Enhance Soil Carbon Sequestration Research Articles

Development of Meso- and Macro-Pore Carbonization Technology from Biochar in Treating the Stumps of Representative Trees in Taiwan

This study uses the tree stumps of the three representative trees in Taiwan (Leucaena leucocephala, Syzygium samarangense, and Ziziphus jujuba) as the material source and recyclable oyster shell powder as an activator. A carbonization process for upgrading and recycling the tree stumps was developed with our homemade, digital-controlled, energy-saving carbonization system. First, the tree stumps are carbonized at a medium temperature of 500 °C and then heated to 900 °C for high-temperature carbonization, followed by the activation procedure as required. With our method, we can produce biochar with a high proportion of fixed carbon and a high proportion of meso- and macropores while maximizing the yield of wood vinegar. The specific surface area of the meso- and macropores can reach up to 70 m2/g or more. The effect of different activation materials on the pore characteristics and specific surface area of biochar was carefully examined. It was found that both KOH and oyster shell powder is the ideal activator for producing biochar with a high proportion of meso- and macropores. The FTIR spectrum, CEC, and contents of the ordinary elements and heavy metals of the biochar were also reported. It is clear from the FTIR data that the absorption peaks of the overall spectrum of the three types of biochar after carbonization at high temperature are cleaner than those of biochar carbonized at low temperature. This research can promote the recycling of agricultural residues, enhance soil carbon sequestration, preserve fertilizers, and suppress diseases and pests, moving towards approaching the goal of net-zero carbon emissions.

In situ formed CaSO4 on waste dander biochar to inhibit the mineralization of soil organic carbon

In order to reduce CO2 emissions, as well as realize the resource utilization of waste dander (WD) and the goal of international “peak carbon dioxide emissions” and “carbon neutrality”, Biochar was prepared with WD via pyrolysis technology, achieving CaSO4 in situ generated on its surface, which could be used to inhibit soil organic carbon (SOC) from mineralizing and enhance soil carbon sequestration ability. The characterization results showed that the unstable carbon (C) structures as well as more conjugated structures were generated on Ca-BC, obtaining an increased C sequestration of Ca-BC to 21.70 %. With the application of Ca-BC, the mineralization rate of SOC was reduced to 0.451 mg CO2/(g·d), and the soil moisture content, pH and TOC content were increased to 45.48 %, 7.96 and 47.19 %. In addition, the bioinformatics analysis and redundancy analysis revealed that the application of Ca-BC promoted bacteria to convert into the stable C-dominant phyla (Firmicutes).

The Role of Soil Salinization in Shaping the Spatio-Temporal Patterns of Soil Organic Carbon Stock

Soil salinization is closely related to land degradation, and it is supposed to exert a significant negative effect on soil organic carbon (SOC) stock dynamics. This effect and its mechanism have been examined at site and transect scales in previous studies while over a large spatial extent, the salinity-induced changes in SOC stock over space and time have been less quantified, especially by machine learning and remote sensing techniques. The main focus of this study is to answer the following question: to what extent can soil salinity exert an additional effect on SOC stock over time at a larger spatial scale? Thus, we employed the extreme gradient boosting models (XGBoost) combined with field site-level measurements from 433 sites and 41 static and time-varying environmental covariates to construct methods capable of quantifying the salinity-induced SOC changes in a typical inland river basin of China between the 1990s and 2020s. Results showed that the XGBoost models performed well in predicting the soil electrical conductivity (EC) and SOC stock at 0–20 cm, with the R2 value reaching 0.85 and 0.81, respectively. SOC stock was found to vary significantly with increasing soil salinity following an exponential decay function (R2 = 0.27), and salinity sensitivity analysis showed that soils in oasis were expected to experience the largest carbon loss (−137.78 g m−2), which was about 4.84, 14.37, and 25.95 times higher than that in the saline, bare, and sandy land, respectively, if the soil salinity increased by 100%. In addition, the decrease in the soil salinity (−0.32 dS m−1) from the 1990s to the 2020s was estimated to enhance the SOC stock by 0.015 kg m−2, which contributed an additional 10% increase to the total SOC stock enhancement. Overall, the proposed methods can be applied for quantification of the direction and size of the salinity effect on SOC stock changes in other salt-affected regions. Our results also suggest that the role of soil salinization should not be neglected in SOC changes projection, and soil salinization control measures should be further taken into practice to enhance soil carbon sequestration in arid inland river basins.

