Seasonal N2O Research Articles

Straw return amplifies the stimulated impact of night-warming on N2O emissions from wheat fields in a rice-wheat rotation system

ContextThe rise in winter and spring nighttime temperatures is a hallmark of global climate change, and warming has been proven to stimulate N2O emissions from wheat fields. However, it remains elusive whether this increasing effect is influenced by straw return, a practice considered globally as a future climate-smart agricultural strategy. Objectives or methodsA 3-year field experiment (2020−2023) was conducted with two straw treatments (S0: straw removal; S1: straw return) and two warming treatments (W0: no-warming; W1: night-warming) to quantify the effects of straw return and night-warming on N2O emissions from wheat fields in a rice-wheat rotation system. ResultsStraw return (S1) boosted post-jointing N2O production, whereas night-warming (W1) stimulated N2O emissions before the booting stage. Notably, the interaction between straw return and night-warming significantly affected seasonal cumulative N2O emissions, with W1 causing an 11.1 % increase under S0 and a more substantial 18.1 % increase observed under S1. Moreover, both S1 and W1 increased N2O warming potential, yield-scaled, and biomass-scaled N2O emissions. Compared to S0W0, soil dissolved organic C and inorganic N content increased in S1W1, while pH declined. Both S1 and W1 enhanced soil nitrification enzyme activity, nitrate reductase activity, and nitrite reductase activity in comparison to their respective controls. Additionally, S1W1 increased N2O production and inhibited N2O reduction by upregulating AOB-amoA and nirS gene abundances and downregulating nosZ gene expression, as evidenced by the elevated (nirS+nirK)/nosZ ratio. Random forest analysis identified that denitrification enzyme activity was the most important factor influencing N2O emissions. Conclusions or implicationsOur findings suggest that rice straw return may amplify the increasing effect of night-warming on N2O emissions from wheat fields. From an environmental protection perspective, straw return under the context of future warming will lead to an increased risk of N2O emissions, which may further exacerbate climate warming.

Improved nitrogen fertilizer management reduces nitrous oxide emissions in a northern Prairie cropland

Arable croplands are a significant source of nitrous oxide (N2O) emissions, largely due to nitrogen (N) fertilizer applications to support crop production. Nevertheless, there is limited research on the N2O dynamics from canola-wheat rotations in the semi-arid northern Prairies, an important agricultural region. Here, we present micrometeorological N2O fluxes measured from January 2021 to April 2024 in Saskatchewan, Canada, to evaluate the impact of N fertilizer management on the year-round N2O emissions from a canola-wheat rotation. A combination of two 4R (Right Source, Right Rate, Right Time, Right Place) N management practices – a reduced N rate and an enhanced efficiency N fertilizer source – was compared to common fertilizer management practices for the region. Two periods at high risk for N2O flux events were identified, after N fertilizer applications and the following spring thaw, with the magnitude of emissions varying over the multi-year period. As for cumulative emissions, the growing season (GS) N2O emissions were 50 % of annual emissions, presenting an opportunity to mitigate N2O emissions through improved N fertilizer management. Indeed, the improved 4R N management reduced N2O emissions by 57 % over the entire study period without impacting yields. The reduction in GS N2O emissions resulted from the 4R N management lowering mean N2O flux at times of high WFPS (>50 %). The non-growing season (NGS) N2O accounted for 11–67 % of annual emissions. Fall soil nitrate levels were a strong explanatory variable of NGS emissions (r2 = 0.69, r2 = 0.39), but the rate of change and magnitude of NGS emissions depended on thawing conditions – lower for drier thaws, higher for wetter thaws. Ultimately, better N fertilizer management reduces cumulative N2O emissions from cropping systems when practiced for several years.

Biochar decreased N loss from paddy ecosystem under alternate wetting and drying in the Lower Liaohe River Plain, China

