Magnitude Of N2O Emissions Research Articles

Investigating key drivers of N2O emissions in heterogeneous riparian sediments: Reactive transport modeling and statistical analysis

Nitrous oxide (N2O) is a potent greenhouse gas that also contributes to ozone depletion. Recent studies have identified river corridors as significant sources of N2O emissions. Surface water-groundwater (hyporheic) interactions along river corridors induce flow and reactive nitrogen transport through riparian sediments, thereby generating N2O. Despite the prevalence of these processes, the controlling influence of physical and geochemical parameters on N2O emissions from coupled aerobic and anaerobic reactive transport processes in heterogeneous riparian sediments is not yet fully understood. This study presents an integrated framework that combines a flow and multi-component reactive transport model (RTM) with an uncertainty quantification and sensitivity analysis tool to determine which physical and geochemical parameters have the greatest impact on N2O emissions from riparian sediments. The framework involves the development of thousands of RTMs, followed by global sensitivity and responsive surface analyses. Results indicate that characterizing the denitrification reaction rate constant and permeability of intermediate-permeability sediments (e.g., sandy gravel) are crucial in describing coupled nitrification-denitrification reactions and the magnitude of N2O emissions. This study provides valuable insights into the factors that influence N2O emissions from riparian sediments and can help in developing strategies to control N2O emissions from river corridors.

Hot Moments of N2O Emission Under Water and Nitrogen Management in Three Types of Steppe

AbstractHot moments of soil nitrous oxide (N2O) emission contribute to large fractions of total annual emissions. Magnitudes of N2O emission during hot moments to increasing water and nitrogen (N) availabilities in different steppe types were not well understood. Based on soil monoliths collected from three steppes (meadow, typical, and desert steppes) in northern China, we found that the typical steppe held the lowest N2O emission among the three steppes. Water and N co‐addition could increase soil N2O emission by up to 245‐fold. Water addition significantly enhanced soil N2O emission in all the three steppes, but the sensitivity of soil N2O emission to water addition decreased from desert steppe (r2 = 0.83) to typical (r2 = 0.73) and meadow (r2 = 0.66) steppes. Nitrogen addition significantly promoted soil N2O emission only in the meadow steppe where soil C:N was relatively higher than the other two steppes. Water and N addition displayed strong positive interaction on soil N2O emission in the meadow steppe while negative interaction in the typical steppe. Different responses of plants, microorganisms and soil NO3− concentration drove the variation in magnitude of soil N2O emission between the two steppes. Our results illustrate different interactions of water and N addition on hot moments of soil N2O emission in the three steppes. We suggest that the pulsed feature of N2O emission should be taken into account in prediction of greenhouse gas emission in the global arid and semiarid grasslands.

Nutrient Management Drives the Direction and Magnitude of Nitrous Oxide Flux in Crop Residue-Returned Soil Under Different Soil Moisture

Crop residues as key organic carbon inputs have the potential for soil carbon sequestration. However, previous studies have shown an inconsistent effect of residue return on the direction and magnitude of soil nitrous oxide (N2O) emission. We used a laboratory-based soil incubation study to test the response of N2O emission to crop residue type, soil moisture, and how nutrient management modulates these responses. In this study, we incorporated crop residues with different qualities (wheat, rice, soybean, and maize) at two soil moisture contents {80% field capacity (FC) and 60% FC} and under seven nutrient levels: N0P0K0 (no nutrients), N0PK, N100PK, N150PK, N100PK + manure@ 5 Mg ha−1, N100PK + biochar@ 5 Mg ha−1, and N150PK + biochar@ 5 Mg ha−1. The results demonstrated significant (p < 0.01) differences in the magnitude of N2O emissions among treatments. However, only the interaction effect of residue × nutrient and nutrient × moisture was significant (p < 0.05). N100PK and N150PK at 80% FC mitigated N2O emission by approximately 20% in wheat residue-amended soil (cf. control soil without residue). In contrast, maize residue amendment (cf. control soil) increased N2O emission by 130% under N0P0K0 and 80% FC. Residue effects were negatively correlated with the C:N ratio, and a strong positive correlation (p < 0.01) was obtained between N2O emission and CO2 respiration, labile carbon, mineral N, and residue total nitrogen (TN). When no nutrients were added, N2O emission was higher in residue returned soil. However, cumulative fluxes of N2O decreased by 6–17% when maize and wheat residues (cf. control soil) were applied with nutrients. Negative fluxes of N2O indicating consumption were observed in every treatment after 57 days of incubation and were most pronounced in control soil without residue and nutrients. Decreasing the soil moisture from 80% FC to 60% FC, the N2O consumption rate increased by 6.6 times across residue types and nutrient management. The regression analysis and structural equation modeling (SEM) results showed that residue TN, soil CO2 emission, NO3-N, and labile SOC were the key predictor variables and could explain 82% variability in the soil N2O emission in the Vertisols of Central India. The results suggested that nutrient addition (NPK) could alter the magnitude and direction of soil N2O flux by residue type and soil moisture by influencing the underlying soil microbial processes of the C and N cycle in the Vertisol of subtropical India.