Deciphering the Effectiveness of Humic Substances and Biochar Modified Digestates on Soil Quality and Plant Biomass Accumulation

The effective use of digestate as exogenous organic matter to enhance soil carbon sequestration depends on the balance between labile and recalcitrant organic carbon, which is influenced by the type of feedstock, the fermentation process, and the fraction (liquid, solid) of the fermented product used. In this work, in order to change the ratio of labile to stable carbon in the resulting fertiliser, the digestate was mixed with organic carbon-rich supplements: biochar and Humac (a humic acid-rich substance). The pot experiment was carried out under controlled conditions with maize (Zea mays L.) in soil amended with the digestate (D), which was incubated with Humac (H), biochar (B), or a combination of both (D + B + H) before the application. Digestate enriched with Humac showed improved short-term nutrient (carbon, phosphorus, nitrogen) transformation, as indicated by soil enzyme activity and the highest maize biomass production of. Total carbon content, C:N ratio, short-term respiration activity, and nitrification were most enhanced by digestate enriched with either biochar or combined biochar + Humac). Long-term nitrogen mineralization was mostly enhanced by digestate + Humac, as indicated by amino-acid-induced respiration and urease activity. Short-term positive effects of digestate + biochar (eventually + Humac) on catabolism were proven, whereas their long-term effects on nutrient mineralization were negative (i.e., biochar-mediated immobilization, sequestration), which should be the focus of further research in future.

Quantifying surface soil organic carbon distribution globally during the COVID-19 pandemic using satellite data

Soil organic carbon (SOC) is an important soil parameter of agricultural soils, ensuring food security and agricultural sustainability. It plays a critical role in the global carbon budget and carbon sequestration. Spatial mapping of SOC can help develop sustainable management approaches to enhance soil carbon sequestration and mitigate greenhouse gas emissions and adverse environmental effects. However, quantifying Spatio-temporal distributions of SOC at the global level is complex because of high land heterogeneity and several climatic and hydrologic influential parameters. The main goal of this study was to quantify the annual global SOC change focusing on cropland using daily soil moisture active passive (SMAP) satellite SOC data. The specific objectives of this study were to assess annual SOC change globally, quantify the annual SOC distribution before and during the COVID-19 pandemic, and evaluate change in SOC on cropland during the study period. Results showed an increase of annual SOC on cropland in several countries in 2020 compared to 2019, which can be attributed to the direct and indirect impact of partial and complete lockdowns due to the COVID-19 pandemic. The change in SOC between 2015 and 2019 was considerably different from the SOC change between 2019 and 2020. For example, between 2019 and 2015, 45.6% of the global area showed a decrease in SOC 0 to 25 g C m−2 and 30.4% area showed an increase in SOC 0 to 25 g C m−2. However, between 2020 and 2019, 11.4% of the global area showed a decrease in SOC 0 to 25 g C m−2, and 55.4% area showed an increase in SOC 0 to 25 g C m−2. There is a good relationship between lockdown measures and improvement in SOC, as 48 out of 50 highly infected countries showed increased SOC in 2020 than in 2019. This study suggests better land use management practices can help enhance carbon sequestration and improve soil health.

