentage of total emission. The corrected adult population from the permanent population using a factor of 0.85 reported by Zhu (1997) was used.

CroplandsSubtotal emissions (ton N)18.4 (92)29.4 (65) 139 (65)  187 (67)
Emission per area (kg N ha−1)5.779.2143.758.7
Residential areaSubtotal emissions (ton N)1.72 (8)15.7 (35)    74.8 (35)     92.2 (33)
Emission per area (kg N ha−1)1.2611.554.867.5
Whole catchmentTotal emission (ton N)20.1 (100)45.0 (100)  214 (100)  279 (100)
Emission per area (kg N ha−1)4.429.8947.061.3
Emission per person (kg N person−1)‡1.312.9313.918.2

Emissions over croplands and residential areas

Emissions of N2O, NOx and NH3 from residential areas and croplands are separated in Table 6. The emission sources from croplands include FSN, FON, FRB, FCR and soil background emission, and the FMON, FHRB and FHE emissions were attributed to residential areas.

The results showed that more reactive gaseous emissions occurred in croplands, accounting for 67% of the total emissions. The proportion of N2O emissions in the cropland areas even reached 92%. However, the per unit area emissions of NOx and NH3 in the residential areas were more than those in the croplands, with 11.5 kg NOx-N and 54.8 kg NH3-N ha−1 in the residential areas, and 9.21 kg NOx-N and 43.7 kg NH3-N ha−1 in the croplands. The per unit area emission for N2O from croplands (5.77 kg N ha−1) was higher than that from residential areas (1.26 kg N ha−1).

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Emissions of N 2 O, NO x and NH 3

On a global scale, livestock waste is the largest contributor to N2O emissions, and is responsible for threefold the amount emitted by synthetic N fertilizer (Mosier and Kroeze 2000). In Australia, estimated N2O emissions originating from N fertilizers and animal waste are almost equal, accounting for 32 and 30%, respectively, of the total (Dalal et al. 2003). In this rural catchment area of China, although there is a large area of rice paddy fields that have a lower fertilizer-induced N2O emission factor than the uplands, synthetic N fertilizer was by far the dominant source of N2O, contributing 63% of the total emission. This is in agreement with the finding of Yan et al. (2003) that, in East, South-East and South Asia, China was the only country where fertilizer was the dominant source of N2O emission, apparently because of the intensive application of N fertilizer for crop production. According to our surveys conducted in 2007 and 2008, synthetic N application rates to croplands in the catchment reach up to 500–600 kg N ha−1 year−1 for summer and winter crops.

Although NOx emissions from crop residue burning in situ and from houses as biofuels only accounted for <4% of the total NOx emissions in China (Streets and Waldhoff 2000), it appears to be a serious environmental problem in the study rural area. The intensive use of synthetic fertilizer has also decreased the necessity of crop residue return as a nutrient source. As a result, most crop residue in the catchment was burnt in houses as biofuel or in the field, leading to large NOx emissions from crop residue burning and contributing 81% of the total NOx emissions. Our investigations showed that 64% of crop straw was burnt in situ after harvest in the study catchment. This is comparable with Cao et al. (2008), that is, approximately 15.2–60% of crop straw was burnt in the field directly in China, and the highest NOx emission from field burning occurred in eastern China.

Emission of NH3 was the biggest contributor to reactive gases emission in the study catchment and accounted for 77% of the total N2O, NOx and NH3 emissions. Heavy synthetic N application to croplands and extensive human waste management in the rural catchment resulted in high NH3 emission. The NH3 emission rate of synthetic N fertilizer was generally higher for summer crops (rice and maize) than for winter crops (wheat and oil rape), probably because of the temperature difference. The average NH3 emission rate of 10% observed in the present study was comparable to the values reported by Zhu and Chen (2002).

Globally, domestic animals are the largest source of NH3 emissions (40%), which is approximately threefold that from synthetic fertilizer and agricultural crops combined (Schlesinger and Hartley 1992). Roe et al. (1998) found a similar trend in the USA; NH3 emissions from livestock waste accounted for 55% of the total NH3 emissions and synthetic N fertilizer application contributed 7%. Owing to the small livestock population and intensive use of synthetic N fertilizer (particularly in the rice fields) in the current rural catchment, synthetic N fertilizer contributed 48% of the total NH3 emissions, which was more than the contributions of total managed and applied excreta (34%).

Although the total emission of NH3 from the croplands was more than that from the residential areas in the catchment, NH3 emission per unit area in the residential areas was higher than that in the croplands. This might be the reason for the higher annual average air concentration of NH3 in the residential areas (5.4 μg m−3) than in the croplands (4.1 μg m−3; R Yang, unpublished data, monitored from October 2007 to September 2008) measured 1.5 m above the surface.

