A global meta-analysis of nitrous oxide emission from drip-irrigated cropping system

Estimating soil N2O emissions induced by organic and inorganic fertilizer inputs using a Tier-2, regression-based meta-analytic approach for U.S. agricultural lands

Consistent methods are essential for generating country and region-specific estimates of greenhouse gas (GHG) emissions used for reporting and policymaking. The estimates of direct N2O emissions from U.S. agricultural soils have primarily relied on the use of emission factors (EFs, Tier-1) and process-based models (Tier-3). However, Tier-1 estimates are relatively crude while Tier-3 calculations can be costly. This work addressed this gap by developing a Tier-2, regression-based approach by leveraging a meta-database containing 1883 field N2O observations together with environmental and management covariates from 139 studies. Our results estimated higher monthly soil N2O emissions (N2Om, kg N/ha) during the growing season (0.38) than the fallow period (0.15), highlighting the importance of considering measurement periods when utilizing meta-databases for analyzing N2O drivers. Significantly different N2Om were found for tillage practices (conventional > no-till: 0.42 > 0.27), fertilizer type (liquid > solid manure: 0.55 > 0.32), and soil texture (fine > coarse: 0.36 > 0.22). The comparisons of the influence of crop type and rotation, water management, and soil order on N2O emissions are complicated by regional data availability and interactions among different factors. Additionally, the finding that N2O emissions reported based on area (N2Om), N input rate (EF), or yield can alter treatment rankings underscores the need to establish transparent criteria for rewarding or discouraging regionally-based management practices using N2O metrics. Finally, we show how General Linear Models (GLMs) can be used to estimate country and regional Tier-2 N2Om using a suite of covariates. Our GLMs identified tillage, water management, N input type and rate, soil properties, and elevation as the most influential covariates for the conterminous U.S. The limited accuracy of regional-scale GLMs, however, suggests the need to further improve the quality and availability of GHG and covariate data through concerted efforts in data collection.

Effectiveness of three nitrification inhibitors on mitigating trace gas emissions from different soil textures under surface and subsurface drip irrigation

Nitrification inhibitors (NIs) and drip irrigation are recommended to mitigate trace gas emissions from agricultural soils. However, studies comparing the effect of different NIs on the release of trace gases from soils with contrasting textures under subsurface (SBD) and surface (SD) drip irrigation are lacking. Therefore, this study aimed to assess the effectiveness of three NIs in mitigating nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) emissions from two soils with different textures under SBD, with pipe buried in 10 cm depth, and SD. Two greenhouse experiments were carried out with silt loam and loamy sand soil textures cultivated with wheat under SBD and SD to assess the effectiveness of the NIs Dicyandiamide (DCD), 3,4-Dimethylpyrazole phosphate (DMPP), and 3-Methylpyrazol combined with Triazol (MP + TZ). Ammonium sulfate was applied at a rate of 0.18 g N kg soil-1. The measured variables were daily and cumulative N2O-N, CO2-C, and CH4-C emissions, as well as soil NH4+-N and NO3--N concentrations. The NIs and SBD had additive effects on reducing N2O-N emissions in the silt loam, but not in the loamy sand soil texture. Under SBD, total N2O-N emissions were 44% and 52% lower than under SD in the silt loam and loamy sand soil textures, respectively. Moreover, DMPP kept the highest NH4+-N concentrations and promoted the lowest N2O-N release. CO2-C and CH4-C total emissions were not affected by the treatments. Our findings supported the hypothesis that SBD decreases N2O-N emissions relative to SD. Among the investigated NIs, DMPP has the highest effectiveness in retarding nitrification and mitigating N2O-N release under the studied treatments. Finally, in coarse-textured soils, the use of NIs could be sufficient to significantly abate N2O-N emissions.

Global energy use and carbon emissions from irrigated agriculture

Irrigation is a land management practice with major environmental impacts. However, global energy consumption and carbon emissions resulting from irrigation remain unknown. We assess the worldwide energy consumption and carbon emissions associated with irrigation, while also measuring the potential energy and carbon reductions achievable through the adoption of efficient and low-carbon irrigation practices. Currently, irrigation contributes 216 million metric tons of CO2 emissions and consumes 1896 petajoules of energy annually, representing 15% of greenhouse gas emissions and energy utilized in agricultural operations. Despite only 40% of irrigated agriculture relies on groundwater sources, groundwater pumping accounts for 89% of the total energy consumption in irrigation. Projections indicate that future expansion of irrigation could lead to a 28% increase in energy usage. Embracing highly efficient, low-carbon irrigation methods has the potential to cut energy consumption in half and reduce CO2 emissions by 90%. However, considering country-specific feasibility of mitigation options, global CO2 emissions may only see a 55% reduction. Our research offers comprehensive insights into the energy consumption and carbon emissions associated with irrigation, contributing valuable information that can guide assessments of the viability of irrigation in enhancing adaptive capacity within the agricultural sector.

