Labile Organic Carbon Research Articles

Correction: Zheng et al. Changes in the Soil Labile Organic Carbon Fractions following Bedrock Exposure Rate in a Karst Context. Forests 2022, 13, 516

The authors wish to make the following corrections to this paper [...]

Effects of different organic fertilisers on the microbial functional diversity and bacterial communities in a tobacco soil

ABSTRACT A long-term field experiment was conducted to investigate the effects of organic manure (commercial organic manure, CFM1; cow manure, CFM2; green manure, CFM3) and chemical fertiliser (CK) on the microbial diversity of a tobacco-planted soil using Biolog ECO and 16S rRNA sequencing technology. The results showed that organic manure treatments increased the available nutrient content in the soil, including nitrogen (AN, 2.1–13.3%), potassium (AK, 14.2–31.8%), labile organic carbon (19.9–37.4%), and microbial biomass carbon (11.9–21.0%), as well as the mean weight diameter and geometric mean diameter. The average well colour development value and McIntosh diversity index in CFM1 treatment increased by 23.6% and 18.9%, respectively, compared with CK. The 16S rRNA sequencing analysis suggested that CFM1 and CFM2 treatments improved the richness and diversity of soil bacteria and recruited more potentially beneficial bacteria. Redundancy analysis showed that soil physicochemical properties, excluding AN and Olsen–P were positively correlated with the abundance of bacteria dominant in the CFM1 treatment. This indicates that application of CFM1 is a sound fertilisation strategy to improve soil fertility and create a good ecological environment.

Long‐term grassland restoration exerts stronger impacts on the vertical distribution of labile over recalcitrant organic carbon fractions in Mollisols

AbstractLand use change influences soil organic carbon (SOC) distribution in soil matrix. Conversion of cropland to grassland or forestland has the potential to sequester more carbon and influence the carbon allocation. Soil carbon sequestration happens within different physical and chemical fractions. This study aimed to investigate the vertical distribution of SOC fractions under 29‐yr of cropland, grassland, and forestland of a typical Mollisol and to derive specific factors for SOC fraction changes associated with land use conversion. Soil samples within 100 cm soil depth were fractionated by density and humic methods. Biomass of litter residues and plant roots were also measured. Together with plant root biomass, the contents of total SOC and organic carbon (OC) fractions decreased along soil profile under three land uses. At each soil depth, total SOC and OC fractions followed the same order of grassland > forestland > cropland except for higher OC contents in heavy fraction, fulvic acid, and humin in cropland than those in forestland at the 0–10 cm layer. Compared with forestland and cropland, 29‐yr grassland exerted stronger effects on the profile distribution of labile OC (water‐soluble and light OC fractions) than recalcitrant OC (humic and heavy fractions), significances were observed at 0–80 cm layers for the labile OC and at 0–40 cm layers for the recalcitrant OC (P < .05). Larger root biomass and better soil structure in grassland might facilitate such changes. Grassland restoration, with greater C sequestration potential and larger liable OC contents, may help improve soil quality better than forestland and cropland in this Mollisol region.

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.

Green Manure Amendment in Paddies Improves Soil Carbon Sequestration but Cannot Substitute the Critical Role of N Fertilizer in Rice Production

Clarifying the benefits of carbon sequestration and crop production of continuous green manure amendment is crucial for sustainable agricultural development. Here, using a long-term located experiment, we assessed the effects of 18 years’ ryegrass/milk vetch amendment with (NF, 150 kg N ha−1) or without nitrogen (N) fertilizer input (CK), on soil carbon management indices, paddy methane (CH4) emissions and rice yields. The results showed that green manure, rather than fertilization, played a critical role in soil CMI, increasing the carbon pool index but reducing the carbon management index. The increased soil organic carbon and the reduced labile organic carbon were the main causes for this performance. Additionally, the effects of both fertilization and green manure amendment on CH4 emissions were insignificant; however, fertilization significantly increased grain yield by 39.30% compared to CK. As a result, the methane emission intensity under fertilization treatment was notably lower than that from CK. The findings suggest that green manure amendment is a profitable manipulation for enhancing carbon sequestration without increasing paddy CH4 emissions. However, this cannot substitute the critical role of N fertilizer in rice production.