Four decades of nitrous oxide emission from Chinese aquaculture underscores the urgency and opportunity for climate change mitigation

As the fastest growing food production sector in the world, aquaculture may become an important source of nitrous oxide (N2O)—a potent greenhouse gas and the dominant source of ozone-depleting substances in the stratosphere. China is the largest aquaculture producer globally; however, the magnitude of N2O emission from Chinese aquaculture systems (CASs) has not yet been extensively investigated. Here, we quantified N2O emission from the CASs since the Reform and Opening-up (1979–2019) at the species-, provincial-, and national-levels using annual aquaculture production data, based on nitrogen (N) levels in feed type, feed amount, feed conversion ratio, and emission factor (EF). Our estimate indicates that over the past 41 years, N2O emission from CASs has increased approximately 25 times from 0.67 ± 0.04 GgN in 1979 to 16.69 ± 0.31 GgN in 2019. Freshwater fish farming, primarily in two provinces, namely, Guangdong and Hubei, where intensive freshwater fish farming has been adopted in the past decades, accounted for approximately 89% of this emission increase. We also calculated the EF for each species, ranging from 0.79 ± 0.23 g N2O kg−1 animal to 2.41 ± 0.14 g N2O kg−1 animal. The results of this study suggest that selecting low-EF species and improving feed use efficiency can help reduce aquaculture N2O emission for building a climate-resilient sustainable aquaculture.

Suppressive effect of the deep placement of lime nitrogen on N2O emissions in a soybean field

Deep placement of slow-release nitrogen (N) fertilizers improves the growth and yield of soybean with a high N use efficiency. This study examined the effectiveness of deep placement of lime nitrogen (LN) in reducing N2O emissions in a soybean field and compared it with conventional fertilization. Before sowing soybeans, the starter N fertilizer (16 kg-N ha−1 ammonium sulfate) was mixed in the surface soil and the following four treatments were installed: the control with only the starter N (CT), conventional top-dressing of 60 kg-N ha−1 coated urea (CV), deep placement (20 cm depth) of 100 kg-N ha−1 urea (DU), and deep placement (20 cm depth) of 100 kg-N ha−1 LN (DL). The seasonal patterns of N2O emission rates measured using the closed chamber method differed among the treatments: in CT, N2O emissions were relatively low; in CV, N2O emissions derived from the top-dressed coated urea were observed from 91 days after sowing; in DU and DL, deeply-placed N was converted to N2O in the early growth stages. The cumulative N2O emissions in DL (1.8 kg-N ha−1) during the soybean cultivation period were significantly lower than those in DU (3.1 kg-N ha−1) and CV (2.8 kg-N ha−1), and slightly higher than CT (1.2 kg-N ha−1). The magnitude of N2O emissions was significantly lower in DL than DU, indicating that the choice of N fertilizer is important to reduce N2O emissions. Focusing on N2O emissions per unit coarse grain yield of soybeans, the value in DL was 0.45 g-N kg−1, which was significantly lower than 0.74 g-N kg−1 in CV. In conclusion, the deep placement of LN has the potential to be a sustainable farming method that can promote yields and reduce N2O emissions in soybean cultivation for high yield with N fertilization.

Comparison of methods for nitrous oxide emission estimation in full-scale activated sludge.