High wet N deposition has been observed in the lower reach of the Yangtze River (26.8 kg N ha−1 year−1; Zhao et al. 2009), as well as in this catchment (25.2 kg N ha−1 year−1; R Yang, unpublished data, monitored from October 2007 to September 2008), whereas the average wet deposition in China was estimated to be 9.9 kg N ha−1 year−1 (Lü and Tian 2007). The total emissions of NOx and NH3 in this catchment averaged 56.9 kg N ha−1 year−1, which was more than double the observed wet N deposition. The high observed N deposition was, therefore, plausible. The other half of the emitted NOx and NH3 probably contributed to the dry N deposition or participated in the photochemical reaction of gases.

Uncertainty in the estimated emissions

We have done our best to reduce the uncertainties in the estimated emissions. First, the N-related activity data were obtained through first-hand investigation. Second, the largest reactive gaseous N source in the catchment, that is, NH3 emission from synthetic fertilizer, was directly measured for four major crops and for two consecutive years. Third, we used local fertilization rate and precipitation to correct the N2O emission factors for upland and local crop residue N data to correct NH3 and NOx emission factors for biomass burning. Nevertheless, there still exist large uncertainties in the estimated emissions owing to the large number of emission factors and parameters that were not measured specifically for the study catchment. The largest source of uncertainty is probably the NH3 emission factor for human and animal excreta, which is difficult to measure and data are rare, except for the default IPCC value. Biomass burning emission factors also have large uncertainty owing to a lack of sufficient measurements.

Conclusions

In a typical rice-based agricultural catchment of 45.5 km2, the annual N2O, NOx and NH3 emissions were estimated to be 20.1 ton N2O-N, 45.0 ton NOx-N and 214 ton NH3-N, totaling 279 ton N. The contributions of the various sources to the reactive gaseous emissions were quite different for the different gases. Synthetic N fertilizer and soil background emission contributed 63 and 18%, respectively, to the total emission of N2O. Crop straw burning in fields and in houses as biofuel was the dominant source of NOx emissions in the study catchment, contributing 52 and 29%, respectively. The total emission of NH3 was far greater than the total emissions of N2O and NOx, and was emitted from synthetic N fertilizer (48%) and managed human and livestock excreta (29%), particularly from synthetic N fertilization of rice fields and human excreta. More N2O, NOx and NH3 emission occurred in croplands than in residential areas. However, the NOx and NH3 emissions per unit area in the residential areas were higher than those in the field area. The average per unit area emission of NOx and NH3 reached 56.9 kg N ha−1 year−1, supporting the high inorganic N deposition rate observed in the catchment. Clearly, more efficient use of N fertilizer and biological utilization of crop straw would be effective in reducing the emission of reactive gases in this rural catchment.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