A theoretical framework to improve the adoption of green Integrated Pest Management tactics

Sustainable agriculture relies on implementing effective, eco-friendly crop protection strategies. However, the adoption of these green tactics by growers is limited by their high costs resulting from the insufficient integration of various components of Integrated Pest Management (IPM). In response, we propose a framework within IPM termed Multi-Dimensional Management of Multiple Pests (3MP). Within this framework, a spatial dimension considers the interactive effects of soil-crop-pest-natural enemy networks on pest prevalence, while a time dimension addresses pest interactions over the crop season. The 3MP framework aims to bolster the adoption of green IPM tactics, thereby extending environmental benefits beyond crop protection.

Comprehensive impacts of different integrated rice-animal co-culture systems on rice yield, nitrogen fertilizer partial factor productivity and nitrogen losses: A global meta-analysis

Integrated rice-animal co-culture (IRAC) is an ecological agricultural system combining rice cultivation with animal farming, which holds significant implications for food security and agriculture sustainable development. However, the comprehensive impacts of the co-culture on rice yield, nitrogen (N) losses, and N fertilizer partial factor productivity (NPFP) remain elusive and may vary under different environmental conditions and N management. Here, we conducted a meta-analysis of data from various IRAC systems on a global scale, including 371, 298, and 115 sets of data for rice yield, NPFP, and N losses, respectively. The results showed that IRAC could significantly increase rice yield (by 3.47 %) and NPFP (by 4.26 %), and reduce N2O emissions (by 16.69 %), NH3 volatilization (by 11.03 %), N runoff (by 17.72 %), and N leaching (by 19.10 %). Furthermore, there were significant differences in rice yield, NPFP, and N loss among different IRAC systems, which may be ascribed to variations in regional climate, soil variables, and N fertilizer management practices. The effect sizes of rice yield and NPFP were notably correlated with the rate and frequency of N application and the soil clay content. Moreover, a higher amount of precipitation corresponded to a larger effect size on rice NPFP. N2O emissions were closely associated with mean annual air temperature, annual precipitation, N application frequency, soil pH level, soil organic matter content, soil clay content, and soil bulk density. However, NH3 volatilization, N runoff, and N leaching exhibited no correlation with either the environmental conditions or the N management. Multivariate regression analysis further demonstrated that the soil clay content and N application rate are pivotal in predicting the effect sizes of rice yield, NPFP, and N2O emissions under IRAC. Specifically, IRAC with a low N application rate in soils with a high clay content could augment the effect size to increase rice NPFP and yield and reduce N2O emissions. In conclusion, IRAC offers a potent strategy to optimize rice yield and NPFP as well as mitigate N losses.

Is Cr(III) re-oxidation occurring in Cr-contaminated soils after remediation: Meta-analysis and machine learning prediction

Whether Cr(III) in Cr(III)-containing sites formed after Cr(VI) reduction and stabilization remediation are re-oxidized and pose toxicity risks again has been a growing concern. In this study, 1030 data were collected to perform a meta-analysis to clarify the effects of various factors (oxidant type, soil and Cr(III) solid compound properties, aging conditions, and testing methods) on Cr(III) oxidation. We observed that the soil properties of clay, pH ≥ 8, the lower CEC capacity, easily reducible Mn content, and Cr(III) content, and the higher Eh value and Fe content can promote the re-oxidation of Cr(III). Publication bias and sensitivity analyses confirmed the stability and reliability of the meta-analysis. Subsequently, we used five machine learning algorithms to construct and optimize the models. The prediction results of the RF model (RMSE <1.36, R2 >0.71) with good algorithm performance showed that after ten years of remediation, the extractable Cr(VI) concentration in the soil was 0.0087 mg/L, indicating a negligible secondary pollution risk of Cr(III) re-oxidation. This study provides theoretical support for subsequent risk management and control after Cr(VI) soil remediation and provides a solution for the quantitative prediction of Cr(III) re-oxidation.

