Emission factors and global warming potential as influenced by fertilizer management for the cultivation of rice under varied growing seasons

Seasonal changes in the spatial structures of N2O, CO2, and CH4 fluxes from Acacia mangium plantation soils in Indonesia

IntroductionFarmlands are key sources of greenhouse gas (GHG) emissions, which are susceptible to changes in precipitation regimes. The soils of seasonal fallow contribute approximately half of annual GHG emissions from farmlands, but the effect of precipitation frequency on soil GHG emissions from seasonal fallow croplands remains virtually unknown.Materials and MethodsWe conducted a microcosm study to evaluate the response of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes from typical paddy and upland soils to the changes in watering frequency simulating precipitation scenarios of subtropical regions during seasonal fallow. We also analyzed changes of soil properties and biotic characteristics associated with GHG emissions, including abundances of soil denitrifiers (nirK, nirS, nosZI and nosZII genes), methanotrophs (pmoA gene) and methanogens (mcrA gene) to altered watering frequency.ResultsIncreased watering frequency led to overall increases in soil N2O and CO2 fluxes compared with low frequency. Compared with low frequency, high watering frequency decreased CH4 flux from the paddy soil by 3.5 times, while enhanced CH4 flux from the upland soil by 60%. Furthermore, the increased watering frequency had positive effects on cumulative N2O and CO2 fluxes from the upland soil, whereas no similar trend was observed for the paddy soil. Hierarchical partitioning analyses showed that N2O fluxes from the paddy soil were mostly related to nitrogen availability, and mcrA gene abundance had more than 90% of relative independent effects on CH4 and CO2 fluxes from the paddy soil. For the upland soil, nosZ (60.34%), pmoA (53.18%) and nir (47.07%) gene abundances were important predictors of N2O, CH4 and CO2 fluxes, respectively.ConclusionOur results demonstrate that increased watering frequency facilitates GHG emissions by changing soil properties and functional gene abundances. These findings provide new insights into GHG fluxes from seasonal fallow croplands in response to altered precipitation patterns.

Exploring a suitable nitrogen fertilizer rate to reduce greenhouse gas emissions and ensure rice yields in paddy fields

This study aimed to evaluate the seasonal variations of Greenhouse Gas fluxes (CH4, CO2, and N2O), Greenhouse Gas (GHG) emissions, and Global Warming Potential (GWP) over the extent of the regions and understand the controlling factors. CH4, CO2, and N2O fluxes were measured along with their environmental variables from the over-mature forest, Korean pine plantation, and five 60-year-old natural secondary forests in mountainous regions in Northeast China from May 2015 to April 2016. The results revealed that secondary forests, except for Betula platyphylla forest, significantly increased CH4 absorption by 19.6% to 51.0% and 32.6% to 67.0% compared with over-mature forest (OMF) and Korean pine plantation (KPP). Five secondary forests significantly increased CO2 flux by 32.9% to 78.6% and 14.1% to 53.4% compared with OMF and KPP, respectively. According to the annual statistics, the N2O fluxes had significant differences among seven forest types and decreased in the following order: mixed deciduous forest (MDF) > OMF > KPP > Populous davidiana forest (PDF) > hardwood forest (HWF) > Mongolian oak forest (MOF) > Betula platyphylla forest (BPF). The CH4 absorption and CO2 emission peaks occurred in summer, while the peak N2O fluxes occurred in spring. Stepwise multiple linear regression showed that CH4 and CO2 fluxes from soils were strongly influenced by air and soil temperature, soil volumetric water content (SVWC), nitrate nitrogen (NO3−-N), ammonium nitrogen (NH4+-N), and soil organic carbon (SOC) across the whole year. Air temperature, SVWC, pH, NO3−-N, and NH4+-N were the dominant factors controlling N2O fluxes from OMF and five secondary forests (except for BPF). No significant relationships were observed between these environmental factors and N2O fluxes from KPP and BPF. Additionally, the total cumulative CH4, CO2, and N2O fluxes were –13.37 t CH4 year−1, 41,608.96 t CO2 year−1, and 3.24 t N2O year−1, and the total cumulative GWP were 42,151.87 t CO2 eq year−1 through the whole year in seven forest types at the Maoershan Ecosystem Research Station in Northeast China. For the annual GWP per hectare, secondary forests and KPP averaged a higher GWP by 33.7%–80.1% and 17.9% compared with OMF. This indicates that the effects of early human activities have not been completely eliminated in the middle stage of KPP and secondary forests.