Nitrous oxide (N2O) gas transfer was studied in a full-scale process to correlate liquid phase N2O concentrations with gas phase N2O emissions and compare methods of determining the volumetric mass transfer coefficient, KLa. Off-gas and liquid phase monitoring were conducted at the Viikinmäki wastewater treatment plant (WWTP) over a two-week period using a novel method for simultaneous measurement of dissolved and off-gas N2O and O2 from the same location. KLa was calculated with three methods: empirically, based on aeration superficial velocity, from experimentally determined O2 KLa, and using a static value of best fit. The findings of this study indicated trends in local emitted N2O consistently matched trends in local dissolved N2O, but the magnitude of N2O emissions could not be accurately estimated without correction. After applying a static correction factor, the O2 method, using experimentally determined O2 KLa, provided the best N2O emission estimation over the data collection period. N2O emissions estimated using the O2 method had a root mean square error (RMSE) of 70.5 compared against measured concentrations ranging from 3 to 1,913 ppm and a maximum 28% error. The KLa value, and therefore the method of KLa determination, had a significant impact on estimated emissions.

X‐ray computed tomography to predict soil N2O production via bacterial denitrification and N2O emission in contrasting bioenergy cropping systems

AbstractWhile renewable biofuels can reduce negative effects of fossil fuel energy consumption, the magnitude of their benefits depends on the magnitude of N2O emissions. High variability of N2O emissions overpowers efforts to curb uncertainties in estimating N2O fluxes from biofuel systems. In this study, we explored (a) N2O production via bacterial denitrification and (b) N2O emissions from soils under several contrasting bioenergy cropping systems, with specific focus on explaining N2O variations by accounting for soil pore characteristics. Intact soil samples were collected after 9 years of implementing five biofuel systems: continuous corn with and without winter cover crop, monoculture switchgrass, poplars, and early‐successional vegetation. After incubation, N2O emissions were measured and bacterial denitrification was determined based on the site‐preference method. Soil pore characteristics were quantified using X‐ray computed microtomography. Three bioenergy systems with low plant diversity, that is, corn and switchgrass systems, had low porosities, low organic carbon contents, and large volumes of poorly aerated soil. In these systems, greater volumes of poorly aerated soil were associated with greater bacterial denitrification, which in turn was associated with greater N2O emissions (R2 = 0.52, p < 0.05). However, the two systems with high plant diversity, that is, poplars and early‐successional vegetation, over the 9 years of implementation had developed higher porosities and organic carbon contents. In these systems, volumes of poorly aerated soil were positively associated with N2O emissions without a concomitant increase in bacterial denitrification. Our results suggest that changes in soil pore architecture generated by long‐term implementation of contrasting bioenergy systems may affect the pathways of N2O production, thus, change associations between N2O emissions and other soil properties. Plant diversity appears as one of the factors determining which microscale soil characteristics will influence the amounts of N2O emitted into the atmosphere and, thus, which can be used as effective empirical predictors.

Parameterizing an agricultural production model for simulating nitrous oxide emissions in a wheat–maize system in the North China Plain

AbstractConcentrations of atmospheric nitrous oxide (N2O), a potent greenhouse gas, have been continuously increasing, and cropland soils are one of the largest sources of N2O. Variations in environmental and anthropogenic factors have substantial impacts on both the frequency and magnitude of N2O emissions. Based on measurements from a wheat–maize system in the North China Plain, the authors parameterized the Agricultural Production Systems Simulator (APSIM) model, which was initially developed in Australia, for simulating N2O emissions under different agricultural management practices. After calibrating one of the key parameters – the fraction of N2O lost in nitrification (k2) – the results showed that the model successfully captured the daily N2O fluxes under different nitrogen fertilization treatments, but underestimated some large peak fluxes. By pooling all data together, the calibrated APSIM model also performed well in representing cumulative N2O emissions under various treatments at annual and fi...

Ecological controls on N<sub>2</sub>O emission in surface litter and near-surface soil of a managed grassland: modelling and measurements