Biochar addition to soil is widely utilized to enhance carbon sequestration and reduce fertilizer N losses. However, little research has been studied on the effect of biochar on reactive gaseous N losses, N leaching and grain yield in paddy ecosystems under water stress, especially in the Lower Liaohe River Plain with a higher water percolation. Our experiment was carried out in 2020 and 2021 utilizing a split-plot design with continuously flooding irrigation and alternate wetting and drying irrigation as main plots and without biochar addition and with 20 t·ha−1 rice husk-derived biochar addition as sub-plots. The results showed that alternate wetting and drying irrigation respectively, decreased N leaching and reactive N losses by 15.9 % and 11.3 % but also respectively, increased seasonal cumulative NH3 volatilization and N2O emissions by 5.0 % and 210 % on average. Rice husk-derived biochar addition significantly mitigated seasonal cumulative NH3 volatilization and N2O emissions by 8.8 % and 19.7 % in 2020, 20.7 % and 19.2 % in 2021, respectively, and decreased inorganic N leaching and reactive N losses by 8.3 % and 14.1 % in 2021. Biochar addition coupling with alternate wetting and drying respectively, mitigated cumulative NH3 volatilization and N2O emissions by 7.3 % and 19.3 % in 2020, and, 22.7 % and 22.0 % in 2021 as compared to that without biochar. Biochar did not differ from without biochar in inorganic N leaching under alternate wetting and drying irrigation in both years but significantly reduced reactive N losses by 17.8 % in 2021, which efficiently inhibited the alternate wetting and drying induced negative effects on the increase in reactive N losses. Therefore, biochar addition to paddy ecosystems under alternate wetting and drying could realize sustainable utilization of water resources, increase soil N fixation, and mitigate N losses.

Seasonal wet–dry transition and denitrifying communities contributed to nitrous oxide emissions in the water-level fluctuating zone of the largest freshwater lake in China

The water-level fluctuating zone (WLFZ) is the alternating dry/wet zone in freshwater lakes, and plays a crucial role in nitrogen (N) biogeochemical cycling and nitrous oxide (N2O) emissions. However, N2O emission fluxes, the underlying microbial mechanisms, and their feedbacks to global warming in the extensive WLFZ of the freshwater lakes with dramatic water-level variations remain unclear. Here, we sampled through both wet and dry seasons and compared the N removal rates, N2O emission fluxes, composition and co-occurrence network properties of the denitrifying microbial communities of the WLFZ, continuously flooded, and non-flooded zones covered with the dominant plant (Carex. cinerascens) in Poyang Lake, the largest freshwater lake of China. We observed higher potential denitrification (1.129–5.657 nmol N g-1h−1) and anammox (0.047–0.756 nmol N g-1h−1) rates in the WLFZ for both wet and dry seasons than those in the other two zones. A large seasonal N2O sink-source transition (−2.297 and 0.297 μg m-2h−1 for wet and dry season, respectively) was observed in WLFZ. Moreover, the composition of nirK and nirS communities significantly varied in WLFZ between the wet and dry seasons. Especially, several keystone taxa (e.g., Mesorhizobium and Rhodanobacter) were enriched in the WLFZ and were responsible for denitrification and N2O emissions under drought stress in the dry season. Variations in denitrification rates and N2O fluxes were driven by pH, C and N substrates, as well as the co-occurrence network properties, including natural connectivity and small-world coefficients of the nirK and nirS communities. Our results suggested that WLFZ in freshwater lakes under future climate change scenarios would be a substantial N2O source and aggravate climate, which would result in the positive feedback.

Composted maize straw under fungi inoculation reduces soil N2O emissions and mitigates the microbial N limitation in a wheat upland

Enhancement of microbial assimilation of inorganic nitrogen (N) by straw addition is believed to be an effective pathway to improve farmland N cycling. However, the effectiveness of differently pretreated straws on soil N2O emissions and soil N-acquiring enzyme activities remains unclear. In this study, a pot experiment with four treatments (I, no addition, CK; II, respective addition of maize straw, S; III, composted maize straw under no fungi inoculation, SC; and IV, composted maize straw under fungi inoculation, SCPA) at the same quantity of carbon (C) input was conducted under the same amount of inorganic N fertilization. Results showed that the seasonal cumulative N2O emissions following the SCPA treatment were the lowest at 4.03 kg N ha−1, representing a significant reduction of 19 % compared with the CK treatment. The S and SC treatments had no significant effects on N2O emissions. The decrease of soil N2O emissions following the SCPA treatment was mainly attributed to the increase of microbial N assimilation and the increased abundance of functional genes related to N2O reductase. The SCPA treatment significantly decreased soil alkaline phosphatase (ALP) activity and increased leucine aminopeptidase (LAP) activity at the basal fertilization, while increased soil ALP and LAP activity, decreased soil N-Acetyl-β-D-Glucosidase (NAG) activity at harvest. Compared with the CK treatment, the S, SC, and SCPA treatment significantly increased soil β-glucosidase (β-GC) activity at harvest. The decrease in the (NAG+LAP)/ALP ratio following the SCPA treatment indicated that the composted maize straw under fungi inoculation alleviated microbial N limitation at harvest. Moreover, PICRUSt analysis also suggested that the SCPA treatment increased the abundance of bacterial genes associated with N assimilation and N2O reduction, whereas the S and SC treatment did not significantly affect the abundance of N2O reduction genes compared with the CK treatment. Our results suggest that the composted maize straw under fungi inoculation would reduce the risk of N2O emissions and effectively mitigate the microbial N limitation in dryland wheat system.

