Soil Carbon Fractions Research Articles

The Short-Term Effects of Heavy Thinning on Selected Soil Carbon Pools and Microbial Activity in a Young Aleppo Pine Forest

Pinus halepensis Miller is a widespread tree species in the western Mediterranean basin, where very dense monospecific stands can be found, especially in natural regeneration after forest fires. Silvicultural thinning can reduce the competition of trees for natural resources and favour their development, although its effect depends on the habitat. The present study aims to know the effects on the soil at the physicochemical and microbiological levels after a heavy thinning in a young pine forest stand with a high stocking density. The stand is on a slope where the soil depth tends to decrease with altitude, and shows changes in its physicochemical properties between the upper and lower zones. Several soil carbon fractions (i.e., soil organic carbon (SOC), water-soluble organic carbon (WSOC), and microbial biomass carbon (MBC)), microbial activity (basal soil respiration (BSR)) and enzyme activities (acid phosphatase (AP) and urease (UA)) were analysed at specific dates over a period of about five years after a heavy thinning. The changes in organic matter content were abrupt in the slope, conditioning the observed differences. It is highlighted that the SOC and WSOC contents in the mineral soil were 2.5- and 3.5-fold significantly higher, respectively, in the upper shallow zone compared to the lower deeper zone. This was also reflected in significantly higher levels of gravimetric water content (GWC) and MBC (both about 1.4-fold higher), with higher levels of BSR and UA, and 2.5-fold significantly higher levels of AP. As a result, most of the properties studied showed no significant differences between the thinning treatment and the untreated control. Results varying between dates, with a strong dependence on climate (soil temperature and humidity) of WSOC and UA. It can be concluded that the heavy thinning applied in this short-term case study favoured the growth conditions of the pine without negatively affecting the soil properties studied.

Alterations of bacterial community related C cycle by affecting soil carbon fractions under aged biochar application

AbstractBiochar is a beneficial substance for sequestering organic carbon in soil. Application of fresh biochar (FB) to the soil leads to an increase in soil organic carbon (SOC). However, the effects of aged biochar on SOC stabilization in acidic soils are unclear. A 90‐day incubation study was assessed to evaluate the impact of adding rice straw biochar on acid soil. The study aimed to assess the alterations in carbon fractions, enzyme activity and bacterial communities in soil. We used different ageing processes (water‐washed biochar [WB] and H2O2 oxidation biochar [OXB]) at a rate of 2%, with control at 0% of biochar. The results indicated that aged biochar reduced CO2 efflux and increased microbial biomass carbon (MBC), reducing the microbial metabolic quotient (qCO2). The SOC and its fractions increased with ageing relative to the FB treatment. Compared with the FB treatment, the carbon pool management index (CPMI) also increased with the OXB application. Additionally, the application of OXB stimulated the soil enzymes involved in carbon cycling, specifically β‐1,4‐glucosidase (βG), β‐1,4‐xylosidase (βX) and cellobiohydrolase (CBH) relative to the FB and WB treatments. Moreover, biochar applications improved the structure and functions of the bacterial population in soil with high acidity. Proteobacteria, Acidobacteria, Actinobacteria and Chloroflexi were the most prevalent species in all treatments, as shown by their relative abundances. The redundancy analysis revealed that the DOC (dissolved organic carbon) and MBC significantly impacted on the microbial community. Furthermore, adding OXB altered the Bacterial community involved in the C cycle by affecting SOC. These findings help us learn more about how applying fresh or aged rice straw biochar changes different carbon fractions and microbial communities in soil. It may serve as an instance for studying the provision of soil organic carbon after applying biochar in acidic soil.

Unraveling the relationship between soil carbon-degrading enzyme activity and carbon fraction under biogas slurry topdressing