Abstract. Large variability in N2O emissions from managed grasslands may occur because most emissions originate in surface litter or near-surface soil where variability in soil water content (θ) and temperature (Ts) is greatest. To determine whether temporal variability in θ and Ts of surface litter and near-surface soil could explain this in N2O emissions, a simulation experiment was conducted with ecosys, a comprehensive mathematical model of terrestrial ecosystems in which processes governing N2O emissions were represented at high temporal and spatial resolution. Model performance was verified by comparing N2O emissions, CO2 and energy exchange, and θ and Ts modelled by ecosys with those measured by automated chambers, eddy covariance (EC) and soil sensors on an hourly timescale during several emission events from 2004 to 2009 in an intensively managed pasture at Oensingen, Switzerland. Both modelled and measured events were induced by precipitation following harvesting and subsequent fertilizing or manuring. These events were brief (2–5 days) with maximum N2O effluxes that varied from < 1 mgNm−2h−1 in early spring and autumn to > 3 mgNm−2h−1 in summer. Only very small emissions were modelled or measured outside these events. In the model, emissions were generated almost entirely in surface litter or near-surface (0–2 cm) soil, at rates driven by N availability with fertilization vs. N uptake with grassland regrowth and by O2 supply controlled by litter and soil wetting relative to O2 demand from microbial respiration. In the model, NOx availability relative to O2 limitation governed both the reduction of more oxidized electron acceptors to N2O and the reduction of N2O to N2, so that the magnitude of N2O emissions was not simply related to surface and near-surface θ and Ts. Modelled N2O emissions were found to be sensitive to defoliation intensity and timing which controlled plant N uptake and soil θ and Ts prior to and during emission events. Reducing leaf area index (LAI) remaining after defoliation to half that under current practice and delaying harvesting by 5 days raised modelled N2O emissions by as much as 80 % during subsequent events and by an average of 43 % annually. Modelled N2O emissions were also found to be sensitive to surface soil properties. Increasing near-surface bulk density by 10 % raised N2O emissions by as much as 100 % during emission events and by an average of 23 % annually. Relatively small spatial variation in management practices and soil surface properties could therefore cause the large spatial variation in N2O emissions commonly found in field studies. The global warming potential from annual N2O emissions in this intensively managed grassland largely offset those from net C uptake in both modelled and field experiments. However, model results indicated that this offset could be adversely affected by suboptimal land management and soil properties.

Effects of different forms of plant-derived organic matter on nitrous oxide emissions.

To investigate the impact of different forms of plant-derived organic matter on nitrous oxide (N2O) emissions, an incubation experiment with the same rate of total nitrogen (N) application was carried out at 25 °C for 250 days. Soils were incorporated with maize-derived organic matter (i.e., maize residue-derived dissolved organic matter and maize residues with different C/N ratios) and an inorganic N fertilizer (urea). The pattern and magnitude of nitrous oxide (N2O) emissions were affected by the form of N applied. Single application of maize-derived organic matter resulted in a higher N2O emission than single application of the inorganic N fertilizer or combined application of the inorganic N fertilizer and maize-derived organic matter. The positive effect of maize residue-derived dissolved organic matter (DOM) addition on N2O emissions was relatively short-lived and mainly occurred at the early stage following DOM addition. In contrast, the positive effect induced by maize residue addition was more pronounced and lasted for a longer period. Single application of maize residues resulted in a substantial decrease in soil nitric nitrogen (NO3(-)-N), but it did not affect the production of N2O. No significant relationship between N2O emission and NO3(-)-N and ammonium nitrogen (NH4(+)-N) suggested that the availability of soil N was not limiting the production of N2O in our study. The key factors affecting soil N2O emission were the soil dissolved organic carbon (DOC) content and metabolism quotient (qCO2). Both of them could explain 87% of the variation in cumulative N2O emission. The C/N ratio of maize-derived organic matter was a poor predictor of N2O emission when the soil was not limited by easily available C and the available N content met the microbial N demands for nitrification and denitrification. The results suggested that the magnitude of N2O emission was determined by the impact of organic amendments on soil C availability and microbial activity rather than on soil N availability. In agricultural management practices, if the N inputs from organic and inorganic N fertilizers are equivalent, addition of organic N fertilizers that contain high amounts of available C will result in a higher N2O emission.

Estimating nitrous oxide emission flux from arable lands in China using improved background emission and fertilizer-induced emission factors

A nitrous oxide (N2O) emission database was compiled for arable land (284 measurements from 62 studies) to establish predictive models for building a greenhouse gas emission inventory in China. Arable lands were grouped into dry land and rice paddy based on the IPCC 2006 guidelines. The results of the meta analysis show that the annual mean N2O fluxes from dry land and rice paddy were 4.69±4.62 (SD) and 5.89±3.23kg N2O–N ha–1 yr–1. Fertilizer–induced N2O emission factors were 0.68±0.41% for dry land, and 0.49±0.43% for rice paddy. The relationship between N2O flux from arable lands and various environmental variables were analyzed, and the magnitude of N2O emissions from zero mineral N addition control plots (background emission) was determined based on precipitation. Based on the above background emissions and correlation coefficients, two new predictive models were established to estimate N2O emissions from arable lands in China. Comparison showed that the precipitation–rectified background emissions could largely improve the model predictions, and the two new models had better performance than the 1996 IPCC guideline method. Therefore, it is strongly recommended that the important local environmental variables be included in the estimates when compiling a national N2O emission inventory.