Can converting raw straw into biochar incorporation achieve both higher maize yield and lower greenhouse gas emissions intensity in drought-prone environment?

Converting raw straw into biochar is considered an effective strategy for soil carbon sequestration. However, it remains uncertain whether biochar is more environmentally friendly for achieving higher crop yield in comparison to raw straw in drought-prone regions. Here, a 5-year experiment with three treatments (no incorporation(CK), raw straw incorporation(SI) and straw-derived biochar incorporation(BI)) was conducted to examine the effects of SI and BI on soil physicochemical properties, grain yield (GY), and greenhouse gas (GHG) emissions. Results indicated both SI and BI increased soil water content (SWC), soil temperature (ST), soil porosity, field capacity, pH, total nitrogen and soil organic carbon (SOC) compared with CK. On average, seasonal soil CO2 emission increased significantly by 42.3% in SI and 16.8% in BI, respectively; seasonal N2O emission increased by 26.9% in SI, while decreased by 17.5% in BI. Particularly, the 5-year average GY was as high as 9.4 t ha-1 in BI, significantly higher than that of SI and CK. The 5-year average global warming potential (GWP) increased by 57.9% and 24.6% under SI and BI, respectively, compared with CK. As a result, the average GHG emission intensity (GHGI) increased by 32.0% in SI, whereas it declined by 8.9% in BI. Attribution analysis showed that the CO2 emission primary driven GHGI change under SI, contributing up to 76.4% to GHGI increase. Conversely, the GY increase primary driven GHGI change under BI, contributing to 55.0% GHGI decrease. Therefore, converting raw straw into biochar incorporation acts as an environment-friendly strategy for higher yield harvest.

Mineral and organic fertilisation influence ammonia oxidisers and denitrifiers and nitrous oxide emissions in a long-term tillage experiment

Nitrous oxide (N2O) emissions from different agricultural systems have been studied extensively to understand the mechanisms underlying their formation. While a number of long-term field experiments have focused on individual agricultural practices in relation to N2O emissions, studies on the combined effects of multiple practices are lacking. This study evaluated the effect of different tillage [no-till (NT) vs. conventional plough tillage (CT)] in combination with fertilisation [mineral (MIN), compost (ORG), and unfertilised control (CON)] on seasonal N2O emissions and the underlying N-cycling microbial community in one maize growing season. Rainfall events after fertilisation, which resulted in increased soil water content, were the main triggers of the observed N2O emission peaks. The highest cumulative emissions were measured in MIN fertilisation, followed by ORG and CON fertilisation. In the period after the first fertilisation CT resulted in higher cumulative emissions than NT, while no significant effect of tillage was observed cumulatively across the entire season. A higher genetic potential for N2O emissions was observed under NT than CT, as indicated by an increased (nirK + nirS)/(nosZI + nosZII) ratio. The mentioned ratio under NT decreased in the order CON > MIN > ORG, indicating a higher N2O consumption potential in the NT-ORG treatment, which was confirmed in terms of cumulative emissions. The AOB/16S ratio was strongly affected by fertilisation and was higher in the MIN than in the ORG and CON treatments, regardless of the tillage system. Multiple regression has revealed that this ratio is one of the most important variables explaining cumulative N2O emissions, possibly reflecting the role of bacterial ammonia oxidisers in minerally fertilised soil. Although the AOB/16S ratio aligned well with the measured N2O emissions in our experimental field, the higher genetic potential for denitrification expressed by the (nirK + nirS)/(nosZI + nosZII) ratio in NT than CT was not realized in the form of increased emissions. Our results suggest that organic fertilisation in combination with NT shows a promising combination for mitigating N2O emissions; however, addressing the yield gap is necessary before incorporating it in recommendations for farmers.

