Increase Soil Carbon Stocks Research Articles

Environmental benefits of ozonated water for sustainable grapevine disease control: A life cycle and carbon sequestration analysis

The oxidative capacity of ozone makes it a highly effective biocide, widely used in the food and processing industry, as well as in drinking water plants. In a context of tighter restrictions on the use of synthetic plant protection products at the regulatory level, wineries are looking for alternative methods to control diseases, making the application of ozonated water an option to consider. To determine the environmental sustainability of this alternative vineyard disease control treatment, an environmental impact assessment was conducted using the Life Cycle Assessment (LCA) methodology. The assessment was carried out in a vineyard located in the D.O. Rías Baixas of Galicia, located in northwestern Spain. The analysis was conducted on the basis of two functional units: i) 1 kg of grapes and ii) 1 ha of land managed and using a cradle-to-gate boundary system. Ten impact categories were assessed using the ReCiPe method, except for the water scarcity indicator, which was quantified using AWARE.The environmental sustainability of the vineyard was further analyzed by measuring its carbon sequestration potential to obtain a more complete environmental profile. The RothC-26.3 model was chosen to estimate absolute carbon sequestration and annual sequestration rate from 2020 to 2040. Since the ozone-only scenarios lost all harvest, no environmental assessment was performed for such scenarios. For the remaining scenarios, the findings suggest that those using a combination of ozonated water and fungicides have the worst environmental performance due to notable reductions in grape yield and more frequent disease control interventions, particularly in certain scenarios. When evaluating environmental performance per hectare of land managed, the scenario using ozonated water with a limited number of disease control interventions exhibited the most favorable environmental profile, primarily due to reduced use of fungicides and disease control passes. In addition, the main contributors to the vineyard environmental profile identified were diesel fuel combustion during field operations, fertilizer use and production, and irrigation. In addition, the research indicates that the vineyard sequesters carbon annually, but this alone is insufficient to offset its greenhouse gas emissions. However, it is estimated that through the application of more appropriate soil management practices, the vineyard could achieve carbon neutrality and potentially increase soil carbon stocks over time.

Response of wheat to arbuscular mycorrhizal fungi inoculation and biochar application: Implications for soil carbon sequestration

The sequestration of atmospheric CO₂ in soil is suggested as an effective climate change mitigation strategy. Biochar application shows promise in this regard, while the role of fungi in soil carbon cycling and sequestration is also under investigation. Using a novel high-throughput plant phenomics approach, we explore the impact of arbuscular mycorrhizal fungi (AMF) inoculation and biochar application on wheat growth and soil carbon, guided by one of the leading global carbon credit schemes. Wheat was successfully colonised by AMF, achieving an average root length colonisation of 35.9%. We uncover an indirect fungal-mediated pathway to soil carbon sequestration, with mycorrhizal plants generating more biomass across all soil treatments without yield penalties, suggesting colonised plants deliver more plant derived carbon to the soil, potentially leading to long-term soil carbon gains. Conversely, fungal-driven carbon loss occurred, significantly reducing soil carbon accumulation in unamended soil, but not in biochar-amended soil, suggesting that biochar moderates fungal activity and positively impacts the soil carbon balance. While both biochar and AMF enhance plant growth, their direct effects on soil carbon are complex. Although biochar did not significantly increase soil carbon stocks beyond its own contribution, its ability to regulate fungal activity could play an important role in influencing soil carbon sequestration.

Selection of Suitable Organic Amendments to Balance Agricultural Economic Benefits and Carbon Sequestration.