Microbial pathways of nitrous oxide emissions and mitigation approaches in drylands

Drylands refer to water scarcity and low nutrient levels, and their plant and biocrust distribution is highly diverse, making the microbial processes that shape dryland functionality particularly unique compared to other ecosystems. Drylands are constraint for sustainable agriculture and risk for food security, and expected to increase over time. Nitrous oxide (N2O), a potent greenhouse gas with ozone reduction potential, is significantly influenced by microbial communities in drylands. However, our understanding of the biological mechanisms and processes behind N2O emissions in these areas is limited, despite the fact that they highly account for total gaseous nitrogen (N) emissions on Earth. This review aims to illustrate the important biological pathways and microbial players that regulate N2O emissions in drylands, and explores how these pathways might be influenced by global changes for example N deposition, extreme weather events, and climate warming. Additionally, we propose a theoretical framework for manipulating the dryland microbial community to effectively reduce N2O emissions using evolving techniques that offer inordinate specificity and efficacy. By combining expertise from different disciplines, these exertions will facilitate the advancement of innovative and environmentally friendly microbiome-based solutions for future climate change vindication approaches.

Soil N2 O emissions from specialty crop systems: A global estimation and meta-analysis

Nitrous oxide (N2 O) exacerbates the greenhouse effect and thus global warming. Agricultural management practices, especially the use of nitrogen (N) fertilizers and irrigation, increase soil N2 O emissions. As a vital sector of global agriculture, specialty crop systems usually require intensive input and management. However, soil N2 O emissions from global specialty crop systems have not been comprehensively evaluated. Here, we synthesized 1137 observations from 114 published studies, conducted a meta-analysis to evaluate the effects of agricultural management and environmental factors on soil N2 O emissions, and estimated global soil N2 O emissions from specialty crop systems. The estimated global N2 O emission from specialty crop soils was 1.5 Tg N2 O-N year-1 , ranging from 0.5 to 4.5 Tg N2 O-N year-1 . Globally, soil N2 O emissions exponentially increased with N fertilizer rates. The effect size of N fertilizer on soil N2 O emissions generally increased with mean annual temperature, mean annual precipitation, and soil organic carbon concentration but decreased with soil pH. Global climate change will further intensify the effect of N fertilizer on soil N2 O emissions. Drip irrigation, fertigation, and reduced tillage can be used as essential strategies to reduce soil N2 O emissions and increase crop yields. Deficit irrigation and non-legume cover crop can reduce soil N2 O emissions but may also lower crop yields. Biochar may have a relatively limited effect on reducing soil N2 O emissions but be effective in increasing crop yields. Our study points toward effective management strategies that have substantial potential for reducing N2 O emissions from global agricultural soils.

Drivers of ammonia volatilization in Mediterranean climate cropping systems

Ammonia (NH3) volatilization is the major source of nitrogen (N) loss resulting from the application of synthetic and organic N fertilizers to croplands. It is well known that in Mediterranean cropping systems, there is a relationship between the intrinsic characteristics of the climate and nitrous oxide (N2O) emissions, but whether the same relation exists for NH3 emissions remains uncertain. Here, we estimated the impact of edaphoclimatic conditions (including meteorological conditions after N fertilization), crop management factors, and the measurement technique on both the cumulative emissions and the NH3 emission factor (EF) in Mediterranean climate zones, drawing on a database of 234 field treatments. We used a machine learning method, random forest (RF), to predict volatilization and ranked variables based on their importance in the prediction. Random forest had a good predictive power for the NH3 EF and cumulative emissions, with an R2 of 0.69 and 0.76, respectively. Nitrogen fertilization rate (N rate) was the top-ranked predictor variable, increasing NH3 emissions substantially when N rate was higher than 170 kg N ha-1. Soil pH was the most important edaphoclimatic variable, showing greater emissions (36.7 kg NH3 ha-1, EF = 19.3%) when pH was above 8.2. Crop type, fertilizer type, and N application method also affected NH3 emission patterns, while water management, mean precipitation, and soil texture were ranked low by the model. Our results show that intrinsic Mediterranean characteristics had only an indirect effect on NH3 emissions. For instance, relatively low N fertilization rates result in small NH3 emissions in rainfed areas, which occupy a very significant surface of Mediterranean agricultural land. Overall, N fertilization management is a key driver in reducing NH3 emissions, but additional field factors should be studied in future research to establish more robust abatement strategies.

