Soil Greenhouse Gas Emissions Research Articles

Optimizing agricultural management in China for soil greenhouse gas emissions and yield balance: A regional heterogeneity perspective

Balancing soil greenhouse gas emissions (SGE) with crop production is crucial for sustainable agriculture in China. Optimizing field management practices regionally can effectively promote carbon reduction and food security, given the varying SGE responses across agroecological regions. This study employed meta-analysis and machine learning techniques to assess SGE responses to nine different farming practices in seven distinct agroecological regions. It aimed to identify optimal management strategies for balancing SGE and crop production within each region. Findings underscore substantial spatial heterogeneity in the effects of management practices on SGE, with the combined use of organic and inorganic fertilizers (MOF-MF) demonstrating the most pronounced variability (standard deviation, SD = 1.80), where MOF resulted in SGE 610% of that with MF in the Southern China (SC) region, yet only 54% in Northwestern China (NWC). Conversely, straw incorporation exhibited the most minor variability (SD = 0.27), influencing SGE by 35%–62%. Additionally, the study reveals that soil and climatic conditions significantly modulate SGE responses. In scenarios characterized by humid and warm climates with soil pH ranging from 5.5 to 8.5 or initial SOC ≤10, the environmental impact on SGE was marginal. However, in highly acidic or alkaline soils or with initial SOC >10, SGE responses varied markedly with management practices in arid and cold conditions. The study further proposes agricultural management strategies to achieve the lowest SGE while maximizing crop yield. It recommends specific methods for fertilizer applications, straw management, irrigation, and tillage practices meticulously tailored to the unique conditions of each agroecological region. This research offers essential insights for agricultural stakeholders regarding cultivation strategies and delivers theoretical guidance for enhancing agricultural management and land-use planning throughout China's heterogeneous landscapes.

Unveiling the hidden impact: How biodegradable microplastics influence CO2 and CH4 emissions and Volatile Organic Compounds (VOCs) profiles in soil ecosystems

Biodegradable plastics promise eco-friendliness, yet their transformation into microplastics (bio-MPs) raises environmental alarms. However, how those bio-MPs affect the greenhouse gases (GHGs) and volatile organic compounds (VOCs) in soil ecosystems remains largely unexplored. Here, we investigated the effects of diverse bio-MPs (PBAT, PBS, and PLA) on GHGs and VOCs emission in typical paddy or upland soils. We monitored the carbon dioxide (CO2) and methane (CH4) fluxes in-situ using the self-developed portable optical gas sensor and analyzed VOC profiles using a proton-transfer reaction mass spectrometer (PTR-MS). Our study has revealed that, despite their biodegradable nature, bio-MPs do not always promote soil GHG emissions as previously thought. Specifically, PBAT and PLA significantly increased CO2 and CH4 emissions up to 1.9–7.5 and 115.9–178.5 fold, respectively, compared to the control group. While PBS exhibited the opposite trend, causing a decrease of up to 39.9% for CO2 and up to 39.9% for CH4. In addition, different types of bio-MPs triggered distinct soil VOC emission patterns. According to the Mann-Whitney U-test and Partial Least Squares Discriminant Analysis (PLS-DA), a recognizable VOC pattern associated with different bio-MPs was revealed. This study claims the necessity of considering polymer-specific responses when assessing the environmental impact of Bio-MPs, and providing insights into their implications for climate change.

Effects of Long-Term Controlled-Release Urea on Soil Greenhouse Gas Emissions in an Open-Field Lettuce System.

