Processes and factors controlling N₂O production in an intensively managed low carbon calcareous soil under sub-humid monsoon conditions

An automated system for continuous measurement of N₂O fluxes on an hourly basis was employed to study N₂O emissions in an intensively managed low carbon calcareous soil under sub-humid temperate monsoon conditions. N₂O emissions occurred mainly within two weeks of application of NH₄⁺-based fertilizer and total N₂O emissions in wheat (average 0.35 or 0.21 kg N ha⁻¹ season⁻¹) and maize (average 1.47 or 0.49 kg N ha⁻¹ season⁻¹) under conventional and optimum N fertilization (300 and 50-122 kg N ha⁻¹, respectively) were lower than previously reported from low frequency measurements. Results from closed static chamber showed that N₂O was produced mainly from nitrification of NH₄⁺-based fertilizer, with little denitrification occurring due to limited readily oxidizable carbon and low soil moisture despite consistently high soil nitrate-N concentrations. Significant reductions in N₂O emissions can be achieved by optimizing fertilizer N rates, using nitrification inhibitors, or changing from NH₄⁺- to NO₃^ˉ-based fertilizers.     

Validation of DNDC for 22 long-term N2O field emission measurements

Twenty-two long-term measurements of direct N₂O emissions from soils in an intensive agricultural area were used for the validation of the process-based DNDC model (version 8.3P). Model simulations were evaluated for temporal patterns of N₂O, NH₄⁺, NO₃⁻ and water-filled pore space (WFPS) and total N₂O emissions. Several soil and crop input parameter adjustments to the model were evaluated but only the recalculation of the WFPS at wilting point and at field capacity, using pedotransfer functions, resulted in a clear improvement of the simulated variables (WFPS in all cases, N₂O in some cases). Therefore, only this adjustment was made to DNDC 8.3P. This change, however, resulted for some cases (both cropland and grassland) in retardation of nitrate leaching and to a lesser extent of NH₄⁺ to the deeper soil layers. The goodness of fit of the simulated temporal pattern of N₂O varied considerably between sites. The total simulated N₂O emissions from cropland showed a good agreement with the measurements, although there was a systematic overestimation of 7.4 kg N₂O-N ha⁻¹. Grassland soils, in contrast, gave a low agreement between total simulated and measured N₂O losses. On the basis of all measured data a regional emission factor of 3.16 with a 95% confidence interval of −0.89 to 7.21 could be calculated. DNDC simulations resulted in an emission factor of 6.49 with a 95% confidence interval of 4.04–8.93. The overall outcome of the N₂O emission measurements and DNDC simulations were compared with several empirical regression models, which may be applicable for a temperate climate system. All of the tested regression models showed reliable results up to a N₂O emission of 10 kg N₂O-N ha⁻¹. Higher emissions, however, were systematically underestimated. Though DNDC both under- and overestimated specific sites, the general agreement, over the whole range between measurements and simulations of total N₂O losses (simulations=0.82×meas.+6.2), was better than for the different regression models.     

N2O emissions at municipal solid waste landfill sites: Effects of CH4 emissions and cover soil

Municipal solid waste landfills are the significant anthropogenic sources of N₂O due to the cooxidation of ammonia by methane-oxidizing bacteria in cover soils. Such bacteria could be developed through CH₄ fumigation, as evidenced by both laboratory incubation and field measurement. During a 10-day incubation with leachate addition, the average N₂O fluxes in the soil samples, collected from the three selected landfill covers, were multiplied by 1.75 (p < 0.01), 3.56 (p < 0.01), and 2.12 (p < 0.01) from the soil samples preincubated with 5% CH₄ for three months when compared with the control, respectively. Among the three selected landfill sites, N₂O fluxes in two landfill sites were significantly correlated with the variations of the CH₄ emissions without landfill gas recovery (p < 0.001). N₂O fluxes were also elevated by the increase of the CH₄ emissions with landfill gas recovery in another landfill site (p > 0.05). The annual average N₂O flux was 176 ± 566 μg N₂O–N m^?2 h^?1 (p < 0.01) from sandy soil–covered landfill site, which was 72% (p < 0.05) and 173% (p < 0.01) lower than the other two clay soil covered landfill sites, respectively. The magnitude order of N₂O emissions in three landfill sites was also coincident by the results of laboratory incubation, suggesting the sandy soil cover could mitigate landfill N₂O emissions.     