Drip fertigation sustains crop productivity while mitigating reactive nitrogen losses in Chinese agricultural systems: Evidence from a meta-analysis

Drip fertigation can synchronize the supply of nutrients and water for crop demand, offering the potential for minimizing negative environmental impacts and sustaining crop productivity. However, there are no comprehensive evaluations on performances of drip fertigation on environmental nitrogen (N) losses and crop productivity, nationwide. Here, a meta-analysis was performed to quantify overall effects of drip fertigation on N losses and crop productivity in Chinese agricultural systems based on 443 observations from 42 field studies. The results showed that drip fertigation significantly increased crop yields by 9.8 % and slightly increased soil NO emission by 13.9 % compared to the traditional irrigation and fertilization practices (e.g. flooding/furrow irrigation and N broadcasting), while significantly decreasing NH3 volatilization by 14.2 %, soil N2O emission by 28.1 % and NO3--N leaching loss by 71.2 %. There were significant mitigation potentials of environmental N losses by drip fertigation for cereal cropping systems, not for horticultural crops in terms of soil NO emission and not for cotton in terms of NH3 volatilization. Non significant promotion effect on NO emission and significant reduction effects on the other all kinds of environmental N losses by drip fertigation were observed for alkaline soils (pH > 7.3) and coarse-textured soils. In addition, the use of different fertilizer sources and/or soil amendments have shown in popularity as strategies to offset the negative feedback associated with agricultural N losses, no direct synthetic result was shown in drip-fertigated soils. We synthesized 19 studies so as to assess the potential mitigation options for further minimizing N losses in drip fertigation systems, which suggested that deleterious environmental pollution could be further reduced while still achieving high crop yields with a combination of enhanced-efficiency fertilizers (e.g. nitrification or urease inhibitors) or soil amendments (e.g. biochar or straw) to drip fertigation systems.

Sustainable irrigation and climate feedbacks

Agricultural irrigation induces greenhouse gas emissions directly from soils or indirectly through the use of energy or construction of dams and irrigation infrastructure, while climate change affects irrigation demand, water availability and the greenhouse gas intensity of irrigation energy. Here, we present a scoping review to elaborate on these irrigation-climate linkages by synthesizing knowledge across different fields, emphasizing the growing role climate change may have in driving future irrigation expansion and reinforcing some of the positive feedbacks. This Review underscores the urgent need to promote and adopt sustainable irrigation, especially in regions dominated by strong, positive feedbacks.

Mitigation of greenhouse gas emissions and improved yield by plastic mulching in rice production

Soil mulching technologies are effective practices which alleviate non-point source pollution and carbon emissions, while ensuring grain production security and increasing water productivity. However, the lack of comprehensive understanding of the impacts of mulching technologies on rice fields has hindered progress in global implementation due to the varying environments and application conditions under which they are implemented. This study conducted a meta-analysis based on 2412 groups of field experiment data from 313 studies to evaluate the effects of soil mulching methods on rice production, greenhouse gas (GHG) emissions and water use efficiency. The results show that plastic mulching, straw mulching and no mulching (PM, SM and NM) have reduced CH₄ emissions (68.8 %, 61.4 % and 57.2 %), increased N₂O emissions (84.8 %, 89.1 % and 96.6 %), reduced global warming potentials (50.7 %, 47.5 % and 46.8 %) and improved water use efficiency (50.2 %, 40.9 % and 34.0 %) compared with continuous flooding irrigation. However, PM increased rice yield (1.6 %), while SM and NM decreased yield (4.3 % and 9.2 %). Furthermore, analysis using random forest models revealed that rice yield, GHG emissions and WUE response to soil mulching were related to climate, soil properties, fertilizer and rice varieties. Our findings can guide the implementation of plastic mulching technology in priority areas, contribute to agricultural carbon neutrality and support the development of practical guidelines for farmers.

Uncertainty in non-CO2 greenhouse gas mitigation contributes to ambiguity in global climate policy feasibility

Despite its projected crucial role in stringent, future global climate policy, non-CO₂ greenhouse gas (NCGG) mitigation remains a large uncertain factor in climate research. A revision of the estimated mitigation potential has implications for the feasibility of global climate policy to reach the Paris Agreement climate goals. Here, we provide a systematic bottom-up estimate of the total uncertainty in NCGG mitigation, by developing 'optimistic', 'default' and 'pessimistic' long-term NCGG marginal abatement cost (MAC) curves, based on a comprehensive literature review of mitigation options. The global 1.5-degree climate target is found to be out of reach under pessimistic MAC assumptions, as is the 2-degree target under high emission assumptions. In a 2-degree scenario, MAC uncertainty translates into a large projected range in relative NCGG reduction (40-58%), carbon budget (±120 Gt CO₂) and policy costs (±16%). Partly, the MAC uncertainty signifies a gap that could be bridged by human efforts, but largely it indicates uncertainty in technical limitations.