Soil carbon, nutrients and their stoichiometry decrement in relation to paddy field degradation: Investigation in a subtropical region

Owing to intensive cultivation, paddy fields suffer from varying degrees of degradation and loss of soil organic carbon (SOC), consequently jeopardizing the industry’s future sustainability. Accurate assessment of soil nutrient loss and SOC stability is not only indispensable for developing measures to arrest and counter this problem but to also gauge the impact of degraded soils in paddy fields towards the global carbon budget. Herein, we examine soil nutrients, their stoichiometric ratios, and carbon pool management index (CPMI) across 26 paddy fields in a subtropical region under three degraded levels – namely, low-risk degradation, high-risk degradation, and severe degradation. Our results showed a 23% likelihood of severe degradation in sampled paddy fields of southeastern China. Compared with low-risk degradation soils, the severe degradation soils had significantly lower concentrations of total nitrogen (N) (31%), labile organic carbon (C) (50%), total phosphorus (P), and available P concentrations, while the iron (Fe) and available N tended to increase. Compared to low-risk degradation, C:N, C:P, N:P ratios were 25, 50, and 30%, respectively, lower in severe degradation plots. Low CPMI values were associated with soils that are at high-risk for degradation and severe degradation, indicating that C pools in degraded paddy soils were gradually deteriorating. Moreover, soil stoichiometric ratio and nutrients were significantly affected by soil pH, Fe3+, sand, and electrical conductivity, and there were significant and positive correlations between CPMI and soil C, N and LOC concentrations. Based on the above results, our work provided evidence that paddy degradation led to a greater loss of soil carbon and nitrogen than phosphorus, reducing the soil’s potential for C sequestration. Therefore, adopting proper agricultural practices whilst minimizing the cultivation of exhaustive crops could mitigate further soil degradation and assist in restoring soil fertility and C sequestration in paddy fields of Southeastern China.

Soil Moisture Affects the Rapid Response of Microbes to Labile Organic C Addition

Pulsed inputs of labile organic carbon (LOC) are common in soils and significantly affect carbon cycling. However, it remains unclear how soil moisture content affects microbial responses to LOC inputs and the relative contributions of native soil organic matter (SOM) and LOC derived from CO2 emissions during this process. In this study, we aimed to elucidate how moisture content affects microbial response to LOC inputs and native SOM. Here, 13C-labeled glucose was added to soils under nine soil moisture treatments [ranging from 10 to 90% of the water holding capacity (WHC)], and the immediate utilization of LOC and native SOM by microbes was measured. We found that the response of soil microbes to LOC was rapid, and promoted native SOM decomposition. Soil moisture content influenced the microbial usage of LOC and native SOM. A soil water content of 60% WHC was the optimal threshold for changes in the proportion of LOC and native SOM utilized by the microbes. Specifically, we found that when the soil moisture content was below 60% WHC, the ratio between LOC and native SOM increased with increasing moisture content levels. It gradually decreased when the soil moisture content was above 60% WHC. Overall, these findings emphasize the important role of moisture and LOC inputs in soil C cycles.

14 year applications of chemical fertilizers and crop straw effects on soil labile organic carbon fractions, enzyme activities and microbial community in rice-wheat rotation of middle China