Characterisation of soil emissions of nitric oxide at field and laboratory scale using high resolution method

Agricultural soils may account for 10% of anthropogenic emissions of NO, a precursor of tropospheric ozone with potential impacts on air quality and global warming. However, the estimation of this biogenic source strength and its relationships to crop management is still challenging because of the spatial and temporal variability of the NO fluxes.Here, we present a combination of new laboratory- and field-scale methods to characterise NO emissions and single out the effects of environmental drivers.First, NO fluxes were continuously monitored over the growing season of a maize-cropped field located near Paris (France), using 6 automatic chambers. Mineral fertilizer nitrogen was applied from May to October 2005. An additional field experiment was carried out in October to test the effects of N fertilizer form on the NO emissions. The automatic chambers were designed to measure simultaneously the NO and N₂O gases. Laboratory measurements were carried out in parallel using soil cores sampled at same site to test the response of NO fluxes to varying soil N–NH₄ and water contents, and temperatures. The effects of soil core thickness were also analysed.The highest NO fluxes occurred during the first 5 weeks following fertilizer application. The cumulative loss of NO–N over the growing season was estimated at 1.5 kg N ha^?1, i.e. 1.1% of the N fertilizer dose (140 kg N ha^?1). All rainfall events induced NO peak fluxes, whose magnitude decreased over time in relation to the decline of soil inorganic N. In October, NO emissions were enhanced with ammonium forms of fertilizer N. Conversely, the application of nitrate-based fertilizers did not significantly increase NO emissions compared to an unfertilized control. The results of the subsequent laboratory experiments were in accordance with the field observations in magnitude and time variations. NO emissions were maximum with a water soil content of 15% (w w^?1), and with a NH₄–N content of 180 mg NH₄–N kg soil^?1. The response of NO fluxes to soil temperature was fitted with two exponential functions, involving a Q₁₀ of 2.0 below 20 °C and a Q₁₀ of 1.4 above. Field and laboratory experiments indicated that most of the NO fluxes originated from the top 10 cm of soil. The characterisation of this layer in terms of mean temperature, NH₄ and water contents is thus paramount to explaining the variations of NO fluxes.     

Responses of CH(4), CO(2) and N(2)O fluxes to increasing nitrogen deposition in alpine grassland of the Tianshan Mountains

To assess the effects of nitrogen (N) deposition on greenhouse gas (GHG) fluxes in alpine grassland of the Tianshan Mountains in central Asia, CH₄, CO₂ and N₂O fluxes were measured from June 2010 to May 2011. Nitrogen deposition tended to significantly increase CH₄ uptake, CO₂ and N₂O emissions at sites receiving N addition compared with those at site without N addition during the growing season, but no significant differences were found for all sites outside the growing season. Air temperature, soil temperature and water content were the important factors that influence CO₂ and N₂O emissions at year-round scale, indicating that increased temperature and precipitation in the future will exert greater impacts on CO₂ and N₂O emissions in the alpine grassland. In addition, plant coverage in July was also positively correlated with CO₂ and N₂O emissions under elevated N deposition rates. The present study will deepen our understanding of N deposition impacts on GHG balance in the alpine grassland ecosystem, and help us assess the global N effects, parameterize Earth System models and inform decision makers.     