Controlled-release urea (CRU) fertilizers are widely used in agricultural production to reduce conventional nitrogen (N) fertilization-induced agricultural greenhouse gas emissions (GHGs) and improve N use efficiency (NUE). However, the long-term effects of different CRU fertilizers on GHGs and crop yields in vegetable fields remain relatively unexplored. This study investigated the variations in GHG emissions at four growth stages of lettuce in the spring and autumn seasons based on a five-year field experiment in the North China Plain. Four treatments were setup: CK (without N application), U (conventional urea-N application), ON (20% reduction in urea-N application), CRU (20% reduction in polyurethane-coated urea without topdressing), and DCRU (20% reduction in polyurethane-coated urea containing dicyandiamide [DCD] without topdressing). The results show that N application treatments significantly increased the GHG emissions and the lettuce yield and net yield, and DCRU exhibited the lowest N2O and CO2 emissions, the highest lettuce yield and net yield, and the highest lettuce N content of the N application treatments. When compared to U, the N2O emission peak under CRU and DCRU treatments was notably decreased and delayed, and their average N2O emission fluxes were significantly reduced by 10.20-20.72% and 17.51-29.35%, respectively, leading to a significant reduction in mean cumulative N2O emissions during the 2017-2021 period. When compared to U, the CO2 fluxes of DCRU significantly decreased by 8.0-16.54% in the seedling period, and mean cumulative CO2 emission decreased by 9.28%. Moreover, compared to U, the global warming potential (GWP) and greenhouse gas intensity (GHGI) of the DCRU treatment was significantly alleviated by 9.02-17.13% and 16.68-20.36%, respectively. Compared to U, the N content of lettuce under DCRU was significantly increased by 6.48-17.25%, and the lettuce net yield was also significantly increased by 5.41-7.71%. These observations indicated that the simple and efficient N management strategy to strike a balance between enhancing lettuce yields and reduce GHG emissions in open-field lettuce fields could be obtained by applying controlled-release urea containing DCD without topdressing.

Sustainable management strategies for balancing crop yield, water use efficiency and greenhouse gas emissions

CONTEXTTo ensure food security in the face of climate change, it is crucial to use effective agricultural management practices that produce the triangular win-win for water, crops, and environments. OBJECTIVEThis study aimed to explore the sustainable management measures for balancing crop yield, water use efficiency (WUE) and greenhouse gas (GHG) emissions in China during 1981–2020. METHODSThe study selected the Beijing-Tianjin-Hebei (BTH) region of China as the research area, where there were sharp contradictions among water shortage, food security and polluted environment. Four irrigation treatments and four fertilization treatments were set referring to the local cultivated experiences. The daily dynamic changes in crop yield, WUE and GHG emissions were simulated by optimized Agricultural Production Systems sIMulator (APSIM) model. RESULTS AND CONCLUSIONSThe irrigations had positive impacts on crop yield and WUE in BTH region. The irrigation amount's rise caused a gradual augmentation in the total yield of winter wheat and summer maize from 1981 to 2020.The highest total yield was achieved under W4 irrigation treatment (320 mm water for winter wheat and 60 mm water for summer maize), with an annual mean of 24,579.2 kg·ha−1. The annual average WUE under the W3 irrigation treatment (240 mm water for winter wheat) was the highest, with an average of 13.9 kg·ha−1·mm−1. However, extensive fertilization exacerbated soil GHG emissions. The soil GHG emissions were found to be significant increase as the input amount of fertilization. The FI fertilization measure (no fertilization) was assessed to have the least impact on the environment, with an average GHG emissions of 0.4 Mg·CO2-eq·ha−1. The optimal goals of high yield, high WUE and low GHG emissions were achieved by choosing effective combination practices of water and nitrogen management. Overall, the W3 irrigation and F3 fertilization (180 kg/ha fertilizer for winter wheat and 120 kg/ha fertilizer for summer maize.) treatments had the maximum water-fertilizer production indexes in the BTH region. SIGNIFICANCEThis study highlights the importance of agricultural management measures for guaranteeing food security and environmental sustainability at the same time under climate change.