Rivers play an important role in greenhouse gas emissions. Over the past decade, because of global urbanization trends, rapid land use changes have led to changes in river ecosystems that have had a stimulating effect on the greenhouse gas production and emissions. Presently, there is an urgent need for assessments of the greenhouse gas concentrations and emissions in watersheds. Therefore, this study was designed to evaluate river-based greenhouse gas emissions and their spatial-temporal features as well as possible impact factors in a rapidly urbanizing area. The specific objectives were to investigate how river greenhouse gas concentrations and emission fluxes are responding to urbanization in the Liangtan River, which is not only the largest sub-basin but also the most polluted one in Chongqing City. The thin layer diffusion model method was used to monitor year-round concentrations of pCO2, CH4, and N2O in September and December 2014, and March and June 2015. The pCO2 range was (23.38±34.89)-(1395.33±55.45) Pa, and the concentration ranges of CH4 and N2O were (65.09±28.09)-(6021.36±94.36) nmol·L-1 and (29.47±5.16)-(510.28±18.34) nmol·L-1, respectively. The emission fluxes of CO2, CH4, and N2O, which were calculated based on the method of wind speed model estimations, were -6.1-786.9, 0.31-27.62, and 0.06-1.08 mmol·(m2·d)-1, respectively. Moreover, the CO2 and CH4 emissions displayed significant spatial differences, and these were roughly consistent with the pollution load gradient. The greenhouse gas concentrations and fluxes of trunk streams increased and then decreased from upstream to downstream, and the highest value was detected at the middle reaches where the urbanization rate is higher than in other areas and the river is seriously polluted. As for branches, the greenhouse gas concentrations and fluxes increased significantly from the upstream agricultural areas to the downstream urban areas. The CO2 fluxes followed a seasonal pattern, with the highest CO2 emission values observed in autumn, then successively winter, summer, and spring. The CH4 fluxes were the highest in spring and the lowest in summer, while N2O flux seasonal patterns were not significant. Because of the high carbon and nitrogen loads in the basin, the CO2 products and emissions were not restricted by biogenic elements, but levels were found to be related to important biological metabolic factors such as the water temperature, pH, DO, and chlorophyll a. The carbon, nitrogen, and phosphorus content of the water combined with sewage input influenced the CH4 products and emissions. Meanwhile, N2O production and emissions were mainly found to be driven by urban sewage discharge with high N2O concentrations. Rapid urbanization accelerated greenhouse gas emissions from the urban rivers, so that in the urban reaches, CO2/CH4 fluxes were twice those of the non-urban reaches, and all over the basin N2O fluxes were at a high level. These findings illustrate how river basin urbanization can change aquatic environments and aggravate allochthonous pollution inputs such as carbon, nitrogen, and phosphorus, which in turn can dramatically stimulate river-based greenhouse gas production and emissions; meanwhile, spatial and temporal differences in greenhouse gas emissions in rivers can lead to the formation of emission hotspots.

How do sand addition, soil moisture and nutrient status influence greenhouse gas fluxes from drained organic soils?

Impact of biochar on greenhouse gas emissions from constructed wetlands under various influent chemical oxygen demand to nitrogen ratios

Horizontal subsurface flow constructed wetlands (HFCWs) are capable of eliminating organic matter and nitrogen while emitting less methane (CH4) and nitrous oxide (N2O) than free water surface flow wetlands. However, the simultaneous removal of pollutants and reduction of greenhouse gases (GHG) emissions from high-strength wastewater containing high levels of organic matter and ammonium nitrogen (NH4 +-N) has not get been investigated. The influent COD concentration affected the efficiency of nitrogen removal, GHG emissions and the presence of iron from iron ore, but the COD and TP removal efficiencies remained unaffected. CO2 and CH4 fluxes were significantly influenced by influent COD concentrations, whereas less N2O emissions were obtained during 7d. The highest CO2 and CH4 fluxes, along with the GHG emissions, were observed in HFCWs with COD concentrations of 375.6 mg/L and NH4 +-N concentrations of 159.0 mg/L at a COD/N ratio of 2.4. Conversely, the lowest CH4 (–1.72 mg/m2/h) and N2O fluxes (0.13 mg/m2/h) were recorded in HFCWs with COD concentrations of 375.6 mg/L and NH4 +-N concentrations of 162.4 mg/L at a COD/N of 4.5, although nitrogen removal was weak in these HFCWs. HFCWs at a COD/N ratio of 3.6 exhibited greater removal of nitrogen and other pollutants, along with a lower global warming potential (GWP). In conclusion, the concentrations of organic matter and NH4 +-N in wastewater affected both pollutant removal and GHG emissions. The simultaneous enhancement of pollutant removal and the reduction of GHG emissions can be achieved in HFCWs with a COD/N ratio of 3.6.