Long-term excessive use of fertilizers and intensive cultivation not only decreases soil organic carbon (SOC) and productivity, but also increases greenhouse gas emissions, which is detrimental to sustainable agricultural development. The purpose of this paper is to identify organic amendments suitable for winter wheat growth in the North China Plain by studying the effects of organic amendments on the economic benefits, carbon emissions, and carbon sequestration for winter wheat fields and to provide a theoretical basis for the wide application of organic amendments in agricultural fields. The two nitrogen rates were N0 (0 kg ha-1) and N240 (240 kg ha-1), and the four organic amendments were straw, manure, mushroom residue (M R), and biochar. The results showed that, compared to N0, N240 significantly increased the yield by 244.1-318.4% and the organic carbon storage by 16.7-30.5%, respectively, but increased the carbon emissions by 29.3-45.5%. In addition, soil carbon stocks increased with all three types of organic amendments compared to the straw amendment, with the biochar treatment being the largest, increasing carbon storage by 13.3-33.6%. In terms of yield and economic benefits, compared to the straw amendment, the manure and biochar amendments increased winter wheat yields by 0.0-1.5% and 4.0-13.3%, respectively, and M R slightly decreased wheat yield; only the economic benefit of the M R amendment was greater than that of the straw amendment, with an increase in economic benefit of 1.3% and 8.2% in the 2021-2022 and 2022-2023 seasons, respectively. Furthermore, according to the net ecosystem productivity (NEP), N0 was the source of CO2, while N240 was a sink of CO2. The TOPSIS results showed that N240 with a mushroom residue amendment could be recommended for increasing soil carbon stocks and economic benefits for winter wheat in the NCP and similar regions. Low-cost M R can increase farmer motivation and improve soil organic carbon, making a big step forward in the spread of organic materials on farmland.

An assessment of Organic and Conventional Farming Practices for Yield, Pest Management and Soil Health

This study contrasts and compares conventional and organic farming. The purpose of the study is to assess the effectiveness and impact of each practice before deciding on the best crop-growing approach. Despite their agricultural systems can be categorized as conventional or sustainable depending on the techniques employed. Organic farming which cultivates a range of crops without the use of synthetic manures, the agricultural method that is most sustainable. While producing enough food, organic farming improves soil composition and supports biodiversity by relying on ecosystem services. The review compares the long-term effects of conventional and alternative organic farming practices on yield in which in short term organic yields were found to be 19.2% lower than conventional yield while in long term yields were lower in conventional systems by 31% and 50%, respectively, due to the long-term improvement in soil health. In soil health point of view long term practices of organic farming improves physical, chemical and biological properties of soil by increase soil carbon stock by 12 %, more nutrient release and microbial activity. Pest management is effectively controlled by crop rotation, increase beneficial population of pest in organic farming which reduce the dependency on chemical pesticides and maintain the sustainability of soil health and ecology. As a result, organic farming methods are being evaluated in a large number of research worldwide as an alternative due to their better physical, chemical and biological qualities than conventional farming methods.

Soil inorganic carbon stocks increase non-synergistically with soil organic carbon after ecological restoration practices in drylands

Ecological restoration practices have been widely adopted to increase soil carbon stocks by improving soil organic carbon (SOC). However, the effects of these practices on the other important soil carbon component, soil inorganic carbon (SIC), remain unclear. To address this, a meta-analysis based on 45 publications and 37 sites was conducted to quantitatively assess the dynamic changes in SIC stocks due to typical restoration practices, including conversion of cropland to forest (C–F), cropland to grassland (C–G), desert to cropland (D–C), conservation agriculture (CA), and desert to forest (D–F). Results showed that, among the restoration practices increasing the SOC stocks, the SIC stocks decreased after the C–F (−34.7%) and C–G (−15.8%) conversions and CA (−6.8%), but increased after the conversion of D–C (2.6%) and D–F (46.9%). Additionally, in terms of recovery duration, the negative effect of C–G on SIC stocks may vanish with increased recovery duration, whereas SIC stocks showed a prominent increase initially after CA and then decreased over time; the response to D–F conversion of SIC stocks remained consistently positive over time. Furthermore, the non-synergistic changes with SIC and SOC could be due to variations in edaphic factors, while the effects edaphic factors on SIC stocks were different under various ecological restoration practices. Among all the impact factors, mean annual temperature, initial SIC stocks, and types of ecological restoration practice, were the most crucial factors explaining the variation in SIC stocks with ecological restoration. Collectively, the results highlight that the change in SIC stocks is asynchronous with the increase in SOC stocks in space and time after ecological restoration, further indicating that changes in SIC stocks should be paid more attention when assessing and predicting carbon sequestration following various ecological restoration practices.