Grass cover and shallow tillage inter-row soil cultivation affecting CO2 and N2O emissions in a sloping vineyard in upland Balaton, Hungary

Greenhouse gas (GHG) emissions can accelerate the current climate change trend, resulting in higher soil temperatures and changes in soil water contents. The aim of the study was to investigate to what extent different cultivation methods and sampling positions on the slope (location along the slope) are affecting soil GHG emissions in vineyards. In the study, different inter-row soil cultivation methods were investigated including shallow soil tillage (ST) and grass cover (GC) inter-rows. Intact soil columns were collected and different soil water contents were applied under a laboratory environment to simulate different precipitation conditions. Our findings showed significant differences in the emitted CO2 and N2O between the cultivation methods, where the GC soil had 2.9 times higher average CO2 and 6.1 times higher N2O emissions compared to the bare, ST soil. The amount of initial and longer term soil water content significantly influenced soil-derived GHG emissions, with the highest averaged values observed for the continuously high water content soil samples (0.377 mgCO2 m−2 s−1 and 0.076 μgN2O m−2 s−1). For the GC inter-rows, we also observed significant differences in the GHG emissions among the different sampling positions of the investigated slopes. We found that besides the different soil water contents, the main causes for these differences could be the variances in the soil physical and chemical properties. The findings of this study can be used to better estimate soil GHG emissions at various water contents, for different inter-row soil management cultivation methods, and potentially mitigate some adverse effects of global warming by reducing the amount of GHG released into the atmosphere.

Effects of Understory Vegetation Conversion on Soil Greenhouse Gas Emissions and Soil C and N Pools in Chinese Hickory Plantation Forests

Forest management, especially understory vegetation conversion, significantly affects soil greenhouse gas (GHG) emissions and soil C and N pools. However, it remains unclear what effect renovating understory vegetation has on GHG emissions and soil C and N pools in plantations. This study investigates the impact of renovating understory vegetation on these factors in Chinese hickory (Carya cathayensis Sarg) plantation forests. Different understory renovation modes were used in a 12-month field experiment: a safflower camellia (SC) (Camellia chekiangoleosa Hu) planting density of 600 plants ha−1 and wild rape (WR) (Brassica napus L.) strip sowing (UM1); SC 600 plants ha−1 and WR scatter sowing (UM2); SC 1200 plants ha−1 and WR strip sowing (UM3); SC 1200 plants ha−1 and WR scatter sowing (UM4); and removal of the understory vegetation layer (CK). The results showed that understory vegetation modification significantly increased soil CO2 and emission fluxes and decreased soil CH4 uptake fluxes (p < 0.01). The understory vegetation transformation significantly improved soil labile carbon and labile nitrogen pools (p < 0.01). This study proposes that understory vegetation conversion can bolster soil carbon sinks, preserve soil fertility, and advance sustainable development of Chinese hickory plantation forests.

Nexus between climate change, agricultural output, fertilizer use, agriculture soil emissions: Novel implications in the context of environmental management

In evaluating the influence of greenhouse gases (GHGs) on climate change, the effectiveness of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) is intricately tied to their atmospheric turnover rates, which play a crucial role in their heat-trapping capacity. Understanding the dynamics of how these gases cycle through the atmosphere is essential for assessing their respective contributions to the greenhouse effect and, consequently, their impact on global warming and climate change. The prime objective of this research is to examine the role of climatic change, agriculture output, and fertilizer use on the agriculture soil's greenhouse gas emissions. In doing so, the present study has focused on the temperature of land, fertilizer consumption, crop and livestock production, and energy used in agriculture soils on the pollution level of agricultural soils. The study further delineates the intricate interdependencies between climate change factors and GHG emissions using novel econometric methodologies, specifically the PMG-ARDL, SC-ARDL, and Dumitrescu Hurlin Panel Causality frameworks. In doing so, we use a large panel dataset spanning 1990 to 2020. The estimations show that climate change, as measured by variations in terrestrial temperature, has a discernible and positive impact on GHG emissions over the short and long term. Energy consumption and livestock production positively correlate with GHG emissions, with the former having a more pronounced effect. The implications of fertilizer usage and overall crop yield become noticeably significant in the long term. It emphasizes the importance of using a diachronic perspective when assessing GHG emissions in the agricultural sector. It is also worth noting that agricultural land use appears to negatively impact GHG emissions, emphasizing the importance of implementing sustainable land management practices to mitigate adverse environmental consequences. The study also explores the causality between climate change, agricultural practices, and GHG emissions, revealing a bidirectional association between climatic change and soil emissions. Additionally, unidirectional causation is observed from fertilizer consumption and crop production to emissions, underscoring the importance of adopting sustainable agricultural practices to reduce emissions. The findings offer valuable insights for governments and researchers to create sustainability-related strategies for dealing with climate change issues, safeguarding natural resources, and ensuring a sustainable future for agriculture.