Traditional fertilization management can damage soil structure and lead to severe soil erosion. The practice of crop straw returning to the field reduces the negative impact of straw burning and improves soil quality. We investigated the effects of these agricultural practices on soil organic carbon components, enzyme activities, and soil microorganisms over 14 years of field experiments. Specifically, we studied four management strategies: no fertilizer or crop straw returning (CK), traditional chemical fertilization (NPK), crop straw returning (S), and crop straw returning with chemical fertilizer (NPKS). We found NPKS treatments significantly (P < 0.05) increased the dissolved organic carbon (DOC), microbial biomass carbon (MBC), particulate organic carbon (POC) and readily oxidized organic carbon (ROC) concentrations by 79.32 %, 82.16 %, 92.46 %, and 104.32 % relative to CK. Furthermore, under NPKS, the activities of soil enzymes related C, N, and P (α-glucosidase (αG), β-glucosidase (βG), cellulase (CBH), xylanase (βX), acetyl β-glucosaminidase (NAG), leucine aminopeptidase (LAP), and acid phosphate (AP)) were increased by 54.66 %, 113.26 %, 76.73 %, 52.41 %, 45.74 %, 56.69 %, and 68.92 % relative to CK, respectively. Redundancy analysis and structural equation modelling showed that straw returning had positive effects on soil microbial community diversity and richness, and also improved microbial activity which is favorable in the degradation of soil carbon. Furthermore, we found that soil fungi were more sensitive than bacteria to changes in soil carbon composition and enzyme activities following straw returning. These results suggest that straw returning combined with chemical fertilizer can be an effective strategy to improve soil labile organic carbon components, enzyme activities, and ecological function of microorganisms.

Potential role of nitrite-dependent anaerobic methane oxidation in methane consumption and nitrogen removal in Chinese paddy fields

Nitrite-dependent anaerobic methane oxidation (n-damo), catalyzed by bacteria closely related to Candidatus Methylomirabilis oxyfera, links the global carbon and nitrogen cycles. Currently, the contribution of n-damo in controlling methane emissions and nitrogen removal, and the key regulatory factors of this process in Chinese paddy fields are poorly known. Here, soil samples from 20 paddy fields located in different climate zones across China were collected to examine the n-damo activity and bacterial communities. The n-damo activity and bacterial abundance varied from 1.05 to 5.97 nmol CH4 g−1 (dry soil) d−1 and 2.59 × 105 to 2.50 × 107 copies g−1 dry soil, respectively. Based on the n-damo activity, it was estimated that approximately 0.91 Tg CH4 and 2.17 Tg N could be consumed annually via n-damo in Chinese paddy soils. The spatial variations in n-damo activity and community structure of n-damo bacteria were significantly (p < 0.05) affected by the soil ammonium content, labile organic carbon content and pH. Furthermore, significant differences in n-damo activity, bacterial abundance and community composition were observed among different climate zones. The n-damo activity was found to be positively correlated with the mean annual air temperature. Taken together, our results demonstrated the potential importance of n-damo in both methane consumption and nitrogen removal in Chinese paddy soils, and this process was regulated by local soil and climatic factors.

Responses of Labile Organic Carbon and Extractable Cadmium Fractions in an Agricultural Soil Following Long-Term Repeated Application of Pig Manure and Effective Microbes.

Long-term pig manure addition has been widely applied in red soil to improve soil fertility. However, the influence of combined utilization of pig manure and effective microbes (EM) on soil organic carbon (SOC) and Cd are not well understood. This study conducted a 23-year (1996-2019) long-term fertilization field trial to investigate the changes of different fractions of SOC and Cd under chemical fertilization (CF), pig manure (PM), and pig manure with effective microbes (PM + EM) treatments in an agricultural soil of Jiangxi Province, South China. The results showed that the pig manure addition significantly enhanced the contents of SOC and Cd in the soils compared with the CF treatments. Furthermore, with the increment of SOC, the PM + EM treatment significantly increased the contents of soil microbial biomass carbon, dissolved organic carbon and easily oxidizable carbon compared with the pig manure application alone. Meanwhile, compared with the CF treatments, the EM addition significantly enhanced the exchangeable and oxidizable fractions of Cd, thus the potential Cd environment risk due to pig manure application should be carefully assessed.

Combined System of Organic Substrate and Straw-Degrading Microbial Agents Improved Soil Organic Matter Levels and Microbial Abundance in a Rice-Wheat Rotation.