Nitrous oxide emissions from an Andosol upland field cropped to wheat and soybean with different tillage systems and organic matter applications

To elucidate effects of tillage systems and organic-matter applications on N2O emissions, we assessed seasonal patterns and magnitudes of N2O emissions from Andosol upland soil growing wheat and soybeans using different tillage systems (conventional tillage and no-tillage) and organic-matter applications (crop-residue, crop-residue and cattle manure, and none). Mean N2O emissions during June 2008 - October 2010 were 41-134 mgN m-2 yr-1. The N2O emissions were observed immediately after manure application, fertilizer application, and during the later growing season in soybean-cropped soil. ANOVA revealed that the kind of crop and the organic-matter applications affect N2O emissions, unlike tillage systems. Greater N2O emissions in soil with residues and manure suggest that NO3--N determines N2O production by denitrification. Additionally, N2O emissions are greater in soybean-cropped soil, probably because of denitrification. The presence of fresh organic matter such as shed roots and degraded root nodules, NO3--N, or NO2--N under wet soil conditions is necessary for N2O production by denitrification. The water-filled pore space (WFPS) in no-tilled soil is consistently greater than that in conventionally tilled soil, but it does not affect N2O emissions, suggesting that soil wetness changes are the cause: tillage is not the sole limiting factor for N2O production in well-aerated soil. Greater N2O emissions during warm, wet periods of the growing season imply that emissions are related to climatic conditions that affect the soil environment and the resultant microbial activity. Nevertheless, N2O emissions from the study site with light-colored Andosol resembled those from Andosol, but were less than those from the other soil types such as those of Brown Forest soil, Brown Lowland soil, Grey Lowland soil, Wet Andosol, and Peat soil. Light-colored Andosol of this study site has lower background emissions.

Changing pH shifts the microbial sourceas well as the magnitude of N2O emission from soil

Here, we examine the effect of long-term pH differences and short-term pH change on N2O emissions from soil, and the microbial source (ammonia oxidation versus denitrification) of 15N-N2O emissions. 15N-fertiliser (20 g N m−2; 10 atom% excess 15N) was applied to (1) a silt loam soil of pH 7 held at 50% and 65% water-filled pore space (WFPS) (experiment 1) and (2) a loamy sand soil maintained at pH 4.5 and pH 7 for over 40 years (experiment 2). Soils were limed with CaCO3 or acidified with H2SO4, and comparisons were made with unadjusted soils. Ammonia oxidation was the main microbial source of 15N-N2O in soils limed to pH 7.0–8.1, unadjusted pH 7.1 (Experiment 1) and long-term pH 7 (experiment 2) soils. Eighty percent of 15N-N2O from the long-term pH 4.5 soil (experiment 2) was derived from denitrification suggesting a possible inhibition of N2O reduction. Short-term acidification to pH 5.6 or 4.3 lowered N2O emissions. Liming of the pH 4.5 soil resulted in over four times greater N2O emission (11 mg 14+15N-N2O m−2 over 41 days) than from the long-term pH 7.0 soil (experiment 2), with an associated increase in ammonia oxidiser-N2O and decrease in denitrifier-N2O production. This is the first report of a pH-induced change in microbial source of N2O. Our results highlight the importance of distinguishing between short- and long-term effects of pH management when predicting N2O emissions from soil, as they exhibit predominance of different microbial groups in N2O production, with likely adaptation of the microbial community.