Common agronomic adaptation strategies to climate change may increase soil greenhouse gas emission in Northern Europe

Climate change poses a significant threat to agriculture, highlighting the need for adaptation strategies to reduce its impacts. Agronomic adaptation strategies, such as changes in planting dates, fertilization, and irrigation, might sustain crop yield. However, their impact on soil greenhouse gas (GHG) emission is unknown under future climate scenarios. Using the LandscapeDNDC model, we assessed the effect of agronomic adaptation strategies (early sowing, increased fertilization dose, and increased irrigation amount) on soil GHG emission, yield, and yield-scaled GHG emission. A diversified crop rotation (potato – winter wheat – spring barley – faba bean) of a long-term experiment in Denmark was used for model validation. The adaptation practices to climate change were implemented for two representative concentration pathways (RCPs; 4.5 and 8.5) and five coupled global circulation and regional climate models. The adaptation scenarios were contrasted against a baseline scenario under current management practices. Soil-related variables showed better model fit (refined index of agreement ≥ 0.38) and lower errors (mean absolute error ≤ 8.18) than crop-based outputs for model validation. A total yield of ∼29 (± 3) t DW ha−1, and soil GHG emission of ∼3.02 (± 1.39) t CO2e ha−1 (RCP8.5) were obtained for the crop rotation system under the baseline for 2071–2100. Early sowing and its combination with increased fertilization decreased the yield compared to the baseline by 6.1 and 4.8 %, respectively (RCP8.5). Conversely, early sowing with increased irrigation, and early sowing with increased fertilization and irrigation, produced higher yields by 2.3 and 4.0 %, respectively (RCP8.5). All the agronomic adaptation strategies increased soil GHG emissions (ranging from 4.1 to 17.8 %) as well as yield-scaled GHG emissions (varying from 3.0 to 12.9 %) (RCP8.5). The highest soil GHG emission was simulated for early sowing in combination with increased fertilization and irrigation. Our study indicates that soil GHG emission will increase in the coming decades and that the agronomic adaptation strategies needed to sustain food production may further exacerbate this emission.

Post-fire soil greenhouse gas fluxes in boreal Scots pine forests–Are they affected by surface fires with different severities?

Although forest fires are one of the main natural disturbance types in boreal forests, there is limited information regarding surface fires (dominant in Northern Europe), and how surface fires of different severities could affect post-fire soil greenhouse gas emissions. The results of our study show that fire severity, time since fire and post-fire changes in soil temperature were the main factors driving soil carbon dioxide (CO2) flux (forest floor ecosystem respiration) from burned boreal forest soils. Approximately two hours after the fire, soil CO2 emissions from burned areas were significantly higher compared to pre-fire conditions, and areas with high-severity fires had significantly higher soil CO2 emissions compared to those with low-severity fires. Later (days, months) after the fire, the unburned control areas always had higher soil CO2 emission values compared to burned areas. In the case of methane (CH4), time since fire and post-fire changes in soil temperatures were the main factors driving soil CH4 fluxes. Unburned study areas were sinks of CH4 through the entire measurement period, while immediately after the fire, the burned areas turned from CH4 sink to CH4 source. For nitrous oxide (N2O) measurements, time since fire was the only factor that significantly affected soil N2O fluxes. Shortly after the fire, N2O emissions increased significantly from both low- and high-intensity study plots. Two days after the fire, post-fire soil C and N content decreased in the O-horizon and increased within the first 5 cm of the soil mineral layer, and the trend was visible both in low- and high-severity fire plots. Samples collected four months after the fire, showed similar total soil C and N content as there was before the fire.