Rice-wheat rotation is one of the most intensive agricultural planting modes in China and is pivotal to develop optimized straw-returning management in situ to improve soil fertility and productivity in agricultural ecosystems. Previous studies have mainly focused on the effects of straw return with a single application of organic fertilizers. The integrated management of different fertilizers in improving the management of straw return in situ is not well known. In this study, a field experiment was conducted from 2017 to 2019 to explore the effects of a combined system of modified organic substrate (MOS) and straw-degrading compound microbial agent (CMA) on soil physiochemical properties, labile organic carbon, microbial activities, and soil microbial community composition under the background of direct crop straw return and chemical fertilizer utilization. Four treatments were designed: (1) control check; (2) CMA; (3) MOS; and (4) MOS + CMA. The results showed that theMOS + CMA treatment had the combined advantages of soil organic matter (SOM) accumulation, soil nutrient increase and soil microbial community alteration, which may be more suitable for improving the quality and fertility of sandy loam soil. This study provides novel insights for further understanding the effects of organic substrates and composite microbial agents on SOM changes and microbial community composition and function in the field, which has important implications for sustainable crop production and agricultural development.

Sloping Farmlands Conversion to Mixed Forest Improves Soil Carbon Pool on the Loess Plateau.

Vegetation restoration is considered a potentially useful strategy for controlling soil erosion and improving soil organic carbon (SOC) in arid and semiarid ecosystems. However, there is still debate regarding which vegetation restoration type is the best choice. In this study, four vegetation restoration types (i.e., grasslands, shrubs, forests and mixed forests) converted from sloping farmlands were selected to explore the SOC variation among the four types and to investigate which soil factors had the greatest effect on SOC. The results showed while the magnitude of effect differed between vegetation restoration type, all studied systems significantly increased SOC and labile organic carbon contents (p < 0.01), soil nutrients such as total nitrogen (TN) (p < 0.01), available nitrogen (AN) (p < 0.01), total phosphorus (TP) (p < 0.05) and available phosphorus (AP) (p < 0.05), soil enzyme activities such as phosphatase (p < 0.01), soil microbial biomass carbon (MBC) (p < 0.05), and basal respiration (BR) (p < 0.05), but had significant negative correlationswith polyphenol oxidase (p < 0.05). However, the effects of vegetation restoration of farmland converted to natural grasslands, shrubs, forests and mixed forests varied. Among the types studied, the mixed forests had the largest overall positive effects on SOC overall, followed by the natural grasslands. Soil nutrients such as N and P and soil microbial activities were the main factors that affected SOC after vegetation restoration. Mixed forests such as Robinia pseudoacacia and Caragana korshinskii are the best choice for farmland conversion on the central of the Loess Plateau.

Soil labile organic carbon indicating seasonal dynamics of soil organic carbon in northeast peatland

Peatlands have persisted as massive carbon pool in terrestrial ecosystem. Labile organic carbon (LOC) plays a vital role in carbon cycling in high-latitude peatlands, which is an important indicator of seasonal soil organic carbon (SOC) dynamics. However, the contributions of LOC fractions are poorly understood. Here, soil samples were collected at a high-latitude peatland site located in Northeastern China, and SOC and its labile fractions, including dissolved organic carbon (DOC), light-fraction organic carbon (LFOC), easily oxidizable carbon (EOC) and microbial biomass carbon (MBC) were determined, as well as the environmental and microbial parameters. The results presented seasonal variations in SOC with 352.09 ± 4.93 g/kg in July, 357.84 ± 14.02 g/kg in September, 366.74 ± 17.41 g/kg in November, 413.58 ± 7.83 g/kg in January, and 422.17 ± 8.74 g/kg in April. It was shown that DOC and LFOC were to be important indicators in seasonal carbon dynamics from an elastic net regression model. Although DOC and LFOC accounted for only 3.88% ± 0.50% and 0.34% ± 0.21% in this peatland, they might drive the changes in SOC. The redundancy analysis (RDA) model indicated that pH, total nitrogen (TN), precipitation, soil temperature and actinomycetes PLFAs are important driving factors of SOC pools. A structural equation modeling (SEM) was used to part the direct and indirect effects of factors on soil carbon dynamics based on the covariance structures. The results showed that environmental factors influenced SOC pools through different pathways. Soil pH affected carbon pools directly, while soil temperature influenced the carbon cycling indirectly by affecting soil microbes based on the path analysis. This study suggests that DOC and LFOC had the potential to cause the changes of carbon dynamics in northeast crater peatlands.