N2O emissions from municipal solid waste landfills with selected infertile cover soils and leachate subsurface irrigation

This study presents the field investigations into the effects of cover soils and leachate subsurface irrigation on N₂O emissions from municipal solid waste landfills. Landfill Site A and Site B, covered with carefully chosen infertile soils, were selected to monitor their diurnal and seasonal variations of N₂O emissions. The annual average N₂O flux was 469 ± 796 μg N₂O-N m⁻² h⁻¹ in Site B with leachate subsurface irrigation, three times that of Site A without leachate irrigation. When an additional soil containing lower contents of carbon and nitrogen was introduced to cover part of Site B, its N₂O fluxes decreased by 1-2 orders of magnitude compared with the left area of Site B. This suggested that carefully selected cover soils could substantially reduce N₂O emissions even under leachate subsurface irrigation. Statistical analysis proved that the availabilities of soil moisture and mineralized nitrogen were the key parameters controlling landfill N₂O emissions.     

Temporal variability of soil-atmospheric CO2 and CH4 fluxes from different land uses in mid-subtropical China

Different land uses in subtropics play an important role in regulating the global environmental changes. To reduce uncertainties of greenhouse gas (GHG) emissions of agricultural soils in subtropical ecosystem, a four years campaign was started to determine the temporal GHG (CO₂ and CH₄) fluxes from seven sites of four land use types (1 vegetable field, 3 uplands, 2 orchards, 1 pine forest). The mean annual budgets of CO₂, and CH₄ were 6.5～10.5 Mg CO₂ ha^?1 yr^?1, and +0.47 ～ ?2.37 kg CH₄ ha^?1 yr^?1, respectively. Pine forest had significantly lower CO₂ emission and higher CH₄ uptake than agriculture land uses. Tilled orchard emitted more CO₂ and oxidized less CH₄ than non-tilled orchard. Upland crops had higher CO₂ emissions than orchards, while abrupt differences of CH₄ uptake were observed between upland crops and orchards. Every year, the climate was warm and wet from April to September (the hot–humid season) and became cool and dry from October to March (the cool–dry season). Driven by seasonality of temperature and WFPS, CO₂ fluxes were significantly higher in the hot–humid season than in cool–dry season. Soil temperature, WFPS, NO₃^?–N and NH₄⁺–N contents interactively explained CH₄ uptake which was significantly higher in cool–dry season than in hot–humid season. We conclude that soil C fluxes from different land uses are strongly under control of different climatic predictors along with soil nutrient status, which interact in conjunction with each other to supply the readily available substrates.     

Nitrogen isotope variations in camphor (Cinnamomum Camphora) leaves of different ages in upper and lower canopies as an indicator of atmospheric nitrogen sources

Nitrogen isotopic composition of new, middle-aged and old camphor leaves in upper and lower canopies has been determined in a living area, near a motorway and near an industrial area (Jiangan Chemical Fertilizer Plant). We found that at sites near roads, more positive δ¹⁵N values were observed in the camphor leaves, especially in old leaves of upper canopies, and ?δ¹⁵N = δ¹⁵N_upper − δ¹⁵N_lower > 0, while those near the industrial area had more negative δ¹⁵N values and ?δ¹⁵N < 0. These could be explained by two isotopically different atmospheric N sources: greater uptake from isotopically heavy pools of atmospheric NO_x by old leaves in upper canopies at sites adjacent to roads, and greater uptake of ¹⁵N-depleted NH_y in atmospheric deposition by leaves at sites near the industrial area. This study presents novel evidence that ¹⁵N natural abundance of camphor leaves can be used as a robust indicator of atmospheric N sources.     