The role of cover crops for cropland soil carbon, nitrogen leaching, and agricultural yields – a global simulation study with LPJmL (V. 5.0-tillage-cc)

Abstract. Land management practices can reduce the environmental impact of agricultural land use and production, improve productivity, and transform cropland into carbon sinks. In our study we assessed the biophysical and biogeochemical impacts and the potential contribution of cover crop practices to sustainable land use. We applied the process-based, global dynamic vegetation model LPJmL (Lund–Potsdam–Jena managed Land) V. 5.0-tillage-cc with a modified representation of cover crops to simulate the growth of grasses on cropland in periods between two consecutive main crops' growing seasons for near-past climate and land use conditions. We quantified simulated responses of agroecosystem components to cover crop cultivation in comparison to bare-soil fallowing practices on global cropland for a period of 50 years. For cover crops with tillage, we obtained annual global median soil carbon sequestration rates of 0.52 and 0.48 t C ha−1 yr−1 for the first and last decades of the entire simulation period, respectively. We found that cover crops with tillage reduced annual nitrogen leaching rates from cropland soils by medians of 39 % and 54 % but also the productivity of the following main crop by an average of 1.6 % and 2 % for the 2 analyzed decades. The largest reductions in productivity were found for rice and modestly lowered ones for maize and wheat, whereas the soybean yield revealed an almost homogenously positive response to cover crop practices replacing bare-soil fallow periods. The obtained simulation results of cover crop with tillage practices exhibit a good ability of the model version to reproduce observed effects reported in other studies. Further, the results suggest that having no tillage is a suitable complementary practice to cover crops, enhancing soil carbon sequestration and the reduction in nitrogen leaching, while reducing potential trade-offs with the main-crop productivity due to their impacts on soil nitrogen and water dynamics. The spatial heterogeneity of simulated impacts of cover crops on the variables assessed here was related to the time period since the introduction of the management practice as well as to environmental and agronomic conditions of the cropland. This study supports findings of other studies, highlighting the substantial potential contribution of cover crop practices to the sustainable development of arable production.

Diverging patterns at the forest edge: Soil respiration dynamics of fragmented forests in urban and rural areas.

As urbanization and forest fragmentation increase around the globe, it is critical to understand how rates of respiration and carbon losses from soil carbon pools are affected by these processes. This study characterizes soils in fragmented forests along an urban to rural gradient, evaluating the sensitivity of soil respiration to changes in soil temperature and moisture near the forest edge. While previous studies found elevated rates of soil respiration at temperate forest edges in rural areas compared to the forest interior, we find that soil respiration is suppressed at the forest edge in urban areas. At urban sites, respiration rates are 25% lower at the forest edge relative to the interior, likely due to high temperature and aridity conditions near urban edges. While rural soils continue to respire with increasing temperatures, urban soil respiration rates asymptote as temperatures climb and soils dry. Soil temperature- and moisture-sensitivity modeling shows that respiration rates in urban soils are less sensitive to rising temperatures than those in rural soils. Scaling these results to Massachusetts (MA), which encompasses 0.25Mha of the urban forest, we find that failure to account for decreases in soil respiration rates near urban forest edges leads to an overestimate of growing-season soil carbon fluxes of >350,000Mg C. This difference is almost 2.5 times that for rural soils in the analogous comparison (underestimate of <143,000Mg C), even though rural forest area is more than four times greater than urban forest area in MA. While a changing climate may stimulate carbon losses from rural forest edge soils, urban forests may experience enhanced soil carbon sequestration near the forest edge. These findings highlight the need to capture the effects of forest fragmentation and land use context when making projections about soil behavior and carbon cycling in a warming and increasingly urbanized world.

Straw return in paddy field alters photodegradation of organic contaminants by changing the quantity rather than the quality of water-soluble soil organic matter

Straw return, an important agricultural management practice, is worldwide adopted to enhance soil carbon sequestration and soil fertility. Although water-soluble soil organic matter (WSOM) in paddy field is known to affect the photodegradation of organic contaminants, how straw return regulates the photosensitization of WSOM by changing its properties remain unclear. Here, we determined the temporal variations in the content, chemical characteristics, and photosensitizing ability of WSOM after wheat straw return in a wheat-rice rotation system using optical spectroscopy and steady-state photodegradation tests. After straw return, the WSOM content first increased to a maximum and then gradually decreased to pre-return level at day 90. Nevertheless, the relative abundance of humic-like components in WSOM was not shifted by straw return, and protein-like component in WSOM just showed a slight decrease at day 45. All the WSOM samples inhibited sulfamethoxazole (SMX) photodegradation by light filtering, reactive species quenching and other mechanisms, while promoted diuron (DIU) degradation via reacting with •OH, 1O2 and excited triplet WSOM. The photodegradation of SMX and DIU was little affected by straw return changing WSOM composition and photochemical activity. However, straw return could decelerate SMX and DIU photodegradation by elevating WSOM content in a relatively short-term. This study emphasizes that straw return may reduce the photodegradation of organic contaminants by increasing WSOM concentration instead of altering WSOM chemical characteristics.