Impact of atrazine on soil microbial properties: A meta-analysis

Atrazine is a biotoxic long-residing herbicide whose toxic effects on soil microorganisms have attracted widespread attention. However, previous studies on the effects of atrazine on soil microorganisms have yielded highly variable results. Therefore, a meta-analysis using a database containing 1141 data points from 39 peer-reviewed papers was conducted to illustrate the response of soil microorganisms to the application of atrazine. The results showed that the application of atrazine significantly increased soil microbial biomass and respiration by 8.9% and 26.77%, respectively, and decreased soil microbial diversity and enzyme activity by 4.87% and 24.04%, respectively. In addition, mixed-effect models were used to explain the influence of moderator variables, including water holding capacity, temperature, pH, organic carbon content, atrazine concentration, duration, and soil texture, on the results to help account for inconsistent conclusions. It was found that soil microbial biomass was significantly positively correlated with temperature, organic carbon content, atrazine concentration, clay content and silt content, while it was negatively correlated with pH and sand content. Soil microbial respiration was negatively correlated with pH and positively correlated with atrazine concentration. Soil microbial diversity was positively correlated with water holding capacity, pH, silt content and sand content, and negatively correlated with organic carbon content and clay content. Soil enzyme activity, the indicator that showed the largest decrease after atrazine application, was significantly positively correlated with water holding capacity, temperature, organic carbon content, and herbicide concentration; it was negatively correlated with soil pH. On the basis of these analysis results, we recommend that atrazine should not be allowed to persist in alkaline sandy soil for long periods of time, as this can result in atrazine having a significant negative impact on soil microorganisms.

Meta-analysis of the effect of nitrification inhibitors on the abundance and community structure of N2O-related functional genes in agricultural soils

Application of nitrification inhibitors (NIs) in agricultural systems is an important strategy to enhance fertilizer nitrogen use efficiency and mitigate soil nitrous oxide (N₂O) emissions. Here, we conducted a global meta-analysis of 88 published studies to assess the response of N₂O-related functional gene and transcript abundances, and community structure to NIs application. Application of NIs significantly reduced the abundance of ammonia-oxidizing bacteria ammonia monooxygenase (AOB amoA) genes, AOB amoA transcript and nitrite reductase (nirS and nirK) genes. The effectiveness of NIs on reducing the AOB amoA abundance was influenced by N form, soil texture, soil pH and the experimental type (field vs. laboratory). Specifically, NIs were more effective when a mixed inorganic and organic N source was applied to a medium-textured soils. The NIs effectiveness increased with increasing soil pH. The response of AOB amoA abundance to NIs application was not affected by NI type, N rate, soil moisture, soil temperature and soil organic carbon (SOC). The inhibitory effect of NIs on nirS abundance increased with increasing soil temperature. NIs decreased soil nitrifying enzyme activity (NEA) and denitrifying enzyme activity (DEA) by 34.5 % and 27.0 %, respectively, leading to an overall 63.6 % reduction of N₂O emissions. Soil NEA correlated positively with the abundance and community structure of AOB amoA but not with AOA amoA. Decrease in DEA with NIs application coincided with the decreasing nirS and nirK abundances. This global-scale assessment demonstrates that the effectiveness of NIs in reducing N₂O emissions was attributed to the inhibiting effects on AOB amoA, nirS and nirK genes. Our findings highlight that NIs' inhibition effects on bacterial ammonia-oxidizing community and the encode enzymes in transformation of nitrite to nitric oxide are the main mechanisms for mitigation of N fertilizer-induced N₂O emissions.

Interactive effects of irrigation system and level on grain yield, crop water use, and greenhouse gas emissions of summer maize in North China Plain