Urbanization-driven forest soil greenhouse gas emissions: Insights from the role of soil bacteria in carbon and nitrogen cycling using a metagenomic approach

Increasing population densities and urban sprawl have induced greenhouse gas (GHG) emissions from the soil, and the soil microbiota of urban forests play a critical role in the production and consumption of GHGs, supporting green development. However, the function and potential mechanism of soil bacteria in GHG emissions from forests during urbanization processes need to be better understood. Here, we measured the fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in Cinnamomum camphora forest soils along an urbanization gradient. 16S amplicon and metagenomic sequencing approaches were employed to examine the structure and potential functions of the soil bacterial community involved in carbon (C) and nitrogen (N) cycling. In this study, the CH4 and CO2 emissions from urban forest soils (sites U and G) were significantly greater than those from suburban soils (sites S and M). The N2O emissions in the urban center (site U) were 24.0 % (G), 13.8 % (S), and 13.5 % (M) greater than those at the other three sites. These results were related to the increasing bacterial alpha diversity, interactions, and C and N cycling gene abundances (especially those involved in denitrification) in urban forest soils. Additionally, the soil pH and metal contents (K, Ca, Mg) affected key bacterial populations (such as Methylomirabilota, Acidobacteriota, and Proteobacteria) and indicators (napA, nosZ, nrfA, nifH) involved in reducing N2O emissions. The soil heavy metal contents (Fe, Cr, Pb) were the main contributors to CH4 emissions, possibly by affecting methanogens (Desulfobacterota) and methanotrophic bacteria (Proteobacteria, Actinobacteriota, and Patescibacteria). Our study provides new insights into the benefits of conservation-minded urban planning and close-to-nature urban forest management and construction, which are conducive to mitigating GHG emissions and supporting urban sustainable development by mediating the core bacterial population.

Regional emissions of soil greenhouse gases across Tibetan alpine grasslands

Soil greenhouse gas (GHG) emissions play an important role in regional climate feedback on the Qinghai-Tibetan Plateau (QTP). Previous studies have focused on soil GHGs based on observations within a limited space on the QTP, however, the regional GHG emissions remain unclear. Analyzing soil samples from 25 sites along a 2,700 km transect across QTP, we showed significantly higher soil CO2 and N2O emission rates in alpine meadows than other upland grassland types, but similar soil CH4 uptake rates across all grassland types. The spatial variations of total soil GHG balance were dominated by CO2 emission. We found that CO2 emission was primarily constrained by high soil pH, low soil moisture and nutrient availability, and fungal abundance, N2O emission was inhibited by high soil pH, while CH4 uptake was dominated by methanotrophic abundance. Furthermore, we estimated a current regional total soil GHG balance of 144.4 Tg CO2-eq yr−1 for surface soil across Tibetan alpine grasslands, which increased by 17.6%, 24.8%, and 38.9% under warming scenarios of 1.5℃, 2℃ and 3℃, respectively. Our results provide a baseline for regional soil GHG emissions responding to climate warming on the QTP.

Effects of Bacillus velezensis strain GH1-13 seed-soaking inoculation on rice productivity and greenhouse gas (CH4 and N2O) emissions in a paddy soil during cultivation: A pot experiment

Effects of Bacillus velezensis strain GH1-13 seed-soaking inoculation on rice productivity and greenhouse gas (CH4 and N2O) emissions in a paddy soil during cultivation: A pot experiment