Rice straw carbon mineralization is affected by the timing of exogenous glucose addition in flooded paddy soil

Crop straw amendment is a farm management approach for enhancing soil carbon sequestration. Moreover, crop straw residue decomposition rates are affected by irregular exogenous organic carbon secretion or metabolism such as that from root exudates or microbial metabolites. To quantify the mineralization rate of straw residue affected by exogenous organic carbon addition and elucidate the underlying mechanisms, in this study, a total of 0.5 g 13C- labeled dry rice straw was added into pre-incubated soil (equivalent to 200 g dry soil) and incubated for 20 days. Then,1mL of a solution with 50 mg glucose was added only once into the soil on day 21 (G(1a)) or day 35 (G(1b)), twice with 25 mg glucose every 14 days (G(2)) or four times with 12.5 mg glucose every 7 days (G(4)). Soil without glucose addition served as a control. The frequent addition of glucose induced higher soil respiration than that induced by only one addition, and stimulated the mineralization of rice straw carbon compared to that in the control in the following order: G(4) (14.6%) > G(1a) (12.7%) > G(2) (12.3%) > G(1b) (11.2%) = control (11.2%). In general, frequent addition of glucose decreased the soil redox potential (Eh) and fungi to bacteria ratio. Structural equation modeling analysis showed that the rice straw carbon mineralization rate was positively correlated with the 13C-dissolved organic carbon (13C-DOC) content and negatively regulated by Eh. Microbial bioactivity exerted indirect positive effects on rice straw carbon mineralization by influencing the 13C-DOC content. A decrease in the fungi to bacteria ratio induced by frequent addition of glucose improved the microbial bioactivity and enhanced rice straw carbon mineralization. Our results suggested that single exogenous organic carbon additions may underestimate residue or soil organic matter decomposition rates in the field.

Soil carbon sequestration and soil quality change between no-tillage and conventional tillage soil management after 3 and 11 years of organic farming

ABSTRACT The aim of this study was to evaluate the long-term effect of no-tillage systems in organic farming on soil carbon sequestration and soil quality, which is associated with nutrient availability. The experiment was conducted on a low-input organic farm since 2009, using a randomized complete block design with four replications. Two treatments, conventional tillage (CT) and no-tillage (NT), were tested. Soil samples were obtained after crops were harvested in 2012 and 2020 from four different soil depth layers between 0‒30 cm, and the physical and chemical properties of soil samples were measured. Data were analyzed using ANOVA with Tukey tests (α = 0.05), while the correlation was analyzed based on Pearson correlation. At 0–2.5 cm and 2.5–7.5 cm depths, soil bulk density (BD) in the NT treatment was 30% and 8% lower, respectively, in 2012, and 25% and 14% lower, respectively, in 2020 compared with the CT treatment. The NT treatment could enhance the soil organic carbon (SOC) better than CT treatment at the same depth, sequestering a greater amount of carbon in the soil. Compared with the CT treatment, SOC concentration in the NT treatment was 76% and 12% higher, respectively, in 2012, and 103% and 38% higher, respectively, in 2020. In 2012, the SOC stock showed a significant difference between NT and CT treatments only at the 0–2.5 cm soil depth, with the value being 24% higher in the NT treatment than in the CT treatment. However, in 2020, the SOC stock was 50% and 19% higher in the NT treatment than in the CT treatment at 0–2.5 cm and 2.5–7.5 cm depths, respectively. The SOC also could significantly expand cation exchange capacity (CEC) and the availability of some nutrients in the soil. However, the relationship between was weak in 2020. Moreover, the NT treatment showed better progression of humification than CT. Finally, long-term NT systems in low-input organic farming could reduce soil bulk density and enhance soil carbon sequestration and soil quality. However, this system must be complemented with the conventional approach to maintain nutrient balance for long-term management.

