Carbon (C) sequestration in soils has been discussed as important climate mitigation option with the potential to generate negative emissions. Agriculture requires such negative emissions since some of their greenhouse gas emissions are unavoidable and require compensation to achieve net zero. Expectation of soils contribution to climate mitigation need to come down from theoretical assumptions to realistic estimates. In order to do so the limitations for soil C sequestration need to be analysed and discussed. Here we present a framework with case studies looking at limitations that are i) intrinsic due to the soils´ ability to stabilize SOC on mineral surfaces (C saturation) and the current state of high SOC stocks ii) constraints by net primary productivity and biomass availability, and iii) restrictions due to limited land area and increasing global demand for food, feed and fibre from agricultural production. For the start of this analysis we used data of the first German Agricultural Soil Inventory comprising more than 3000 sites. In total 34% of agricultural topsoils (0-10 cm depth) in Germany contain high SOC stocks with more than 4% soil organic matter. In particular soils with ground water influence and grassland land-use contain high SOC stocks, which need to be maintained first before further SOC accumulation can be achieved. C saturation was frequently discussed as reason for preventing further built up of stabilised SOC in C-rich soils. However, based on data from long-term field experiments and the national soil inventory we challenge the perception that C saturation is a limiting factor for soil C sequestration in our soils.

Biomass is required to maintain and enhance SOC. However, the quality and form of biomass influences the effectiveness for SOC formation. Roots are more important than above ground biomass. This shifts the view of C-management to below ground. Above ground biomass, such as straw, maybe harvested without harms to SOC stocks and used in industrial processes or converted to biochar. Strongly limited is the land area on which measures for SOC built-up can be implemented without compromising other ecosystem services. Avoiding leakage of greenhouse gas emissions due to measures for SOC sequestration are a major challenge. With the example of cover crops as agricultural management option we illustrate these limitations and discuss how some of the limitations for SOC sequestration could be removed.

How to cite: Don, A., Schneider, F., Heinemann, H., Seitz, D., Begill, N., and Poeplau, C.: What limits carbon sequestration in soils?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13898, https://doi.org/10.5194/egusphere-egu23-13898, 2023.

Carbon sequestration has become a buzz word and generates large expectations on ecosystems to take up carbon (C) from the atmosphere. These so-called negative emissions could compensate greenhouse gas emissions and help to stabilise the global climate.  However, the term C sequestration is often misleadingly used fostering biased conclusions and exaggerated expectations. C sequestration is defined as net uptake of C from the atmosphere. Soils have a particularly large potential to take up C yet many soils currently continuously loose C. Measures to build up soil C may only reduce soil C losses (C loss mitigation) but will not result in a net C sequestration. While checking 100 recent papers we found only 5% correctly using the term C sequestration. Even worse, 13% of the papers used C sequestration equivalent to soil C stocks. Here we call for a rigorous and concise use of the term C sequestration and discuss implications of misleading applications.

How to cite: Seidel, F., Don, A., Chenu, C., Seitz, D., Kätterer, T., and Leifeld, J.: Soil carbon-sequestration and climate mitigation – definitions and their implications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12579, https://doi.org/10.5194/egusphere-egu23-12579, 2023.

Fires belong to the most intensive disturbances in ecosystems, but do have different effects on the soil depending on their intensity and fuel materials. Taiga ecosystems contain significant reserves of potentially fire-prone materials, and as temperatures rise in the circumpolar region and precipitation patterns change, an increase in the frequency and intensity of fires is observed. In these fires, incomplete combustion processes result in the formation of black carbon (BC), which is known as a long-term carbon sink due to its chemical properties. As the majority of forest fires are ground fires burning at a rather low intensity in terms of duration and temperature, it is discussed that the BC species formed under these circumstances are chemically less stable than those formed at high temperatures and should therefore only be considered as temporary carbon sinks.

Here we studied the effects of low intensity ground fire shortly after the event and tracked changes in BC within the first four years after the fire event at the southern edge of the boreal forest. We analysed a fire transect running through the two main forest types of this region, focusing on the BC species that we could quantify using the BPCA method. Our results indicate a decline in BC after the fire within the four years of observations, which mainly mainly occurred for the low condensed BPCAs. This finding is independent of the forest typ. Since the precipitation within the experimental period was also negligible and only occurred in very small amounts, we exclude leaching as well as a possible significant aeolian losses, since the trees remained unaffected by the fire and covered the soil against strong wind. We therefore deduce that in situ degradation of the BC must have occurred.
Concluding, the general assumption that BC is a stable, long-term carbon sink needs to be questioned more critically. Together with other studies, our results show a quite fast decrease in the concentration of low-condensed BC species in soil over time, indicating a potential for degradation.