This research was financially supported by the National Natural Science Foundation of China (No. 40721140018). We are grateful to Xiaosan Jiang and Jianchao Liu of the Nanjing Agricultural University and Aijun Ma of the Jiangsu Polytechnic College of Agriculture and Forestry for their assistance in conducting household surveys on agricultural activities.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
  • Andreae MO, Merlet P 2001: Emissions of trace gases and aerosols from biomass burning. Global Biogeochem. Cycles, 15, 955966.
  • Brasseur GP, Orlando JJ, Tyndall GS 1999: Atmospheric Chemistry and Global Change. Oxford University Press, New York.
  • Cao GL, Zhang XY, Wang YQ, Zheng FC 2008: Estimation of emissions from field burning of crop straw in China. Chin. Sci. Bull., 53, 784790.
  • China Fertilizer Information Web, http://natesc.agri.gov.cn/sites/tf/
  • Crutzen PJ 1970: The influence of nitrogen oxides on the atmospheric ozone content. Q. J. Roy Meteor. Soc., 96, 320325.
  • Crutzen PJ 1979: The role of NO and NO2 in the chemistry of the troposphere and stratosphere. Annu. Rev. Earth Planet Sci., 7, 443472.
  • Dalal RC, Wang WJ, Robertson GP, Parton WJ 2003: Nitrous oxide emission from Australian lands and mitigation options: a review. Aust. J. Soil Res., 41, 165195.
  • Delmas R, Serca D, Jambert C 1997: Global inventory of NOx sources. Nutr. Cycl. Agroecosyst., 48, 5160.
  • Dong WX, Hu CS, Zhang YM 2006: In situ determination ammonia volatilization in field of North China. Chin. J. Eco-Agric., 14, 4648 (in Chinese).
  • Galloway JN, Cowling EB 2002: Reactive nitrogen and the world: 200 years of change. Ambio., 31, 6477.
  • Galloway JN, Dentener FJ, Capone DG et al. 2004: Nitrogen cycles: past, present, and future. Biogeochemistry, 70, 153226.
  • Geadah ML 1985: National of Natural and Anthropogenic Sources and Emissions of Ammonia (1980). EPS 5/IC/1 Environment Canada, Ottawa, Ontario.
  • IPCC (Intergovernmental Panel on Climate Change). 2006 Guidelines for National Greenhouse Gas Inventories. http://www.ipcc-nggip.iges.or.jp/.
  • Krafenbauer A, Wriessning K 1995: Anthropogenic environmental pollution-the share of agriculture. Bodenkultur(abstract), 46, 269283.
  • Li YE, Lin ED 2000: Emission of N2O, NH3 and NOx from fuel combustion, industrial processes and the agricultural sectors in China. Nutr. Cycl. Agroecosyst., 57, 99106.
  • Lu YY, Huang Y, Zou JW, Zheng XH 2006: An inventory of N2O from agriculture in China using precipitation-rectified emission factor and background emission. Chemosphere, 65, 19151924.
  • Lü CQ, Tian HQ, 2007: Spatial and temporal patterns of nitrogen deposition in China: synthesis of observational data. J. Geophys. Res., 112, D22S05, DOI: 10.1029/2006JD007990.
  • Mosier A, Kroeze C 2000: Potential impact on the global atmospheric N2O budget of the increased nitrogen input required to meet future global food demands. Chemosphere-Global Change Science, 2, 465473.
  • Rochette P, Janzen HH 2005: Towards a revised coefficient for estimating N2O emissions from legumes. Nutr. Cycl. Agroecosyst., 73, 171179.
  • Roe SM, Strait RP, Niederreiter ML 1998: Methods for Improving National Ammonia Emission Estimates, Technical Memorandum. EH Pechan and Associates, Rancho Cordova, California.
  • Schlesinger WH, Hartley AE 1992: A global budget for atmospheric NH3. Biogeochemistry, 15, 191211.
  • Streets DG, Waldhoff ST 2000: Present and future emissions of air pollutants in China: SO2, NOx, and CO. Atmos. Environ., 34, 363374.
  • Wang XH, Dai XQ, Zhou YD 2002: Domestic energy consumption in rural China: a study on Sheyang County of Jiangsu Province. Biomass and Bioenergy, 22, 251256.
  • Wu JX, Cheng X, Xiao HS, Wang HQ, Yang LZ, Ellis EC 2009: Agricultural landscape change in China’s Yangtze Delta, 1942–2002: a case study. Agric. Ecosyst. Environ., 129, 523533.
  • Xing GX, Yan XY 1999: Direct nitrous oxide emissions from agricultural fields in China estimated by the revised 1996 IPCC guidelines for national greenhouse gases. Environ. Sci. Policy, 2, 355361.
  • Xing GX, Zhu ZL 2002: Regional nitrogen budgets for China and its major watersheds. Biogeochemistry, 57/58, 405427.
  • Yan XY, Akimoto H, Ohara T 2003: Estimation of nitrous oxide, nitric oxide and ammonia emissions from croplands in East, Southeast and South Asia. Glob. Chang. Biol., 9, 10801096.
  • Yan WJ, Yin CQ, Zhang S 1999: Nutrient budgets and biogeochemistry in an experimental agricultural watershed in Southeastern China. Biogeochemistry, 45, 119.
  • Zhao X, Yan XY, Xiong ZQ et al. 2009: Spatial and temporal variation of inorganic nitrogen wet deposition to Yangtze River Delta Region, China. Water Air Soil Pollut., 203, 277289.
  • Zhu ZL 1997: Nitrogen Balance and Cycling in Agroecosystems of China. In Nitrogen in Soils of China, Ed. ZLZhu, QXWen and JRFreney., pp. 323330, Kluwer Academic Publishers, Dordreche/Boston/London.
  • Zhu ZL, Chen DL 2002: Nitrogen fertilizer use in China-Contributions of food production, impacts on the environment and best management strategies. Nutr. Cycl. Agroecosyst., 63, 117127.
  • Zou JW, Lu YY, Huang Y 2010: Estimates of synthetic fertilizer N-induced direct nitrous oxide emission from Chinese croplands during 1980–2000. Environ. Pollut., 158, 631635.