N2O Emission Fluxes Research Articles

Ridge and furrow rainfall harvesting can significantly reduce N2O emissions from spring maize fields in semiarid regions of China

The ridge and furrow rainfall harvesting (RFRH) system is an effective method for enhancing the rainfall water use efficiency and crop yield. Determining how the fertilization rate affects soil nitrous oxide (N2O) emissions under the RFRH system has important practical significance for improving fertilization strategies and evaluating the environmental effects of the RFRH system. Therefore, we conducted a three-year field experiment in the Loess Plateau, China, to compare the RFRH system with traditional flat planting (T) at four different fertilizer rates (no fertilizer, N:P2O5 at 150:75 kg ha–1, N:P2O5 at 300:150 kg ha–1, and N:P2O5 at 450:225 kg ha–1). Under the same fertilization level, the soil water content (SWC) and dry matter were higher under RFRH compared with T, and the nitrate nitrogen (NO3−-N) content and N2O emissions were reduced. In the two planting models, SWC and NO3−-N of each treatment and its corresponding N2O emission flux were significantly positively correlated. Under the same planting model, SWC decreased but NO3−-N and the N2O emission increased with increasing fertilization rate. SWC was the key variable affecting the N2O emission flux in the RFRH system. In addition, the grain yield under RFRH increased by 2.2–28.0%, whereas the global warming potential (GWP) and greenhouse gas intensity (GHGI) decreased by 1.0–16.1% and 13.0–56.8%, respectively, compared with T. The grain yield and GHGI had quadratic relationships with the fertilization rate. Moreover, GWP increased in a linear manner with the fertilizer rate. These findings suggest that the RFRH system is an effective tillage measure for reducing N2O emissions. When the N:P2O5 fertilization rate was 200:100 to 307:154 kg ha−1, the RFRH system could maintain a higher grain yield and reduce the N2O emissions.

The effect of early season rice varieties and establishment methods on greenhouse gas emissions in southeast China

Methane (CH4) and nitrous oxide (N2O) emissions from rice fields are considered to be important sources of greenhouse gases. In order to clarify the emission characteristics of CH4 and N2O at different growth stages and to find optimal early season rice varieties and cultivation methods to control greenhouse gas emissions in southeast China, we conducted research in Jinhua City, Zhejiang Province, China in 2017 and 2018. Four different early season rice varieties were planted using three different rice establishment methods (machine transplanting, artificial transplanting, and direct seeding). The grain yield, CH4, and N2O emission rates and flux and economic profit were compared between the early varieties and establishment methods. Our results show that during the rice growth period, the CH4 and N2O emission fluxes and emission rates of the early season rice varieties increased first and then decreased, reaching the maximum at booting and the minimum at the grain filling stage. Direct seeding had the lowest cost and emission fluxes and emission rates compared to machine transplanting and artificial transplanting. The emission rates and flux of ‘Zhuliangyou609’ and ‘Zhongjiazao17’ were lower than in the other varieties. However, the yield of ‘Zhuliangyou609’ was higher than that of ‘Zhongjiazao17’ under identical conditions. Hence, direct-seeded rice shows good potential for cultivation in Zhejiang Province, and ‘Zhuliangyou609’ is the optimal early variety. This study provides theoretical support for the development of environmentally friendly early season rice establishment methods in southeast China.

Methane and nitrous oxide emission characteristics of high-yielding rice field.

As representative varieties of the four phases of the super rice breeding project in China, Lianyoupei 9 (LYP9), Y Liangyou 1 (YLY1), Y Liangyou 2 (YLY2), and Y Liangyou 900 (YLY900) achieved higher yield under optimal cultivation techniques. However, the impact of these high-yield rice varieties on greenhouse gas (GHG) emissions under high-yield cultivation management practices remains poorly understood. In this study, we conducted field experiments to investigate CH4 and N2O emissions from paddies containing four elite rice varieties, managed with field drying at the ineffective tillering stage and alternate wet/dry irrigation at the grain-filling stage. The plants were fertilised with nitrogen (N) at three different rates. The results showed that CH4 emission was highest at the tillering stage. N2O emission flux was dramatically increased by field drying at the ineffective tillering stage, and with the rate of N application. Rice variety was among the most important factors affecting CH4 emission and global warming potential (GWP). N2O emission was mainly related to N application rate rather than rice variety. YLY2 achieved higher yield than LYP9, YLY1, and YLY900, and lower GHG emission than YLY900. Our results indicate that rice variety should be considered as a key factor to reduce GHG emissions from rice paddies under high-yield cultivation practices. Based on its high yield and low GHG emission at the study site, YLY2 may be an optimal rice variety.

