Soil Organic Carbon Fractions Research Articles

Influence of land use types on soil carbon fractions in the Qaidam Basin of the Qinghai-Tibet Plateau

Soil carbon is an essential component that influences soil health and agronomic productivity, and land-use practices significantly impact soil carbon stocks. In this study, the researchers investigated the impact of various land-use types (farmland, orchards, grasslands, and facility lands) on soil organic carbon (SOC) fractions in the Qaidam Basin of China's Qinghai-Tibet Plateau. The soil samples were taken from the 0–10 and 10–20 cm depths. The particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) fractions of various land uses have been measured. The results revealed that grasslands had the greatest POC/SOC ratio (0.59), with POC accounting for the majority of the SOC fraction. In contrast, all other land-use types (facility land, orchards, and farmland) had greater MAOC/SOC ratios than POC/SOC. The facility land had the highest SOC content (17.75 g kg−1), and orchard had the lowest (8.51 g kg−1). The grassland had the highest POC content (9.82 g kg−1) at a depth of 0–10 cm. The trend for MAOC content among the various land-use types was facility lands > farmlands > grasslands > orchards. The soil pH was also observed to be moderately alkaline, with an average of 8. The orchard has the highest bulk density (BD), measuring 1.38 g cm−3. The grasslands contained the highest amount of total nitrogen (TN) (2.2 g kg−1) while the agricultural fields contained the highest amount of total phosphorus (TP) (1.16 g kg−1). In addition, facility lands showed the highest level of microbial activity compared to other land-use types. According to the findings, SOC, POC, and MAOC fractions had considerably positive associations with TN and microbial biomass carbon (MBC), but were significantly negatively associated with metabolic CO2. The findings imply that different land-use types can have a considerable impact on the quality and amount of soil organic carbon, which has consequences for soil health and ecosystem processes. The findings also highlight the significance of long-term land management practices that promote the preservation and enhancement of soil organic carbon in various land-use systems.

Environmental controls on density‐based soil organic carbon fractionations in global terrestrial ecosystems

AbstractCategorization of soil organic carbon (SOC) into different functional subpools according to their recalcitrance and protective mechanisms helps better understand ecosystems organic carbon (OC) dynamics, and various attempts have been made to explore the suitable experimental fractionation method for such purpose. However, most previous studies neglected the influences of environmental factors on the effectiveness of varying fractionation methods. Density fractionation has shown great promise in elucidating SOC immobilization mechanisms. Here, we compared three varying types of density fractionation methods (density, density + dispersion, and density + other procedures) for categorizing the SOC into three functional pools, that is, active OC (OCactive), moderately stable OC (OCm‐stable), and stable OC, (OCstable) using global data compiled for 95 sites in 31 published studies, and examined the influences of climate (mean annual temperature [MAT] and annual precipitation), vegetation type, and soil properties (soil depth, clay content, and soil type) on SOC fractions determined by the three density fractionation methods. The percentage of OCm‐stable fraction was found to be highest using the density method and lowest using the density + dispersion method, due to differential density ranges between the two methods. At a global scale, the contents of total SOC and its OC fractions decreased with temperature. Precipitation had no apparent influences on the subdivided SOC fractions using either the density + dispersion method or the method of density + other procedures, whereas soil type constrained the effect of precipitation on SOC fractions using the density method. The percentage of OCm‐stable determined by the density + dispersion method was more responsive to MAT and vegetation type than that by the other two methods. The percentage of OCstable determined by the method of density + other procedures was significantly and positively related to the clay content as the OCstable based on this method included small particles. For all the three methods of fractionation, soil type had a greater influence than the clay content on the SOC fractions, especially the OCm‐stable and the OCstable. For soil type characterized by rich metal oxides, both the density method and the method of density + other procedures could be used for SOC fractionation. For soil type rich in nutrients, the density + dispersion method would have higher sensitivity for distinguishing the OCm‐stable.