Biogas slurry, a by-product of the anaerobic digestion of biomass waste, predominantly consisting of livestock and poultry manure, is widely acclaimed as a sustainable organic fertilizer owing to its abundant reserves of essential nutrients. Its distinctive liquid composition, when tactfully integrated with a drip irrigation system, unveils immense potential, offering unparalleled convenience in application. In this study, we investigated the impact of biogas slurry topdressing as a replacement for chemical fertilizer (BSTR) on soil total organic carbon (TOC) fractions and carbon (C)-degrading enzyme activities across different soil depths (surface, sub-surface, and deep) during the tasseling (VT) and full maturity stage (R6) of maize. BSTR increased the TOC content within each soil layer during both VT and R6 periods, inducing alterations in the content and proportion of individual C component, particularly in the topsoil. Notably, the pure biogas slurry topdressing treatment (100%BS) compared with the pure chemical fertilizer topdressing treatment (CF), exhibited a 38.9% increase in the labile organic carbon of the topsoil during VT, and a 30.3% increase in the recalcitrant organic carbon during R6, facilitating microbial nutrient utilization and post-harvest C storage during the vigorous growth period of maize. Furthermore, BSTR treatment stimulated the activity of oxidative and hydrolytic C-degrading enzymes, with the 100%BS treatment showcasing the most significant enhancements, with its average geometric enzyme activity surpassing that of CF treatment by 27.9% and 27.4%, respectively. This enhancement facilitated ongoing and efficient degradation and transformation of C. Additionally, we screened for C components and C-degrading enzymes that are relatively sensitive to BSTR. The study highlight the advantages of employing pure biogas slurry topdressing, which enhances C component and C-degrading enzyme activity, thereby reducing the risk of soil degradation. This research lays a solid theoretical foundation for the rational recycling of biogas slurry.

Effects of Four Amendments on Fertility and Labile Organic Carbon Fractions of Acid Purple Soil

The aim of this study was to explore the effects of four amendments on soil fertility and labile carbon fraction characteristics of acid purple soil, so as to provide scientific basis for nutrient management and carbon storage stability in purple soil. Field experiments were carried out, and six treatments were set up:no fertilization (CK), only chemical fertilizer (F), lime + chemical fertilizer (SF), organic fertilizer + chemical fertilizer (OM), biochar + chemical fertilizer (BF), and vinasse biomass ash + chemical fertilizer (JZ). The contents of soil organic matter, pH, available nutrients, soil integrated fertility index (IFI), dissolved organic carbon (DOC), microbial biomass carbon (MBC), particulate organic carbon (POC), their effective rates, and soil carbon pool management index (CPMI) under different treatments were studied to clarify their relationships. The results showed that:① the application of amendments significantly increased soil pH and the contents of organic matter, alkali-hydrolyzed nitrogen, available phosphorus, and available potassium (P<0.05). The OM and JZ treatments had the most significant increase in soil comprehensive fertility index (P<0.05), with increases of 1.96 and 0.77 and 170.43% and 66.96%, respectively. ② Compared with those in the control treatment, the contents of POC, MBC, and DOC in JZ and OM increased by 110.30% and 84.81%, 61.08% and 46.56%, and 195.87% and 141.67%, respectively. The application of amendments significantly increased the soil carbon pool index (CPI) and CMPI (P<0.05), in which the OM treatment showed the most significant increase, with soil CPI and CMPI values increasing by 107.34% and 90.75% compared with those of the control, respectively. ③ Soil organic carbon and its labile fractions were positively correlated with IFI (P<0.05), and redundancy analysis showed that there were significant differences among different treatments. The interpretation rates of soil IFI, pH, and available potassium to organic carbon and its components reached significant levels, and the order of interpretation rates was IFI(74.6%)>pH (11.7%)>AK(6.5%). The application of vinasse biomass ash and organic fertilizer to acid purple soil had the most significant effect on improving soil fertility and soil quality and was conducive to promoting the accumulation and activation of soil carbon fractions.

Changes in soil microbial carbon fixation pathways along the oasification process in arid desert region: A confirmation based on metagenome analysis