Effects of substrate type on enhancing pollutant removal performance and reducing greenhouse gas emission in vertical subsurface flow constructed wetland

Constructed wetlands (CWs), known as an alternative clean technology, have been widely used for sewage treatment. However, greenhouse gas (N2O, CH4 and CO2) emissions are the accompanying problem in CWs. To mitigate the net global warming potential (GWP) with the constant removal efficiency for contaminants is attracting wide attention recently. In this study, four CWs were established to explore the effects of substrate types (gravel, walnut shell, manganese ore and activated alumina) on contaminant removal and greenhouse gas emissions. CWs using manganese ore substrate with function of electronic exchange showed high removal efficiencies on COD (90.1%), TN (65.1%), TP (97.1%) and low greenhouse gas flux. The emission fluxes of N2O, CH4 and CO2 were 0.07–0.20, 2.00–252.30 and 337.54–782.57 mg m−2 h−1, respectively. Especially, the lowest average CH4 emission flux in the manganese ore CW was only 2.00 mg m−2 h−1 while those of N2O in walnut shell CW was only 0.07 mg m−2 h−1, which will make a significant contribution on the mitigation of GWP of CWs. High-throughput sequencing results indicated that microbial community diversity and richness changed significantly among different substrates. The high pmoA and low mcrA, caused by the introduction of manganese ore as substrate, also explained why there was little CH4 emission in CWs. Our study provided new insights into GWP mitigation and contaminant removal enhancement in CWs using optimal substrate.

Effect of biochar and compost application on nitrogen dynamics in organically managed nutrient-poor paddy soil system and in organic rice cultivation system

Nitrogen (N) is an essential plant nutrient, and its retention in the soil is beneficial to plant growth and productivity. High levels of N can leach from soil with organic amendments, particularly in water-rich paddy rice cultivation. Biochar has the potential to influence the soil N cycle. The study included four treatments applied to organically managed nutrient-poor paddy soil (S) and rice cultivation (R) systems, respectively over two growing seasons: biochar only (BA), compost only (CA), biochar and compost mixed at an equal rate (BC), and no amendment (control). Biochar produced from mangrove (Rhizophora apiculata) which obtained from slow pyrolysis in a traditional kiln, whereas compost generated from organic municipal solid waste. The results showed that, on average, BA and BC maintained NO3--N and NH4+-N in the soil and reduced absolute N leaching compared to the control and CA, respectively. System R maintained nitrogen better than system S. BA reduced N mass leaching by 27.25% in system S and by 59.21% in system R, compared to the control, while BC reduced N mass leaching by 24.85% in system S and by 58.48% in system R, compared to CA. However, the reduction in N2O emission fluxes was not significant in both BA and BC in both seasons, although cumulative emission fluxes after a year of cultivation decreased significantly. BC significantly boosted water use efficiency relative to yield in system R. These results show that co-application of biochar and compost to nutrient-poor soil in an organically managed system substantially reduced N leaching and suggests that it could be an effective management option for organic rice cultivation in Thailand. Keywords: Biochar, compost, nitrogen leaching, N2O emmision, nitrogen balance, organic rice cultivation.