Overwinter and Spring Thaw Nitrous Oxide Fluxes in a Northern Prairie Cropland Are Limited but a Significant Proportion of Annual Emissions

AbstractCroplands that experience seasonal soil freezing and thawing have been shown to be significant sources of N2O emissions. Yet, there is a paucity of year‐round N2O emission data for one of the most significant crop production regions that seasonally freeze, the Prairies. Here, we present micrometeorological N2O fluxes measured over 4 years in Saskatchewan, Canada, to evaluate the magnitude of freeze‐thaw N2O emissions and investigate its driving factors. Significant thaw related emissions occurred in 2 of the 4 years and were associated with relatively higher fall nitrate levels and a more gradual soil thawing period. Overall, fall soil nitrate levels were a strong explanatory variable for the differences in non‐growing season (NGS) N2O emission (r2 = 0.485). Measured cumulative N2O emissions for the NGS were 123–938 g N ha−1 and were much smaller than those obtained at other cold climate sites but amounted to 52% of annual totals on average. The November to April period contributed 30% of the annual total emissions in years without major thaw events, but 70% in years with significant thaws. NGS N2O emissions were not explained by cumulative freezing degree days unlike most other cold climate sites. We propose that NGS N2O emissions are more strongly influenced by thaw dynamics during freezing‐thawing conditions in dry regions, whereas freezing intensity is the dominant factor for wetter regions. Our results indicate that even for a semi‐arid region freeze‐thaw is an important source of N2O emissions and must be considered for more accurate reporting and development of mitigation strategies.

A potential of iron slag-based soil amendment as a suppressor of greenhouse gas (CH4 and N2O) emissions in rice paddy

Iron slag-based silicate fertilizer (SF) has been utilized as a soil amendment in rice paddy fields for over 50 years. SF, which contains electron acceptors such as oxidized iron (Fe3+) compounds, is known to reduce methane (CH4) emissions, which have a global warming potential (GWP) of 23, higher than that of carbon dioxide (CO2). However, the dynamics of nitrous oxide (N2O), which has a GWP of 265, were questionable. Since the reduced Fe (Fe2+) can react as an electron donor, SF application might suppress N2O emissions by progressing N2O into nitrogen gas (N2) during the denitrification process. To verify the influence of SF application on two major greenhouse gas (GHG) dynamics during rice cultivation, three different kinds of SF were prepared by mixing iron rust (>99%, Fe2O3) as an electron acceptor with different ratios (0, 2.5, and 5%) and applied at the recommended level (1.5 Mg ha−1) for rice cultivation. SF application was effective in decreasing CH4 emissions in the earlier rice cropping season, and seasonal CH4 flux was more highly decreased with increasing the mixing ratio of iron rust from an average of 19% to 38%. Different from CH4 emissions, approximately 70% of seasonal N2O flux was released after drainage for rice harvesting. However, SF incorporation was very effective in decreasing N2O emissions by approximately 40% over the control. Reduced Fe2+ can be simultaneously oxidized into Fe3+ by releasing free electrons. The increased electron availability might develop more denitrification processes into N2 gas rather than NO and N2O and then decrease N2O emissions in the late rice cultivation season. We could find evidence of a more suppressed N2O flux by applying the electron acceptor-added SFs (SF2.5 and SF5.0) to a 49%–56% decrease over the control. The SF application was effective in increasing rice productivity, which showed a negative-quadratic response to the available silicate (SiO2) concentration in the soil at the harvesting stage. Grain yield was maximized at approximately 183 mg kg−1 of the available SiO2 concentration in the Korean rice paddy, with a 16% increase over no-SF application. Consequently, SF has an attractive potential as a soil amendment in rice paddy to decrease GHG emission impacts and increase rice productivity.

Effects of Biodegradable Plastic Film Mulching on the Global Warming Potential, Carbon Footprint, and Economic Benefits of Garlic Production

This paper clarifies the farm applicability and feasibility of spreading biodegradable plastic film mulching for garlic production to ensure the green and sustainable development of the garlic industry. We set up a field trial of garlic planting with biodegradable plastic film mulching (BM) and plastic film mulching (PM), using no film mulching (CK) as the control, and measured CH4 and N2O emissions in the garlic fields. The yield-scaled global warming potential, carbon footprint, and net ecosystem economic benefit (NEEB) were used to assess the comprehensive impact of the different treatments. Compared to the CK, film mulching significantly increased CH4 absorption, with significantly higher seasonal cumulative CH4 emissions (20.5%) in BM than PM, but significantly increased N2O emissions, with significantly lower seasonal cumulative N2O emissions (23.53%) in BM than PM. Both BM and PM improved garlic yield, with PM significantly increasing garlic yield by 18.86% compared to the CK. Moreover, film mulching significantly decreased the yield-scaled global warming potential (by 52.06% and 40.82% in PM and BM, respectively). PM had a significantly higher carbon footprint than BM. Film mulching improved NEEB by 9.29–11.78%. Considering crop yields and environmental benefits, we propose BM as an effective method for a green and efficient garlic production.