Salty bio-converted organic fertilizer modulates soil greenhouse gas emissions

The black soldier fly frass (BSFF) can be applied as a bio-converted organic fertilizer in agriculture and has been shown to affect soil properties and plant growth. However, the impacts of salty BSFF derived from kitchen waste (KW) on soil properties and greenhouse gas emissions are unclear. The impacts of salty black soldier fly (Hermetia illucens) frass derived from KW on soil properties and greenhouse gas emissions were investigated. The frass amendments increased soil dissolved organic carbon and nitrogen (0.5–1.6 and 0.1–15 fold) and soil ammonium (0.5–31 fold) content, with a similar trend as soil pH (0∼0.4 fold) and electrical conductivity (2–131 fold). Soil gas emissions (CO2 and N2O) increased by frass amendments. The frass amendment affected the microbial communities followed by the addition rates, with the enriched beneficial bacteria (Nocardioides) and depleted denitrification fungi (Penicillium) as well as the C- and N-cycle related microbial functional genes. The nirS and amoB genes were the critical factors in the soil N2O emission with the frass amendment ratio in the soil. The lig and glx genes involved in lignin decomposition contributing to the increase of soil CO2 emission. These findings indicated that there is a need to inform research and policy decisions aimed at developing and promoting appropriate standards and guidelines for quality production, sustainable utilization, and successful integration of the frass into existing organic fertilizer framework and soil systems.

Earthworms and plants can decrease soil greenhouse gas emissions by modulating soil moisture fluctuations and soil macroporosity in a mesocosm experiment.

Earthworms can stimulate microbial activity and hence greenhouse gas (GHG) emissions from soils. However, the extent of this effect in the presence of plants and soil moisture fluctuations, which are influenced by earthworm burrowing activity, remains uncertain. Here, we report the effects of earthworms (without, anecic, endogeic, both) and plants (with, without) on GHG (CO2, N2O) emissions in a 3-month greenhouse mesocosm experiment simulating a simplified agricultural context. The mesocosms allowed for water drainage at the bottom to account for the earthworm engineering effect on water flow during two drying-wetting cycles. N2O cumulative emissions were 34.6% and 44.8% lower when both earthworm species and only endogeic species were present, respectively, and 19.8% lower in the presence of plants. The presence of the endogeic species alone or in combination with the anecic species slightly reduced CO2 emissions by 5.9% and 11.4%, respectively, and the presence of plants increased emissions by 6%. Earthworms, plants and soil water content interactively affected weekly N2O emissions, an effect controlled by increased soil dryness due to drainage via earthworm burrows and mesocosm evapotranspiration. Soil macroporosity (measured by X-ray tomography) was affected by earthworm species-specific burrowing activity. Both GHG emissions decreased with topsoil macropore volume, presumably due to reduced moisture and microbial activity. N2O emissions decreased with macropore volume in the deepest layer, likely due to the presence of fewer anaerobic microsites. Our results indicate that, under experimental conditions allowing for plant and earthworm engineering effects on soil moisture, earthworms do not increase GHG emissions, and endogeic earthworms may even reduce N2O emissions.

Effects of intercropping on soil greenhouse gas emissions - A global meta-analysis

Diversified cropping systems, such as intercropping, have shown multifunctionality in agronomic productivity promotion, pest control, and soil health improvement. However, the intense interaction between crop species stimulates soil carbon and nitrogen turnover, and intercropping systems cause inexplicit effects on soil greenhouse gas emissions (GHG). Therefore, a comprehensive meta-analysis using 52 published articles (531 paired observations) was conducted to elucidate the effects of intercropping on soil N2O, CO2, and CH4 emissions under different environmental conditions and field practices to identify the primary driving factors, such as climate, soil and field practices. The results showed that intercropping treatment had a non-significant impact on the three GHG emissions on average. However, using a cereal-legume intercropping regime, adopting moderate N application rate or intercropping in alkaline soils could significantly mitigate soil N2O emission. Additionally, intercropping in soils with high soil organic carbon reduce soil CH4 emission. On the contrary, increasing intercropping duration, or adopted in soils with moderate soil total N tended to stimulate CO2 emission. The mixed-effect model selection indicated that initial soil pH, MAP, MAT, tillage regime, and intercropping duration and type were significant moderators in regulating soil GHG emissions. Our findings explicitly elucidated soil GHG responses to intercropping practice. Further studies are warranted on the evaluation of long-term intercropping effects to improve the comprehensive understanding of C and N balance and global warming potential under intercropping.