Microbial carbon fixation has been proved to play a key role in soil carbon accumulation in arid desert oasis, but the fixation mechanism remains unclear. To solve it, we used metagenomic sequencing technology to measure the changes of soil microbial community structure, carbon fixation–related genes and carbon fixation pathway, as well as their relationships with soil properties between natural desert shrubbery (CK) and four oasis farmlands with different cultivation years (i.e., 3, 18 and 30 years) in the arid desert region of northwest China. The results showed that the contents of four soil carbon fraction (soil organic carbon/SOC, soil recalcitrant organic carbon/ROC, soil water solution carbon /WSC, and microbial biomass carbon/MBC) all significantly increased with the cultivation years (30 years ≥ 18 years > 6 years ≥ 3 years ≥ CK) (P < 0.05). Microbial composition was significant difference among CK, 3-, 6-, 18- and 30-years cultivated farmlands. Bacteria were the soil dominant taxa, and its relative abundance gradually decreased with the cultivation years. Proteobacteria, Actinobacteria, Bacteroidetes and Acidobacteria were the dominant phylum of soil microorganisms in desert shrubbery and oasis farmlands. Their relative abundance changed obviously with cultivation years. Six microbial carbon fixation pathways. i.e., the reductive tricarboxylic acid cycle (rTCA), dicarboxylate/4–hydroxybutyrate cycle (DC/4–HB cycle), 3–hydroxypropionate bicycle (3–HP bi–cycle), 3–hydroxypropionate/4–hydroxybutyrate cycle (3–HP/4–HB cycle), Calvin cycle and the Wood–Ljungdahl pathway (WL pathway), were found in all soils, but only the rTCA, DC/4–HB, 3–HP/4–HB cycles and WL pathway significantly changed with the cultivation years. The rTCA cycle was the most common fixation pathway, followed by DC/4–HB cycle and 3–HP/4–HB cycle, while WL pathway was least detected. Soil properties, especially pH, recalcitrant organic carbon, bulk density, total salinity and soil water contents, affected microbial community composition and carbon fixation–related genes in the oasification process. Our results suggested that oasification affected microbial carbon fixation by changing the soil environment due to human agricultural activities. Limited by energy supply in the nutrient–poor soils, rTCA and DC/4–HB cycles were mainly used by microorganisms to fix carbon in oasis farmlands.

Long-term fertilization differentially increased the CAZyme encoding genes responsible for soil organic matter decomposition under winter wheat on the Loess Plateau of China

Long-term fertilization greatly affects soil organic matter (SOM) decomposition in cropping systems, but less information was related to carbohydrate active enzyme (CAZyme) encoding genes in decomposing the components that derived from plant and microbial biomass. Using high-throughput metagenomic sequencing, the responses of CAZyme encoding genes to 35-yr fertilization were assessed in a winter wheat field on the Loess Plateau of China. Four treatments were included as chemical nitrogen fertilizer (N), manure (M), chemical nitrogen plus manure (NM), and control with no fertilization (CK). The results showed that the abundances of genes encoding auxiliary activities and glycosyl transferases were greater in N, and those encoding carbohydrate esterases and glycoside hydrolases were higher in NM than in other treatments. The abundance of genes encoding glycosyl hydrolases was lower in M than in other treatments. Compared to CK, long-term fertilization increased the abundances of CAZyme encoding genes in decomposing the SOM that derived from plant and bacteria biomass, but did not affect those in decomposing fungi-derived component. The Actinobacteria and Proteobacteria were the main phyla contributing to plant- and microbe-derived SOM decomposition. Mantel test indicated that the abundance of CAZyme encoding genes for plant-derived SOM decomposition was mainly affected by the content of microbial biomass nitrogen, while that for bacteria-derived SOM decomposition was associated with soil carbon and nitrogen fractions. Overall, long-term fertilization improved the CAZyme encoding genes in decomposing SOM especially derived from plant and bacteria biomass. These findings help to better understand the decomposition potential of SOM in cropping systems.

Long-term management of rice agroecosystem towards climate change mitigation

The Intergovernmental Panel on Climate Change recognize to agriculture the responsibility for about 15 % of global anthropogenic greenhouse gas (GHG) emissions, contributing to global warming. The increasing nutrient inputs in industrial agriculture affect the GHG concentration in the atmosphere and varies substantially due to rate and type of fertilizers applied to the crops, making the management more or less sustainable. In this perspective, this study has investigated at small scale the effect of different adjusted agricultural management practices, based on different nutrient dosage, to optimize the effect of rice cropping systems on carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions. Farmyard manure (FYM), rice stubbles and Azolla integrated with chemical fertilizers have been correlated with microbial and enzymatic activities, and with different carbon and nitrogen fractions in acid Inceptisol. Results have revealed that the integrated nutrient management used in rice-rice agroecosystem yielded a peak for CO2 and CH4 emissions, whereas two peaks for N2O emission. This study has shown an increase in greenhouse gas emission intensity (GHGI) and grain yield of rice in the following order: rice stubbles > FYM > Azolla and it has confirmed CH4 emission as the dominant contributor to GHGI from the rice-rice agroecosystem. When analyzed together GHGs emission and soil properties, a positive correlation was found with biological properties as well as with the different carbon and nitrogen fractions in soil. The highest GHGI has been highlighted in the treatment where recommended dose of chemical fertilizers has been combined with rice stubbles, primarily due to the increase in CH4 emissions. In contrast, the lowest GHGI has been exhibited in Azolla treated plot, probably due to the cumulative effects of the photosynthetic rate of Azolla, the release of oxygen from the Azolla roots, and the physical protection capacity of the Azolla cover, which partially avoid the CH4 diffusion from the standing water. The seasonality did not affect the estimated rates of GHGI that have been lower both in case of winter and autumn rice compared to previous studies, probably for dissimilarities in management practices. Further research is required in other cropping sequences for addressing the ecological contribution of smallholder agriculture to help reducing GHG emissions, thus, mitigating global warming with actions at local scale.