Spatiotemporal distribution of nitrous oxide (N2O) emissions from cascade reservoirs in Lancang‐Mekong River Yunnan section, Southwestern China

AbstractThe current issue of river damming causing the release of greenhouse gas nitrous oxide (N2O) from reservoirs has led to a debate over whether hydropower can still provide clean energy. In January (dry season) and August 2019 (wet season), we detected the N2O concentrations from cascade reservoirs in Lancang‐Mekong River Yunnan section by using static headspace gas chromatography and estimated the emission flux by the boundary layer approach to explore the influencing factors, especially the impact of cascade reservoirs development and operation. In the Lancang River (Yunnan section), the longitudinal distribution of N2O concentration along the cascade reservoirs showed seasonal differences. The average concentrations of N2O during the dry season and the wet season were 13.50 ± 2.00 nmol/L and 16.40 ± 4.10 nmol/L, respectively. The reservoirs with thermal stratification in both seasons were the Xiaowan (XW), Nuozhadu (NZD), and Jinghong (JH) reservoirs. The vertical distribution of N2O concentration was depth dependent (i.e., the deeper the location, the higher the concentration) in reservoirs with thermal stratification and uniform in reservoirs without thermal stratification. Dissolved oxygen (DO), water temperature, and other biogenic elements were the main factors affecting N2O distribution. The average N2O emission flux in the cascade reservoirs was 12.80 ± 2.60 μmol m2·day−1 during the dry season and 16.10 ± 4.75 μmol m2·day−1 during the wet season. The annual average N2O emission fluxes of all reservoirs were in an order of JH > XW > Dachaoshan (DCS) > NZD > Miaowei (MW) > Gongguoqiao (GGQ) > Manwan (Man W). In 2019, a total of 3.37 × 106 mol year−1 (94.39 ton N2O‐N year−1) was released from the water surface of the cascade reservoirs, which accounted for approximately 0.31% of the total N2O emissions from reservoirs worldwide. This study shows the cascade reservoirs development and operations have made the Lancang River (Yunnan section) a major area for N2O emissions.

Soil N<sub>2</sub>O emissions after perennial legume termination in an alfalfa-wheat crop rotation system under Mediterranean conditions

Agricultural activities are potential sources of greenhouse gas (GHG) emissions, and nitrous oxide (N2O) is one of the most important non-carbon-dioxide GHGs. Perennial legumes such as alfalfa (Medicago sativa L.) have potential roles for reduction of soil GHG emissions as part of crop rotation systems. However, the implications of perennial legume termination by tillage and subsequent soil incorporation of the residues for reduced GHG emissions have been poorly examined in Mediterranean environments. With the aim to assess the magnitude of soil N2O emissions (important for the definition of mitigation strategies) after perennial legume termination in alfalfa-wheat crop rotation systems in a Mediterranean environment, we defined the hypothesis that alfalfa termination by tillage with incorporation of the crop residues will increase soil N2O emissions during the subsequent wheat season. To test this hypothesis, closed static chambers were used in a field–plot experiment, using a complete randomised block design with three replicates. Soil N2O emissions were monitored across 33 sampling dates from October 2017 to July 2018, as a comparison between an original 6-year-old alfalfa field (‘continuous alfalfa’) and alfalfa termination followed by wheat (‘alfalfa+ wheat’). The soil N2O emission fluxes varied markedly across the treatments and throughout the monitoring period (from – 0.02±0.01 to 0.53±0.14 g N-N2O ha–1 h–1, and from 0.02±0.07 to 0.37±0.11 g N-N2O ha–1 h–1 for continuous alfalfa and alfalfa+wheat, respectively), generally following the changes in soil temperature. Several soil N2O emission peaks were recorded for both treatments, which mainly coincided with rainfall and with increased soil water content. In the 2 months following alfalfa termination, alfalfa+wheat showed higher cumulative weekly soil N2O emissions compared to continuous alfalfa. Following alfalfa termination for alfalfa+wheat, the increased cumulative weekly soil N2O emissions appeared to be due to asynchrony between nitrogen (N) released into the soil from mineralisation of the alfalfa residues and N uptake by the wheat. Despite these initial high soil N2O emissions for alfalfa+wheat, the seasonal cumulative soil N2O emissions were not significantly different (0.77±0.09 vs 0.85±0.18 kg N-N2O ha–1 for continuous alfalfa and alfalfa+wheat, respectively). These data suggest that legume perennial crop termination in alfalfa–wheat rotation systems does not lead to significant loss of N2O from the soil. The alfalfa termination by tillage performed in autumn might, on the one hand, have slowed the mineralisation process, and might, on the other hand, have synchronised the N release by the mineralised crop residues, with the N uptake by the wheat reducing the soil N2O emissions.
 Highlights - Soil N2O emissions peak after alfalfa termination and rainfall. - Soil N2O emissions increase after spring alfalfa mowing. - Seasonal cumulative soil N2O emissions are similar for alfalfa and alfalfa followed by wheat. - Mitigation effects of perennial legume on soil N2O emissions are not lost after termination by tillage under alfalfa-wheat rotation.