Seasonal variations of CH(4) and N(2)O emissions in response to water management of paddy fields located in Southeast China

Water management is one of the most important practices that affect methane (CH₄) and nitrous oxide (N₂O) emissions from paddy fields. A field experiment was designed to study the effects of controlled irrigation (CI) on CH₄ and N₂O emissions from paddy fields, with traditional irrigation (TI) as the control. The effects of CI on CH₄ and N₂O emissions from paddy fields were very clear. The peaks of CH₄ emissions from the CI paddies were observed 1-2 d after the water layer disappeared. Afterward, the emissions reduced rapidly and remained low until the soil was re-flooded. A slight increase of CH₄ emission was observed in a short period after re-flooding. N₂O emissions peaks from CI paddies were all observed 8-10 d after the fertilization at the WFPS ranging from 78.1% to 85.3%. Soil drying caused substantial N₂O emissions, whereas no substantial N₂O emissions were observed when the soil was re-wetted after the dry phase. Compared with TI, the cumulative CH₄ emissions from the CI fields were reduced by 81.8% on the average, whereas the cumulative N₂O emissions were increased by 135.4% on the average. The integrative global warming potential of CH₄ and N₂O on a 100-year horizon decreased by 27.3% in the CI paddy fields, whereas no significant difference in the rice yield was observed between the CI and TI fields. These results suggest that CI can effectively mitigate the integrative greenhouse effect caused by CH₄ and N₂O emissions from paddy fields while ensuring the rice yield.     

Effect of bulking agents on maturity and gaseous emissions during kitchen waste composting

This study investigated the effect of bulking agents on the maturity and gaseous emissions of composting kitchen waste. Three different bulking agents (cornstalks, sawdust, and spent mushroom substrate) were used to compost kitchen waste under aerobic conditions in 60-L reactors for a 28-d period. A control treatment was also studied using kitchen waste without a bulking agent. During the experiment, maturity indexes such as temperature, pH value, C/N ratio, and germination index were determined, and continuous measurements of leachate and gaseous emissions (CH₄, N₂O, and NH₃) were taken. The results showed that all of the composts with bulking agents reached the required maturity standard, and the addition of spent mushroom substrate gave the highest maturity (C/N ratio decreased from 23 to 16 and germination index increased from 53% to 111%). The bulking agents also reduced leachate production and CH₄ and N₂O emissions, but had little impact on NH₃ emissions. Composting with sawdust as a bulking agent was found to emit less total greenhouse gas (33 kg CO₂-eq t⁻¹ dry matter) than the other treatments.     

Measurements and modeling of reactive nitrogen deposition in southeast Brazil

Increased reactive nitrogen (N_r) deposition due to expansion of agro-industry was investigated considering emission sources, atmospheric transport and chemical reactions. Measurements of the main inorganic nitrogen species (NO₂, NH₃, HNO₃, and aerosol nitrate and ammonium) were made over a period of one year at six sites distributed across an area of ∼130,000 km² in southeast Brazil. Oxidized species were estimated to account for ∼90% of dry deposited N_r, due to the region’s large emissions of nitrogen oxides from biomass burning and road transport. NO₂-N was important closer to urban areas, however overall HNO₃-N represented the largest component of dry deposited N_r. A simple mathematical modeling procedure was developed to enable estimates of total N_r dry deposition to be made from knowledge of NO₂ concentrations. The technique, whose accuracy here ranged from <1% to 29%, provides a useful new tool for the mapping of reactive nitrogen deposition.     

Differences in the Spatial Variability Among CO2, CH4, and N2O Gas Fluxes from an Urban Forest Soil in Japan

The spatial variability of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) fluxes from forest soil with high nitrogen (N) deposition was investigated at a rolling hill region in Japan. Gas fluxes were measured on July 25th and December 5th, 2008 at 100 points within a 100 × 100 m grid. Slope direction and position influenced soil characteristics and site-specific emissions were found. The CO₂ flux showed no topological difference in July, but was significantly lower in December for north-slope with coniferous trees. Spatial dependency of CH₄ fluxes was stronger than that of CO₂ or N₂O and showed a significantly higher uptake in hill top, and emissions in the valley indicating strong influence of water status. N₂O fluxes showed no spatial dependency and exhibited high hot spots at different topology in July and December. The high N deposition led to high N₂O fluxes and emphasized the spatial variability.     