Context Conversion of grasslands to croplands can usually result in the degradation of soils and increased greenhouse gas (GHG) emissions such as carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). However, little is known about the impacts of grassland conversion to recently tilled croplands on soils and GHG fluxes. Aims A field experiment was established in 2016 to evaluate the impacts of grassland conversion to tilled cropland under different landscape positions (upslope, backslope, and footslope) on select soil properties and soil GHG fluxes. Key results The findings showed that the grassland conversion significantly increased soil bulk density and electrical conductivity but reduced pH and total nitrogen (TN). The conversion impacted soil biome community grassland and tilled croplands. The landscape position significantly impacted soil pH (footslope < upslope) and TN (footslope > upslope). The grassland conversion significantly decreased soil CO2 fluxes, but increased soil CH4 and N2O fluxes. The landscape position significantly impacted soil CO2 (footslope > upslope and backslope) and CH4 (upslope > footslope and backslope) fluxes for some periods. Soil CO2 and N2O fluxes generally followed upward and downward trends over time, respectively. Conclusions These results indicate that grassland conversion was able to lose soil N, increase soil compaction, acidity, salts, and soil N2O and CH4 fluxes, and decrease the diversity of abundant genera and CO2 fluxes. Footslope increased TN, soil acidity, CO2, and CH4 fluxes, compared with upslope and backslope. CO2 fluxes under grassland and tilled cropland significantly increased over time, whereas N2O fluxes under grassland significantly reduced. Implications Conversion of grassland to tilled cropland significantly impacted on sol quality. It caused a loss in soil N and increased soil compaction, acidity and salts. Grassland conversion also decreased the abundance and diversity soil microbiome.

The study is focused on impact of manure application, rice varieties and water management on greenhouse gas (GHG) emissions from paddy rice soil in pot experiment. The objectives of this study were a) to assess the effect of different types of manure amendments and rice varieties on greenhouse gas emissions and b) to determine the optimum manure application rate to increase rice yield while mitigating GHG emissions under alternate wetting and drying irrigation in paddy rice production. The first pot experiment was conducted at the Department of Agronomy, Yezin Agricultural University, Myanmar, in the wet season from June to October 2016. Two different organic manures (compost and cow dung) and control (no manure), and two rice varieties; Manawthukha (135 days) and IR-50 (115 days), were tested. The results showed that cumulative CH4 emission from Manawthukha (1.084 g CH4 kg-1 soil) was significantly higher than that from IR-50 (0.683 g CH4 kg-1 soil) (P<0.0046) with yield increase (P<0.0164) because of the longer growth duration of the former. In contrast, higher cumulative nitrous oxide emissions were found for IR-50 (2.644 mg N2O kg-1 soil) than for Manawthukha (2.585 mg N2O kg-1 soil). However, IR-50 showed less global warming potential (GWP) than Manawthukha (P<0.0050). Although not significant, the numerically lowest CH4 and N2O emissions were observed in the cow dung manure treatment (0.808 g CH4 kg-1 soil, 2.135 mg N2O kg-1 soil) compared to those of the control and compost. To determine the effect of water management and organic manures on greenhouse gas emissions, second pot experiments were conducted in Madaya township during the dry and wet seasons from February to October 2017. Two water management practices {continuous flooding (CF) and alternate wetting and drying (AWD)} and four cow dung manure rates {(1) 0 (2) 2.5 t ha-1 (3) 5 t ha-1 (4) 7.5 t ha-1} were tested. The different cow dung manure rates did not significantly affect grain yield or greenhouse gas emissions in this experiment. Across the manure treatments, AWD irrigation significantly reduced CH4 emissions by 70% during the dry season and 66% during the wet season. Although a relative increase in N2O emissions under AWD was observed in both rice seasons, the global warming potential was significantly reduced in AWD compared to CF in both seasons (P<0.0002, P<0.0000) according to reduced emission in CH4. Therefore, AWD is the effective mitigation practice for reducing GWP without compromising rice yield while manure amendment had no significant effect on GHG emission from paddy rice field. Besides, AWD saved water about 10% in dry season and 19% in wet season.