How to cite: Donnerhack, O., Liebmann, P., Maurischat, P., and Guggenberger, G.: Alteration of the Black Carbon pool shortly after a fire under dry conditions at the boreal southern border, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15783, https://doi.org/10.5194/egusphere-egu23-15783, 2023.

Climate-smart land management practices that replace shallow-rooted annual crop systems with deeply-rooted perennial plants can contribute to soil carbon sequestration. However, deep soil carbon accrual may be influenced by active microbial biomass and their capacity to assimilate fresh carbon at depth. Incorporating active microbial biomass, dormancy, and growth in microbially-explicit models can improve our ability to predict soil’s capacity to store carbon. But, so far, the microbial parameters that are needed for such modeling are poorly constrained, especially in deep soil layers. Here, we used a lab incubation experiment and growth kinetics model to estimate how microbial parameters vary along 240 cm of soil depth in profiles under shallow- (soy) and deeply-rooted (switchgrass) plants 11 years after plant cover conversion. We also assessed resource origin and availability (total organic carbon, 14C, extractable organic carbon, specific UV absorbance of K2SO4 extractable organic C, total nitrogen, total dissolved nitrogen) along the soil profiles to examine associations between soil chemical and biological parameters. Even though root biomass was greater and rooting depth was deeper under switchgrass than soy, resource availability and microbial growth parameters were generally similar between vegetation types. Instead, depth significantly influenced soil chemical and biological parameters. For example, resource availability and total and relative active microbial biomass decreased with soil depth. Decreases in the relative active microbial biomass coincided with increased lag time (response time to external carbon inputs) along the soil profiles. Even at a depth of 210–240 cm, microbial communities were activated to grow by added resources within a day. Maximum specific growth rate decreased to a depth of 90 cm and then remained consistent in deeper layers. Our findings show that >10 years of vegetation and rooting depth changes may not be long enough to alter microbial growth parameters, and suggest that at least a portion of the microbial community in deep soils can grow rapidly in response to added resources. Our study determined microbial growth parameters that can be used in microbially-explicit models to simulate carbon dynamics in deep soil layers.

How to cite: Min, K., Slessarev, E., Kan, M., Pett-Ridge, J., McFarlane, K., Oerter, E., and Nuccio, E.: Microbial growth kinetics under deeply- vs. shallow-rooted plants with soil depth profiles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2191, https://doi.org/10.5194/egusphere-egu23-2191, 2023.

How to cite: Janes-Bassett, V., Bassett, R., Phillipson, J., Towe, R., Henrys, P., and Blair, G.: Data science approaches for soil carbon mapping – a call for greater transparency, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2591, https://doi.org/10.5194/egusphere-egu23-2591, 2023.

Soils play a major role in mitigating climate change, as they sequester vast stocks of organic carbon and thereby buffer atmospheric CO2 concentrations. Inorganic nitrogen has been shown to have varying effects on soil C, sometimes promoting soil C buildup yet enhancing C loss in other cases. This contradiction may be a function of how soil C is stored, with C in particulate organic matter (POM) being much more susceptible to microbial decomposition than C in mineral-associated organic matter (MAOM). We have compiled a global dataset of over 200 papers which used a rigorous density fractionation methodology for quantifying stocks of C in POM and MAOM. Preliminary results suggest that inorganic N addition via deposition decreases organic C storage in MAOM, while not affected POM. Further, soil C storage in both pools increased with lower pH, countering our hypothesized negative effect of acidification on microbial activity.

How to cite: Willard, S. and Waring, B.: Quantifying the global impact of nitrogen deposition on persistent and vulnerable soil C pools, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16023, https://doi.org/10.5194/egusphere-egu23-16023, 2023.