Carbon persistence of soils with long‐term biosolids amendments in California agroecosystems

AbstractBiosolids can build soil organic matter, but their ability to increase carbon and nitrogen in persistent fractions in deep soil is not well understood. We aimed to assess the mechanisms that influence soil carbon and nitrogen dynamics at three sites—Sacramento (irrigated, grazed grassland), Solano (rainfed, grazed grassland), and Merced (feed cropping system with alfalfa–corn rotation)—where soils were amended with biosolids for 20 years using density fractionations, organomineral extractions, and correlations between calcium and soil organic carbon at three depths (0–10, 30–50, and 75–100 cm). We found that amended soils had higher carbon and nitrogen content in the free‐ and occluded‐light fractions at all depths relative to the control in the Sacramento and Solano sites; however, the Merced site had a greater relative increase of carbon and nitrogen associated with the heavy fraction. Effect sizes show that biosolids increase carbon and nitrogen content in free‐ and occluded‐light fractions in the surface soil (0–10 cm), and in both light and heavy fractions in the deep soil layer (75–100 cm). Ratios of carbon to iron and aluminum show that chelation is an important mechanism of carbon stabilization in Sacramento and Solano sites throughout the soil profile. No (0–10 cm) to negative (75–100 cm) correlations were observed between calcium and soil carbon in the amended soils in the Merced site. Our results indicate that, while biosolids are typically incorporated at shallow depths, long‐term application of biosolids can increase the amount of free‐ and occluded‐light carbon fractions in deep soil.

Long-term application of organic manures and chemical fertilizers improve the organic carbon and microbiological properties of soil under pearl millet-wheat cropping system in North-Western India

An on-going long term field experiment started in Rabi 1995 at the Research Farm of the Department of Soil Science, Chaudhary Charan Singh Haryana Agricultural University, Hisar, Haryana (India) under the pearl millet-wheat cropping system was selected to study the effect of long-term application of organic manures and fertilizers on soil organic carbon and microbiological properties. Highest soil organic carbon (SOC: 1.18 %), dissolved OC (DOC: 64.74 mg kg−1) content, microbial biomass C (MBC: 618.40 mg kg−1), dehydrogenase (DHA: 72.83 μg TPF g−1 24 hr−1), alkaline phosphatase (APA: 685.44 μg PNP g−1 soil hr−1) and aryl sulfatase (ASA: 12.56 μg PNP g−1 soil hr−1) activities were observed with the application of 15 Mg FYM+150 kg N+30 kg P2O5 ha−1. Integrated application of chemical fertilizers with pressmud showed superiority in the improvement of microbial biomass nitrogen (MBN: 73.73 mg kg−1) and urease activity (69.54 μg NH4+ g−1 hr−1) than FYM or poultry manure plus NP. Beneficial impacts of the sole application of organic manures on SOC, DOC, MBC content, DHA, APA, and ASA were found in order as: FYM > pressmud > poultry manure. Impacts of nutrient management practices on soil carbon fractions decreased with depth. Poultry manure application, either alone or in combination with NP fertilizers was inferior to FYM and pressmud. The SOC had a positive relationship with MBC (R2 = 0.95) and MBN (R2 = 0.75) and, also showed a highly positive and significant correlation with microbiological properties of soil. This dynamic equilibrium among soil properties indicated that the nutrient management practices that improve SOC could lead to improve soil fertility and accrued microbiological properties in these soils. This study revealed that conjuctive use of organic manures and chemical fertilizers have positive impact on soil fertility and microbiological properties as compared to sole application of organic manures or fertilizers; and among organic manures, FYM was superior to pressmud followed by poultry manure.