C3 and C4 Grass Species: Who Can Reduce Soil Nitrous Oxide Emissions in a Continental Arid Region?

In order to relieve grazing pressure, drought-tolerant grass species are widely cultivated in arid regions. However, soil N emission is largely neglected while pursuing forage yield. We carried out a randomized block study to investigate whether and how the C3 and C4 grass species differ in soil N emission in a typical salinized field with temperate continental arid climate in the northwest inland regions, China. We quantified soil N2O flux from two C3 (barley and rye) and two C4 grass species [corngrass and sorghum hybrid sudangrass (SHS)] in fields during the growing season (from May to September) by using the static box method, and then determined the relationships between soil N2O fluxes and forage yield and soil properties. Results show that soil available nitrogen, soil temperature, pH, soil organic carbon, and total nitrogen were correlated, but soil water was anti-correlated with soil N2O fluxes. In addition, N2O flux increased significantly faster with soil temperature in C4 than in C3 grass fields. Although the lower total N2O emission fluxes were detected for C3 species, the lower yield-scaled N2O was detected for C4 species. Our study provided insights into the determination of grass species and the understanding of mechanisms regulating N2O fluxes in C3 and C4 species in the continental arid regions.

Evaluating Cropland N2O Emissions and Fertilizer Plant Greenhouse Gas Emissions With Airborne Observations

AbstractAgricultural activity is a significant source of greenhouse gas emissions. The fertilizer production process emits N2O, CO2, and CH4, and fertilized croplands emit N2O. We present continuous airborne observations of these trace gases in the Lower Mississippi River Basin to quantify emissions from both fertilizer plants and croplands during the early growing season. Observed hourly emission rates from two fertilizer plants are compared with reported inventory values, showing agreement for N2O and CO2 emissions but large underestimation in reported CH4 emissions by up to a factor of 100. These CH4 emissions are consistent with loss rates of 0.6–1.2%. We quantify regional emission fluxes (100 km) of N2O using the airborne mass balance technique, a first application for N2O, and explore linkages to controlling processes. Finally, we demonstrate the ability to use airborne measurements to distinguish N2O emission differences between neighboring fields, determining we can distinguish different emission behaviors of regions on the order of 2.5 km2 with emissions differences of approximately 0.026 μmol m−2 s−1. This suggests airborne approaches such as outlined here could be used to evaluate the impact of different agricultural practices at critical field‐size spatial scales.

Estimation of Greenhouse Gas Emission from Hanwoo (Korean Native Cattle) Manure Management Systems

The agricultural sector is considered one of the major sources of greenhouse gas (GHG) emissions globally. The livestock industry as a significant contributor, is accounting for about 18% of GHG emissions measured in carbon dioxide (CO2) equivalent from agricultural practices. Depending on farming practices and climatic conditions, GHGs such as methane (CH4) and nitrous oxide (N2O) emissions from livestock agriculture can vary significantly. Country-specific emission factors are, therefore, needed for a precise estimation of GHG emissions and to avoid uncertainties. This study was aimed at estimating the CH4 and N2O emission fluxes from Hanwoo (the most famous and popular Korean native cattle) manure management systems. CH4 and N2O emission fluxes from litter in the Hanwoo cattle barn and composting lot were monitored and calculated for 52 weeks using the dynamic chamber method. The calculated monthly average fluxes of CH4 and N2O from litter in the cattle barn ranged from 0.0 to 30.0 ± 13.7 and 0.896 ± 0.557 to 2.925 ± 2.853 μg/m2 s, respectively during the whole measurement period. While during the composting period, the monthly average of CH4 and N2O emission fluxes were varied from 1.449 ± 0.783 to 86.930 ± 19.092 and 0.511 ± 0.410 to 2.629 ± 1.105 μg/m2 s, respectively. The calculated emission fluxes of CH4 and N2O from manure management systems in this study were almost 5.4 and 2.1 times, respectively higher than the values reported for the Asian, South and North American countries in the 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas Inventories. Overall, this study initiates the process along with signifies the importance of developing country-specific GHG inventories for the effective reduction of GHG emissions from the livestock sector in Korea.