Benefits of organic amendments on soil C stock may be offset by increased methane flux in rice paddy field

Periodic application of organic manure (OM) has been suggested to increase soil carbon stock and mitigate global warming. However, in irrigated rice fields, OM amendment greatly increases methane (CH4) emissions, which in turn may offset the effect of increased soil carbon storage on mitigating global warming. Research on the effects of OM application on net global warming potential that integrates greenhouse gas (GHG) fluxes and soil carbon stocks change in rice cultivating systems has been elusive. To determine the impact of organic amendments on global warming in a rice paddy, chemical (NPK) and organic fertilization were installed, and straw removal and recycling plots were added in two fertilization treatments. Annual CH4 and nitrous oxide (N2O) fluxes were evaluated using the static closed chamber method. Soil C stock changes were estimated using the net ecosystem C budget (NECB) which indicates the difference between C input and output. In chemical fertilization, straw removal decreased soil C stock by an average of 751 kg C ha−1 year−1, but straw recycling significantly increased soil C stock by an average of 464 kg C ha−1 year−1. In organic fertilization, soil C stock was strongly affected by cover crop productivity. Under favorable climatic conditions for cover cropping, soil C stocks were greatly increased by green manuring and even more so by straw recycling. However, under an unfavorable climate, soil C stock was not statistically increased, regardless of straw addition. Straw recycling increased annual CH4 flux by approximately 220–310 and 130–190% over straw removal in chemical (7.9 Mg CO2-eq. ha−1 year−1) and organic fertilization (40 Mg CO2-eq. ha−1 year−1), respectively, but negligibly affected N2O flux. Irrespective of fertilization background, net GWP was mainly decided by CH4 flux with 54–98% coverage, and then followed by soil C stock change and N2O flux. As a result, straw addition increased net GWP by around 110–140 and 120–150% over straw removal in chemical and organic fertilization, respectively. Rice yield was stable between years in the chemical fertilization but showed a big difference in organic fertilization, due to the difference in cover crop biomass productivity. However, rice productivity was not significantly affected by straw recycling. Organic amendment and straw applications increased greenhouse gas intensity (GHGI) by an average of 131% and 269% in a rice paddy, respectively, due to a high increase of CH4 flux but a low increase of soil C stock. In conclusion, more effective OM management which can decrease CH4 emissions and increase SOC stock is required in rice paddies.

The role of plant species diversity in maintaining ecological balance in oil palm plantation

The level of plant species diversity in oil palm plantations is thought to be decreasing in number. The existence of other plant species is considered to be a competitor for oil palm plants in obtaining water and plant nutrients. Thus, the diversity of plant species gets less attention because they are considered to have no role. We address this problem by analyzing the level of plant species diversity and the role of plant species diversity in maintaining the ecological balance in the plantation environment. This research was conducted on 4 types of landcover in TPR oil palm plantations (young growth, medium growth, old growth, HCV) and 2 smallholder oil palm plantations, by vegetation analysis with the single plot method. The results showed that the number of species on the research site was 49 species. The highest value of species richness and diversity was obtained in smallholder oil palm plantations (Dmg=3.11 and H′=2.18), while the highest evenness value was found in old growth (E=0.79). Based on the literature study, there were 23 species that have a direct ecological role in oil palm plantations. The ecological role of plants in oil palm plantations are as a ground cover for regulating soil moisture (4 species), producing litter for nutrient formation (5 species), fertilizing the soil and absorbing toxins (3 species), regulating water management and preventing erosion (3 species), increase soil carbon stocks and groundwater availability (2 species), animal feed (5 species), feed for wildlife (6 species), control pests and diseases (4 species), etc. The ecological role of this plant species will have a positive impact on oil palm plantations, especially in maintaining soil fertility, availability of groundwater, providing feed for animals, and also as biopesticides for oilpalm plants to avoid pests and diseases.