Tillage effects on growing season nitrous oxide emissions in Canadian cropland soils

Minimizing tillage has been promoted as an agricultural practice that may mitigate greenhouse gas emissions through carbon sequestration. However, there is some ambiguity regarding the effect of minimum tillage (MT) on emissions of other greenhouse gases, in particular soil nitrous oxide (N2O) emissions. To determine how effective MT could be in helping Canada mitigate greenhouse gas emissions, we used a meta-analysis to compare growing season N2O emissions from MT versus conventional tillage (CT). Overall, MT had 12% lower N2O emissions compared to CT ( P = 0.03). However, there was high variability due to soil texture and growing season precipitation (GSP), with MT tending to emit more N2O than CT in climates where GSP exceeded 600 mm, particularly for soils with sand content less than 60%. Therefore, unless long-term tillage trials, which are urgently needed in eastern Canada, show a reduction in N2O emissions over time, MT should be used as a greenhouse gas mitigation measure only in dry climates or on sandy soils.

Rice planting reduced N2O emissions from rice-growing seasons due to increased nosZ gene abundance under a rice-wheat rotation system

Paddy fields experience more frequent events because of redox-induced changes during their growth period, which further govern the processes that influence soil N2O emissions. However, studies on the effects of rice planting on soil N2O emissions and the relevant mechanisms are scarce. Thus, a field employing rice-wheat rotation (RW) in central China, including treatments with rice planting (RW-CC) and without rice planting (RW-NC), was selected to investigate the effects of rice planting on N2O emissions. Several key soil variables and functional genes (nirS, nirK, and nosZ) related to N2O-production and consumption were selected to determine the mechanisms underlying the effects of rice planting on N2O emissions. The results showed that seasonal N2O emissions from RW-NC treatment were 0.88 ± 0.08 and 1.69 ± 0.24 kg N ha−1 for the first and subsequent rice cultivation seasons, respectively, and were significantly higher than those from RW-CC treatment (0.51 ± 0.10 and 1.04 ± 0.18 kg N ha−1, respectively). This indicated the mitigation effect of rice planting on field N2O emissions. For both the RW-CC and RW-NC treatments, N2O fluxes were positively correlated with soil ammonium (NH4+), microbial biomass carbon (MBC), and nirK genes, and negatively correlated with the nosZ gene, indicating that the production- and consumption-related functional genes of soil available C, N, and N2O are the key factors controlling N2O emissions. Compared to RW-NC treatment, a higher abundance of the nosZ gene and lower (nirS+nirK)/nosZ ratios for RW-CC treatment may contribute to a greater reduction of N2O to N2, thus resulting in decreased N2O emissions. Structural equation model (SEM) analysis showed that soil moisture (flood depth), NH4+, MBC, and functional genes together accounted for more than 85 % of the explanatory effects on N2O emissions for both treatments. In general, our research indicates that promoting rice planting could reduce soil N2O emissions during the rice-growing season, thereby reducing the exposure of soil to N fertilization when adopting field agronomic practices; our results also suggest that crop rotation and intercropping should be encouraged.

High-resolution temporal variations of nitrate in a high-elevation pond in alpine tundra (NW Italian Alps)

High-resolution temporal measurements in remote, high-elevation surface waters are required to better understand the dynamics of nitrate (NO3−) in response to changes in meteoclimatic conditions. This study reports on the first use of a UV–Vis submersible spectrophotometric probe (UV–Vis probe) to measure the hourly concentration of nitrate nitrogen (NO3−-N) in a pond located at 2722 m a.s.l. in an alpine tundra area (NW Italian Alps), during two snow-free seasons (July–October) in 2014 and 2015. Weekly analyses of NO3−-N and stable isotopes of water (δ18O and δ2H), together with continuous meteorological, water temperature, and turbidity measurements, were performed over the same period. The integration of in-situ UV–Vis spectrophotometric measurements with weekly samples allowed depicting the role of summer precipitation, snow melt, and temperature (air and water) in influencing NO3− dynamics. Short-duration meteorological events (e.g., summer storms and rain-on-snow events) produced rapid variations of in-pond NO3− concentration, i.e., fivefold increase in 18 h, that would not be detectable using the traditional manual collection of discrete samples. The observed seasonal variability of NO3− concentration, negatively correlated with water temperature, highlighted the important role of in-pond biological processes leading to an enhanced N uptake and to the lowest NO3− concentration in the warmer periods. The occurrence of heavy rainfall events critically altered the expected seasonal NO3− trends, increasing the N supply to the pond. The comparison of N dynamics in two years characterised by extremely different meteoclimatic conditions allowed us to obtain insights on the potential effects of climate changes (e.g., high air temperature, heavy rainfalls, and rain-on-snow events) on sensitive aquatic ecosystems as high-elevation ponds.