Soil organic matter consists of components that differ in their specific stabilization/decomposition dynamics, and turnovers. From a simplified viewpoint, two fractions in particular can be distinguished from one another. Particulate organic matter (POM) is predominantly unbound in the soil matrix. The POM decomposition rate is defined by its inherent chemical recalcitrance and occlusion within aggregates. Mineral-associated organic matter (MAOM) is significantly smaller and is protected from decomposition by its adsorption to mineral surfaces. MAOM-C has therefore significantly longer mean residence times in soil than POM-C. Since the soil organic carbon (SOC) stocks are determined by C input/output balances, it is important to decrease C output quantities by increasing the long-term stabilization of OC within the MAOM-C stocks. However, MAOM-C cannot be enriched indefinitely. It is limited by the amount of clay and fine silt particle surfaces it can adsorb to and to the general land-use management. We investigated the validity of a POM-C/MAOM-C ratio indicator on 25 long-term field experiments in Central Europe to evaluate the sustainability of SOC management measures. We found that the POM-C/MAOM-C ratio might be used to assess the sustainability of agricultural management in before/after management change comparisons. Accordingly, a sharply increasing ratio indicates that the change in management does not adequately affect the long-term MAOM-C storage of soil. Moreover, we found a dependence between the POM-C/MAOM-C ratio and the MAOM-C sequestration deficits in soils, where arable soils with a POM-C/MAOM-C ratio indicator > 0.35 are close to MAOM-C saturation. If these observations are repeatable on further arable soils, the POM-C to MAOM-C ratio of 0.35 could be used as a management target to avoid organic over-fertilization and N loss, especially in coarse-textured soils. Thereby, the indicator might help to optimize SOC management and sequestration on arable soils and support climate change mitigation strategies.

How to cite: Just, C., Kögel-Knabner, I., and Wiesmeier, M.: The POM-C / MAOM-C ratio as a compliance indicator for sustainable soil organic carbon management of arable soils in Central Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16476, https://doi.org/10.5194/egusphere-egu23-16476, 2023.

The management of Soil Organic Carbon (SOC) is a critical component of both nature-based solutions for climate change mitigation and global food security. Agriculture has contributed substantially to a reduction in global SOC through cultivation, thus there has been renewed focus on management practices which minimize SOC losses and increase SOC gain as pathways towards maintaining healthy soils and reducing net greenhouse gas emissions. Mechanistic models are frequently used to aid in identifying these pathways due to their scalability and cost-effectiveness. Yet, they are often computationally costly and rely on input data that are often only available at coarse spatial resolutions. Herein, we build statistical meta-models of a multifactorial crop model in order to both (a) obtain a simplified model response and (b) explore the biophysical determinants of SOC responses to management and the geospatial heterogeneity of SOC dynamics across Europe. Using 35 years of multifactorial, spatially-explicit simulation data from the gridded Environmental Policy Integrated Climate-based Gridded Agricultural Model (EPIC-IIASA GAM), we build multiple polynomial regression ensemble meta-models for unique combinations of climate and soils across Europe in order to predict SOC responses to varying management intensities. We find that our biophysically-determined meta-models are highly accurate (R² = .97) representations of the full mechanistic model and can be used in lieu of the full EPIC-IIASA GAM model for the estimation of SOC responses to cropland management. Model stratification by means of climate and soil clustering improved the meta-model’s performance compared to the full EU-scale model. In regional and local validations of the meta-model predictions, we find that the meta-model accurately predicts broad SOC dynamics while it often  underestimates  the measured SOC responses to management.  Furthermore, we find notable differences between the results from the biophysically-specific models throughout Europe, which point to spatially-distinct SOC responses to management choices such as nitrogen fertilizer application rates and residue retention that illustrate the potential for these models to be used for future management applications.While more accurate input data, calibration, and validation will l be needed to accurately predict SOC change, we demonstrate the use of our meta-models for biophysical cluster and field study scale analyses of broad SOC dynamics with basically zero fine-tuning of the models needed. This work provides a framework for simplifying large-scale agricultural models and identifies the opportunities for using these meta-models for assessing SOC responses to management at a variety of scales.

How to cite: Ippolito, T., Balkovič, J., Skalsky, R., Folberth, C., and Neff, J.: Predicting Spatiotemporal Soil Organic Carbon Responses to Management Using EPIC-IIASA Meta-Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9063, https://doi.org/10.5194/egusphere-egu23-9063, 2023.