Aggregate‐associated soil organic carbon fractions in subtropical soil undergoing vegetative restoration

AbstractPrecise assessment of soil organic carbon (SOC) storage requires understanding how vegetation and soil physico‐chemical properties differ in SOC fractions. Therefore, we aimed to analyze the dynamics of aggregate‐associated, labile organic carbon (LOC) fractions corresponding to depth to clarify the effect of vegetation and soil properties on water stable aggregate (WSA) mineral adsorption in subtropical, red soil with five vegetation restoration regimes. The results showed that the large macro‐aggregate fraction dominated the degraded red soil, which had the highest content of dissolved organic carbon (DOC). WSA‐associated, easily oxidized organic carbon (EOC) varied from 6.26 to 20.02 g/kg and was not affected by vegetation types. Schima superba pure forest significantly increased DOC (0.38 g/kg on average) and particulate organic carbon (POC, 7.92 g/kg on average), which had the highest biomass. Along with soil depth, WSA‐associated POC declined, while exhibiting a growth trend with decreasing particle size, for example, the highest POC was found in <0.053 mm aggregates. The redundancy analysis ordination indicated that soil porosity and total nitrogen (TN) were the main soil parameters that explained the most variance. Meanwhile, the vegetation biomass, except for litter, were all significantly positively correlated with <0.053 mm aggregates. Leaf biomass played the most important role on DOC in macro‐aggregates with a 53.42% contribution. For aggregate‐related POC, the largest contribution was from the interactions between branch biomass and pH (47.78%) followed by TN (35.1%) of micro‐aggregate‐related POC. Leaf biomass, <0.053 mm aggregates, and TN can be used as indicators to evaluate the impact of vegetation restoration on WSA‐associated SOC fractions. Broad‐leaved forest or in combination with indigenous coniferous species was a better choice for SOC sequestration improvement in the study area for managing C supply, process, and flux in subtropical terrestrial ecosystems.

Soil organic carbon fractionation of spoiled and unspoiled soils under different land use and land cover systems.

Alteration in land use and land cover is the key factor affecting the soil carbon fractions and its distribution. A study was carried out to estimate the carbon fractions in soils of agricultural, forest and pasture lands in two different areas separated on the basis of industrial activities (spoiled and unspoiled) to get an insight on the long-term soil carbon storage potential. The results showed that the mean values of the total organic carbon (TOC) and various fractions are significantly different between the land use types (p < 0.05). Irrespective of the land uses, the forest land showed significantly higher TOC (7.97) than agricultural land (6.98) and pasture lands (6.68). Further, evaluation of carbon management index (CMI) indicated that forest lands had highest CMI value compared to the other land uses. The spoiled area had significantly higher TOC and carbon fractions than their respective counterparts in the unspoiled area (p < 0.05) due to the negative industrial impact on soil biological processes. The PCA separates the sources of different carbon fractions and revealed an association of N (nitrogen) and K (potassium) with VL (very labile) and L (labile) fractions and the association of P (phosphorous) with stable R (recalcitrant) form. Therefore, it can be inferred from the present study that alterations in land use not only result in soil quality degradation but also trigger a reduction in potential for long term soil C sequestration.

Response of soil organic carbon and its fractions to natural vegetation restoration in a tropical karst area, southwest China