Prediction Potential of Remote Sensing-Related Variables in the Topsoil Organic Carbon Density of Liaohekou Coastal Wetlands, Northeast China

Wetland ecosystems contain large amounts of soil organic carbon. Their natural environment is often both at the junction of land and water with good conditions for carbon sequestration. Therefore, the study of accurate prediction of soil organic carbon (SOC) density in coastal wetland ecosystems of flat terrain areas is the key to understanding their carbon cycling. This study used remote sensing data to study SOC density potentials of coastal wetland ecosystems in Northeast China. Eleven environmental variables including normalized difference vegetation index (NDVI), difference vegetation index (DVI), soil adjusted vegetation index (SAVI), renormalization difference vegetation index (RDVI), ratio vegetation index (RVI), topographic wetness index (TWI), elevation, slope aspect (SA), slope gradient (SG), mean annual temperature (MAT), and mean annual precipitation (MAP) were selected to predict SOC density. A total of 193 soil samples (0–30 cm) were divided into two parts, 70% of the sampling sites data were used to construct the boosted regression tree (BRT) model containing three different combinations of environmental variables, and the remaining 30% were used to test the predictive performance of the model. The results show that the full variable model is better than the other two models. Adding remote sensing-related variables significantly improved the model prediction. This study revealed that SAVI, NDVI and DVI were the main environmental factors affecting the spatial variation of topsoil SOC density of coastal wetlands in flat terrain areas. The mean (±SD) SOC density of full variable models was 18.78 (±1.95) kg m−2, which gradually decreased from northeast to southwest. We suggest that remote sensing-related environmental variables should be selected as the main environmental variables when predicting topsoil SOC density of coastal wetland ecosystems in flat terrain areas. Accurate prediction of topsoil SOC density distribution will help to formulate soil management policies and enhance soil carbon sequestration.

Manganese limitations and the enhanced soil carbon sequestration of temperate rainforests

Manganese (Mn) has been identified as a regulatory bottleneck in carbon (C) turnover because of its role as an enzymatic co-factor in the oxidative decomposition of C by Mn-peroxidase (MnP). We tested this limit on decay using forest soils from coastal British Columbia with contrasting Mn concentrations. Moderately weathered soils (Brunisols) had an average 3.6-fold increase in MnP activity within the upper soil profile in comparison to highly weathered Podzols. Ordination of the Agaricomycete fungal community, which are responsible for MnP production, confirmed significant differences in assemblages between soil types for saprotrophic fungi, particularly species within Agaricales, Trechisporales and Auriculariales. Ectomycorrhizal fungi of Pseudotsuga menziesii were equally aligned with soil type and select taxa more abundant on Brunisols may have supplemented MnP activity. A laboratory incubation with an Mn amendment produced significant interactions in MnP activity by soil type. Surprisingly, MnP activity of both Brunisol substrates declined substantially with an amendment (− 56 and − 40% for forest floor and mineral soil, respectively), in contrast to Podzols (− 30 and + 26%, respectively). This inhibitory response was linked to considerable uptake of the added Mn in Brunisols, presumably by saprotrophic fungi, and underscores how Mn likely operates directly on fungi as a regulator of gene transcription for MnP production. Our study highlights a new perspective concerning the abiotic drivers underpinning the expansive soil C stocks across perhumid temperate rainforests of the Pacific Northwest.