The Effects of Season and Agriculture on Nitrous Oxide Production in Headwater Streams

Streams and rivers are a globally significant source of nitrous oxide (N(2)O), a potent greenhouse gas. However, there remains much uncertainty in the magnitude of N(2)O emissions from these sources, partly due to an incomplete understanding of the factors that control microbial N(2)O production in lotic sediments. During 2004-2005 we measured sediment N(2)O production in 12 headwater streams across an agricultural land use gradient. Stream water nitrate (NO(3)(-)) concentrations were positively related to the proportion of agricultural land use in the basin and frequently exceeded 20 mg N L(-1) in the stream draining the most agricultural basin. Stream sediments were nearly always a net source of N(2)O, and production rates were positively related to stream water NO(3)(-) concentrations and sediment carbon content. There were no seasonal patterns in N(2)O production rates during 2004, but stream water NO(3)(-) and N(2)O production both peaked during the winter of 2005. The spike in NO(3)(-) concentrations likely resulted from winter rain and snowmelt that flushed NO(3)(-) from the soils following a dry summer and fall. In turn, the elevated stream water NO(3)(-) concentrations stimulated in-stream N(2)O production rates. Overall, we were only able to explain 29% of the variation in N(2)O production rates on a log scale. The unexplained variation may be due to differences in the fraction of denitrified NO(3)(-) that is converted to N(2)O among the study sites, or that our measures of substrate availability in the water column were not reflective of substrate availability in the porewater used by denitrifiers.

Grazing removal decreases the magnitude of methane and the variability of nitrous oxide emissions from spring-fed wetlands of a California oak savanna

Spring-fed wetlands are embedded within Californian oak savannas whose understory is dominated by annual grasslands that are grazed by livestock. Because there is mounting pressure to remove livestock from riparian areas in the western U.S., we excluded livestock from one-half of three spring-fed wetlands and monitored greenhouse gas (CH4 and N2O) fluxes in 2000 and 2002. In 2003, we also measured several ecosystem characteristics to help understand treatment differences in gas fluxes. Bootstrapped estimates of mean CH4 and N2O fluxes over the study period showed that these wetlands were sources of CH4 and N2O to the atmosphere; we compare the magnitude of these fluxes to estimates from other wetland studies. Grazing removal decreased the magnitude of CH4 emissions and their variability during our study period. A regression tree analysis showed lower soil temperature and higher soil water content to be the best predictors of lower CH4 emissions, both of which were observed under grazing removal. The magnitude of N2O emissions was not influenced by grazing removal, but fluxes from ungrazed plots were less variable. Grazing exclusion during hot summer months in California should reduce CH4 emissions from spring-fed wetlands, but have little effect on the magnitude of N2O loss to the atmosphere. Implications of climate change for these processes are discussed.

Effects of nitrogen application and maize growth on N2O emission from soil

With pot experiment and using static chamber-GC technique, this paper studied the effects of N application (150 and 300 mg x kg(-1) soil) and maize growth on N2O emission from soil. In maize-planted soil, the N2O emission rate increased with increasing N application rate, its peak appeared at seedling stage, and there was no significant correlation between N2O emission and air temperature. Contrarily, in bare soil, the peak of N2O emission rate occurred at the anaphase of the experiment, and there was a significant exponential correlation between N2O emission and air temperature. The total amount of N2O emission increased remarkably with increasing N application rate in both planted and bare soils. In comparing with bare soil, maize-planting reduced N2O emission by 92% and 87%, respectively at high and low N application rates, which suggested that maize-planting not only affected the seasonal variation and magnitude of N2O emission from soil, but also altered the relationship between air temperature and soil N2O emission.

Estimation of global warming potential from upland cropping systems in central Hokkaido, Japan

Seven upland cropping systems in Central Hokkaido, Japan, were investigated during the growing season in 2003 to evaluate the magnitude of N2O emission, CH4 uptake and soil carbon sequestration, and their net effect on the global warming potential (GWP). N2O and CH4 fluxes were measured from field soils planted with crops and CO2 fluxes were measured from bare soils in attached plots at each site using the closed chamber method. Cumulative N2O emissions ranged from 0.02 g N m−2 to 0.62 g N m−2 for different soil types, which accounted for 0.35–4.44% of the applied fertilizer nitrogen. Cumulative CH4 uptake rates ranged from −0.08 g C m−2 to 0 g C m−2. Soil carbon sequestration, defined as the difference between the net primary production and carbon loss through harvest and soil microbial decomposition, ranged from −410 to −193 g C m−2, indicating that the carbon loss from soils could not be compensated by the carbon input through plant photosynthesis. The net GWP from the investigated cropping systems ranged from 749 to 1790 g CO2 equivalents m−2. CO2 emission contributed to 84–99% of the net GWP and N2O contributed 1–16%.