Irrigation management is one of most critical factors influencing soil N₂O and CO₂ emissions in dryland agriculture. To explore the effects of irrigation systems and levels on the mitigation of N₂O and CO₂ emissions from maize fields and to determine the balance among greenhouse gases (GHG) emission, water-saving and grain yield, a two-year field experiment was conducted in the North China Plain (NCP) during the growing seasons of 2018 and 2019. Two irrigation systems (i.e., flood irrigation, FI, and drip irrigation, DI) were adopted with four irrigation levels in each system, including 65 mm/event (sufficient irrigation, CK), 50 mm/event (decreased by 23 %), 35 mm/event (by 46 %) and 20 mm/event (by 69 %), respectively. The results showed that both irrigation systems and levels had significant effects on soil N₂O and CO₂ emissions (P < 0.05). Nitrous oxide (N₂O) and CO₂ emissions peaked following irrigation or irrigation + fertilization events during sowing to early filling stage (R1), with the peak values increasing with irrigation levels. Meanwhile, peak values from FI were higher than those from DI at 50 mm and 65 mm irrigation levels. The average cumulative N₂O and CO₂ emissions of DI treatments were 14.9 % and 6.23 % lower than those of FI treatments (P < 0.05), respectively. Soil moisture was identified as one of the most crucial factors influencing N₂O and CO₂ fluxes. Deficit irrigation efficiently deceased cumulative N₂O and CO₂ emissions, but moderate to severe deficit irrigation brought significant reduction in grain yield. Drip irrigation with a slight deficit irrigation level (decreased by 23 %) obtained the best economic and environmental benefits, which achieved the dual goal of lower GHG emissions but higher WUE without sacrificing grain yield.

Cropland nitrous oxide emissions exceed the emissions of RCP 2.6: A global spatial analysis

Nitrous oxide (N₂O), as a potent greenhouse gas, must be limited to prevent the global temperature increasing by >2 °C. Cropland is the largest source of anthropogenic N₂O emissions; however, earlier estimates for emissions and their exceedances still remain uncertainties. Here, we used a spatially explicit model to estimate cropland N₂O emission in 2014 by refined grid-level crop-specific EFs and considered the background emission. We also sought to determine where N₂O emissions exceed the "boundary" through analysis of spatial data from representative concentration pathway (RCP) 2.6. The global cropland N₂O emission was 2.92 ± 0.59 Tg N yr^-1, which far exceeds the 0.82 Tg N yr^-1 boundary, over 90 % of cropland areas exceeded the boundary. Western Europe, Southeastern China, Pakistan, and the Ganges Plain exceeded the boundary by >2 kg N ha^-1 yr^-1. The boundary exceedances showed a positive linear response with respect to total cropland emission and a quadratic response to GDP per capita at the country level. Our study highlights the necessity of accurate estimations of spatial variations in cropland N₂O emissions and evaluation of exceedances, to facilitate the development of more effective mitigation measures in different regions.

Integrating major agricultural practices into the TRIPLEX-GHG model v2.0 for simulating global cropland nitrous oxide emissions: Development, sensitivity analysis and site evaluation

Nitrous oxide (N₂O) emissions from croplands are one of the most important greenhouse gas sources while the estimation of which remains large uncertainties globally. To simulate N₂O emissions from global croplands, the process-based TRIPLEX-GHG model v2.0 was improved by coupling the major agricultural activities. Sensitivity experiment was used to measure the impact of the integrated processes to modeled N₂O emission found chemical N fertilization have the highest relative effect sizes. While the coefficient of the NO₃^- consumption rate for denitrification (COE_dNO3), controlling the first step of the denitrification process was identified to be the most sensitive parameter based on sensitivity analysis of model parameters. The model performed well when simulating the magnitude of the daily N₂O emissions for 39 calibration sites and the continental mean of the parameters were used to producing reasonable estimations for the means of the measured daily N₂O fluxes (R² = 0.87, slope = 1.07) and emission factors (EFs, R² = 0.70, slope = 0.72) during the experiment periods. The model reliability was further confirmed by model validation. General trend of modeled daily N₂O emissions were reasonably consistent with the observations of selected validated sites. In addition, high correlations between the results of modeled and observed mean N₂O emissions (R² = 0.86, slope = 0.82) and EFs (R² = 0.66, slope = 0.83) from 68 validation sites were obtained. Further improvement on more detailed estimations for the variation of the environmental factors, management effects as well as accurate model input model driving data are required to reduce the uncertainties of model simulations. Consequently, our simulation results demonstrate that the TRIPLEX-GHG model v2.0 can reliably estimate N₂O emissions from various croplands at the global scale, which contributes to closing global N₂O budget and sustainable development of agriculture.

Emitter clogging characteristics under reclaimed wastewater drip irrigation: a meta-analysis

BACKGROUND

Although reclaimed wastewater drip irrigation (RWDI) is an effective technology for alleviating agricultural crop water stress and protecting the environment, the reclaimed wastewater (RW) may cause emitter clogging. Discharge ratio variation (Dra) and coefficient of uniformity (CU) play a key role in exploring the clogging degree of the emitter. Therefore, a meta-analysis was conducted to identify optimal management methods with an acceptable Dra and CU under RWDI.