The dynamics of soil organic carbon (SOC) and its fractions are important for evaluating the vegetation restoration effect and carbon cycle of the ecosystem. Here, SOC fractions, including light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), and labile organic carbon (LOC) fractions (including water-soluble organic carbon, WSOC, readily oxidizable organic carbon, ROC, particulate organic carbon, POC, and microbial biomass carbon, MBC), were investigated at four soil depths under five restoration stages in a tropical karst area in southwest China. This study showed that the content of SOC and its fractions significantly increased with vegetation restoration and decreased with increasing soil depth at each restoration stage (p &amp;lt; 0.05). Additionally, LFOC was more sensitive to vegetation restoration, whereas HFOC was the main storage form of SOC. The LOC fractions in the surface soil layer were significantly higher than those in the lower, and the percentages of some LOC fractions (POC/SOC and MBC/SOC) significantly decreased with increasing soil depth, indicating that SOC was more stable in the lower layer than in the surface layer. Correlation analysis showed that SOC was significantly and positively correlated with its fractions. Moreover, SOC and its fraction were positively correlated with soil chemical factors (TN, TP, AP, AK, ECa, EMg, NH4+-N, and NO3–-N) and negatively correlated with bulk density (BD) at a significant level (p &amp;lt; 0.05). Moreover, redundancy analysis showed that the 12 soil physicochemical factors explained 70.99% of the variation in SOC and its fractions, with AK, NH4+-N, and BD being the main factors, explaining 19.38, 17.24, and 10.52% of the variation, respectively. The structural equation mode analysis showed that soil properties, above-ground biomass, and litterfall explained most of the variation in SOC (59%), LFOC (79%), HFOC (81%), and LOC (61%). Soil properties and above-ground biomass significantly affected SOC, LFOC, and HFOC content mainly through indirect effects, while the total phosphorus content of the litterfall could directly and significantly affect SOC, LFOC, and HFOC content. NH4+-N and AK of soil factors had direct effects on LFOC and LOC accumulation, respectively. This study provides a valuable perspective for estimating carbon sink potential and constructing carbon sink models in karst areas.

Soil organic carbon fractions in response to soil, environmental and agronomic factors under cover cropping systems: A global meta-analysis

Cover crops may improve soil health and increase soil carbon sequestration, thus contributing to both the adaptation to and mitigation of climate change. Despite these potential benefits, there currently lacks a global synthesis of the impacts of cover crops on soil organic carbon (SOC) fractions. We conducted a global meta-analysis of 93 peer-reviewed studies to quantify the effect of cover crops on changes in SOC fractions and the influence of environmental and management factors. Compared to bare soil management, cover crops increased SOC by 12% and increased seven SOC fractions, including microbial biomass carbon (MBC) by 33%, dissolved organic carbon (DOC) by 18%, particulate organic carbon (POC) by 15%, light-fraction organic carbon (LFOC) by 14%, permanganate oxidizable carbon (POXC) by 13%, short-term mineralizable carbon (SMC) by 10%, and mineral-associated organic carbon (MAOC) by 7%. The effect size of SOC was positively correlated with the effect sizes of MBC, POC, LFOC, and MAOC, but negatively correlated with the effect size of DOC. Soil taxonomic order and experimental duration were key factors affecting the beneficial effect of cover crops on the SOC fractions. Greater increases in SOC fractions due to cover crops were found in Entisols and Ultisols in comparison with other soil orders. The effect size of MAOC increased with experimental duration. Our study suggests that cover crops can significantly increase various SOC fractions, which likely serves as a building block for SOC sequestration and improvement of many aspects of soil health.

Soil organic carbon fractions in agroforestry system in Brazil: seasonality and short-term dynamic assessment

Soil organic carbon fractions in agroforestry system in Brazil: seasonality and short-term dynamic assessment

The Assessment of Soil Organic Carbon Pools in Different Soils Using Four Fractionation Methods

ABSTRACT The sensitivity of SOC (soil organic carbon) fractions can provide information on soil organic matter proxies and kinetically defined components related to their chemical composition and oxidability. The purpose of this study was to assess the stability of SOC on five soil types (Arenosols, Chernozems, Fluvisols, Vertisols and Solonetz) and three land uses (cropland, meadow and forest). To obtain SOC functional fractions chemical, physical and density fractionating methods were used as follows: SOC susceptible to oxidation with 333 mM KMnO4 (SOCKMnO4S), SOC with varying degrees of oxidation resistance by the modified Walkley-Black method (SOCwb1, SOCwb2, SOCwb3, SOCwb4), particulate SOC (SOCpar); mineral-associated SOC (SOCmas), aggregate-associated size classes of the SOC (SOC >2000, SOC2000–250, SOC250–53, SOC <53). The relative contribution of fractions in SOC was as follows: SOCKMnO4S (7.9–42.5%), SOCwb1 (35.6%) > SOCwb2 (27.5%) > SOCwb4 (22.7%) > SOCwb3 (14.2%), SOCmas (56.6–76.4%) > SOCpar (23.6–43.4%), SOC >2000 (8.2–44.8), SOC 2000–250 (27.4–34.9), SOC 250–53 (13.4–27.4%), SOC <53 (5.4–28.8%). Fractions SOCpar, SOCwb4, SOC >2000 and SOC <53 showed sensitivity to land use, whereas SOCmas, SOC KMnO4S, SOCwb3 showed variations among soil types. The fraction SOCwb1 indicated sensitivity to both land use and soil type. Considering obtained functional fractions of SOC it was possible to determine discriminators between particular soil types or indicators of land use changes due the anthropogenization.

