Threshold Soil Moisture Levels Influence Soil CO2 Emissions: A Machine Learning Approach to Predict Short-Term Soil CO2 Emissions from Climate-Smart Fields

Conventional agriculture is the dominant contributor to negative environmental impacts such as the growth in global greenhouse gas (GHG) emissions, and the challenges are likely to increase with the increasing global food demand as well as the agricultural expansion. Agroforestry is a sustainable management practice with strong potential to provide ecosystem services and environmental benefits through increasing carbon sequestration, nutrient availability, water use efficiency and biodiversity, and reducing soil erosion and nitrogen losses. Therefore, the establishment of agroforestry practices offers an opportunity to reduce GHG emissions. Previous studies have showed the effects of agroforestry on soil nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) fluxes in many parts of the world. In temperate Europe, the information on the GHG mitigation potential of agroforestry compared to cropland monoculture is still unclear. The present thesis consists of two studies, which was designed to explore whether the conversion of cropland monoculture to agroforestry systems reduces trace gases N2O, CO2, and CH4 emissions from the soil. The study was carried out at three sites varied with soil types in Germany. Each site had adjacent alley cropping agroforestry and cropland monoculture systems and the trees in agroforestry system were planted 1 to 11 years prior to this research. We measured soil N2O, CO2, and CH4 fluxes monthly using vented static chambers at the three sites from March 2018 to January 2020. On each day of gas sampling, soil temperature, water-filled pore space and extractable mineral nitrogen (N) were measured in the top 5 cm. The objective of our first study was to quantify the spatial-temporal dynamics of soil N2O fluxes from cropland agroforestry and monoculture systems, following different crop rotations and fertilization rates. The pattern of soil N2O fluxes were predominantly controlled by soil mineral N in both agroforestry and monoculture systems. The positive relationship between water-filled pore space with soil N2O fluxes during the cropping seasons, indicating soil moisture acts as a limiting factor under N-sufficient conditions. The entire agroforestry systems tended to reduce soil N2O emissions by 9% to 56% compared to monocultures, during the corn phase of the rotation that had typically high fertilization rates. The lowest soil N2O emissions in the unfertilized tree rows (occupied 20% of the agroforestry area) represent a potential for mitigating N2O emissions from croplands. The objective of our second study was to investigate the changes in soil CO2 and CH4 fluxes after conversion from cropland monoculture to alley cropping agroforestry systems. Our results showed that seasonal variations of soil CO2 and CH4 fluxes were strongly regulated by soil temperature and moisture, and the spatial variations were mainly controlled by texture. The establishment of agroforestry systems had no effect on reducing soil CO2 emissions, possibly because there was no significant difference in soil temperature between management systems. Annual soil CH4 uptake in the agroforestry systems was increased by up to 300% compared to monocultures, which may be related to the regulation of trees on soil moisture in agroforestry systems. The present research provides the first insight into the systematic comparison of soil N2O, CO2 and CH4 fluxes from cropland agroforestry and monoculture systems, and it provides a unique dataset for estimating the net balance of carbon emissions after conversion of cropland monoculture to alley cropping agroforestry system in temperate regions. Although soil CO2 emissions showed no differences between management systems, the total annual soil emissions of non-CO2 GHG from agroforestry systems were reduced by 0.22 Mg CO2 eq ha-1 compared to the monocultures. Considering the driving function of soil moisture and mineral N on soil GHG fluxes from cropland agroforestry and monoculture systems, our findings suggest that improved system management (e.g. optimal adjustments of the areal coverages between tree and crop rows) and optimized fertilizer input will enhance the potential of cropland agroforestry for mitigating N2O emissions and increasing CH4 uptake and C sequestration in the long run.