RESULTS

The results indicate that the higher the concentration of various substances in RW, the higher is the risk of the emitter clogging. Suitable concentrations of iron (Fe), manganese (Mn), total suspended solids (TSS), chemical oxygen demand (COD), water hardness and calcium ions (Ca²⁺ ) in RW were determined to be 0-0.2, 0-0.02, 0-50, 20-30, 200-250 and 0-40 mg L^-1 , respectively. Pressure-compensating emitters with relatively high discharge (>2 L h^-1 ) could prevent clogging in RWDI systems.

CONCLUSION

Based on the data analysis, a cumulative RWDI operation time of 375 h was determined as the most suitable time for lateral flushing to prevent clogging. This study identifies the conditions under which an increase in the service life of RWDI systems can be achieved. © 2022 Society of Chemical Industry.

Evaluating Gas Emissions from Different Feed Cropping Systems in the North China Plain: A Two-Year Field Measurement

The cultivation of silage crops is encouraged to enhance the connection between crop and livestock production in the North China Plain (NCP). A field experiment was designed to evaluate the ammonia (NH3), nitrous oxide (N2O), and methane (CH4) emissions of five silage cropping systems, including triticale-summer maize (Tr-SuM), triticale-spring maize (Tr-SpM), triticale-double forage maize (Tr-DFM), double forage maize (DFM), and winter wheat-summer maize (WW-SuM), as well as their biomass- and crude protein-scaled emission intensities, with respect to NH3 and greenhouse gas (GHG). The annual nitrogen (N) emissions through NH3, N2O, and CH4 emissions of these systems were 13.43–23.77 kg ha−1 (4.2–5.6% of N fertilizer input), 3.43–4.56 kg ha−1 (0.75–1.08% of N fertilizer input) and 2.10–2.85 kg ha−1, respectively. The total GHG emissions of these systems was dominated by the contributions of N2O. Ranking these systems according to their biomass and crude protein production gave Tr-DFM > DFM > WW-SuM > Tr-SuM and Tr-SpM, their partial factor productivity was in the order of Tr-DFM > WW-SuM > Tr-SuM and Tr-SpM > DFM, and the order of their emission intensity was DFM > Tr-SuM > Tr-DFM > WW-SuM > Tr-SpM. In conclusion, the Tr-DFM needs to be further investigated for its suitability in the NCP, owing to its superior productivity and moderate emission intensities.

Appropriate N fertilizer addition mitigates N2O emissions from forage crop fields

Forage crops are widely cultivated as livestock feed to relieve grazing pressure in agro-pastoral regions with arid climates. However, gaseous losses of soil nitrogen (N) following N fertilizer application have been considerable in response to the pursuit of increased crop yield. A two-year experiment was carried out in a typical saline field under a temperate continental arid climate to investigate the effect of N application rate on N₂O emissions from barley (Hordeum vulgare L.), corngrass (Zea mays × Zea Mexicana), rye (Secale cereale L.), and sorghum-sudangrass hybrid (Sorghum bicolor × Sorghum sudanense). The dynamics of N₂O emissions, hay yield, and crude protein (CP) yield were measured under four N application rates (0, 150, 200, and 250 kg ha^-1) in 2016 and 2017. An N₂O emission peak was observed for all crop species five days after each N application. Cumulative N₂O fluxes in the growing season ranged from 0.66 to 2.40 kg ha^-1 and responded exponentially to N application rate. Emission factors of N₂O showed a linear increase with N application rate for all crop species, but the linear slopes significantly differed between barley or rye and corngrass and sorghum-sudangrass hybrid. The hay and CP yields of all forage grasses significantly increased with the increase of N application rate from 0 to 200 kg ha^-1. Barley and rye with lower hay and CP yields showed higher N₂O emission intensities. The increased level of N₂O emission intensity was higher from 200 to 250 kg ha^-1 than from 150 to 200 kg ha^-1. At N application rates of 200 and 250 kg ha^-1, CP yield had a significantly negative correlation with cumulative N₂O emission and explained 50.5% and 62.9% of the variation, respectively. In conclusion, ~200 kg ha^-1 is the optimal N rate for forage crops to minimize N₂O emission while maintaining yield in continental arid regions.