High-quality fine particulate organic matter drives SOM stocks: Insights from Mollisols in Northeast China

How the quantity and quality of particulate organic matter (POM) affect the mineral-associated organic matter (MAOM) accumulation and the aggregate stability has not been systematically studied, which limits the in-depth understanding of the relationship between POM and SOM stocks. This study investigated the changes in the biomass and C:N ratio of fine roots, the C contribution of POM to SOM and the C:N ratio of POM within different particle sizes in native grassland, plantations and croplands in the Mollisols region of Northeast China. Then, the influence of fine roots and POM characteristics on MAOM accumulation and aggregate stability was analyzed. The results showed that (1) the C contribution of fine POM (fPOM, 0.053–0.25 mm) to SOM and the C:N ratio of fPOM in the native grassland was significantly higher and lower than that in the other sites (P < 0.05), respectively. (2) The C contribution of MAOM to SOM and the mean weight diameter (MWD) of water-stable aggregates were significantly positively correlated with the C contribution of fPOM to SOM (P < 0.01), and negatively correlated with the fPOM C:N ratio (P < 0.01). (3) The effect of fPOM C:N ratio on MWD of water-stable aggregates was stronger compared to the C contribution of fPOM to SOM. (4) The fine roots biomass showed a significant indirect effect on the C contribution of MAOM to SOM and the MWD of water-stable aggregates by influencing the C contribution of fPOM to SOM (P < 0.05). In general, both the quantity and quality (C:N ratio) of fPOM were lower in other land use types than that in native grassland, which significantly affected the SOM stocks. At the same time, the fPOM was also a medium for the fine roots to affect the soil characteristics. Promoting the accumulation of fine POM and focusing on improving the quality of fine POM could be a promising measure to ensure food production and increase soil carbon stocks. Conservation tillage practices such as no-till may be effective.

Climate-Neutral Agriculture?

Regarding the achievement of worldwide agricultural climate neutrality, the focus is on a worldwide net-zero emission of cradle-to-farmgate greenhouse gases (GHGs), while, when appropriate, including the biogeophysical impacts of practices on the longwave radiation balance. Increasing soil carbon stocks and afforestation have been suggested as practices that could be currently (roughly) sufficient to achieve agricultural climate neutrality. It appears that in both cases the quantitative contributions to climate neutrality that can actually be delivered are very uncertain. There is also much uncertainty about the quantitative climate benefits with regard to forest conservation, changing feed composition to reduce enteric methane emission by ruminants, agroforestry and the use of nitrification and urease inhibitors to decrease the emission of N2O. There is a case for much future work aimed at reducing the present uncertainties. The replacing of animal husbandry-based protein production by plant-based protein production that can reduce agricultural GHG emissions by about 50%, is technically feasible but at variance with trends in worldwide food consumption. There is a case for a major effort to reverse these trends. Phasing out fossil fuel inputs, improving nitrogen-use efficiency, net-zero GHG-emission fertilizer inputs and reducing methane emissions by rice paddies can cut the current worldwide agricultural GHG emissions by about 22%.

Effects of biochar and wood ash amendments in the soil-water-plant environment of two temperate forest plantations

Forest biomass is considered an alternative to fossil fuels in energy production, as part of global strategies for climate change mitigation. Application of by-products such as wood ash (WA) and biochar (BC) to soil could replace the nutrients removed by tree harvesting and could also increase soil carbon stocks. However, the extent to which these amendments can provide benefits depends on how the by-products interact with the soil-water-plant system. We studied the short-term responses of WA and BC application in two different mineral soil-water-plant systems in temperate forests: A. Typic Udorthent (TU) with mature Pinus radiata; B. Typic Dystrudept (TD) with young Quercus pyrenaica, to test the following hypotheses: (1) the application of WA and BC will increase nutrient uptake by plants, but (2) these products could induce toxicity in the soil-water-plant system, and (3) in case of no toxicity, plant biomass growth in these temperate forest soils will increase due to increased plant nutrient uptake. Biochar was applied at rates of 3.5, 10, and 20 Mg ha–1 and WA at rates of 1.5, 4.5, and 9 Mg ha–1 (calcium equivalent). A nitrogen enriched treatment was applied with the intermediate doses. Ecotoxicity testing indicated that WA and BC were not toxic, although Ni uptake increased in biomass of the TU after BC + N application. BC increased SOC stocks of both sites, depending on treatment. In TD BC increased K uptake by plants, but did not increase biomass. In summary, this study shows that the application of BC and WA had different effects on the soil -water-plant system in two different forest soils. This difference was attributed to (i) the soil characteristics, (ii) the application rates and (iii) whether or not nitrogen was applied. Long-term field experiments are required to test the performance and potential toxicity of these by-products as soil enhancers.