The study is focused on impact of manure application, rice varieties and water management on greenhouse gas (GHG) emissions from paddy rice soil in pot experiment. The objectives of this study were a) to assess the effect of different types of manure amendments and rice varieties on greenhouse gas emissions and b) to determine the optimum manure application rate to increase rice yield while mitigating GHG emissions under alternate wetting and drying irrigation in paddy rice production. The first pot experiment was conducted at the Department of Agronomy, Yezin Agricultural University, Myanmar, in the wet season from June to October 2016. Two different organic manures (compost and cow dung) and control (no manure), and two rice varieties; Manawthukha (135 days) and IR-50 (115 days), were tested. The results showed that cumulative CH4 emission from Manawthukha (1.084 g CH4 kg-1 soil) was significantly higher than that from IR-50 (0.683 g CH4 kg-1 soil) (P<0.0046) with yield increase (P<0.0164) because of the longer growth duration of the former. In contrast, higher cumulative nitrous oxide emissions were found for IR-50 (2.644 mg N2O kg-1 soil) than for Manawthukha (2.585 mg N2O kg-1 soil). However, IR-50 showed less global warming potential (GWP) than Manawthukha (P<0.0050). Although not significant, the numerically lowest CH4 and N2O emissions were observed in the cow dung manure treatment (0.808 g CH4 kg-1 soil, 2.135 mg N2O kg-1 soil) compared to those of the control and compost. To determine the effect of water management and organic manures on greenhouse gas emissions, second pot experiments were conducted in Madaya township during the dry and wet seasons from February to October 2017. Two water management practices {continuous flooding (CF) and alternate wetting and drying (AWD)} and four cow dung manure rates {(1) 0 (2) 2.5 t ha-1 (3) 5 t ha-1 (4) 7.5 t ha-1} were tested. The different cow dung manure rates did not significantly affect grain yield or greenhouse gas emissions in this experiment. Across the manure treatments, AWD irrigation significantly reduced CH4 emissions by 70% during the dry season and 66% during the wet season. Although a relative increase in N2O emissions under AWD was observed in both rice seasons, the global warming potential was significantly reduced in AWD compared to CF in both seasons (P<0.0002, P<0.0000) according to reduced emission in CH4. Therefore, AWD is the effective mitigation practice for reducing GWP without compromising rice yield while manure amendment had no significant effect on GHG emission from paddy rice field. Besides, AWD saved water about 10% in dry season and 19% in wet season.

Monthly measurements of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes in peat soils were carried out and compared with groundwater level over a year at four sites (drained forest, upland cassava,upland and lowland paddy fields) located in Jambi province, Indonesia. Fluxes from swamp forest soils were also measured once per year as the native state of this investigated area. Land-use change from drained forest to lowland paddy field significantly decreased the CO2 (from 266 to 30 mg C m−2 h−1) and N2O fluxes (from 25.4 to 3.8 μg N m−2 h−1), but increased the CH4 flux (from 0.1 to 4.2 mg C m−2 h−1) in the soils. Change from drained forest to cassava field significantly increased N2O flux (from 25.4 to 62.2 μg N m−2 h−1), but had no significant influence on CO2 (from 266 to 200 mg C m−2 h−1) and CH4 fluxes (from 0.1 to 0.3 mg C m−2 h−1) in the soils. Averaged CO2 fluxes in the swamp forests (94 mg C m−2 h−1) were estimated to be one-third of that in the drained forest. Groundwater levels of drained forest and upland crop fields had been lowered by drainage ditches while swamp forest and lowland paddy field were flooded, although groundwater levels were also affected by precipitation. Groundwater levels were negatively related to CO2 flux but positively related to CH4 flux at all investigation sites. The peak of the N2O flux was observed at –20 cm of groundwater level. Lowering the groundwater level by 10 cm from the soil surface resulted in a 50 increase in CO2 emission (from 109.1 to 162.4 mg C m−2 h−1) and a 25% decrease in CH4 emission (from 0.440 to 0.325 mg C m−2 h−1) in this study. These results suggest that lowering of groundwater level by the drainage ditches in the peat lands contributes to global warming and devastation of fields. Swamp forest was probably the best land-use management in peat lands to suppress the carbon loss and greenhouse gas emission. Lowland paddy field was a better agricultural system in the peat lands in terms of C sequestration and greenhouse gas emission. Carbon loss from lowland paddy field was one-eighth of that of the other upland crop systems, although the Global Warming Potential was almost the same level as that of the other upland crop systems because of CH4 emission through rice plants.