Seven-year experimental warming decreases labile but not recalcitrant soil organic carbon fractions in a coastal wetland

Seven-year experimental warming decreases labile but not recalcitrant soil organic carbon fractions in a coastal wetland

Composition and contribution of Stipa bungeana root exudates to soil organic carbon fractions in the Loess Plateau

Root exudates play an important role in carbon sequestration in grassland, but the contribution of root exudates to soil organic carbon (SOC) fractions remains unclear. In this study, Stipa bungeana was analyzed, determined the composition and content of root exudates by GC–MS in a soil culture experiment and labeled with 13CO2 in a rhizibox experiment. Esters accounted for 65.38 % of root exudates, among which 1-propen-1, 2, 3-tricarboxylic acid-tributyl ester, and acetyl-tributyl citrate were the main components. During a 65-day chase period, the contents of SOC and its fractions in the rhizosphere were higher than those in bulk soil. After first day of labeling, the SOC concentration decreased by 16.95 % in the rhizosphere and reached the minimum level. Except for 13C-HC in bulk soil, which was detected three days after labeling, the rest were detected 2 h after labeling. In the rhizosphere soil, the amount of 13C in MBC and HC peaked after one day of labeling. At 65 days after labeling, the 13C-DOC, 13C-HC, and 13C-MBC in the rhizosphere significantly decreased by 59.79 %, 75.99 %, and 55.56 %, respectively. Root exudates had a rapid effect on active organic carbon fractions (MBC and DOC), and also affect the humus carbon (HC) in the short term. This study reveals the mechanism of root exudates on SOC pool during plant growth.

Effects of Short-term Nitrogen Addition on Soil Organic Carbon Components in Robinia pseudoacacia L. Plantation

Nitrogen (N) deposition in the context of human activities continuously affects the carbon cycle of ecosystems. The effect of N deposition on soil organic carbon is related to the differential responses of different carbon fractions. To investigate the changes in soil organic carbon fraction and its influencing factors in the context of short-term N deposition, four N addition gradients:0 (CK), 1.5 (N1), 3 (N2), and 6 (N3) g·(m2·a)-1 were set up in acacia plantations based on field N addition experiments, and the soil physicochemical properties, microbial biomass, and enzyme activities were measured in June and September. The results showed that:① exogenous N input reduced soil pH, promoted the increase in soluble organic carbon content, and increased soil nitrogen effectiveness. ② Short-term N addition significantly reduced soil organic carbon content, and the response of each component of organic carbon to N addition was different. Among them, the content of easily oxidized organic carbon was significantly reduced and reached the lowest value under the N2 treatment, with 54.4% and 48.2% reduction compared with that of the control, respectively, and the content of inert organic carbon increased, although the increase was not significant. Nitrogen addition reduced the soil carbon pool activity and improved the stability of the soil carbon pool. Soil carbon pool activity reached its lowest under the N3 and N2 treatments, with a decrease of 53.3% and 52.80%, respectively, compared to that of the control. ③Random forest modeling indicated that the soil microbial biomass stoichiometry ratio, microbial biomass carbon, and AP were the key factors driving the changes in soil organic carbon activity under short-term N addition, explaining 65.96% and 66.68% of the changes in oxidizable organic carbon and inert organic carbon, respectively. Structural equation modeling validated the results of the random forest modeling, and soil microbial biomass stoichiometric ratios significantly influenced carbon pool activity. Short-term nitrogen addition changed soil microbial biomass and its stoichiometric ratio in the acacia plantation forest mainly through two pathways, i.e., increasing soil nitrogen effectiveness and promoting soil acidification and inhibiting extracellular carbon hydrolase activity, thus changing the soil carbon fraction ratio and participating in the soil organic carbon cycling process.