Novel Methodology for the Assessment of Organic Carbon Stocks in German Arable Soils

There is currently a significant focus on oil organic carbon, as interest in mitigating climate change by increasing soil carbon stocks is leading to efforts to include this within carbon farming and the trade of CO2 certificates. In addition, soil organic carbon controls many other soil functions, such as soil productivity. However, results from long-term field experiments suggest that an ever-increasing carbon content in soil, at some point, will no longer increase productivity, but will cause environmental risks, especially from excess nitrogen. In Germany, the most widely recognized soil organic matter (SOM) balance method, VDLUFA (Association of German Agricultural Investigation and Research Institutions), addresses soil management only, without a relation to the soil carbon stock. To close this gap, a methodology is developed based on results from European long-term field experiments that allows for an assessment of agricultural management both in terms of the carbon input to soil and the amount of carbon stored in soil. Due to the transformation of carbon stock into carbon flux, it is possible to apply the classification scheme of the VDLUFA balance to the carbon content of topsoils. This provides information to qualify further decisions about fostering carbon accumulation. This was demonstrated on experimental results from Bad Lauchstädt, as well as on data from the German Agricultural Soil Inventory (BZE-LW) for arable soils on a regional scale.

Carbon Soil Storage and Technologies to Increase Soil Carbon Stocks in the South American Savanna

The expansion of the agricultural frontiers that occurred in the last decades in the South American savanna (Cerrado), the second-largest biome in Brazil (covering an area of 204 million hectares), has accounted for a substantial portion of South America’s CO2 emissions. In this context, our research investigated the potential for soil carbon storage in the biome. The analysis of previous data (n = 197) shows a vertical distribution pattern of soil carbon stock: 26.17% for the upper 0–30 cm layer, 37.67% for the 30–100 cm layer, and 36.15% for the 100–200 cm layer. The total soil carbon storage for the biome is 13.5 ± 6.7 gigatons (n = 71) for the upper 0–30 cm layer, 30.5 ± 18.9 Gt (n = 64) for the 0–100 cm layer, and 47.8 ± 4.3 (n = 9) for the 0–200 cm layer. The results indicate that the soil carbon stock up to 1 m deep in the Cerrado ranges from 0.5% to 2.29% of the global soil organic carbon storage for this depth. Further research is necessary to investigate what happens at a depth of at least 2 m. The results also indicate that the soil under pasture lands constitutes the largest manageable pool for increasing soil carbon stocks via the restoration of degraded pastures.

A review and meta-analysis of mitigation measures for nitrous oxide emissions from crop residues

Crop residues are of crucial importance to maintain or even increase soil carbon stocks and fertility, and thereby to address the global challenge of climate change mitigation. However, crop residues can also potentially stimulate emissions of the greenhouse gas nitrous oxide (N2O) from soils. A better understanding of how to mitigate N2O emissions due to crop residue management while promoting positive effects on soil carbon is needed to reconcile the opposing effects of crop residues on the greenhouse gas balance of agroecosystems. Here, we combine a literature review and a meta-analysis to identify and assess measures for mitigating N2O emissions due to crop residue application to agricultural fields. Our study shows that crop residue removal, shallow incorporation, incorporation of residues with C:N ratio > 30 and avoiding incorporation of residues from crops terminated at an immature physiological stage, are measures leading to significantly lower N2O emissions. Other practices such as incorporation timing and interactions with fertilisers are less conclusive. Several of the evaluated N2O mitigation measures implied negative side-effects on yield, soil organic carbon storage, nitrate leaching and/or ammonia volatilization. We identified additional strategies with potential to reduce crop residue N2O emissions without strong negative side-effects, which require further research. These are: a) treatment of crop residues before field application, e.g., conversion of residues into biochar or anaerobic digestate, b) co-application with nitrification inhibitors or N-immobilizing materials such as compost with a high C:N ratio, paper waste or sawdust, and c) use of residues obtained from crop mixtures. Our study provides a scientific basis to be developed over the coming years on how to increase the sustainability of agroecosystems though adequate crop residue management.