Greenhouse gas emissions in response to tillage, nitrogen fertilization, and manure application in the tropics

Although greenhouse gas (GHG) emissions from soils are important, reclaimed mine soil (RMS) ecosystems are not widely assessed. Postreclamation land uses (forest, hay, and pasture) were investigated to: (i) monitor the magnitude of GHG fluxes, (ii) estimate their global warming potential (GWP), (iii) identify the relationship between GHG fluxes and soil properties, and (iv) develop a soil quality index by principal component analysis (PCA). The GHG fluxes were measured for 1 yr cycle and simultaneous measurements were also made for soil moisture and temperature. The RMS-forest, -hay, and -pasture land uses had weighted average fluxes of 1.16, 1.66, and 3.06 g CO(2)-C m(-2) d(-1); 0.33, 0.48 and 1.1 mg CH(4)-C m(-2) d(-1); and 0.33, 0.70, and 1.06 mg N(2)O-N m(-2) d(-1), respectively. The CO(2), CH(4), and N(2)O fluxes were consistently high in the RMS-pasture and low in the RMS-forest. The GWP (CO(2)-C equivalent) of the postreclamation land uses was in the order of RMS-forest (4.5 Mg ha(-1) yr(-1)) = RMS-hay (6.8 Mg ha(-1) yr(-1)) < RMS-pasture (12.3 Mg ha(-1) yr(-1)). The PCA showed that four PCs with eigenvalues > 1 explained 88.8% of the total variance in the soil properties. The first PC is mostly characterized by soil physical properties and the second by chemical properties. Soil and air temperatures were positively correlated with CO(2), CH(4), and N(2)O fluxes. The results suggest that GWP from RMS can be minimized by establishing forest land use.

To mitigate greenhouse gas (GHG) emissions of intensified agriculture, conservation practices are gradually being implemented in Chinese wheat–maize cropping systems. However, the effects of different tillage practices on agricultural field GHG emissions and subsequent global warming potential (GWP) are poorly documented. In this study, a three-year field experiment was conducted from 2019 to 2021 to assess the effects of tillage on the emissions of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and eventually GWP. Compared to conventional tillage (CT), no-tillage (NT) significantly decreased CO2, CH4, and N2O emissions by 35.43%, 67.33%, 339.07%, respectively, which resulted in a decrease of 37.25% in GWP during three annual cycles. Based on the results of this study, soil could potentially act as a net source of CO2 and CH4 under both CT and NT, and a net sink of N2O under NT. Annually, non-growing season contributed 16.9%, 15.6%, and 13.8% soil CO2, CH4, and N2O fluxes, and 16.6% GWP under CT and 17.3%, 16.4%, 21.6%, and 17.3% under NT, respectively. Compared to CT, NT improved the aboveground biomass and grain yields of wheat by 21.3% and 13.3% from averaged results, respectively; no significant differences were found for maize yields. Although principal component analysis showed that soil temperature had higher correlations with CO2 emissions and GWP as compared to soil moisture, soil moisture affected GHG emissions more than soil temperature as demonstrated by the structural equation model. The modeling analysis found that NT increased soil moisture, pH, and bulk density, thus increasing soil organic carbon and decreasing total nitrogen content, eventually inhibiting GHG emissions. This research demonstrated that NT had the potential to mitigate GHG emissions, yet stability needed further investigation on long-term scales.∙Graphical