Global reactive nitrogen loss in orchard systems: A review

Orchards account for about 5% of the agricultural land in the world, however the amount of nitrogen (N) fertilizer input in orchards is relatively large. Little is known about N input and its impact in orchards at the global scale. Therefore, in this study we systematically evaluated reactive nitrogen (Nr) loss in global orchards. A meta-analysis of 97 studies reported from 2000 to 2021 from different countries showed that the mean global N fertilizer input in orchards was 303 kg N ha^-1 yr^-1, and the estimated emission factor (EF) of nitrous oxide (N₂O) and ammonia (NH₃) were 1.39% and 3.64%, respectively. Also, during the same period, orchard nitrate leaching factor (LF) reached 18.5%, and the runoff N loss factor (RF) and net fruit N removal factor (NRF) were estimated to be 2.75% and 5.31%, respectively. The apparent N balance of the global orchard system reached 68.4% of N input. N application increased the Nr loss in various pathways in the orchard. The N₂O and NH₃ emission and nitrate leaching were linearly correlated with N fertilizer application, and overuse of N resulted in substantial Nr loss. Regionally, the total Nr loss in developing countries was higher than developed countries. Average N input (405 kg N ha^-1 yr^-1) and Nr loss (102 kg N ha^-1 yr^-1) of orchards in Asia were the highest. The NH₃ volatilization and runoff N loss of deciduous orchards were significantly higher than that of evergreen orchards. N application increased fruit yield, but excessive N input reduced the net fruit N removal (FNR). The results reported here fill an important knowledge gap of N balance analysis of orchards at a global scale and provided a framework for optimizing N management to achieve sustainable fruit production.

Environmental drivers of nitrous oxide emission factor for a coastal reservoir and its catchment areas in southeastern China

While Asia is projected to be one of the major nitrous oxide (N₂O) sources in the coming decades, a more accurate assessment of N₂O budget has been hampered by low data resolution and poorly constrained emission factor (EF). Since urbanized coastal reservoirs receive high nitrogen loads from diverse sources across a heterogeneous landscape, the use of a single fixed EF may lead to large errors in N₂O assessment. In this study, we conducted high spatial resolution sampling of dissolved N₂O, nitrate-nitrogen (NO₃^--N) and other physico-chemical properties of surface water in Wenwusha Reservoir and other types of water bodies (river, drainage channels, and aquaculture ponds) in its catchment areas in southeastern China between November 2018 and June 2019. The empirically derived EF (calculated as N₂O-N:NO₃^--N) for the reservoir showed considerable spatial variations, with a 10-fold difference ranging from 0.8 × 10^-3 to 8.8 × 10^-3. The average EF varied significantly among the four types of water bodies in the following descending order: aquaculture ponds > river > drainage channels > reservoir. Across all the water bodies, the mean EF in summer was 1.8-3.5 and 1.7-2.8 fold higher than that in autumn and spring, respectively, owing to the elevated water temperature. Overall, our derived EF deviated considerably from the IPCC default value, which implied that the use of default EF could result in over- or under-estimation of N₂O emissions by up to 42%. We developed a multiple regression model that could explain 82% of the variance in EF based on water temperature and the ratio between dissolved organic carbon and nitrate-nitrogen (p < 0.001), which could be used to improve the estimate of EF for assessing N₂O emission from coastal reservoirs and other similar environments.

Mitigating global warming potential while coordinating economic benefits by optimizing irrigation managements in maize production

China is the second largest irrigated country in the world. Increasing irrigation intensity costs more water and energy, and produces more greenhouse gas (GHG). In the present study, the responses of maize economic and environmental benefits to different irrigation managements were analyzed in a 2-year field study. A purposely designed tube-study was conducted to explore mechanism underlying effects of irrigation managements in detail. Three treatments, rainfed (RF), flood irrigation (FI), and drip irrigation (DI) were included in the field. Five treatments, no irrigation, flood irrigation, irrigation in 0-30, 30-60, and 0-90 cm depth were conducted in the tube study. Compared to RF, grain yields of FI and DI significantly increased by 22.1 % and 35.7 %, respectively, the net ecosystem economic budget significantly increased by 34.2 % and 35.6 %, and carbon footprint decreased by 7.0 % and 12.7 % in the field study. The irrigation treatments in the tube study increased the global warming potential by 12.0-32.8 % and grain yield by 44.5-203.9 %, and reduced GHG intensity by 24.3-57.4 %, compared with no irrigation treatment. Water content at the top soil layer had the greatest impact on GHG emissions. In conclusion, the differences in grain yield and GHG emissions among irrigation managements are mainly due to the soil water content in space and time. Drip irrigation decreases GHG intensity by producing more grain yield due to the optimized soil water distribution in the root zone. Irrigation management with appropriate amount and frequency can increase economic benefit and reduce environmental cost in maize production.