Soil carbon and nitrogen responses to forage cropping systems following irrigation retirement

AbstractLimited annual precipitation and increasing scarcity of irrigation water are forcing farmers in arid and semi‐arid regions to convert irrigated fields into dryland farming, yet their impacts on soil carbon (C) and nitrogen (N) fractions are not fully understood. This study evaluated changes in soil C and N fractions and forage production under four cropping systems after irrigation retirement in a semi‐arid condition. Treatments included an annual winter wheat forage (Triticum aestivum L.) (AWW), a perennial wheat (PW) forage (T. aestivum L. × Thinopyrum spp.) (PW), a mixture of native grasses (NG), and a pasture crop (PC = AWW and NG mixture). Evaluation of various soil C and N fractions, forage dry matter yield, and nutritive value parameters suggested that soil inorganic N and potentially mineralizable N (PMN) were 38%–45% and 36%–44% greater in autumn 2020 and 62%–68% and 46%–55% greater in spring 2021 under AWW and PW, respectively, than NG and PC. Soil potentially mineralizable carbon (PMC) was 58%–129% and 64%–138% greater under NG and PW than AWW and PC. The responses of other soil C and N fractions varied with soil sampling dates but not with crops or crop × sampling date interaction. Total forage dry matter yield was 4016, 7849, 12,517, and 13,869 kg ha−1 for AWW, PW, PC, and NG, respectively, and PW had the best forage nutritive value. These results suggest soil C and N mineralization could be enhanced by adopting perennial systems, including NG, PW, and PC, while PW maintains good‐quality forage production.

Impacts of stocking densities on soil biochemical and microbial properties in a mixed-grass prairie ecosystem at two landscape positions

Grazing management is a critical land-use requirement that facilitates the preservation of plant community composition, soil properties and environmental quality. Grazing density of livestock has a significant impact on soil health, and there is a need to study the interactions of grazing densities and topographical positions influencing soil biochemical and microbial properties. This study was conducted at Cottonwood Field Station in Philip, South Dakota to assess the influence of more than 7 years of low, medium, and high grazing stocking densities (0.33, 0.41, 0.72 animal units/ac, respectively) at summit and footslope landscape positions on soil carbon (C) and nitrogen (N) fractions, microbial community composition, and enzymatic activities in a mixed-grass prairie ecosystem. Medium grazing density showed a 16% increase in soil N at the footslope compared with summit. Low grazing density significantly reduced microbial biomass C (~269 μg g−1 soil) and N (~26 μg g−1 soil) at summit compared with other grazing densities and landscape positions, except, the summit at high grazing density. Medium grazing density significantly enhanced hot-water extractable N by 21–23% at footslope compared with low grazing density at the footslope and high grazing density at the summit. Low grazing density increased urease (3.64 μg NH4+ g−1 soil h−1) at footslope than all other grazing densities and landscape positions. Low grazing density enhanced β-glucosidase by 75% than high grazing density; alkaline phosphatase was significantly greater by 60% at footslope than summit. High grazing density at the summit decreased total PLFA (mean 56.53 nmol g−1 soil) due to lower AM fungi, G (+), G (−) and actinomycetes biomass. Microbial stress indicators such as G (+)/G (−), saturated/unsaturated, monosaturated/polysaturated, GNeg stress revealed that high grazing density especially at summit position posed elevated physiological stressed conditions to the microbial community. Overall, long-term medium grazing density of 0.41 animal units/ac may enhance soil N, microbial composition, microbial biomass C and N, hot-water extractable C and N fractions, and reduce stress conditions for microbial community at both footslope as well as summit landscape positions. Moreover, long-term overgrazing of pastures, particularly at summit slopes, appears to inhibit microbial populations and degrade overall soil health.

Straw and phosphorus applications promote maize (Zea mays L.) growth in saline soil through changing soil carbon and phosphorus fractions.