The effect of diet manipulation on nitrous oxide and methane emissions from manure application to incubated grassland soils

Changes to agricultural management, particularly of the nitrogen (N) input to farms, have great potential for mitigating emissions of N containing gases, especially the greenhouse gas nitrous oxide (N₂O). Manipulating diets fed to livestock is a potential method for controlling N excretion and emissions of greenhouse gases (GHG's) to the atmosphere. We selected three slurries derived from sheep that had been fed, either ensiled ryegrass (Lolium hybridicum), lucerne (Medicago sativa) or kale (Brassica oleracea) and applied them to a grassland soil from the UK in a laboratory experiment using a special He/O₂ atmosphere incubation facility. The resulting fluxes of N₂O, CH₄ and N₂ were measured, with the largest total N fluxes generated by the ryegrass slurry treatment (14.23 ryegrass, 10.84 lucerne, 13.88 kale and 4.40 kg N ha⁻¹ from the control). Methane was emitted only from the ryegrass slurry treatment. The isotopomer signatures for N₂O in the control and lucerne slurry treatments indicated that denitrification was the main process responsible for N₂O emissions.     

Nitrous oxide emission from an agricultural field: Comparison between measurements by flux chamber and micrometerological techniques

The soil in a drained fjord area, reclaimed for arable farming, produced N₂O mainly at 75–105 cm depth, just above the ground water level. Surface emissions of N₂O were measured from discrete small areas by closed and open-flow chamber methods, using gas chromatographic analysis and over larger areas by integrative methods: flux gradient (analysis by FTIR), conditional sampling (analysis by TDLAS), and eddy covariance (analysis by TDLAS). The mean emission of N₂O as determined by chamber procedures during a 9-day campaign was 162–202 μg N₂ONm⁻²h⁻¹ from a wheat stubble and 328–467 μg N₂ONm⁻² h⁻¹ from a carrot field. The integrative approaches gave N₂O emissions of 149–495 μg N₂ONm⁻² h⁻¹, i.e. a range similar to those determined with the chamber methods. Wind direction affected the comparison of chamber and integrative methods because of patchiness of the N₂O emission over the area. When a uniform area with a single type of vegetation had a dominant effect on the N₂O gradient at the sampling mast, the temporal variation in N₂O emission determined by the flux gradient/FTIR method and chamber methods was very similar, with differences of only 18% or less in mean N₂O emission, well below the variation encountered with the chamber methods themselves. A detailed comparison of FTIR gradient and chamber data taking into account the precise emission footprint showed good agreement. It is concluded that there was no bias between the different approaches used to measure the N₂O emission and that the precision of the measurements was determined by the spatial variability of the N₂O emission at the site and the variability inherent in the individual techniques. These results confirm that measurements of N₂O emissions from different ecosystems obtained by the different methods can be meaningfully compared.     

Nitrous oxide emissions from mineral and organic soils of a Norway spruce stand in South–West Germany

Due to the high temporal and spatial variability of N₂O fluxes, estimates of N₂O emission from temperate forest ecosystems are still highly uncertain, particularly at larger scales. Although highest N₂O emissions with up to 7.0 kg N ha⁻¹ yr⁻¹ were mainly reported for soils affected by stagnant water, most of the reported gas flux measurements were performed at forest sites with well-aerated soils yielding mostly to low mean annual emission rates less than 1.0 kg N ha⁻¹ yr⁻¹. This study compares N₂O fluxes from upland (Cambisols) and temporally water-logged (Gleysols, Histosols) soils of the Central Black Forest (South-West Germany) over a period of 2 yr. Mean annual N₂O fluxes from investigated soils ranged between 0.2 and 3.9 kg N ha⁻¹ yr⁻¹. The fluxes showed a large variability between the different soil types. Emissions could be clearly ranked in the following order: Cambisols (0.26–0.75 kg N ha⁻¹ yr⁻¹)<Gleysols (1.37–2.68 kg N ha⁻¹ yr⁻¹)<Histosol (3.66–3.95 kg N ha⁻¹ yr⁻¹). Although the Cambisols cover two-thirds of the investigated area, only about half of the overall N₂O is emitted from this soil type. Therefore, regional or national N₂O fluxes from temperate forest soils are underestimated if soils characterised by intermediate aeration conditions are disregarded.     