Accumulation of SOC and Carbon Fractions in Different Age Red Fescue Permanent Swards

One of the practices often mentioned to achieve climate change mitigation is the long-term cultivation of perennial plants. The objective of the study was to estimate changes in the accumulation of soil organic carbon (SOC) and its fractions in 0–10, 10–20, 20–30 cm, and within 0–30 cm soil layer of red fescue (Festuca rubra L.) swards that differ in age (5, 10 and 15 years) as well as to compare them with the arable field. Our results show that SOC accumulation at 5-year-old cultivation of red fescue is high, later this SOC increase slowed down from 71% in the 0–30 cm soil layer when land use was converted from arable field to 5-year-old sward to 1% from 10 to 15 years. The level of water extractable organic carbon (WEOC) in the 0–30 cm soil layer of swards was significantly higher compared to the arable field. The positive effect of these swards in the accumulation and stabilization of organic carbon during humification in the soil was also determined. The largest amounts of mobile humic substances (MHS) and mobile humic acids (MHA) accumulated in the 0–10 cm layer of sward soil (3.30–4.93 and 1.53–2.48 g kg−1, respectively). In conclusion, the findings suggest that a conversion from arable to soil under permanent grass cover significantly improves carbon status.

Effects of erosion and deposition on the extent and characteristics of organic carbon associated with soil minerals in Mollisol landscape

The physicochemical interactions between soil organic carbon (SOC) and minerals are important for the long-term stabilization of OC. However, in the dynamic landscape, the mechanisms of OC stabilized by different types of minerals remains unclear. Herein, we investigated the effects of erosion and deposition on the distribution of SOC pools and the interaction of OC with different minerals in an agricultural Mollisol landscape. We quantified the SOC fractions using a physically separated technique and measured the polyvalent cation bound-OC using a mineral reduction release method. Sorption experiments and specific mineral surface area (SSA) were determined. Results show that 77.6%−96.9% of SOC was mineral-associated OC (MAOC). MAOC contents in the topsoil (0–20 cm) and subsoil (60–80 cm) of the depositional sites were 1.17 and 1.64 times higher than those in the topsoil and subsoil of the eroding sites, respectively. A higher MAOC content in the depositional sites suggests that MAOC in the middle slope migrates directly to the downslope through erosion, and subsequent depositional and burial processes promote OC interactions with minerals. Furthermore, Fe and Al oxides were the main minerals that stabilized OC compounds at each slope, while Ca played a vital role in OC interactions in the depositional sites. The Fe- and Al-bound OC (Fe/Al-OC) showed higher aromaticity, humification, and molecular weight than Ca-OC and bulk soil dissolved OC, which remained unaffected by erosion and deposition. These OC interactions with Fe/Al increased the chemical structural stability of SOC. Furthermore, the depositional sites showed the highest MAOC contents, MAOC loading, BET-C constant, adsorption capacity, and the lowest SSA covered by SOC (%SSASOC-covered). These results indicate that depositional sites have the highest capacities for OC sequestration. Based on these results, the deposition or burying of eroding OC plays a key role in stabilizing soil OC.

Periodic flooding enhances the function of soil Fe/Al oxides in stabilizing particulate organic carbon in a water level drawdown zone