Soils are a significant store of organic carbon, globally storing an estimated 1550 Gt C to a depth of 1 metre. They are also substantial sources of greenhouse gas (GHG) emissions, contributing one-fifth of global CO₂ emissions, one-third of CH₄ emissions and two-thirds of N₂O emissions. Soil carbon in agricultural lands can represent a net sink or source of CO₂ depending on microclimate, cropping history and land management. Zero-tillage is an increasingly popular strategy to minimise soil erosion, increase biological activity and promote soil health. However, the extent to which zero-tillage reduces GHG emissions whilst increasing soil carbon, compared to other management strategies, is extensively debated, and represents a crucial knowledge gap in the context of climate change mitigation. Contrasting tillage strategies not only affect the stability and formation of soil aggregates but also modify the concentration and thermostability of soil organic matter (SOC) associated within them. Understanding the thermostability and carbon retention ability of aggregates under different tillage systems is essential to ascertain potential terrestrial carbon storage and greenhouse gas release.

Across Brazil, zero-tillage accounts for c. 45% of agricultural management, thereby making it a critical agricultural management practice throughout South America. This has been a popular management strategy since the 1940s and provides long-term field sites for which to understand and elucidate the key mechanisms which govern carbon retention/mineralization across different tillage managements. We measured GHG release and characterized the concentration and thermostability of SOC within various aggregate size classes under both zero and conventional tillage using Rock-Eval pyrolysis. The geometry of the pore systems was quantified by X-ray Computed Tomography and used to link soil structural characteristics to organic carbon preservation, thermostability and GHG release. Soil samples were collected from experimental fields across Brazil, which had been under zero-tillage for as little as one year up to 31 years, and from adjacent fields under conventional tillage.

Soils under zero-tillage had significantly increased pore connectivity whilst simultaneously decreasing interaggregate porosity, providing a potential physical mechanism for protection of SOC in the 0–20-cm soil layer. Changes in the soil physical characteristics associated with the adoption of zero-tillage resulted in improved aggregate formation compared to conventionally tilled soils, especially when implemented for at least 15 years. In addition, we identified a chemical change in composition of organic carbon to a more recalcitrant fraction following conversion to zero-tillage, suggesting aggregates were accumulating rather than mineralizing SOC. This study also revealed that, when combining all three GHG fluxes, potential global warming potential from zero-tilled soils was 50% smaller than that of conventionally tilled soils. These data reveal profound effects of different tillage systems upon soil structural modification, with important implications for the potential of zero-tillage to simultaneously increase carbon sequestration and decrease GHG release compared to conventional tillage, contributing to mitigating against climate change in these soils.

How to cite: Cooper, H., Lark, M., Sjogersten, S., and Mooney, S.: The role of zero-tillage in mitigating climate change in tropical soils, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2817, https://doi.org/10.5194/egusphere-egu23-2817, 2023.

Purpose

SOMPACS is a project recommended by EJP SOIL for funding under the 1st External Call "Towards Healthy, Resilient and Sustainable Agricultural Soils". The purpose of SOMPACS is to disclose management practices enriching soils with the organic matter pools that are most resistant to microbial decomposition. The project started in 2022 and will be implemented by a consortium of 12 research institutions from Poland, Germany, Ireland, Lithuania, UK, Italy and the USA until 2025.

Methods

Soil samples from eight long-term field experiments with different soil management and cultivation systems (conventional tillage vs. no-tillage; mineral vs. organic fertilization; management with and without catch crop; arable land vs. grassland; and cultivated vs. non-cultivated soils) will be investigated. Field experiments will include trials of increasing duration: 22-year (Lithuania); 26-year (Italy); 30-year (Poland, Ireland); 46-year (Poland); 54-year (Lithuania); 100-year (Poland), and 178-year Broadbalk experiment (UK). Experiments will also be carried out in production fields, where additives that stimulate root growth and provide very stable C (commercial humic products, biochar, and biogas digestate) will be applied. The effects of these additives on the content and properties of SOM will be investigated also in experimental plots accompanied by the incubation studies on the microbial decomposition of SOM and these additives. In parallel with soil sampling, plant productivity will be measured in all field experiments. Basic soil properties will be supplemented by the following investigations based on state-of-the-art approaches: SOM composition and stability by Py-GC-MS; aggregate size classes and C pools of increasing physicochemical protection; analysis of δ¹³C and δ¹⁵N of the separated SOM pools; microbiological properties (community-level physiological profiling, selected functional genes involved in C and N cycles, microbiome and mycobiome analyzes by next-generation sequencing, genetic diversity using terminal restriction fragment length polymorphism);  enzymatic activity; soil water retention and soil water repellency; mineral composition of clay fraction; soil structure stability. The most resistant SOM pool (humin) will be isolated by different methods (isolation vs. extraction) and examined for chemical composition and structure, using spectrometric and spectroscopic techniques (mass spectrometry, NMR, FTIR, EPR, UV-Vis-NIR, fluorescence). The C stocks in the soil profile will be evaluated and the extractable C in cold water will be determined to assess the potential leaching and microbial availability of C. Additionally, CO₂ emissions from the soil of chosen experiments will be measured directly under field conditions.