Spatial and temporal variations of nitrous oxide flux between coastal marsh and the atmosphere in the Yellow River estuary of China

To investigate the spatial and seasonal variations of nitrous oxide (N₂O) fluxes and understand the key controlling factors, we explored N₂O fluxes and environmental variables in high marsh (HM), middle marsh (MM), low marsh (LM), and mudflat (MF) in the Yellow River estuary throughout a year. Fluxes of N₂O differed significantly between sampling periods as well as between sampling positions. During all times of day and the seasons measured, N₂O fluxes ranged from ?0.0051 to 0.0805 mg N₂O m^?2 h^?1, and high N₂O emissions occurred during spring (0.0278 mg N₂O m^?2 h^?1) and winter (0.0139 mg N₂O m^?2 h^?1) while low fluxes were observed during summer (0.0065 mg N₂O m^?2 h^?1) and autumn (0.0060 mg N₂O m^?2 h^?1). The annual average N₂O flux from the intertidal zone was 0.0117 mg N₂O m^?2 h^?1, and the cumulative N₂O emission throughout a year was 113.03 mg N₂O m^?2, indicating that coastal marsh acted as N₂O source. Over all seasons, N₂O fluxes from the four marshes were significantly different (p?<?0.05), in the order of HM (0.0256?±?0.0040 mg N₂O m^?2 h^?1)?>?MF (0.0107?±?0.0027 mg N₂O m^?2 h^?1)?>?LM (0.0073?±?0.0020 mg N₂O m^?2 h^?1)?>?MM (0.0026?±?0.0011 mg N₂O m^?2 h^?1). Temporal variations of N₂O emissions were related to the vegetations (Suaeda salsa, Phragmites australis, and Tamarix chinensis) and the limited C and mineral N in soils during summer and autumn and the frequent freeze/thaw cycles in soils during spring and winter, while spatial variations were mainly affected by tidal fluctuation and plant composition at spatial scale. This study indicated the importance of seasonal N₂O contributions (particularly during non-growing season) to the estimation of local N₂O inventory, and highlighted both the large spatial variation of N₂O fluxes across the coastal marsh (CV?=?158.31 %) and the potential effect of exogenous nitrogen loading to the Yellow River estuary on N₂O emission should be considered before the annual or local N₂O inventory was evaluated accurately.     

High concentrations and dry deposition of reactive nitrogen species at two sites in the North China Plain

Atmospheric concentrations of major reactive nitrogen (N_r) species were quantified using passive samplers, denuders, and particulate samplers at Dongbeiwang and Quzhou, North China Plain (NCP) in a two-year study. Average concentrations of NH₃, NO₂, HNO₃, pNH₄⁺ and pNO₃⁻ were 12.0, 12.9, 0.6, 10.3, and 4.7 μg N m⁻³ across the two sites, showing different seasonal patterns of these N_r species. For example, the highest NH₃ concentration occurred in summer while NO₂ concentrations were greater in winter, both of which reflected impacts of N fertilization (summer) and coal-fueled home heating (winter). Based on measured N_r concentrations and their deposition velocities taken from the literature, annual N dry deposition was up to 55 kg N ha⁻¹. Such high concentrations and deposition rates of N_r species in the NCP indicate very serious air pollution from anthropogenic sources and significant atmospheric N input to crops.     