Silicate fertilizer application reduces soil greenhouse gas emissions in a Moso bamboo forest

Silicate fertilizer application in croplands is effective in mitigating soil methane (CH4) emissions and increasing rice yield. However, the effects of silicate fertilizer on soil greenhouse gas (GHG) emissions in Moso bamboo forests, and the underlying mechanisms are poorly understood. In the present study, a two-year field experiment was conducted to investigate the effect of silicate fertilizer rates (0 (CK), 0.225 and 1.125 Mg ha−1) on soil GHG emissions in a Moso bamboo forest. The results showed that silicate fertilizer application significantly reduced soil CO2 and N2O emissions, and increased soil CH4 uptakes. Compared to the CK treatments, the cumulative soil CO2 emission fluxes decreased by 29.6% and 32.5%, and the cumulative soil N2O emission fluxes decrease by 41.9% and 48.3%, the CH4 uptake fluxes increased by 13.5% and 32.4% in the 0.225 and 1.125 Mg ha−1 treatments, respectively. The soil GHG emissions were significantly positively related to soil temperature (P < 0.05), but negatively related to soil moisture; however, this relationship was not observed between CH4 uptake fluxes and moisture in CK treatment. Soil CO2 emission and CH4 uptake were significantly positively related with water-soluble organic C (WSOC) and microbial biomass C (MBC) concentrations in all treatments (P < 0.05). Soil N2O emissions were significantly positively related to MBC, NH4+-N, NO3−-N, and microbial biomass N (MBN) concentrations in all treatments (P < 0.05), but not with WSOC concentration. Structural equation modeling showed that application of silicate fertilizer directly reduced soil GHG emission by decreasing the labile C and N pools, and indirectly by influencing the soil physicochemical properties. Our findings suggest that silicate fertilizer can be an effective tool in combatting climate change by reducing soil GHG emissions in Moso bamboo forests.

Effects of biochar and straw on greenhouse gas emission and its response mechanism in seasonally frozen farmland ecosystems

Freeze-thaw cycle promotes the decomposition of soil organic matter in cold regions, causing carbon and nitrogen to be emitted in the forms of CO2, CH4 and N2O, resulting in positive feedback to climate warming. To effectively regulate greenhouse gas emissions, four different regulation modes, namely, biochar addition (BA), straw addition (SA), combined biochar and straw (CBS) and a natural control (BL), were established. The characteristics of soil greenhouse gas emissions under different treatments and their response relationships to soil water, heat, carbon and nitrogen were explored. The results revealed that the SA and CBS treatments effectively inhibited the substantial reduction in soil temperature, moisture content, inorganic nitrogen and dissolved organic carbon during the freezing period; among them, the average soil inorganic nitrogen under the SA and CBS treatments increased by 15.36 and 11.62 mg·kg−1 compared to that in the BL treatment, respectively. Simultaneously, both N2O and CO2 emission fluxes were low, and the difference was small under the various treatments. However, the soil showed an absorption trend with respect to CH4, and the BA and CBS treatments promoted this effect; furthermore, the response relationships between CH4 and soil water, heat and carbon were enhanced. During the thawing period, the CBS treatment most effectively promoted the increase in soil water, heat, carbon and nitrogen, while it inhibited the flux of CH4 and N2O in soils, and the average CH4 emission flux under the CBS treatment decreased by 8.25 ~ 30.75 μg∙kg−1 relative to that under the other treatments. Concurrently, the responses of CH4 and N2O emission fluxes to soil water, heat, carbon and nitrogen were weakened under this treatment. Although the CBS treatment increased the CO2 emissions flux during this period, in view of the overall effect of the entire freeze–thaw period, the CBS treatment most effectively reduced the global warming potential (GWP) of the soil. Therefore, it is suggested that the joint application of biochar and straw is the most effective strategy for greenhouse gas budget management and soil nutrient restoration in seasonally frozen areas.