Results

In the first stage of the research, soil samples were collected from a depth up to 100 cm and the humin fraction from surface horizons was isolated for spectroscopic studies. Meantime, the impact of various types of cultivation on the yield was determined. 

Conclusions

A closer understanding of the persistence of SOC in top- and subsoil, as well as identifying management practices that contribute to minimizing greenhouse gas emissions, will show the possibilities of increasing the stable SOM pools, thus improving the potential of C sequestration. Understanding the impact of soil management on sustainable agricultural production and the environment, and in particular on climate change mitigation, should be widely promoted and put into practice.

Project partly financed by NBCR (project EJPSOIL/I/78/SOMPACS/2022).

How to cite: Weber, J., Leinweber, P., Kuzyakov, Y., Hewelke, E., Frąc, M., Hayes, M., Boguzas, V., Mielnik, L., Leahy, J. J., Norton, U., Gregory, A., Jerzykiewicz, M., Spaccini, R., Stępień, W., and Di Meo, V.: Soil management effects on soil organic matter properties and carbon sequestration (SOMPACS), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1101, https://doi.org/10.5194/egusphere-egu23-1101, 2023.

While the importance of soil organic carbon (SOC) in the global carbon cycle is well-established, many knowledge gaps remain related to how land management affects changes in SOC stocks, and protection mechanism of SOC. This is particularly the case for the tropics, as is clear from multiple recent meta-analyses on data related to soil biogeochemistry. In addition, while current knowledge on SOC dynamics is derived from the topsoil, studies on how land management affects subsoil OC properties are scarce.

Therefore, we studied how two types of land management affect SOC characteristics down to 1 m depth in two locations in southern Kenya. At one location (Embu), the effect of nutrient management on protection mechanisms of SOC is assessed, while at the second location (Mau Forest region) we study the effect of land use changes on soil biogeochemistry. The focus of this study is on assessing how land management affects SOC protection mechanisms (using carbon fractionation) and the contribution of microbial necromass to total SOC (using amino sugar analysis). In addition, multiple other soil properties, including microbial ecology, have been quantified to improve our understanding of the effect of land management on subsoil OC dynamics.

Using our results, we aim (i) to improve understanding of these processes and (ii) to use this knowledge to improve a mechanistic model simulating soil C and N dynamics along the soil profile.

How to cite: Van de Broek, M., Müller, C., Vanlauwe, B., and Six, J.: The effect of land management on soil organic carbon dynamics along the soil profile in a tropical region (southern Kenya), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14004, https://doi.org/10.5194/egusphere-egu23-14004, 2023.

In June of 2009, a long-term field experiment was conducted in the Shang-zhuang Experimental Station of China Agricultural University (CAU) at Haidian District, Beijing (N 40° 08′ 21″, E116°10′ 52″). The soil is calcareous fluvisol and the field located on an alluvial plain at an altitude of 51 m and a shallow groundwater level of 1-1.5 m. The region has a typical continental monsoon climate with an annual average air temperature of 11.6 °C and an annual average precipitation of 400 mm. The typical cropping system is winter wheat (from October each year to June of the following year) and summer maize (from June to September each year).

There are 6 treatments in the experiment: chemical fertilization with returned-straws both of wheat and maize was as experiment control (CK, or B0); 30, 60, and 90 t/ha Biochar were applied on the base of CK, coding as B30, B60, and B90; meanwhile, returning straw of wheat and maize but no chemical fertilizer (WM) and only wheat straw returning (W) were also as a treatment. After application of Biochar in June of 2009, all other agronomic practices were same as local real production way.