A Warmer and Wetter World Would Aggravate GHG Emissions Intensity in China's Cropland

AbstractMany agricultural regions in China are likely to become appreciably wetter or drier as the global climate warming increases. However, the impact of these climate change patterns on the intensity of soil greenhouse gas (GHG) emissions (GHGI, GHG emissions per unit of crop yield) has not yet been rigorously assessed. By integrating an improved agricultural ecosystem model and a meta‐analysis of multiple field studies, we found that climate change is expected to cause a 20.0% crop yield loss, while stimulating soil GHG emissions by 12.2% between 2061 and 2090 in China's agricultural regions. A wetter‐warmer (WW) climate would adversely impact crop yield on an equal basis and lead to a 1.8‐fold‐ increase in GHG emissions relative to those in a drier‐warmer (DW) climate. Without water limitation/excess, extreme heat (an increase of more than 1.5°C in average temperature) during the growing season would amplify 15.7% more yield while simultaneously elevating GHG emissions by 42.5% compared to an increase of below 1.5°C. However, when coupled with extreme drought, it would aggravate crop yield loss by 61.8% without reducing the corresponding GHG emissions. Furthermore, the emission intensity in an extreme WW climate would increase by 22.6% compared to an extreme DW climate. Under this intense WW climate, the use of nitrogen fertilizer would lead to a 37.9% increase in soil GHG emissions without necessarily gaining a corresponding yield advantage compared to a DW climate. These findings suggest that the threat of a wetter‐warmer world to efforts to reduce GHG emissions intensity may be as great as or even greater than that of a drier‐warmer world.

Balancing Non‐CO2 GHG Emissions and Soil Carbon Change in U.S. Rice Paddies: A Retrospective Meta‐Analysis and Agricultural Modeling Study

AbstractU.S. rice paddies, critical for food security, are increasingly contributing to non‐CO2 greenhouse gas (GHG) emissions like methane (CH4) and nitrous oxide (N2O). Yet, the full assessment of GHG balance, considering trade‐offs between soil organic carbon (SOC) change and non‐CO2 GHG emissions, is lacking. Integrating an improved agroecosystem model with a meta‐analysis of multiple field studies, we found that U.S. rice paddies were the rapidly growing net GHG emission sources, increased 138% from 3.7 ± 1.2 Tg CO2eq yr−1 in the 1960s to 8.9 ± 2.7 Tg CO2eq yr−1 in the 2010s. CH4, as the primary contributor, accounted for 10.1 ± 2.3 Tg CO2eq yr−1 in the 2010s, alongside a notable rise in N2O emissions by 0.21 ± 0.03 Tg CO2eq yr−1. SOC change could offset 14.0% (1.45 ± 0.46 Tg CO2eq yr−1) of the climate‐warming effects of soil non‐CO2 GHG emissions in the 2010s. This escalation in net GHG emissions is linked to intensified land use, increased atmospheric CO2, higher synthetic nitrogen fertilizer and manure application, and climate change. However, no/reduced tillage and non‐continuous irrigation could reduce net soil GHG emissions by approximately 10% and non‐CO2 GHG emissions by about 39%, respectively. Despite the rise in net GHG emissions, the cost of achieving higher rice yields has decreased over time, with an average of 0.84 ± 0.18 kg CO2eq ha−1 emitted per kilogram of rice produced in the 2010s. The study suggests the potential for significant GHG emission reductions to achieve climate‐friendly rice production in the U.S. through optimizing the ratio of synthetic N to manure fertilizer, reducing tillage, and implementing intermittent irrigation.

Large contribution of soil N2O emission to the global warming potential of a large-scale oil palm plantation despite changing from conventional to reduced management practices