Nitrous oxide emissions from tea garden soil following the addition of urea and rapeseed cake

Tea gardens, being a key agroecosystem type, are an important source of nitrous oxide (N2O) emissions. However, main factors that regulate N2O emissions following urea and organic matter amendments have yet to be clarified. To investigate the influence of different fertilization management measures on N2O emissions in tea garden soil, a 50-day laboratory incubation experiment was conducted. Five treatments were designed for this experiment: control (CK), urea (U), rapeseed cake (R), urea + rapeseed cake (2:1, UR1), and urea + rapeseed cake (1:2, UR2). N2O emission flux in the R treatment peaked at 14.12 μg kg−1 h−1 on day 19, which occurred later than the UR1, UR2, and U treatments. Cumulative N2O emissions from the R and UR2 treatments were 6073 and 4296 μg kg−1, respectively, which were greater by a factor of 11.2 and 7.9, respectively, compared to the U treatment. Moreover, N2O emissions of the UR1 and UR2 treatments were significantly lower than the R treatment. Additionally, N2O emissions were also significantly positively correlated to pH levels and microbial biomass carbon (MBC) content. MBC content had the most direct and greatest influence on soil N2O emissions, indicating that MBC could be the key limiting factor for N2O emissions in this experiment. A single application of rapeseed cake caused an increase in N2O emissions, whereas the combined application of rapeseed cake and a synthetic N fertilizer (urea) caused a decrease in N2O emissions. Results from this study offer potential strategies to mitigate soil N2O emissions from tea garden agroecosystems through improved field fertilization management.

N2 O Emissions from Tea Plantations with Sorghum Intercropping and Application of Big Urea Pills

A large amount of fertilizers are applied to the tea plantations resulting in high nitrous oxide (N2O) emissions. The area of Chinese tea plantations has been expanding in recent years, making them an important source of agricultural N2O emissions. There is an urgent need for effective mitigation measures for N2O emissions from tea plantations. In this study, the N2O emission flux and related environmental factors are measured in Chinese mid-subtropical typical hilly tea plantation under three kinds of management measures, namely intercropping sorghum, applying big urea pills, and under conventional fertilization conditions. The aim of this experiment is to determine the main factors controlling N2O emissions from the soils of the tea plantation and confirm the true effectiveness of the proposed N2O emission mitigation measures. The results of a 2-year field experiment show that:① N2O emissions were significantly correlated with soil chemical properties, temperature and rainfall, interaction between soil physical and chemical properties; soil chemical properties have the greatest impact on soil N2O emissions. The concentration of soil NO3--N is the most important factor determining the size of N2O flux in the tea plantation. The most important task of N2O emission mitigation research in the tea plantation is to reduce the concentration of soil NO3--N; ② sorghum intercropping reduces N2O emissions by 51.2% while not affecting the tea yield. From the perspective of mitigating global warming, sorghum intercropping is the best tea plantation management measure per the results of this study; ③ applying big urea pills effectively increases tea yield while simultaneously reducing the N2O emissions by 34.7%. From the perspective of balancing economic benefits as well as mitigating global warming, application of big urea pills is undoubtedly the best tea plantation management measure as indicated by this study.

Effects of influent salinity on water purification and greenhouse gas emissions in lab-scale constructed wetlands.

Salinity has a significant impact on the sewage treatment efficiency of constructed wetlands (CWs), as well as affecting the greenhouse gas emissions of CWs. A lab-scale CW simulation system was constructed to observe the treatment efficiency and greenhouse gas flux occurring in CWs at different influent salinities (0%, 0.5%, 1.0%, 1.5%, and 2.0%). The results show that (1) the removal rates of COD, TN, NH4+-N, NO3--N, and TP reach the highest at salinity of 0 or 0.5%. And the lowest removal rates are all at a salinity of 2.0%. (2) The emission flux of CO2, CH4, and N2O in CWs varies with an increase in salinity. The trends of CO2 and CH4 emission flux were consistent with those of COD reduction rate. However, it was opposite for N2O flux to that of TN, NH4+-N, and NO3--N removal rate. Affected by salinity, the greenhouse gas emission flux in this study is generally lower than what was reported in literature. (3) Correlation analysis showed that CO2 and CH4 emission fluxes were positively correlated with the COD reduction rate. N2O emission flux was negatively correlated with the removal rates of TN, NH4+-N, and NO3--N. The results suggest that different pollutants are inhibited by salinity to different degrees. COD is more affected by salinity than nitrogen and phosphorus, while nitrogen is more easily inhibited by salinity than phosphorus. CWs can have a high removal rate of pollutants in treating low-salinity wastewater. Although increased salinity reduces treatment efficiency of wastewater to some extent, it also inhibits the emission of CO2 and CH4.