Straw return has been widely recognized as an important carbon (C) enhancement measure in agroecosystems, but the C-phosphorus (P) interactions and their effects on plants in saline soils are still unclear. In this study, we investigated the effects of straw return and three P application levels, no P fertilizer (Non-P), a conventional application rate of P fertilizer (CP), and a high application rate of P fertilizer (HP), on maize growth and soil C and P fractions through a pot experiment. The results revealed that the dry matter weight of maize plant was no difference between the two straw return levels and was 15.36% higher under HP treatments than under Non-P treatments. Plant nutrient accumulations were enhanced by straw addition and increased with increasing P application rate. Straw application reduced the activities of peroxidase (POD), superoxide dismutase (SOD), catalase, and the content of malondialdehyde (MDA) in maize plants by 31.69%, 38.99%, 45.96% and 27.04%, respectively. P application decreased SOD, POD activities and MDA content in the absence of straw. The contents of easily oxidized organic carbon (EOC), particulate organic carbon (POC) and the ratio of POC/SOC in straw-added soils were 10.23%, 17.00% and 7.27% higher, respectively, than those in straw-absent soils. Compared with Non-P treatments, HP treatments led to an increase of 12.05%, 23.04% in EOC, POC contents respectively, while a decrease of 18.12% in the contribution of MAOC to the SOC pool. Straw return improved the P status of the saline soil by increasing soil available P (14.80%), organic P (35.91%) and Ca2-P contents (4.68%). The structural equation model showed that straw and P applications could promote maize growth (indicated by dry matter weight, P accumulation, antioxidant enzyme activity and MDA content) through improving soil C and P availabilities. This study provides evidence that straw return together with adequate P supply in saline soil can promote crop nutrient accumulation, attenuate the oxidation damage on crop growth, and be beneficial for SOC turnover and soil P activation.

Effects of Straw Return Duration on Soil Carbon Fractions and Wheat Yield in Rice–Wheat Cropping System

In China’s subtropical rice–wheat cropping system, the changes in the soil organic carbon (SOC) pool due to long-term straw return and its connection with crop yield remain unclear. This study aims to provide insights into establishing a sensible straw return system by evaluating the differences in the distribution and variation rates of SOC, light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), particulate organic carbon (POC), and mineral-associated organic carbon (MOC) in the 0–20 cm soil layer under different durations of straw return. Additionally, the study analyzes the relationship between the changes in SOC and its fractions and wheat yield. The experiment was conducted in 2019 in a rice–wheat rotation field with ten years of straw return treatments: no straw return (NR) or 1, 2, 3, 4, 5, 6, 7, 8, 9 year(s) of straw return (SR1–9), and an additional treatment in 2020 (10 years of straw return, SR10). The results revealed that with an increase in the duration of straw return, the contents of SOC, LFOC, HFOC, and POC gradually increased, showing the highest increments of 45.88%, 187.22%, 41.55%, 97.89%, and 28.21%, respectively, compared to the NR treatment. However, after eight years of straw return, the compound annual increase in soil organic carbon and its components was lower than in years 1–8, indicating a trend of diminishing increments. The SOC content and its variation were significantly correlated with the content and variation of LFOC, HFOC, POC, and MOC, with the highest sensitivity observed for the variation in LFOC, indicating the strong influence of the duration of straw return. The SOC and its fraction contents showed significant positive correlations with wheat yield, with the highest contribution to wheat yield increase attributed to an increase in LFOC content. In summary, straw return enhances the 0–20 cm deep soil carbon pool, with LFOC being the most sensitive indicator, reflecting the influence of the duration of straw return on soil carbon pools.

Spatial Distribution Characteristics of Soil Carbon and Nitrogen in Citrus Orchards on the Slope of Purple Soil Hilly Area

Since the 1990s, a large area of sloping farmland in a purple soil hilly region of southwest China was converted into an orchard to prevent soil erosion, increase soil fertility, and elevate economic benefits for farmers. In order to explore the spatial distribution of soil carbon (C) and nitrogen (N) fractions on the slope of returning arable lands to citrus orchards in purple soil hilly areas, a soil sampling event was carried out in a citrus orchard at the Yanting Agro-ecological Experimental Station of Purple Soil, Chinese Academy of Sciences, to examine the differences in soil C and N fractions and their influencing factors. The results showed that the slope position had significant effects on the contents of soil total nitrogen (TN), nitrate nitrogen (NO3--N), and dissolved organic carbon (DOC) (P &lt; 0.05), but the effects were not obvious regarding the total organic carbon (SOC) and ammonia nitrogen (NH4+-N) of the soil (P &gt; 0.05). For topsoil (0-30 cm), the variation trend of soil NO3--N content along the slope was upper slope &lt; middle slope &lt; lower slope, whereas the TN and DOC contents along the slope exhibited the trend of upper slope &gt; middle slope &gt; lower slope. The contents of soil C and N in each slope position generally showed a downward trend with increasing soil depth (0-30 cm). The contents of soil TN, SOC, NO3--N, and DOC were significantly affected by soil depth (P &lt; 0.05). The TN storage (0-30 cm) significantly decreased from the top to the bottom within the soil slope, with a value of 2.37, 1.89, and 1.62 t·hm-2 (reported as N) for the upper slope, middle slope, and lower slope, respectively. There was no significant difference in SOC reserves along the slope, with a range from 56.12 to 58.48 t·hm-2 (reported as C). Our results provide scientific basis for understanding the spatial distribution of soil nutrients of the restored farmland in purple soil hilly areas. Our research suggests that the spatial distribution of soil carbon and nitrogen storage should not be ignored when predicting the response of soil nutrients to land use change.