Although the field experiment is going on, we have got important conclusions till now, that are, (1) About 40% biochar lost from the 0-20 cm soil layer during the first 5 years after Biochar application; (2) No more than 25% biochar located in the aggregates >53 um in the 5^th year after Biochar application; (3) Biochar decreased the turnover of C in the returned-straw to SOC by 11% to 31% during the first 5 years after Biochar application, and the main decrease occurred from the wheat straw; (4) Biochar decreased soil labile organic carbon pool about 50%; (5) Priming effect caused by Biochar was positive during the first 3 years but negative during the 3 to 5 years after Biochar application; (6) Biochar decreased wheat-straw-derived SOC in larger aggregates, but accumulated more in smaller aggregates; (7) Biochar increased soil pedogenic carbonate content in the 0-20 cm soil layer during the 8 years after Biochar application; (8) Biochar amendment significantly increased subsoil pH (0.3−0.5 units) during the 10 years after biochar application; (9) The transported Biochar in subsoil acted as nuclei to precipitate pedogenic carbonate; (10) Biochar amendment enhanced soil inorganic carbon pool by up to 80% in the 2m soil profile. All these results have been published on international journals such as Science of the Total Environment, Soil Tillage Research, CATENA, Journal of Soils and Sediments, Journal of Integrative Agriculture, Agricultural Ecosystems & Environment, Soil Use Management, and Environmental Science & Technology.

How to cite: Li, G.: Long-term field experiment for exploring effects of Biochar on soil processes in winter wheat-summer maize cropping system in Northern China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2157, https://doi.org/10.5194/egusphere-egu23-2157, 2023.

The combination of biochar and nitrogen (N) addition has been proposed as a potential strategy to mitigate climate change by sequestering carbon (C), while simultaneously boosting crop yields. However, our current knowledge about how biochar and N addition alter mineralization of native soil organic C, which is referred to priming effects (PEs), is largely limited. To address these uncertainties, three C₃ biochar (pyrolyzing rice straw at 300, 550, and 800 ℃) and its combination with N fertilizer (urea) were incubated in a C₄-derived soils at 25 ℃ in the laboratory. Our results showed that all these 3 types of biochar with different addition rate caused positive priming of native soil organic C decomposition (up to +58.4%), but negative or no priming occurred in biochar bound N treatments. The maximum negative PEs (-14.5%) were observed in 300 ℃ biochar with 1% addition rate bound N (B₁300N) treatment. We find a negative correlation between the priming intensity and soil inorganic N content across all treatments. Furthermore, the biochar-induced PEs regulated by microbial biomass, fungi/bacteria ratio, and microbial metabolic efficiency. These findings indicated that eligible biochar used for blending traditional mineral fertilizer has a larger climate-change mitigation potential than biochar and fertilizer alone, while sustain relatively high crop yields.

How to cite: He, Y. and Zhou, X.: Nitrogen input alleviates the priming effect of biochar addition on soil organic carbon decomposition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4092, https://doi.org/10.5194/egusphere-egu23-4092, 2023.

Paddy field is one of the important sources for CH4 emissions, and can also be the carbon sink by soil carbon sequestration. In this study, a ten-year study was conducted to evaluate the long-term effects of biochar amendment on greenhouse gas emissions and soil carbon sequestration. Straw-derived biochar was applied once in 2012 at 24 and 48 t ha-1. The results showed that the annual CH4 emissions decreased by 20-50% as compared with no biochar amendment in the first four years after biochar addition. There were consistent CH4 emission reduction in the 10th year after biochar addition, with a reduction rate of 18-27%. The reduction of CH4 emission from paddy field was mainly related the improve of aeration, and the redution of the abundance ratio of methanogen/ methanotrophy. Biochar only increased N2O emissions in the first year after biochar addition due to additional nitrogen input caused by biochar addition. Biochar addition increased soil total organic content (TOC) in the first year after biochar addition, and the TOC contents showed no decrease after 10 years. Biochar addtion did not increase or decrease rice yield in a ten-year average. This indicated that biochar can be a useful measure for decreasing greenhouse gases emissions from subtropical paddy fields, and for increasing soil carbon sequestration in a long-term period. 

How to cite: Shen, J., Li, Y., Li, Z., Wang, J., and Wu, J.: Biochar amendment on greenhouse gases emissions and soil carbon sequestration in subtropical paddy fields: a ten-year study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16809, https://doi.org/10.5194/egusphere-egu23-16809, 2023.

Background: The application of composts to agricultural soil is a well-established practice with evidence showing multiple benefits within the field and beyond through changes in a number of soil functions. With soil health and function becoming increasingly important it is critical to understand the impact of soil management on function and changes in soil carbon, both within the root growth zone and, more importantly, within soil below the plough pan, an area of increasing interest.