Responses of soil CO2 and CH4 emissions to changing water table level in a coastal wetland

The effect of water table decline on soil CO2 emission of Zoige peatland on eastern Tibetan Plateau: A four-year in situ experimental drainage

This study aimed to characterize soil carbon dioxide (CO2) emission associated with soil pore distribution in an Oxisol and Ultisol under chiseling in the planting row and in total area for sugarcane (Saccharum officinarum) cultivation. The experimental design was a large paired-plot design. Treatments consisted of chiseling in the planting row (CPR) and chiseling in total area (CTA) in an Oxisol and Ultisol. Soil CO2 emission, soil temperature, and soil moisture were assessed over 12 days in the Oxisol and 11 days in the Ultisol at a depth of 0–0.10 m. Organic carbon associated with minerals (OCAM) and particulate organic carbon (POC) were also assessed. OCAM, pore class C2 (0.05 ≤ ɸ < 0.1 mm), soil moisture, and soil temperature explained 72 and 53% of the variability of soil CO2 emission in CPR and CTA, respectively. In the Ultisol, pore class C1 (ɸ ≥ 0.1 mm) and OCAM explained 82% of the variability of soil CO2 emission in CPR. In CTA, soil moisture, OCAM, and POC explained 67% of the variability of soil CO2 emission. In the Oxisol, CPR and CTA affected soil structure, causing changes in both soil porosity and soil CO2 emission. In the Oxisol, the lowest average value of soil CO2 emission (2.8 μmol m−2 s−1) was observed in CPR whereas its highest value (3.4 μmol m−2 s−1) was observed in CTA. In the Ultisol, soil tillage (CPR and CTA) did not affect soil CO2 emission. These results indicate that the intensity of soil tillage in more clayey textured soils favors soil CO2 emission possibly due to a higher carbon availability for microbial activity when compared to more sandy textured soils. A less intensive soil tillage can be considered as an efficient strategy to reduce soil CO2 emission and hence soil organic carbon losses. Thus, this management strategy proved to be efficient in terms of mitigating greenhouse gas emissions, reducing the contribution of agriculture to global climate change.

Agriculture is responsible for a large share of global greenhouse gas (GHG) emissions, especially for methane and nitrous oxide emissions. Applying a bio-economic whole-farm model, we assessed five GHG mitigation options on their economic suitability to reduce emissions from grassland-based suckler cow farms. Among the assessed options, only compensation by agroforestry systems and the choice of an adequate production system showed the potential to significantly reduce emissions. If an adequate production system is chosen, GHG emissions per kilogram of meat can be reduced by up to 18% – from 21.9 to 18 kg CO2-eq./kg of meat – while total gross margin can be increased by up to 14%. Through the application of an agroforestry system, GHG emissions in all systems can be further reduced to 7.5 kg CO2-eq./kg meat – equating to a reduction of GHG emissions of 48% to 66% – at costs between 0.03 CHF/kg meat and 0.38 CHF/kg meat depending on the production system and the state of the system before the reduction. In contrast, the addition of lipids to the diet or a cover to the slurry tank has neither the potential to reduce GHG emissions significantly nor are they cost-effective enough to be implemented. Nitrification inhibitors can reduce GHG emissions up to 10%, but costs for this reduction are much higher than for agroforestry systems. The application of agroforestry systems to suckler farming in Switzerland therefore seems to be an adequate option to reduce GHG emission significantly for a relatively low price.

This paper examined the determinants (decomposed into enablers and de-enablers) of global greenhouse gas (GHG) emissions to deepen the debate on enhancing the implementation of the social cost of carbon or carbon pricing. Data from world development indicators were utilized in this study. The study leverages the autoregressive distributive lag model, pairwise granger causality, and impulse response function tests. This study found that there is a long-run relationship between selected economic indicators and GHG emissions in the global economy. In the long run, the GHG emissions enablers are FDI inflow and fossil fuel consumption. On the other hand, de-enablers of GHG emissions are GDP growth rate and merchandise trade. However, gas, oil, and coal use for electricity and fertilizer consumption have mixed finding across the regions. Also, the study observed that there exists no causality between GHG emissions and selected finance-related variables. A 1% shock in GHG emissions generates monetary volatility. Based on the findings that global trade generates a similar impact on GHG emissions across high-income countries, low-income countries, and middle-income countries. This study recommends the imposing of carbon tax and cap-and-trade on the GHGs polluting sectors and countries involved in the production and distribution of economic goods (activities) enabling GHG emissions.