The stabilization of soil organic carbon is closely linked to edaphic properties and environmental variables. Despite this, the mechanism of soil organic carbon stabilization, as well as the primary factor controlling soil organic carbon in riparian ecosystems, remains unclear. To address this gap, our study investigated the impact of flooding regimes on soil organic carbon fractions and other chemical properties in the riparian zone, focusing on the dominant intrinsic factors controlling soil organic carbon content within the three soil types (Anthrosols, Luvisols, and Regosols). Our results demonstrated that flooding regimes significantly affect soil chemical properties in the riparian zone, with varying effects among the three soil types. Specifically, Regosols showed an increase in the particulate organic carbon with flooding intensity. Organic carbon fractions in Anthrosols and Luvisols are found to respond similarly to flooding regimes. The effects of soil chemical properties on organic carbon fractions varied across the three soil types. The variations in POCc, POCf, and MOC for Anthrosols were explained by path models by 43 %, 95 %, and 33 %, respectively. Similarly, for Luvisols, the path models accounted for 66 %, 90 %, and 29 % of the variations, whereas for Regosols, the variations were explained by 43 %, 93 %, and 21 %. Overall, for all tested soils combined, the path models explained 36 %, 89 %, and 12 %, respectively. Therefrom, under flooding regimes, soil oxides played a more significant role in stabilizing soil organic carbon for the three soil types than clay, silt, and cations. Specifically, in Anthrosols, Luvisols, and Regosols, the path coefficient for soil oxides was 0.90, 0.95, and 0.97, respectively, for POCf; while it was 0.30, 0.21, and 0.22 for POCc. In conclusion, we revealed that flooding regimes enhance the role of soil oxides in stabilizing organic carbon. Therefore, we recommend that soil oxides shall be included in organic carbon saturation models for riparian zones subjected to flooding regimes.

Soil carbon fractions in response to mineral and organic fertilizer types and rates

The use of organic fertilizers from pig slurry and poultry litter can increase soil organic carbon and crop productivity. This study aimed to evaluate soil organic carbon fractions and corn yield after applying organic and mineral fertilizers. The experiment was conducted in the western region of Santa Catarina State, southern Brazil on a Nitossolo Vermelho Eutroférrico típico (Rhodic Kandiudox). The production system was an integrated crop-livestock using corn and soybean in the summer and black oat and rye with [...]

Limited impacts of occasional tillage on dry aggregate size distribution and soil carbon and nitrogen fractions in semi-arid drylands

Tillage management that minimizes the frequency and intensity of soil disturbance can increase soil carbon (C) and nitrogen (N) sequestration and improve the resilience of dryland cropping systems, yet the impact of occasional disturbance on soil aggregate formation and the soil organic carbon (SOC) storage within aggregates has not been studied well. We evaluated the effect of four tillage management practices on soil dry aggregate size distribution, aggregate-protected C and N, mineral-associated organic matter carbon (MAOM-C), particulate organic matter carbon (POM-C), and corn (Zea mays L.) and sorghum (Sorghum bicolor (L.) Moench) yields in a semi-arid dryland cropping system. Treatments included conventional tillage (CT), strip-tillage (ST), no-tillage (NT), and occasional tillage (OT) management in a corn-sorghum rotation. Soil macro-aggregates were 51–54% greater under ST, NT, and OT, while small and micro-aggregates were greater in CT. Conventional tillage reduced soil aggregate-associated C by 28–31% in macro-aggregates and 47–53% in small aggregates at 26 months (M) sampling compared to ST, NT, and OT. In clay + silt fraction, CT had 14–16%, 21–26%, and 36–43% less SOC at 7, 14, and 26M samplings, respectively, than ST, NT, and OT. Aggregate associated N was generally similar under ST, NT, and OT, which was greater on average than CT. Soil MOAM-C and POM-C under ST, NT, and OT were generally greater than respective SOC fractions under CT at 19 and 26 M after OT implementation. Corn and sorghum yields were similar among tillage systems in 2020, but greater under ST, NT, and OT than CT in 2021. Our results suggest that while frequent intensive tillage can lower SOC and N storage, a single stubble mulch occasional tillage after several years of NT does not lead to soil C and N losses and soil structural instability in semi-arid drylands.