Methods: A long-term compost application trial was established in 2004 under continuous spring barley with 3 differing compost application rates and a unamended control treatment. Following establishment in 2004 all treatments, except the control, received 50 t ha^-1 of municipal green compost, no amendments in 2005, low (35 t ha^-1), medium (100 t ha^-1), and high (200 t ha^-1), applications in 2006 and 2007 before continuous 35 t ha^-1 annual applications from 2008 to 2022. Plot structure is a randomised block design with soil being a sandy silt loam cultivated under minimum tillage practices. Intact soil cores were collected from both surface soils (~20mm) and subsoils (~300mm) for each plot in spring 2022 prior to compost application, cultivation, and sowing. Full water release data was collected including characterisation of the least limiting water range (LLWR), the available water beyond which mechanical impedance restricts root elongation (2.0 MPa). Additionally, soil resilience tests were performed to simulate trafficking with impacts on soil bulk density quantified and data on wet aggregate stability, visual evaluation of soil structure, and hydraulic conductivity were also collected.

Results: Within surface soils, medium and high compost application rates increased hydraulic conductivity when compared to control plots, the low compost application rate decreased hydraulic conductivity when compared to unamended plots. Surprisingly, within subsoil, compost application was found to significantly impact hydraulic conductivity (P<0.04) with hydraulic conductivity shown to be higher within the medium rate compost application treatment. A significant difference in water stable aggregates (WSA) within surface soils was observed between treatments (P<0.01) and a significant difference in soil bulk density (BD) between treatments (P<0.01) with BD decreasing with increasing compost levels. No significant differences in sub soil bulk density were observed between treatments (P=0.131) however WSA was found to be significantly different in sub soils between treatments (P<0.01). Data on carbon, soil water release characteristics, and nutrient status will also be presented highlighting the long-term benefits of compost application.

Conclusions: Results show that the surface application of compost under minimum tillage practice and the production of continuous spring barley can influence subsoil functions with wider ecosystem benefits.

How to cite: Loades, K., Barclay, A., Boldrin, D., Caul, S., Giles, M., and Hanlon, M.: Impacts on surface and sub soil physical properties under minimum tillage through long-term compost application, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7401, https://doi.org/10.5194/egusphere-egu23-7401, 2023.

Enhanced silicate weathering (ESW) is an innovative technique to leverage natural processes which usually operate over millions of years to potentially replenish nutrients and carbon (C) in soil. ESW involves applying pulverized silicates to increase reactive mineral surfaces which in turn may speed-up the weathering and scale to aid in global CO₂ removal. However, current studies supporting ESW has been relying on theoretical estimates and short-term laboratory experiments whose results are difficult to extrapolate to the field. Also, many studies have focused on inorganic C chemistry while soil is a rich medium that mediates a multitude of chemical and biological processes, many of which are not well studied but may play an important role in controlling ESW. To address this gap, the Working Lands Innovation Center (WLIC) Project was launched in 2019 for a field scale test, and three commercial amendments (compost, biochar, and silicate powder—meta-basalt) have been applied yearly with a full factorial design in a 2.07 ha corn field at the Campbell Tract research facility located on the UC Davis campus. My project within WLIC evaluates the impact of ESW on soil surface C pools related to microbial processes and its potential synergies with traditional organic amendments. We hypothesized that co-applying organic amendments plus pulverized silicate minerals will: 1) increase microbial biomass with distinct microbial community composition; and 2) increase the formation of stable carbon pools (e.g., mineral associated organic matter) relative to only silicate applied soil. To test this, we sampled soils from all possible amendment combinations at pre-, and post-harvesting seasons in 2021 and 2022. We completed a suite of analyses to monitor temporal changes of soil chemistry, multiple C pool sizes, and microbial parameters. Here, we will examine the causal mechanisms that explain how adding extra C with silicates may change microbial environments and carbon pool dynamics over a two-year period. Our findings will provide critical information whether natural soil processes, such as rock weathering and soil organic C stabilization, can be engineered (and accelerated) for management purposes at agricultural field scale.

How to cite: Sohng, J., Holzer, I., Goertzen, H., Schmidt, R., and Scow, K.: Influence of enhanced silicate weathering on microbial processes and soil carbon formation in agricultural soil, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14924, https://doi.org/10.5194/egusphere-egu23-14924, 2023.

How to cite: Schepens, J. and Koopmans, C.: Evaluating carbon sequestration of different alternatieve management practices in the Netherlands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16990, https://doi.org/10.5194/egusphere-egu23-16990, 2023.