Soil carbon and nitrous oxide dynamics in corn (Zea mays L.) production under different nitrogen, tillage and residue management practices

Reducing tillage frequency and intensity and returning crop residues to the soil are two agricultural management practices to increase soil organic carbon (SOC). Timing and rates of nitrogen fertilizer, coupled with tillage methods and residue incorporation, can also influence nitrous oxide emissions. In this study, we used measured data from a long term (23 years) tillage and residue management experiment, under intensive grain corn production, together with the DNDC (DeNitrification-DeComposition) process-based model, to ascertain the most effective fertilizer and tillage management practices to reduce nitrous oxide emissions and nitrate leaching, and increase soil carbon stocks. The field experiment consisted of no-till [NT], reduced [RT], and conventional tillage [CT], with and without corn residue return. After calibration and validation, using field observed data, the DNDC model was run with 108 management scenarios (six N application rates, spring single N fertilization, spring split N fertilization and fall fertilization, three tillage practices and two residue-return options). N application rate was predicted to be a significant driver for corn yield, SOC sequestration, N2O emissions and nitrate leaching, indicating the need to identify a critical N rate to both optimize production and achieve sustainability goals. Split (vs. single) N application did not significantly affect corn yield, nitrate leaching, N2O emissions or SOC, while fall fertilization should be avoided due to greater nitrate leaching and higher N2O emissions as well as lower crop yield. Although stimulating N2O emissions, both NT and residue return are recommended for their ability to enhance SOC stocks. Results of this study can be used for policy development regarding carbon sequestration and GHG emissions for intensive grain cropping systems in the humid regions of North America.

On the impact of grassland management on soil carbon stocks: a worldwide meta-analysis

Grasslands occupy 70% of whole agricultural land and hold significant amounts of carbon, a key element in the regulation of Earth's soils fertility, biomass production and climate. Previous work has shown that carbon stocks of grassland soils have been largely depleted worldwide due to missuse or mismanagement but that shifts in management could also potentially increase soil carbon stocks and mitigate against the degradation of natural ecosystems. However, the existing literature points to large discrepancies in the impact of grassland management practices on soil carbon, which the present study investigated. Here we considered 235 experimental sites in 18 countries across the world where shifts in grassland management involved different grazing strategies (free, F vs controlled, C; high, H vs low, L density grazers), grazers exclusion (E), mowing (M) and burning (B). The best performing practice was controlled grazing with high density of grazers (CHG) with an average soil organic carbon content (SOCC) increase of 21% and with 100% of the studies pointing to a SOCC increase. This was followed by E (14.9%; 60%) and FLG (13.3%; 80%). On average, burning grasslands, decreases SOCC by 9.3% but 31% of the studies pointed to an increase, thus indicating discrepancies in the impact of grassland management. CLG and mowing did not significantly impact SOCC. These results also indicated that B decreased SOCC the most under moist to humid climates (−10.9% vs −1.7% under arid to semi-arid), while that E was only beneficial in arid to semi-arid grasslands. Adoption of rotational high-intensity grazing in place of free grazing grasslands, should be seriously considered by policy and decision makers to mitigate against climate change while fostering economic and social development.