Short-Term Effects of Bamboo Biochar and Oyster Shell Powder on Soil Organic Carbon Fraction, Microbial Respiration, and Enzymatic Stoichiometry in a Lei Bamboo Plantation

Both biochar and oyster shell powder have been known as promising amendments to ameliorate soil acidity and enhance soil fertility. However, it is still unclear how their application alone and in combination affect the soil organic carbon (C) fraction and microbial activity in subtropical bamboo plantations. Therefore, to investigate the effects of biochar and oyster shell powder on soil microbial respiration, organic C fractions, microbial biomass, and enzyme activities related to C, N and P cycling, topsoil samples were collected from plots in a bamboo (Phyllostachys praecox) plantation that has been amended with oyster shell powder at 4 t ha−1 (T), bamboo biochar at 10 t ha−1 (B), and their combination (TB, with 4 t ha−1 T and 10 t ha−1 B) for 8 months. Our results showed that T alone significantly increased soil microbial respiration by 21.5%, whereas B alone and TB significantly decreased soil microbial respiration and metabolic quotient compared with T. T alone also increased soil pH, the size of labile C pool and the activities of β−glucosidase and cellobiosidase, whereas TB rather than B increased soil pH, the recalcitrant C pool size and declined these enzyme activities relative to T. T alone significantly enhanced microbial C limitation by 28.6% and decreased P limitation by 13.0%, while TB decreased microbial C limitation and increased microbial C use efficiency (CUE). Structural equation modeling indicated that T enhanced soil microbial respiration through increasing soil pH and enzyme activity, while biochar co-addition weakened the stimulation of T on microbial respiration by increasing soil recalcitrant C pool size and microbial metabolic quotient. Our study suggests that adding bamboo biochar together with oyster shell powder could be a better strategy to decrease soil C loss and ameliorate soil acidity in bamboo plantations compared with the application of oyster shell powder alone.

Soil organic carbon sequestration and modeling under conservation tillage and cropping systems in a rainfed agriculture

Conservation agriculture is a well-established method for promoting carbon sequestration and reducing greenhouse gas emissions, but little is known about how it affects subtropical dryland farming systems. The goal of this study was to evaluate the potential of conservation agriculture in Pakistan's subtropical dryland to reduce atmospheric CO2 enrichment and alter soil organic carbon fractions. In a field experiment, fallow-wheat (farmers' practice) and the conservation tillage methods minimum tillage (MT), reduced tillage (RT), and zero tillage (ZT) were compared to conventional tillage (CT) in the main plots and the cropping systems sorghum-wheat (S-W) and mungbean-wheat (M-W) to fallow-wheat (F-W) in the sub-plots. Multiple assessments taken over a two-year period revealed that CT plots lacked greater soil organic carbon and its fractions than ZT and RT plots. In comparison to CT, ZT, and RT exhibited higher average total organic carbon (TOC), microbial biomass carbon (MBC), particulate organic carbon (POC), and mineral-associated organic carbon (MOC) concentrations, respectively, of 1.43% and 1.31%, 4.61% and 2.83%, 2.42% and 1.97%, and 1.66% and 1.76%. In comparison to the S-W cropping system, the F-W and M-W cropping systems showed increased MBC and MOC, but POC and TOC were little impacted. The maximum TOC (0.589% and 0.589%), MBC (0.021% and 0.021%), POC (0.195% and 0.192%), and MOC (0.489% and 0.485%) were found in the combinations of ZT with F-W and M-W. Regardless of the cropping systems, cumulative CO2 flow was lowest in ZT plots compared to the other tillage techniques. The CENTURY model confirmed that the use of continuous tillage is a major threat to both soil fertility and production. The study, therefore, concludes that ZT and RT systems in particular are potential possibilities for carbon sequestration in subtropical dryland soils for CO2 reduction.

Mapping soil organic carbon fractions for Australia, their stocks, and uncertainty