Spatiotemporal variations of nitrous oxide (N2O) emissions from two reservoirs in SW China

Greenhouse gas emissions from hydroelectric dams have recently given rise to controversies about whether hydropower still provides clean energy. China has a large number of dams used for energy supply and irrigation, but few studies have been carried out on aquatic nitrous oxide (N₂O) variation and its emissions in Chinese river-reservoir systems. In this study, N₂O spatiotemporal variations were investigated monthly in two reservoirs along the Wujiang River, Southwest China, and the emission fluxes of N₂O were estimated. N₂O production in the reservoirs tended to be dominated by nitrification, according to the correlation between N₂O and other parameters. N₂O saturation in the surface water of the Wujiangdu reservoir ranged from 214% to 662%, with an average fluctuation of 388%, while in the Hongjiadu reservoir, it ranged from 201% to 484%, with an average fluctuation of 312%. The dissolved N₂O in both reservoirs was over-saturated with respect to atmospheric equilibrium levels, suggesting that the reservoirs were net sources of N₂O emissions to the atmosphere. The averaged N₂O emission flux in the Wujiangdu reservoir was 0.64 μmol m^?2 h^?1, while it was 0.45 μmol m^?2 h^?1 in the Hongjiadu reservoir, indicating that these two reservoirs had moderate N₂O emission fluxes as compared to other lakes in the world. Downstream water of the dams had quite high levels of N₂O saturation, and the estimated annual N₂O emissions from hydropower generation were 3.60 × 10⁵ and 2.15 × 10⁵ mol N₂O for the Wujiangdu and the Hongjiadu reservoir, respectively. These fluxes were similar to the total N₂O emissions from the reservoir surfaces, suggesting that water released from reservoirs would be another important way for N₂O to diffuse into the atmosphere. It can be concluded that dam construction significantly changes the water environment, especially in terms of nutrient status and physicochemical conditions, which have obvious influences on the N₂O spatiotemporal variations and emissions.     

Effects of land use conversion and fertilization on CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O fluxes from typical hilly red soil

Land use conversion and fertilization have been widely reported to be important managements affecting the exchanges of greenhouse gases between soil and atmosphere. For comprehensive assessment of methane (CH₄) and nitrous oxide (N₂O) fluxes from hilly red soil induced by land use conversion and fertilization, a 14-month continuous field measurement was conducted on the newly converted citrus orchard plots with fertilization (OF) and without fertilization (ONF) and the conventional paddy plots with fertilization (PF) and without fertilization (PNF). Our results showed that land use conversion from paddy to orchard reduced the CH₄ fluxes at the expense of increasing the N₂O fluxes. Furthermore, fertilization significantly decreased the CH₄ fluxes from paddy soils in the second stage after conversion, but it failed to affect the CH₄ fluxes from orchard soils, whereas fertilizer applied to orchard and paddy increased soil N₂O emissions by 68 and 113.9 %, respectively. Thus, cumulative CH₄ emissions from the OF were 100 % lower, and N₂O emissions were 421 % higher than those from the PF. Although cumulative N₂O emissions were stimulated in the newly converted orchard, the strong reduction of CH₄ led to lower global warming potentials (GWPs) as compared to the paddy. Besides, fertilization in orchard increased GWPs but decreased GWPs of paddy soils. In addition, measurement of soil moisture, temperature, dissolved carbon contents (DOCs), and ammonia (NH₄ ⁺-N) and nitrate (NO₃ ^?-N) contents indicated a significant variation in soil properties and contributed to variations in soil CH₄ and N₂O fluxes. Results of this study suggest that land use conversion from paddy to orchard would benefit for reconciling greenhouse gas mitigation and citrus orchard cultivation would be a better agricultural system in the hilly red soils in terms of greenhouse gas emission. Moreover, selected fertilizer rate applied to paddy would lead to lower GWPs of CH₄ and N₂O. Nevertheless, more field measurements from newly converted orchard are highly needed to gain an insight into national and global accounting of CH₄ and N₂O emissions.