Study on the effect of biomass charcoal-biogas application technology on soil carbon and nitrogen fractions and soil microbiological properties based on biomass charcoal-biogas application technology

Abstract The application of biogas and biomass charcoal to terrestrial crops and vegetables can promote their growth. The effects of the combined application of the two on soil carbon and nitrogen fractions and soil microbiological properties are not well-studied. Therefore, in this experiment, the red and yellow soil of Hangzhou City, Zhejiang Province, was used as the research object, and two factors, biomass charcoal and biogas, were set up to investigate the soil changes under the conditions of biomass charcoal-biogas application. One-way ANOVA and correlation analysis examined the differences in soil and crop radish under biomass charcoal-biogas application technology. The experimental results showed that the 2% application of hog manure charcoal at 350°C and 100% N amount of replacement of biosolids dosing treatments were the most effective, which could increase the content of organic matter, soluble organic carbon, etc., as well as the content of nitrogen in the soil, and improve the activity of soil enzymes. The enhancement of radish yield was greater with the application of swine manure charcoal with biogas than with the single application of both, and the maximum radish yield was achieved with the 100% N amount substitution of biogas with the application of swine manure charcoal at 2%-350°C treatment. The heavy metal contents in radish were below the limit values after 9 months of application of both biogas and biomass charcoal, which did not affect the edible safety of radish.

Straw return-enhanced soil carbon and nitrogen fractions and nitrogen use efficiency in a maize–rice rotation system

Summary Considering straw resource utilization and air pollution prevention, straw return has been commonly practiced in China. However, the practicability of plenty straw return in an emerging maize–rice rotation and their effects on soil C and N pools have not been extensively investigated. This study has been conducted to examine the effects of straw return on soil nutrients, soil functional C and N fractions, and then to figure out their relationships with yield and N use efficiency. Two treatments of straw return (S2Nck) and without straw return (S0Nck) were compared in 3-year field experiment, and subplots without N application were added in their respective plots in the third year. The results showed that, relative to the control (S0Nck), straw return significantly increased soil mineralized nitrogen (Nmin), available P, and exchange K content by 11.7%, 41.1%, and 17.4% averaged across 3-year experiments, respectively. Straw return substantially increased soil dissolved organic C, microbial biomass C, and microbial biomass N content by 73.0%, 25.2%, and 36.8%, respectively. Furthermore, straw return markedly increased C and N retention in particulate organic matter in microaggregates (iPOM) and mineral associated organic matter within microaggregates (intra-SC), but significantly reduced in free mineral associated organic matter (free-SC) fraction. The structural equation modeling analysis showed that yield and the partial factor productivity of N were positively correlated with labile and slow soil C and N fractions. Consequently, straw incorporation significantly increased grain yields of maize by 14.7% and rice by 15.1%. The annual potential reduction proportion in fertilizer-N induced by straw return was estimated to be 25.7% in the third year. This study suggests that the incorporation of straws is an effective way to enhance soil nutrients and regulate soil C and N pools to improve crop production and has the potential to reduce N fertilizer application under maize–rice rotation in subtropical regions.

Long-term Fertility Management Effect on Soil Carbon Fractions under Godavari Zone

Long-term Fertility Management Effect on Soil Carbon Fractions under Godavari Zone

The Effects of Various Long-Term Fertilizer Applications on Soil Carbon Fractions in a Winter Wheat Monoculture Area