Abstract. Soil organic carbon (SOC) is the largest terrestrial carbon pool. SOC is composed of a continuous set of compounds with different chemical compositions, origins, and susceptibilities to decomposition that are commonly separated into pools characterised by different responses to anthropogenic and environmental disturbance. Here we map the contribution of three SOC fractions to the total SOC content of Australia's soils. The three SOC fractions, mineral-associated organic carbon (MAOC), particulate organic carbon (POC), and pyrogenic organic carbon (PyOC), represent SOC composition with distinct turnover rates, chemistry, and pathway formation. Data for MAOC, POC, and PyOC were obtained with near- and mid-infrared spectral models calibrated with measured SOC fractions. We transformed the data using an isometric-log-ratio (ilr) transformation to account for the closed compositional nature of SOC fractions. The resulting back-transformed ilr components were mapped across Australia. SOC fraction stocks for 0–30 cm were derived with maps of total organic carbon concentration, bulk density, coarse fragments, and soil thickness. Mapping was done by a quantile regression forest fitted with the ilr-transformed data and a large set of environmental variables as predictors. The resulting maps along with the quantified uncertainty show the unique spatial pattern of SOC fractions in Australia. MAOC dominated the total SOC with an average of 59 % ± 17 %, whereas 28 % ± 17 % was PyOC and 13 % ± 11 % was POC. The allocation of total organic carbon (TOC) to the MAOC fractions increased with depth. SOC vulnerability (i.e. POC/[MAOC+PyOC]) was greater in areas with Mediterranean and temperate climates. TOC and the distribution among fractions were the most influential variables in SOC fraction uncertainty. Further, the diversity of climatic and pedological conditions suggests that different mechanisms will control SOC stabilisation and dynamics across the continent, as shown by the model covariates' importance metric. We estimated the total SOC stocks (0–30 cm) to be 13 Pg MAOC, 2 Pg POC, and 5 Pg PyOC, which is consistent with previous estimates. The maps of SOC fractions and their stocks can be used for modelling SOC dynamics and forecasting changes in SOC stocks as a response to land use change, management, and climate change.

Inclusion of peanut in wheat–maize rotation increases wheat yield and net return and improves soil organic carbon pool by optimizing bacterial community

Improving soil quality while achieving higher productivity is the major challenge in the agricultural industry. Wheat (Triticum aestivum L.)–maize (Zea mays L.) (W–M) rotation is the dominant planting pattern in the Huang-Huai-Hai Plain and is important for food security in China. However, the soil quality is deteriorating due to the W–M rotation's long-term, intensive, and continuous cultivation. Introducing legumes into the W–M rotation system may be an effective way to improve soil quality. In this study, we aimed to verify this hypothesis by exploring efficient planting systems (wheat–peanut (Arachis hypogaea L.) (W–P) rotation and wheat rotated with maize and peanut intercropping (W–M/P)) to achieve higher agricultural production in the Huang-Huai-Hai Plain. Using traditional W–M rotation as the control, we evaluated crop productivity, net returns, soil microorganisms (SMs), and soil organic carbon (SOC) fractions for three consecutive years. The results indicated that wheat yields were significantly increased under W–P and W–M/P (382.5–579.0 and 179.8–513.1 kg ha−1, respectively) compared with W–M. W–P and W–M/P provided significantly higher net returns (58.2 and 70.4%, respectively) than W–M. W–M/P and W–M retained the SOC stock more efficiently than W–P, increasing by 25.46–31.03 and 14.47–27.64%, respectively, in the 0–20 cm soil layer. Compared with W–M, W–M/P improved labile carbon fractions; the sensitivity index of potentially mineralizable carbon, microbial biomass carbon (MBC), and dissolved organic carbon was 31.5, 96.5–157.2, and 17.8% in 20–40, 10–40, and 10–20 cm soil layers, respectively. The bacterial community composition and bacteria function were altered as per the soil depth and planting pattern. W–M/P and W–M exhibited similar bacterial community composition and function in 0–20 and 20–40 cm soil layers. Compared with W–P, a higher abundance of functional genes, namely, contains mobile elements and stress-tolerant, and a lower abundance of genes, namely, potentially pathogenic, were observed in the 10–20 cm soil layer of W–M and the 0–20 cm soil layer of W–M/P. SOC and MBC were the main factors affecting soil bacterial communities, positively correlated with Sphingomonadales and Gemmatimonadales and negatively correlated with Blastocatellales. Organic input was the main factor affecting SOC and SMs, which exhibited feedback effects on crop productivity. In summary, W–M/P improved productivity, net returns, and SOC pool compared with traditional W–M rotation systems, and it is recommended that plant–soil–microbial interactions be considered while designing high-yield cropping systems.