Projected soil organic carbon loss in response to climate warming and soil water content in a loess watershed

BackgroundSoil organic carbon (SOC) plays a crucial role in the global carbon cycle and terrestrial ecosystem functions. It is widely known that climate change and soil water content (SWC) could influence the SOC dynamics; however, there are still debates about how climate change, especially climate warming, and SWC impact SOC. We investigated the spatiotemporal changes in SOC and its responses to climate warming and root-zone SWC change using the coupled hydro-biogeochemical model (SWAT-DayCent) and climate scenarios data derived under the three Representative Concentration Pathways (RCPs2.6, 4.5, and 8.5) from five downscaled Global Climate Models (GCMs) in a typical loess watershed––the Jinghe River Basin (JRB) on the Chinese Loess Plateau.ResultsThe air temperature would increase significantly during the future period (2017–2099), while the annual precipitation would increase by 2.0–13.1% relative to the baseline period (1976–2016), indicating a warmer and wetter future in the JRB. Driven by the precipitation variation, the root-zone SWC would also increase (by up to 27.9% relative to the baseline under RCP4.5); however, the SOC was projected to decrease significantly under the future warming climate. The combined effects of climate warming and SWC change could more reasonably explain the SOC loss, and this formed hump-shaped response surfaces between SOC loss and warming-SWC interactions under both RCP2.6 and 8.5, which can help explain diverse warming effects on SOC with changing SWC.ConclusionsThe study showed a significant potential carbon source under the future warmer and wetter climate in the JRB, and the SOC loss was largely controlled by future climate warming and the root-zone SWC as well. The hump-shaped responses of the SOC loss to climate warming and SWC change demonstrated that the SWC could mediate the warming effects on SOC loss, but this mediation largely depended on the SWC changing magnitude (drier or wetter soil conditions). This mediation mechanism about the effect of SWC on SOC would be valuable for enhancing soil carbon sequestration in a warming climate on the Loess Plateau.

Soil carbon and plant richness relationships differ among grassland types, disturbance history and plant functional groups

Understanding the relationship of soil carbon storage and species diversity in grasslands can provide insights into managing these ecosystems. We studied relationships among soil C and plant species richness within ~ 9700 ha of grasslands in Colorado, US. Using 141 grassland transects, we tested how soil C was related to plant species richness, grassland type, soil texture, and prairie dog presence. Soil C was significantly, positively related to plant species richness, while native perennial graminoid species richness exhibited an even stronger positive relationship. However, the relationship of soil C and plant richness was not found in all three grassland types studied, but instead was unique to the most common grassland type, mixed grass prairie, and absent from both xeric tallgrass and mesic tallgrass prairie. The presence of a single indicator species, Andropogon gerardii, showed a significant, positive relationship with soil carbon. Our best possible model explained 45% of the variance in soil C using species richness, grassland type, and their interaction. Surprisingly, soil C was negatively related to soil clay, suggesting that surface clays amplify evaporation and water runoff rather than protecting soil organic matter from decomposition. Soil C was negatively related to prairie dog presence, suggesting that prairie dogs do not enhance soil carbon sequestration; in fact, prairie dog occupied sites had significantly lower soil C, likely related to loss of topsoil from prairie dog colonies. Our results suggest that management for species richness provides the co-benefit of soil C storage, and high clay and prairie dog disturbance compromises both.

Short term fallow and partitioning effects of green manures on wheat systems in East African highlands