The Loess Plateau in China has long grappled with issues such as chronic soil erosion, poor soil structure, and diminished organic matter. Soil organic carbon plays a crucial role in enhancing soil fertility, and fertilization is a key tool that influences it. In a comprehensive field experiment, we examined five fertilization methods: no fertilization (CK); traditional fertilization used by local farmers (FP); nutrient-balanced fertilization with nitrogen, phosphorus, and potassium (OF); chemical fertilizers used in conjunction with organic fertilizers (OFM); and chemical fertilizers paired with bio-organic fertilizers (OFB). Our findings revealed that the OFM and OFB treatments were the most effective, explaining 84.35% and 81.26% of the variation in soil carbon sequestration, respectively. Further, the OF, OFM, and OFB treatments demonstrated superior effectiveness compared with the FP treatment in enhancing the soil carbon fractions. However, these fertilization patterns did not significantly alter the active-to-inert carbon ratio of the soil. OF, OFM, and OFB treatments enhanced the stability of soil carbon pools more than FP treatment. In structural equation modeling, factors such as microbial biomass nitrogen and phosphorus, soil pH, and β-N-acetyl glucosidase indirectly exhibited a limiting effect on the carbon pool stability index (CPSI), while β-glucosidase displayed an indirect positive correlation with the carbon fractions. In contrast, dissolved organic carbon, low-molecular-weight organic carbon, high-molecular-weight organic carbon, and crop yield demonstrated direct positive correlations with the CPSI. Consequently, both a balanced application of chemical fertilizers and the combination of organic and chemical fertilizers were effective in enhancing and sustaining the soil’s organic carbon content, thereby contributing to soil fertility stability. To this end, this study can inform the efficient selection and use of fertilizers, improving crop yield and soil carbon content.

Coastal distribution and driving factors for blue carbon fractions in the surface soil of a warm-temperate salt marsh in China

A better understanding of blue carbon (BC) sequestration can not only contribute to a better elucidation of global carbon cycle processes but can also lay the foundation for the incorporation of BC ecosystems into regional and global carbon offset schemes. In this study, the surface soils of seven plots along a landward to seaward distance gradient were analyzed for the concentrations and stocks of soil organic carbon (SOC), soil inorganic carbon (SIC), dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC), as well as soil physical (bulk density, texture, moisture), chemical (pH, electrical conductivity), and microbiological (phospholipid fatty acid) properties in the coastal wetlands. Correlation, variation partition and random forest (RF) analyses were used to identify key variables correlating with BC fraction distribution patterns. The results suggested that SIC, DIC, and DOC, exhibited similar landward-increasing trends but the driving factors were distinct from each other. Based on correlation and RF analysis, both SIC and DIC were closely related to soil moisture and clay contents, but microbial indicators of arbuscular mycorrhizal fungi and actinomycete, were found to be associated with SIC, and abiotic properties played less important but still substantial roles in predicting DIC dynamics. In contrast with the other three investigated BC fractions, SOC showed a slight tendency toward enrichment in the seaward direction, and SIC was identified as the main driving factor. DOC showed no significant correlations with the other BC fractions, and its variation could not be explained well by the selected edaphic parameters. The soils in the YRD's tidal Suaeda salsa salt marshes showed a significant negative coupled SOC–SIC correlation, which was potentially related to divergent sedimentary processes and potential biotransformation between SOC and SIC. These results highlight the importance of integrating multiple BC fractions and their interactions into attempts to explore key mechanisms of BC cycling.

Changes in soil organic carbon stocks and its physical fractions along an elevation in a subtropical mountain forest

Soil microorganisms are the drivers of soil organic carbon (SOC) mineralization, and the activities of these microorganisms are considered to play a key role in SOC dynamics. However, studies of the relationship between soil microbial carbon metabolism and SOC stocks are rare, especially in different physical fractions (e.g., particulate organic carbon (POC) fraction and mineral-associated organic carbon (MAOC) fraction). In this study, we investigated the changing patterns of SOC stocks, POC stocks, MAOC stocks and microbial carbon metabolism (e.g., microbial growth, carbon use efficiency and biomass turnover time) at 0–20 cm along an elevational gradient in a subtropical mountain forest ecosystem. Our results showed that SOC and POC stocks increased but MAOC stocks remained stable along the elevational gradient. Soil microbial growth increased while microbial turnover time decreased with elevation. Using structural equation modeling, we found that heightened microbial growth is associated with elevated POC stocks. Moreover, MAOC stocks positively correlate with microbial growth but show negative associations with both POC stocks and soil pH. Overall, the increase in SOC stocks along the elevational gradient is primarily driven by changes in POC stocks rather than MAOC stocks. These findings underscore the importance of considering diverse soil carbon fractions and microbial activities in predicting SOC responses to elevation, offering insights into potential climate change feedbacks.