Differences in soil organic carbon (SOC) distribution, water holding capacity, and soil temperature between no-tillage (NT) and conventional tillage (CT) systems can result in different soil CO2 emissions which could affect global warming but few studies have addressed this concern. An open warming experiment was conducted in situ by infrared heating of long-term conservation tillage management plots in North China Plain (NCP) to determine the effects of warming on soil CO2 emissions and the correlation to changes in soil temperature and moisture. This experiment was conducted from February 2010 to June 2012 and included CT and NT plots with and without warming. Warming treatment increased soil temperature by 2.1 and 1.5°C, and decreased volumetric soil-water content by 14 and 10% for CT and NT systems, respectively. Soil CO2 emissions tended to decrease with time in CT while it consistently increased in NT system over the three wheat seasons and two maize seasons under warming. Our results suggest that differences in soil temperature and soil moisture between the two tillage systems could be enlarged with time by warming, and the potential exist for warming to promote more soil CO2 emission under NT relative to CT. There is a need to consider the differences in response to global warming between these two tillage systems to properly assess the benefits of NT to C sequestration.

Short-term carbon dioxide emission under contrasting soil disturbance levels and organic amendments

Based on the pattern of citrus tree/stropharia mushrooms intercropping, returning-straw was used as the raw material for the stropharia mushrooms, and an in-situ experiment was conducted to monitor soil CO2 emissions under different dosage of straw application during the stropharia growth period. Soil CO2 emissions and the influencing factors were analyzed under different treatments of cultivated (HSM, ASM, and DSM) and uncultivated stropharia mushrooms (HS, AS, and DS). The mushroom yield and soil carbon emission efficiency (CEE) were used to provide a theoretical basis for improving the use of land under citrus orchards. The results showed that:① Straw return increased the cumulative CO2 emissions compared with the control system (conventional planting, CK) and cumulative CO2 emissions increased with the dosage of straw application. Cumulative CO2 emissions from soil treated with cultivated stropharia mushrooms were higher than those from soil treated with uncultivated stropharia mushrooms, in the order of DSM (52.09 t·hm-2) > ASM (41.10 t·hm-2) > HSM (33.20 t·hm-2) > DS (27.15 t·hm-2) > AS (25.34 t·hm-2) > HS (18.94 t·hm-2) > CK (12.16 t·hm-2). Cumulative CO2 emissions under the DSM treatment significantly increased by 328.37% compared with CK. ② For the treatment of cultivated stropharia mushrooms, peak soil CO2 emissions occurred during the period of mycelium growth. The highest cumulative CO2 emissions during this period were obtained under the DSM treatment and accounted for 43.27% of the total cumulative emissions. This was followed by ASM and HSM which accounted for 42.63% and 40.57% of emissions, respectively. ③ Cultivated stropharia mushrooms reduced the temperature sensitivity coefficient (Q10). The soil temperature (5 cm depth) had a significant effect on the soil CO2 emission rate (P<0.01) but soil moisture did not (P>0.05). Soil temperature explained 27% to 71% of the variation in soil CO2 emissions rates, and the two-factor fitting of soil temperature and soil moisture explained 36% to 82% of the variation. ④ For the treatment of cultivated stropharia mushrooms, the ranked yield of each treatment was DSM (49.7 t·hm-2) > ASM (47.0 t·hm-2) > HSM (23.3 t·hm-2), and ASM had the highest soil CEE (1.14). Therefore, under the system of citrus tree/stropharia mushroom intercropping, straw return can increase soil CO2 emissions, with the highest emissions being obtained when a double dosage of straw was applied. However, the optimal amount of straw still needs to be determined in combination with changes in soil nutrients and crop yields.