• Short term fallows enhance productivity, improve soil fertility and serve dual purpose in crop-livestock systems. • Green manuring increased wheat grain yield by 18–26 % over mineral fertilizers. • Root biomass of green manures alone increased yield of subsequent crop by 25 %. • Green manuring improved soil water, soil pH, organic carbon and nutrients. • Residual effect of green manuring compensates 33 % of N demands of wheat. Soil fertility depletion is a major constraint of smallholder farming in sub-Saharan Africa. We tested the aftereffects of green manures, namely vetch (Vicia sativa L.), lupin (Lupinus polyphyllus L.), and lablab ( Lablab purpureus L.) incorporated into the soil compared to three fertilizer levels (0/0, 23/0, and 78/20 kg N/P ha −1 ) and evaluated their effect on soil fertility status and wheat yield in acidic Nitisols of southern Ethiopia, for three consecutive years (2017–2019). The treatments were laid out in a randomized complete block design with three replications. In 2017 and 2018, green manures were sown in March and April, respectively, using short rains and incorporated into the soil during late flowering stage, either (i) the whole shoot and root biomass were plowed under, (ii) shoot biomass was transferred to non-treated plots or (iii) only the below ground root biomass was used. Wheat was sown during long rains during the same growing season a month after the incorporation of green manures. In 2019, wheat was grown on the residual plots with the application of an additional 64/20 kg N/P ha −1 . Results revealed that in 2017 and 2018 the application of vetch and lupin green manure resulted in grain yield advantages of 49 and 32 % and 34 and 19 %, respectively, over 0/0 and 23/0 kg N/P ha −1 , though it produced less grain yield compared to higher fertilizer rates. In 2019, the addition of vetch and lupin whole biomass treatments gave significantly higher wheat yield over fertilizer treatments, with yield advantages of 18–26 %. Similarly, root biomass only also produced a significantly higher yield than fertilized plots. The yield benefits from green manures were due to improved soil water content, improved P-availability, significantly increased exchangeable K, Ca, and Mg, and increased pH by about 0.5 units. The residual effect of green manures could compensate for up to 33 % of the recommended rate of 78 N kg ha −1 . We conclude that niche-based integration of green manures could improve yield, enhance soil carbon sequestration and sustain crop-livestock systems, whereby the above ground biomass could serve as quality livestock feed without compromising soil fertility benefits.

Conservation Agriculture Mitigates the Effects of Climate Change

Intensive tillage based conventional agriculture have high global warming potential. Alternative to this, conservation agriculture (CA) systems utilize soils for the production of crops by reducing excessive tillage, maintaining crop residue on the soil surface, and adoption of crop rotations. The paper attempts to review the findings of CA based experiments under different cropping systems within and outside of the country. It has been found that CA increases and sustains the crop productivities, mitigates green house gas emissions from agriculture by enhancing soil carbon sequestration, improving soil nutrient status and water use efficiencies, and reducing fuel consumption. Mainstreaming of CA systems in Nepal is hindered by its knowledge gap, inadequate farm machineries and tools, small holdings, poor infrastructures, and lack of CA friendly policy support. Therefore, there is an urgent need to test, verify and scale-out the CA based technologies by Nepal Agricultural Research Council (NARC) across the different agro-ecologies through farmer-centered partnership among the international institutions, public and private sector of Nepal.&#x0D;

Organic vegetable farming system enhancing soil carbon sequestration in Bali, Indonesia

Climate change as an implication of global warming due to the influence of increasing concentrations of greenhouse gases in the atmosphere has become an important issue in recent decades. Organic farming plays an important role in mitigating climate change by reducing atmospheric greenhouse gas emissions through increased soil carbon sequestration. This study was designed to compare soil carbon sequestration levels between conventional and organic vegetable farming fields in Bali, Indonesia. Soil samples were taken from organic fields and conventional fields in pairs. Variables of soil organic carbon, soil labile carbon, and soil bulk density are measured. Vegetable yields were estimated by fresh weights from a quadrant of 45 plants (1.12 m2) in each farming system, which is then converted to the fresh weight per hectare. The results from soil analysis indicate that organic farming leads to soil with significantly higher soil carbon storage capacity than conventional farming. The labile C fraction shows a more significant increase compared to total C. Organic farming can increase by 1.13 tons C per hectare per year compared with the conventional farming system. The use of manure compost as an alternative in vegetable fields of Bali has resulted in increased soil organic carbon storage and gross benefits for farming. Although more research is needed on the actual emissions of CO2 gas from organic and conventional farming, this research can be used as an early indication that organic vegetable farming system can increase the mitigation of global warming, and build sustainable agriculture in Bali, Indonesia.