Diurnal variations of greenhouse gases emissions from reclamation mariculture ponds

Dissolved concentrations, saturation status, and emission fluxes of greenhouse gases (GHGs) in two reclamation mariculture ponds in the Bohai Gulf, China, were measured using the static headspace gas chromatography method and computed using a two-layer model of diffusive gas exchange. The study was conducted during August 2016 to assess diurnal variations in GHGs emissions. The main influencing factors of GHGs emissions from the ponds under the disturbance of artificial management were identified using Spearman correlation analyses and multiple stepwise regression analyses. Results showed that dissolved GHGs concentrations were stable throughout the day, whereas GHGs emission fluxes showed a clear diurnal variation with larger daytime values. The diurnal variation of N2O emission fluxes was greater than that of CO2 and that of CH4. Results also showed that pH of pond water was negatively correlated with CO2 and N2O emission fluxes and that air temperature was positively correlated with CH4 and N2O emission fluxes. In addition, ammonia (NH4+-N) was positively correlated with CH4 emission fluxes; water temperature and salinity were positively correlated with N2O emission fluxes. The estimated annual emissions from the reclamation aquaculture in Tianjin and the Bohai Rim region were 2.53 × 105 kg C–CO2, 6.94 × 103 kg C–CH4 and 1.11 × 103 kg N–N2O, and 3.42 × 107 kg C–CO2, 9.36 × 105 kg C–CH4 and 1.50 × 105 kg N–N2O respectively, indicating the important contribution of this fishery sector to GHGs emissions.

Ridge-furrow mulching system and supplementary irrigation can reduce the greenhouse gas emission intensity

In this study, in order to explore the greenhouse gas emissions and global warming potential (GWP) in winter wheat fields under the ridge-furrow mulching system (RF) with supplementary irrigation, three rainfall conditions (heavy rainfall = 275 mm, normal rainfall = 200 mm, and light rainfall = 125 mm) and four irrigation treatments (150, 75, 37.5, and 0 mm) were simulated during the growth period. Traditional flat planting (TF) was used as the control and we determined the emissions of N2O, CO2, and CH4, as well as the GWP and greenhouse gas emission intensity (GHGI). The results obtained after three years (October 2016 to June 2019) showed that when the amount of irrigation was the same during the winter wheat growth period, the N2O emission flux, CO2 emission flux, and GHGI under RF decreased by 3.30–23.78%, 5.93–6.45%, and 5.01–23.72% with rainfall at 275 mm, respectively, compared with those under TF. Under the same level of supplementary irrigation, the N2O emission flux, CO2 emission flux, and GHGI decreased by 0.8–4.18%, 5.05–13.53%, and 7.83–13.72%, respectively, with rainfall at 200 mm, and they decreased by 17.49–32.46%, 25.57–35.35%, and 6.22–30.20% with rainfall at 125 mm. Under the three rainfall conditions, the absorption of CH4 in the winter wheat field increased as the supplementary irrigation decreased. Our results showed that the RF system can satisfy the goal of achieving high yields and saving water, as well as reducing the GHGI to contribute less to global climate warming as an environmentally friendly irrigation method.

Response of winter wheat yield and soil N2O emission to nitrogen fertilizer reduction and nitrapyrin application in North China Plain