Abstract. To track progress towards keeping global warming well below 2 ∘C or even 1.5 ∘C, as agreed in the Paris Agreement, comprehensive up-to-date and reliable information on anthropogenic emissions and removals of greenhouse gas (GHG) emissions is required. Here we compile a new synthetic dataset on anthropogenic GHG emissions for 1970–2018 with a fast-track extension to 2019. Our dataset is global in coverage and includes CO2 emissions, CH4 emissions, N2O emissions, as well as those from fluorinated gases (F-gases: HFCs, PFCs, SF6, NF3) and provides country and sector details. We build this dataset from the version 6 release of the Emissions Database for Global Atmospheric Research (EDGAR v6) and three bookkeeping models for CO2 emissions from land use, land-use change, and forestry (LULUCF). We assess the uncertainties of global greenhouse gases at the 90 % confidence interval (5th–95th percentile range) by combining statistical analysis and comparisons of global emissions inventories and top-down atmospheric measurements with an expert judgement informed by the relevant scientific literature. We identify important data gaps for F-gas emissions. The agreement between our bottom-up inventory estimates and top-down atmospheric-based emissions estimates is relatively close for some F-gas species (∼ 10 % or less), but estimates can differ by an order of magnitude or more for others. Our aggregated F-gas estimate is about 10 % lower than top-down estimates in recent years. However, emissions from excluded F-gas species such as chlorofluorocarbons (CFCs) or hydrochlorofluorocarbons (HCFCs) are cumulatively larger than the sum of the reported species. Using global warming potential values with a 100-year time horizon from the Sixth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC), global GHG emissions in 2018 amounted to 58 ± 6.1 GtCO2 eq. consisting of CO2 from fossil fuel combustion and industry (FFI) 38 ± 3.0 GtCO2, CO2-LULUCF 5.7 ± 4.0 GtCO2, CH4 10 ± 3.1 GtCO2 eq., N2O 2.6 ± 1.6 GtCO2 eq., and F-gases 1.3 ± 0.40 GtCO2 eq. Initial estimates suggest further growth of 1.3 GtCO2 eq. in GHG emissions to reach 59 ± 6.6 GtCO2 eq. by 2019. Our analysis of global trends in anthropogenic GHG emissions over the past 5 decades (1970–2018) highlights a pattern of varied but sustained emissions growth. There is high confidence that global anthropogenic GHG emissions have increased every decade, and emissions growth has been persistent across the different (groups of) gases. There is also high confidence that global anthropogenic GHG emissions levels were higher in 2009–2018 than in any previous decade and that GHG emissions levels grew throughout the most recent decade. While the average annual GHG emissions growth rate slowed between 2009 and 2018 (1.2 % yr−1) compared to 2000–2009 (2.4 % yr−1), the absolute increase in average annual GHG emissions by decade was never larger than between 2000–2009 and 2009–2018. Our analysis further reveals that there are no global sectors that show sustained reductions in GHG emissions. There are a number of countries that have reduced GHG emissions over the past decade, but these reductions are comparatively modest and outgrown by much larger emissions growth in some developing countries such as China, India, and Indonesia. There is a need to further develop independent, robust, and timely emissions estimates across all gases. As such, tracking progress in climate policy requires substantial investments in independent GHG emissions accounting and monitoring as well as in national and international statistical infrastructures. The data associated with this article (Minx et al., 2021) can be found at https://doi.org/10.5281/zenodo.5566761.

The application of organic amendments can be an appropriate solution to reclaim and improve physical propertiesof saline-sodic soils. In this research, an experiment was performed under greenhouse conditions to study the effect ofamendments to the physical properties of loamy saline-sodic soil. The five treatments were control (withoutamendment), municipal solid waste compost (MC), vermicomposting (VC), poultry manure (PM), and gypsumpowder (G). They were carried out in a completely randomized design with three replications. Each treatmentcomprised 10 ton/ha of the specified soil added to the soil. The results showed that soil amendments decreased bulkdensity (p<0.05) and increased mean weight diameter of aggregates (MWD) (p<0.05) over the control. The saturatedhydraulic conductivity (Ks) for the G treatment was significantly higher than other treatments (p<0.05). The additionof amendments significantly increased the Sgi index, which is defined as the slope of the retention curve at itsinflection point, but the Sgi index between the G and MC treatments was not significant (p<0.05). In addition, plantavailable water content (PAWC) increased significantly (p<0.05) for organic amendments over the G and controltreatments, and a maximum value was observed for the PM treatment. The positive effects of the amendmentsshowed that the application of organic and/or inorganic amendments can be recommended for saline-sodic soil toimprove soil physical quality.