Effects of biochar aging in the soil on its mechanical property and performance for soil CO2 and N2O emissions

Biochar application into the soils has been reported to have huge carbon sequestration potential, although it remains unclear that how the biochar aging in the soil affects its mechanical properties and soil CO2 and N2O emissions. This work assessed the impact of soil biochar aging on its physicochemical properties, microbiota community in the biochar, and soil CO2 and N2O emissions. Various characterizations (e.g., SEM-EDS, XRD, and FTIR) of fresh and aged biochar indicated that soil minerals accumulated on the biochar during the field aging process, forming organo-mineral complexes and blocking the cracks and channels on the biochar. The measured hardness and compressive strength of aged biochar were significantly higher than those of fresh biochar, consistent with the presence of soil minerals on the aged biochar. The soil CO2 and N2O emissions were significantly decreased after the addition of aged biochar particles, as compared to fresh biochar particles. This was probably because that the improved mechanical properties could inhibit the fragmentation of biochar particles, reducing the release of labile fractions from the biochar and the subsequent CO2 and N2O emissions. Moreover, the presence of CO2-fixing bacteria (e.g., Chloroflexi) and inhibited nitrification and ammonia oxidation in aged biochar particles might also reduce CO2 and N2O emissions. These findings suggest aged biochar particles with improved physical stability to the soil could enhance soil carbon sequestration and greenhouse gas emission reduction.

Changes in Acidic Soil Chemical Properties and Carbon Dioxide Emission Due to Biochar and Lime Treatments

To mitigate global climate change and simultaneously increase soil productivity, the use of biochar in agriculture can be a modern agro-technology that can help in reducing greenhouse gas emissions, enhancing soil carbon sequestration, and ultimately increasing crop yield. This study aimed to evaluate the effects of biochar and lime application on the chemical properties of acid soil and the emission of CO2. A 60-day incubation study was conducted with eleven treatments (T) in which two different biochar produced from rice husk (RHB) and oil palm empty fruit bunches (EFBB) at two rates (10 and 15 t ha−1) and on three rates of dolomitic limestone (100%, 75%, and 50%), recommended rate of NPK and a control (no amendment). The result showed that biochar and lime significantly increased soil pH, available P, and decreased exchangeable Al compared to the control. The pH increase was 44.02% compared to the control treatment on day 15, and the available P was found to be 22.44 mg kg−1 on day 30 from Treatment 7 (75% lime + 15 t ha−1 RHB). The cumulative CO2 emission from T7 was 207.40 μmol CO2 m−2 that decreased 139.41% compared to the control. Our findings conclude that RHB with 75% lime has more potential than EFBB to increase nutrient availability and reduce the emission of CO2 in acid soil.

Biogas residues in the battle for terrestrial carbon sequestration: A comparative decomposition study in the grassland soils of the Greater Region

The recycling of biogas residues resulting from the anaerobic digestion of organic waste on agricultural land is among the means to reduce chemical fertilizer use and combat climate change. This in sacco decomposition study investigates (1) the potential of the granulated biogas residue fraction to provide nutrients and enhance soil carbon sequestration when utilized as exogenous organic matter in grassland soils, and (2) the impact of different nitrogen fertilizers on the organic matter decomposition and nutrient release processes. The experiment was conducted in two permanent grasslands of the Greater Region over one management period using rooibos tea as a comparator material. The decomposition and chemical changes of the two materials after incubation in the soil were assessed by measuring the mass loss, total carbon and nitrogen status, and fibre composition in cellulose, hemicellulose and lignin. Overall, after the incubation period, granulated biogas residue maintained up to 68% of its total mass, organic matter and total carbon; increased its content in recalcitrant organic matter by up to 45% and released 45% of its total nitrogen. Granulated biogas residue demonstrated resilience and a higher response uniformity when exposed to different nitrogen fertilizers, as opposed to the comparator material of rooibos tea. However, the magnitude of fertilizer-type effect varied, with ammonium nitrate and the combinatorial treatment of raw biogas residue mixed with urea leading to the highest organic matter loss from the bags. Our findings suggest that granulated biogas residue is a biofertilizer with the potential to supply nutrients to soil biota over time, and promote carbon sequestration in grassland soils, and thereby advance agricultural sustainability while contributing to climate change mitigation.