Seasonal and annual methane and nitrous oxide emissions affected by tillage and cover crops in flood-irrigated rice

Soil tillage plays an important role in methane (CH4) and nitrous oxide (N2O) emissions in flood-irrigated rice production. Hence, this study measured the effects of soil tillage and cover crops on the seasonal and annual CH4 and N2O emissions in flood-irrigated rice. A field experiment was conducted for two agricultural years with conventional tillage (CT), minimum tillage (MT), no-tillage (NT), and NT with Persian clover (Trifolium resupinatum) (NT+PC). The effect of different tillage systems on CH4 emissions, which occur predominantly in rice cultivation, depends on the impact of tillage and the amount of straw remaining at the time of rice seeding. When straw incorporation in MT and CT reduces the quantity of straw remaining relative to NT, lower CH4 emissions occurred in the CT and MT. In contrast, when the amount of straw remaining on the soil is similar among the types of soil tillage, lower CH4 emissions occurred in the NT. The effect of tillage on annual N2O emissions was unclear, although the highest in-season N2O emissions occurred in the NT, where the highest water-filled pore space values were recorded in both years. High N2O emissions during rice cultivation occurred in the CT after nitrogen fertilization. The effect of the cover crop in the NT varied as a function of the performance of the clover. When the PC biomass production was satisfactory in the second year, annual CH4 and N2O emissions increased by 8 % and 23 %, respectively. The seasonal and annual quantification of CH4 and N2O emissions is important to reduce the uncertainty of the effect of different land management systems on CH4 and N2O emissions.

Effects of five-year field aged zeolite on grain yield and reactive gaseous N losses in alternate wetting and drying paddy system

Clinoptilolite zeolite has been widely used in agricultural production systems for enhancing water and fertilizer savings, mitigating greenhouse gas emissions, and increasing yield. However, there is little information on field-aged effects of zeolite on reactive gaseous N losses under alternate wetting and drying irrigation (AWD). We conducted a five-year field experiment to investigate field-aged effect of natural zeolite addition at 0 (Z0), 5 (Z5), and 10 (Z10) t ha−1 on reactive gaseous N losses (NH3, N2O), N-related global warming potential (GWPN), soil properties and grain yield under two irrigation regimes (CF: continuous flooding irrigation; AWD) in the 4th (2020) and 5th (2021) years since its initial application in 2017. As compared with CF, AWD did not significantly affect grain yield and NH3 volatilization but increased seasonal N2O emissions by 46 %–71 % over two years. Zeolite increased rice yield for five consecutive years. Z10 reduced averaged cumulative NH3 volatilization and GWPN by 23 % and 26 %, compared to zeolite-free treatment, respectively, in the 4th and 5th years. Soil NH4+-N was increased with the increased rate of Z application under both CF and AWD. Z10 increased soil NH4+-N by 27 %–38 % and NO3−-N by 14 %–22 % in five years, compared to Z0, respectively. Compared to AWD without zeolite, the addition of 10 t ha−1 zeolite under AWD lowered NH3 volatilization, cumulative N2O emissions, and GWPN by an average of 28 %, 29 %, and 30 % in two years, respectively. IAWDZ10 did not differ from ICFZ0 on reactive gaseous N losses but significantly lowered reactive gaseous losses relative to IAWDZ0. Therefore, zeolite addition could mitigate the reactive gaseous N losses and GWPN for at least five years after initial application, which is beneficial to promoting zeolite application and ensuring sustainable agriculture.