Greenhouse gas mitigation strategies and opportunities for agriculture

AbstractTo cope with increasing demands for food, feed, and energy along with environmental challenges due to climate change, the agricultural sector has a unique opportunity to meet sustainable development goals set by the United Nations through innovative and regenerative agriculture practices that enhance agricultural productivity, ecosystem services, and human well‐being simultaneously. Among many sustainability metrics to measure agriculture's impacts on sustainability and contribution to its improvements, we focus on the greenhouse gas (GHG) emissions from the agricultural sector as a key environmental indicator to assess several GHG mitigation practices from the perspective of life‐cycle analysis applied to agriculture. We first analyze the key factors contributing to farming GHG emissions and then identify a range of GHG mitigation strategies, such as optimizing farm fertilizer/chemical inputs, manufacturing low‐carbon fertilizer/chemical, reducing on‐farm energy/fuel consumption, and increasing soil carbon stocks. Furthermore, we elaborate on how these strategies can be successfully implemented to different scales of farming through policies and incentives and better quantification and verification schemes for effective policies and incentives. Finally, we present the holistic evaluation of agricultural GHG emissions in terms of landscape management approaches and provide ecosystem services to address social and economic issues.

Different mechanisms underlying the divergent responses of soil respiration components to an introduction of N2-fixer tree species into Eucalyptus plantations

Soil respiration (Rs), primarily rhizospheric (Rr) and heterotrophic respiration (Rh) is an important CO2 efflux from soil to the atmosphere. Previous studies demonstrated that introducing N2- fixing species into plantations could increase soil carbon stock and modify carbon chemical composition by altering microbial community and associated enzymes activities. However, their responses of Rs and its two components (Rr and Rh) remain poorly understood. This study investigated how Rs and its components responded to the introduction of N2-fixer tree species in a subtropical eucalyptus plantation and to further ascertain its underlying mechanisms. We measured Rs and its components (Rr and Rh) and used phospholipid fatty acids (PLFAs) as bioindicators to study soil microbial communities and activities of four extracellular enzymes as indicators of soil microbial functioning in an 8-year-old pure Eucalyptus urophylla plantation (PP) and an 8-year-old mixed E. urophylla and Acacia mangium (N2-fixer tree species) plantation (MP) in subtropical China. We found that Rs was significantly reduced by approximately 12.5%, with divergent responses of Rr and Rh in the MP. Compared with PP, the Rr decreased by 41.7% and Rh increased by 36.6% in plantation with N2-fixer species. The decreased Rr in the MP was largely associated with a reduction in fine root biomass. In contrast, the increased Rh in the MP was induced by an increase in total microbial biomass, changing the microbial community structure and enhancing the activities of β-1,4-glucosidase. The enzymatic changes were associated with an increase in N availability. Our results indicate that shifts in both biotic and abiotic factors resulting from the introduction of N2-fixer species shaped changes in Rs and its components.

Accumulation of C4‐carbon from Miscanthus in organic‐matter‐rich soils

AbstractTo evaluate the sustainability of biomass plantations, effects on soil organic carbon (SOC) need to be quantified. Miscanthus × giganteus is increasingly used as a bioenergy plant, and it has been hypothesized that, after conversion from cropland, Miscanthus cropping increases SOC storage, whereas conversion from grassland to Miscanthus provides, on average, no sequestration. All field studies hitherto were carried out on mineral soils with topsoil SOC contents of below 3.3%. Here, we analyze in the temperate zone of Switzerland five sites that have been cultivated with Miscanthus for 19–24 years and of which four sites are higher in topsoil SOC content (4.7%–16.2%) and storage (188–262 t SOC) than any previously studied Miscanthus plantation in Europe. We used the difference in carbon isotopic signature between C4 (Miscanthus) and neighboring plots with C3 vegetation (grassland) to quantify the accumulation of new SOC from Miscanthus down to 0.75 m. Annual C4‐C accumulation rates were 1.66 (standard error ± 0.14) t C4‐C ha−1 year−1 (range: 1.26–2.01) in the upper 0.3 m of soil and 1.96 (±0.18) t C4‐C ha−1 year−1 (1.40–2.38) in 0–0.75 m. Average rates for 0–0.3 m were higher than those of mineral soils (n = 37) published previously (0.96 [±0.10] t C4‐C ha−1 year−1). However, high rates of C4‐C accumulation were also reported previously for some mineral soils. Nevertheless, the one mineral soil in our study did not reveal a systematically different accumulation of Miscanthus‐derived carbon compared with the four carbon‐rich soils. We therefore conclude that soils rich in organic matter do not show a different C4‐C accumulation pattern as compared with mineral soils. However, their C4‐C accumulation rates are at the upper end of the data ensemble. Our results further underpin that conversion to Miscanthus, despite C4‐C accumulation, provides no means to increase soil carbon stocks relative to grassland management.