Prediction of GHG emissions from Chengdu Metro in the construction stage based on WOA-DELM

Agricultural transformation towards delivering deep carbon cuts in China’s arid inland areas

Agriculture accounts for a large proportion of global greenhouse gas (GHG) emissions. It is therefore crucial to identify effective and efficient GHG mitigation potentials in agriculture, but also in related upstream sectors. However, previous studies in this area have rarely undertaken a cross-sectoral assessment. There is also a gap in research on the GHG mitigation potential of innovations such as green ammonia in arable farming at a larger spatial scale. The study therefore aimed to analyze how selected technological adaptations or innovations can be used to contribute to efficient and effective cross-sectoral GHG mitigation in conventional arable farming systems. Germany, one of the largest agricultural producers and contributors of GHG emissions from agriculture in the EU, was chosen as a case study. The GHG mitigation potential and abatement cost of four selected measures were analyzed using an integrated land use model and life cycle assessment. Their GHG mitigation potential varied between 0.3Mt CO2-eq. for nitrification inhibitors under lower mitigation rate assumptions and 4.7Mt CO2-eq. for green ammonia with upper mitigation rate assumptions on GHG emission impacts, i. e. rather high mitigation. While crop varieties based on new genomic technologies (NGT) were introduced at no GHG abatement cost, the average mitigation costs ranged from 48 € for the use of nitrification inhibitors (upper mitigation rate) to 1233 € per t CO2-eq. for N sensors (lower mitigation rate). There were also regional differences due to different land use structures, regional farm sizes, economic and agronomic conditions. Based on these results we recommend for agricultural and environmental policy to foster the use of nitrification inhibitors due to the identified GHG reduction potential and the comparatively low GHG abatement costs. Additionally, the use of green ammonia in fertilizer production should be further promoted. Although the results are exemplary for Germany, they can be very informative for other EU Member States with comparable socio-economic and agronomic conditions.

Milk and beef production cause 9% of global greenhouse gas (GHG) emissions. Previous life cycle assessment (LCA) studies have shown that dairy intensification reduces the carbon footprint of milk by increasing animal productivity and feed conversion efficiency. None of these studies simultaneously evaluated indirect GHG effects incurred via teleconnections with expansion of feed crop production and replacement suckler-beef production. We applied consequential LCA to incorporate these effects into GHG mitigation calculations for intensification scenarios among grazing-based dairy farms in an industrialized country (UK), in which milk production shifts from average to intensive farm typologies, involving higher milk yields per cow and more maize and concentrate feed in cattle diets. Attributional LCA indicated a reduction of up to 0.10kg CO2 e kg-1 milk following intensification, reflecting improved feed conversion efficiency. However, consequential LCA indicated that land use change associated with increased demand for maize and concentrate feed, plus additional suckler-beef production to replace reduced dairy-beef output, significantly increased GHG emissions following intensification. International displacement of replacement suckler-beef production to the "global beef frontier" in Brazil resulted in small GHG savings for the UK GHG inventory, but contributed to a net increase in international GHG emissions equivalent to 0.63kg CO2 e kg-1 milk. Use of spared dairy grassland for intensive beef production can lead to net GHG mitigation by replacing extensive beef production, enabling afforestation on larger areas of lower quality grassland, or by avoiding expansion of international (Brazilian) beef production. We recommend that LCA boundaries are expanded when evaluating livestock intensification pathways, to avoid potentially misleading conclusions being drawn from "snapshot" carbon footprints. We conclude that dairy intensification in industrialized countries can lead to significant international carbon leakage, and only achieves GHG mitigation when spared dairy grassland is used to intensify beef production, freeing up larger areas for afforestation.