Sheepfolds induce significant increase of seasonal CO2, CH4 and N2O emissions in temperate steppes of Inner Mongolia

IntroductionThe changes in grassland management and grassland types are strongly linked with dynamics in soil physico-chemical properties and vegetation attributes, with important implications for carbon/nitrogen cycling and greenhouse gas (GHG) fluxes. However, the seasonal variations of GHG emissions from sheepfolds, and the underlying biotic and abiotic drivers affecting GHG exchanges across different steppe and management types remain largely unclear.MethodsTaking the Inner Mongolian grassland as a model system, we measured the fluxes of CO2, CH4 and N2O, as well as soil and vegetation variables, in three contrasting grassland management areas (grazing, sheepfold, enclosure) and in three representative (wet typical, dry typical, desert) grassland ecosystems in July, September and November 2016.ResultsOur results showed that: (1) GHG fluxes were mostly higher in the plant growing season (July and September) than in the nongrowing season (November); sheepfold area had significantly higher GHG emissions (in July and mean over the season) than enclosed and grazing areas, with the effects being most pronounced in dry typical steppe. (2) The high GHG emissions in dry typical steppe were closely associated with the interactions among favorable soil temperature and moisture, high total organic carbon (TOC) content, and high aboveground biomass. The important predictors for CO2 emission were soil TOC and pH, whereas that for CH4 and N2O emissions were soil temperature and moisture content, in sheepfold areas. (3) Three GHG emissions were negatively affected by species richness across all steppe and management types, which might be a consequence of indirect effects through the changes in soil TOC and total nitrogen (TN).DiscussionThese results indicate that sheepfold areas are intensive hotspot sources of GHGs in the steppes, and it is of great importance to help to account GHG emissions and develop mitigation strategies for sheepfold areas for sustainable grassland management in the natural steppe based pastoral production ecosystems.

Sub-surface drip irrigation reduced N2O emissions via inhibiting denitrification pathways in northern China

Water-saving irrigation has become an important method for alleviating water scarcity in semi-arid regions. However, the lack of knowledge about the effects of different water-saving irrigation techniques on soil nitrogen conversion limits the understanding of the underlying mechanisms involved in soil N2O emissions. To determine the effects of different irrigation methods on N2O emissions, we conducted a two-season experiment under four different irrigation methods (DI, surface drip irrigation; SDI, sub-surface drip irrigation; PRI, partial rootzone irrigation; FP, flood irrigation). Also, we studied the dynamics of nitrifier and denitrifier community structures and compositions and their associations and effects on N2O emissions. The results showed that seasonal N2O emissions were affected by irrigation practices and significantly correlated with the amount of irrigation and soil moisture. Drip irrigation significantly reduced N2O emissions, with 38–45 % (DI), 51–59 % (SDI), and 64–68 % (PRI) decreases compared to FP treatment. Under SDI, the copy numbers of ammonia-oxidizing archaea amoA significantly decreased and nirK displayed an increase compared to FP. The abundance of unclassified_Proteobacteria dominant among nirK-type denitrifiers under FP was observed to be strongly and positively correlated with N2O emissions, and the dominant bacteria shifted to Bosea under drip irrigation. Irrigation practices had a strong effect on the Shannon and ACE indexes of five key genes. PRI showed a similar effect under SDI treatment on nitrifier and denitrifier community structures. Furthermore, PRI, with only a 38 % reduction of irrigation water consumption, produced a 4.4–11.3 % lower yield than SDI. Therefore, SDI treatment can inhibit the denitrification process led by nirS-type denitrifiers and reduce the abundance of the dominant genus of nirK and promote nosZ abundance, thus decreasing N2O emissions. Our findings indicate that (i) drip irrigation increased ammonia-oxidizing bacteria amoA abundance and diversity but decreased nirS abundance, which led to N2O mitigation and (ii) SDI might be the best method for maintaining high crop yield with lower N2O emissions in intensively farmed fields.

Seasonal variations of nitrous oxide in a populous urban estuary and its adjacent sea