Effects of Organic Fertilizers on the Soil Microorganisms Responsible for N2O Emissions: A Review.

The use of organic fertilizers constitutes a sustainable strategy to recycle nutrients, increase soil carbon (C) stocks and mitigate climate change. Yet, this depends largely on balance between soil C sequestration and the emissions of the potent greenhouse gas nitrous oxide (N2O). Organic fertilizers strongly influence the microbial processes leading to the release of N2O. The magnitude and pattern of N2O emissions are different from the emissions observed from inorganic fertilizers and difficult to predict, which hinders developing best management practices specific to organic fertilizers. Currently, we lack a comprehensive evaluation of the effects of OFs on the function and structure of the N cycling microbial communities. Focusing on animal manures, here we provide an overview of the effects of these organic fertilizers on the community structure and function of nitrifying and denitrifying microorganisms in upland soils. Unprocessed manure with high moisture, high available nitrogen (N) and C content can shift the structure of the microbial community, increasing the abundance and activity of nitrifying and denitrifying microorganisms. Processed manure, such as digestate, compost, vermicompost and biochar, can also stimulate nitrifying and denitrifying microorganisms, although the effects on the soil microbial community structure are different, and N2O emissions are comparatively lower than raw manure. We propose a framework of best management practices to minimize the negative environmental impacts of organic fertilizers and maximize their benefits in improving soil health and sustaining food production systems. Long-term application of composted manure and the buildup of soil C stocks may contribute to N retention as microbial or stabilized organic N in the soil while increasing the abundance of denitrifying microorganisms and thus reduce the emissions of N2O by favoring the completion of denitrification to produce dinitrogen gas. Future research using multi-omics approaches can be used to establish key biochemical pathways and microbial taxa responsible for N2O production under organic fertilization.

Assessing the Returns to Land and Greenhouse Gas Savings from Producing Energy Crops on Conservation Reserve Program Land.

Using land already enrolled in the Conservation Reserve Program (CRP) in the eastern region of the U.S. for producing energy crops for bioenergy while reducing land rental payments offers the potential for lowering the program costs, increasing returns to CRP landowners, and displacing greenhouse gas (GHG) emissions from fossil fuels. We develop an integrated modeling approach to analyze the combination of biomass prices and CRP land rental payment reductions that can incentivize energy crop production on CRP land and its potential to increase soil carbon stocks and displace fossil fuel emissions. We find that conversion of 3.4 million ha in the CRP can be economically viable at a minimum biomass price of $75 Mg-1 with full CRP land rental payment or at $100 Mg-1 with 75% of this land rental payment; this conversion can result in savings of 0.52 and 1.25 billion Mg CO2-eq in life-cycle emissions through the displacement of energy-equivalent fossil fuels and coal-based electricity, respectively, and an additional 0.11 billion Mg CO2-eq soil carbon sequestration relative to the status quo, with CRP left unharvested over the 2016-2030 period. The soil carbon debt due to the transition from unharvested CRP land to energy crops is short-lived and more than offset by the reduction in fossil fuel emissions. The net discounted benefits from producing energy crops on CRP land through a reduced need for government payments to maintain existing enrollment, higher returns to CRP landowners, and the value of the reduction in GHG emissions could be as high as $16-$30 billion by using them for cellulosic biofuels to displace gasoline and $35-$68 billion by displacing coal-based electricity over the 2016-2030 period if biomass prices are $75-$125 Mg-1 and land rental payments are reduced by 25%.