ABSTRACTOver-fertilization could lead to nitrogen (N) losses and environmental risks, and the appropriate nitrogen fertilizer could reduce the nitrous oxide (N2O) emission and increase the N utilization of crops in the North China Plain. We investigated the effects of rationally reduced N fertilizer input and nitrapyrin (CP) application on N2O dynamic emission, soil N balance, yield, N utilization and net income during the whole wheat season. Five fertilization treatments included zero N (CK), farmers’ traditional N rate (FN), recommended N rate (RN), the 20% reduction of RN (80%RN) and the 20% reduction of RN added with CP (80%RN+CP). The N2O emission fluxes from seedling stage to greening stage contributed to 51.1%-74.2% during the whole wheat growth stages. Moreover, the first peak of N2O emission was observed within half a month after N basal fertilizer, irrigation, and sowing, which was two times higher than the other peaks occurred after N top-dressing and irrigation. The cumulative N2O emission and N2O emission factor were significantly declined by 27.3%-43.4% and 8.9%-51.1% with 80%RN and 80%RN+CP as compared to FN, respectively. Grain yield, agronomic N use efficiency, apparent N use efficiency and N production efficiency with 80%RN+CP were increased by 1.74%-10.83%, 0.9–8.91 kg kg−1, 1.9%-27.5% and 1.22–22.79 kg kg−1 than other N treatments, respectively. Moreover, 80%RN+CP also decreased N loss by 7.88–55.62 kg ha−1 as compared to FN and RN, which resulted in less soil NO3− retention. Consequently, the application of nitrapyrin with 20% reduction of N rate should be recommended to increase winter wheat economic benefits and mitigate environmental pollution in North China Plain.

Evaluating Greenhouse Gas Emissions From Soil Application of Anaerobic Organic Digestive Compared With Conventional Manure

The state of California is investing in anaerobic digesters to reduce methane emissions from agriculture. However, little is known about the impact of anaerobic digesters on nitrous oxide (N2O) and carbon dioxide (CO2) emissions from soils after land application of digestate. The purpose of this study was to compare soil CO2 and N2O emission fluxes from anaerobic digestate treatment in conjunction with manure, manure treatment, and a control group without treatment on agricultural soils from two dairy farms. In addition to comparing treatments and sites, we tested the effects of temperature at either 23°C or 28°C to compare predicted future average temperatures. Soil samples were placed in mason jars with 18 jars per location: three manure treatments x 2, temperatures x 3 replications per treatment, and incubated for six weeks according to the temperature treatment. Soils were watered once a week to maintain 65% water holding capacity. Cavity ring-down spectrometers were used to collect gas emissions in a closed-loop system, and elemental analyzers were used to evaluate soil and treatment nutrient composition. We hypothesized that three main variables — manure, lower temperatures, and soils with low-nutrient content in conjunction with anaerobic diges- tate would all lead to lower emissions. Anaerobic digestate has been found to reduce greenhouse gas emissions while also being a nutrient-rich energy source. Microbial soil communities are also more active in warmer temperatures, which may increase the production of gas emissions. Overall, the results were inconclusive for either argument.

Effects of Biochar on N2O Emission from Four Typical Soils in the North China Plain

As a potential soil conditioner, biochar plays an important role in alleviating greenhouse gas (GHG) emissions. To clarify the influence of biochar on soil N2O emissions during the winter wheat seedling stage, four typical soils in the North China Plain (paddy soil, shajiang black soil, cinnamon soil, and fluvo-aquic soil) were adopted for field experiments, and four treatments were set:Control (CK), Fertilizer (NPK), Biochar (BC), and Fertilizer+Biochar (NPK+BC). The results showed that fertilization (NPK) significantly increased the N2O emissions of the four soils. Compared with that of the CK, the N2O emissions of four soils were increased by 314%, 116%, 240%, and 282%, respectively. The effect of biochar addition on N2O emissions of the four soils in the North China Plain was different. Compared with that of the CK treatment, the N2O emissions of paddy soil and cinnamon soil in the BC treatment significantly increased by 72.4% and 50.9%, respectively, whereas the shajiang black soil and fluvo-aquic soil exhibited no significant differences. The combined application of biochar and fertilizer significantly reduced the N2O emissions of the four soils, compared to that of NPK. The addition of biochar increased the pH of soil. In particular, paddy soil had the lowest initial pH and was most affected by biochar. Fertilization reduced the pH of the four soils. N2O flux under fertilizer treatment for the shajiang black soil, cinnamon soil, and fluvo-aquic soil was significantly positively correlated with ammonium nitrogen content, whereas N2O emission fluxes under single biochar treatment on paddy soil and shajiang black soil were significantly positively correlation with nitrate nitrogen content.