The first investigations of seasonal N2O variations and water-to-air fluxes in the Tamsui River estuary and its adjacent sea were carried out in this study. In the Tamsui River estuary, the concentration of N2O decreased with increasing salinity. The seasonal variations of N2O concentrations in the estuary were 46.8–148.5 nM in autumn, 15.9–82.5 nM in spring, 11.0–42.0 nM in summer and 13.1–120.6 nM in winter. When salinity regressed to zero, N2O concentration was highest in autumn, followed by winter, spring, and summer, which might be influenced by the DO and NO3− concentrations as well as temperature. Because of mountains occlusion, the seasonal variations in wind speed were not large in the Tamsui River estuary. Seasonal variations of N2O fluxes in the estuary were 10.9–35.6 μmol m−2 d−1 in autumn, 2.8–15.1 μmol m−2 d−1 in spring, 2.4–9.5 μmol m−2 d−1 in summer and 2.7–26.8 μmol m−2 d−1 in winter. In the adjacent sea of Tamsui River estuary, seasonal average N2O concentrations in the surface seawater were 10.3 ± 0.2 nM in autumn, 11.6 ± 1.2 nM in spring, 11.4 ± 0.7 nM in summer and 13.8 ± 0.9 nM in winter, with no significantly seasonal changes while wind speed varied greatly seasonally. Seasonal variations of average N2O fluxes in Tamsui River estuary’s adjacent sea were 40.3 ± 0.7 μmol m−2 d−1 in autumn, 19.7 ± 2.1 μmol m−2 d−1 in spring, 20.9 ± 1.3 μmol m−2 d−1 in summer and 49.0 ± 3.3 μmol m−2 d−1 in winter. As a result, seasonal variations in N2O fluxes in the estuary were dominated by N2O concentrations in the water, whereas in the sea, it was dominated by wind speed. Overall, the Tamsui River estuary and its adjacent sea were net sources of atmospheric N2O with annual average fluxes 10.6 ± 6.7 and 32.5 ± 14.5 μmol m−2 d−1, respectively.

The impacts of soil tillage combined with plastic film management practices on soil quality, carbon footprint, and peanut yield

Soil tillage and plastic film management practices are essential agricultural production strategies for improving crop yield. Furthermore, they can also play important roles in affecting soil quality, greenhouse gas (GHG) emissions, and carbon footprint (CF), and the overall impacts of tillage and plastic film management on these indicators and the potential links among them are rarely assessed. A 4-year-long field experiment was performed under the winter wheat–summer peanut rotation pattern to investigate how the tillage (plow tillage and rotary tillage) and plastic film management practices (plastic film mulching and no plastic film mulching) affected the summer peanut fields' soil quality (soil carbon (C) stock, enzyme activity, and nutrients concentration), soil GHG (N2O and CH4) emissions, CF components, and peanut yield. The present results showed that plow tillage management improved peanut yield and decreased seasonal cumulative soil N2O and CH4 emissions and CF relative to rotary tillage management. However, the seasonal cumulative emissions of soil N2O and CH4 under plastic film mulching were higher than those under no mulching. The application of plastic film mulching also increased soil TOC stock, soil enzymes (invertase, unease, and catalase) activities, and soil nutrients (microbial biomass C, microbial biomass nitrogen (N), ammonium N, and nitrate N) concentrations. The mulching-induced improvements in soil quality can promote an increase in crop productivity; thus, plastic film mulching showed increased peanut yield and decreased yield-scaled CF. In conclusion, plow tillage combined with plastic film mulching (PTM) treatment maintained higher peanut productivity and produced lower CF while generating suitable soil conditions and therefore may be a more high-yielding, eco-friendly, and sustainable development management strategy for summer peanut production.

Optimized tillage methods increase mechanically transplanted rice yield and reduce the greenhouse gas emissions

Biaxial rotary tillage in dryland (DBRT) can complete biaxial rotary tillage with straw incorporation, secondary suppression, and ditching, and it has been previously studied in direct-seeded rice and wheat. However, the effects of DBRT on the mechanically transplanted rice yield and greenhouse gas emissions remain unclear. To evaluate the effects of DBRT on improving the food security of mechanically transplanted rice and reducing the greenhouse gas emissions, we conducted an experiment for two years with wheat straw incorporation. Three tillage methods were set up: DBRT, uniaxial rotary tillage in dryland and paddy (DPURT), and uniaxial rotary tillage in paddy (PURT). The results showed that compared with DPURT and PURT, DBRT increased the yield of machine-transplanted rice by 7.5–11.0% and 13.3–26.7%, respectively, while the seasonal cumulative CH4 emissions were reduced by 13.9–21.2% and 30.2–37.0%, respectively, and the seasonal cumulative N2O emissions were increased by 13.5–28.6% and 50.0–73.1%, respectively. Consequently, DBRT reduced the global warming potential by 10.7–15.5% and 23.7–28.6%, respectively, and the yield-scaled global warming potential by 18.2–21.8% and 36.4–39.3%, respectively, compared to DPURT and PURT. These results were mainly related to the fact that DBRT significantly reduced soil bulk density and increased soil redox potential (Eh). Therefore, implementing DBRT in machine-transplanted rice fields is feasible, which cannot only increase the rice yield, but also reduce the greenhouse gas emissions.