Abstract. Conventional management of oil palm plantations, involving high fertilization rate and herbicide application, results in high yield but with large soil greenhouse gas (GHG) emissions. This study aimed to assess a practical alternative to conventional management, namely reduced fertilization with mechanical weeding, to decrease soil GHG emissions without sacrificing production. We established a full factorial experiment with two fertilization rates (conventional and reduced fertilization, equal to nutrients exported via fruit harvest) and two weeding methods (herbicide and mechanical), each with four replicate plots, since 2016 in a ≥ 15-year-old, large-scale oil palm plantation in Indonesia. Soil CO2, N2O, and CH4 fluxes were measured during 2019–2020, and yield was measured during 2017–2020. Fresh fruit yield (30 ± 1 Mgha-1yr-1) and soil GHG fluxes did not differ among treatments (P≥ 0.11), implying legacy effects of over a decade of conventional management prior to the start of the experiment. Annual soil GHG fluxes were 5.5 ± 0.2 Mg CO2-C ha−1 yr−1, 3.6 ± 0.7 kg N2O-N ha−1 yr−1, and −1.5 ± 0.1 kg CH4-C ha−1 yr−1 across treatments. The palm circle, where fertilizers are commonly applied, covered 18 % of the plantation area but accounted for 79 % of soil N2O emission. The net primary production of this oil palm plantation was 17 150 ± 260 kgCha-1yr-1, but 62 % of this was removed by fruit harvest. The global warming potential of this planation was 3010 ± 750 kgCO2eqha-1yr-1, of which 55 % was contributed by soil N2O emission and only < 2 % offset by the soil CH4 sink.

Elucidating the impacts of microplastics on soil greenhouse gas emissions through automatic machine learning frameworks

With the rise in global plastic production and agricultural demand, the released microplastics (MPs) have increasingly influenced the elemental cycles of soils, leading to notable effects on greenhouse gas emissions. Despite initial research, there remains a gap in establishing a detailed modeling approach that comprehensively explores the impacts of MPs on GHG emissions. Herein, we utilized literature mining to assemble a comprehensive dataset examining the interplays between MPs and emissions of CO2, CH4, and N2O. Five automated machine learning frameworks were employed for predictive modeling. The GAMA framework was particularly effective in predicting CO2 (Q2 = 0.946) and CH4 (Q2 = 0.991) emissions. The Autogluon framework provided the most accurate prediction for N2O emission, though it exhibited signs of overfitting. Interpretability analysis indicated that the type of MPs significantly influenced CO2 emission. Degradable MPs (i.e., polyamide) inherently led to elevated CO2 emission, and the environmental aging further exacerbated this effect. Although both linear and nonlinear correlations between MPs and CH₄ emission were not identified, the incorporation of specific MPs that elevate soil pH, augment soil water retention, and cultivate anaerobic conditions may potentially elevate soil CH₄ emission. This research underscores the profound influence of MPs on soil GHG emissions, providing vital insights for shaping agricultural policies and soil management practices in the context of escalating plastic use.

Higher rice yield and lower greenhouse gas emissions with cattle manure amendment is achieved by alternate wetting and drying

ABSTRACT Climate change and water scarcity threaten the sustainability of rice production systems. Alternate wetting and drying (AWD) is a promising option to reduce methane (CH4) emission from irrigated paddy fields. However, its effect on rice yield remains to be clarified. Organic amendment can increase rice yield but may also increase CH4 emission. We therefore hypothesized that the combination of AWD with organic amendment could both increase rice yield and decrease CH4 emission. We carried out field experiments in six consecutive rice seasons during 2019 − 2022 in Central Java, Indonesia. We examined the effect of water management (continuous flooding [CF] and AWD) with (+M) and without (−M) the amendment of cattle manure as a locally available organic matter on rice growth and yield and the emissions of CH4 and nitrous oxide (N2O). AWD significantly (p < 0.05) decreased CH4 emission by 29% but marginally (p < 0.1) increased N2O emission by 10% relative to CF. There was no significant effect of AWD alone on rice yield. AWD significantly increased water productivity (the ratio of rice yield to irrigated water volume) by 50%. Cattle manure amendment significantly increased CH4 emission by 12% and rice yield by 5% but did not affect N2O emission. The combination effect of AWD+M relative to CF−M (control) was additive and resulted in a 7% increase in rice yield, a 19% decrease in the global warming potential (GWP) of CH4 + N2O emissions during both growing and fallow periods, and a 24% decrease in yield-scaled GWP. Our results indicated that the combination of AWD with cattle manure amendment would be a promising means to increase rice yield while reducing total soil greenhouse gas emission from irrigated rice paddies.