Chemical composition of labile carbon fractions in Hungarian forest soils: Insight into biogeochemical coupling between DOM and POM

Understanding how the chemical composition of dissolved and particulate organic matter (DOM and POM) is affected by environment factors is critical because these labile pools of carbon are involved in an array of biological, chemical and physical processes. In this study, the chemical composition of DOM and POM was measured in 13 forest soils using UV–Vis spectroscopy, fluorescence spectroscopy with parallel factor analysis (PARAFAC modelling) and FT-IR spectroscopy.There were significant differences between the soils for the SUVA indexes, PARAFAC components and relative intensities of different IR bands. Redundancy analysis (RDA) revealed that soil parameters had a strong influence on the chemical composition of DOM and POM with high constrained variability (77.9 and 77.1 %, respectively). The pH of the soils proved to be an important controlling factor for both DOM and POM, regulating the concentration of the C3 PARAFAC component (low-molecular-weight compounds associated with biological activity) and the aromatic compounds of POM (aromaticity, rA1630 and rA1515). The silt content was the other main regulating factor controlling the chemical characteristics of the labile pool, having a strong negative correlation with the specific UV absorbance (SUVA) values of DOM due to the preferential adsorption of hydrophobic moieties. RDA analysis also revealed that there is a strong correlation between the chemical composition of POM and DOM: the relative amount of aromatic compounds (rA1515, rA1630 for aromatic rings and rA1270 for phenolic compounds) in the POM fraction was closely correlated with the SUVA values of the DOM. This clearly indicates a strong biogeochemical link between the two labile organic carbon fractions; the high molecular weight compounds of the DOM fraction may be derived from lignin-like structures of the POM fraction.

Effects of magnetite on phosphorus storage and carbon cycling in Lake Michigan shoreline sediments

Lake Michigan, one of the Laurentian Great Lakes, hosts the world's largest freshwater sand dune system and is ecologically and economically important. Phosphorus (P) plays a key role in the lake biota, while industrial P runoff, pollution controls, and invasive species add to the complexity of P dynamics in the shoreline ecosystem. Rich in iron oxide minerals, the Lake Michigan shoreline has been little studied with respect to P bioavailability and cycling. In this study, we analyzed magnetite concentrations in samples collected from 19 beach and sand dune sites located along the eastern shore of Lake Michigan, and we examined the mineral effects on P bioavailability through adsorption experiments, sediment fractionation and extraction, and microcosm incubations. We find that magnetite is widely distributed in the sand dune ecosystem and its content can reach very high levels (>30% dry weight) in natural beach sediments. P has the strongest adsorption affinity to magnetite when compared to prominent sediment minerals calcite and quartz, and the native magnetite holds up to 10 and 28 times more moderately and strongly bound P, respectively, than the bulk sediments. Microcosm incubations with native sediments showed that the addition of P significantly increased microbial decomposition of labile organic carbon, whereas the added synthetic magnetite did not significantly reduce the P bioavailability or decrease the carbon degradation. This research highlights the multiple effects of magnetite on P storage, bioavailability, and labile organic carbon degradation in the shoreline sand dunes, which may provide new insights into understanding nutrient and carbon cycling in the Great Lakes ecosystem.

Changes in the Soil Labile Organic Carbon Fractions following Bedrock Exposure Rate in a Karst Context

Soil labile organic carbon fractions (SLOCFs) mainly include microbial biomass carbon (MBC), dissolved organic carbon (DOC), easily oxidized organic carbon (EOC) and light fraction organic carbon (LFOC). The link between bedrock exposure rates with SLOCFs and the carbon pool management index under karst rocky desertification has not been well understood. We selected the bedrock exposure rate and vegetation coverage of 30–50% (light bedrock exposure, LBE), 50–70% (moderate bedrock exposure, MBE) and &gt;70% (intense bedrock exposure, IBE) as the experimental sample plots according to the classification standard of karst rocky desertification, and then selected a sample plot of 0–30% (secondary forest, SF) as the control. This study compared the concentrations and stocks of soil organic carbon (SOC) and SLOCFs and analyzed the relevant carbon pool management index on karst landforms at Anshun, S.W. China. The aims were to determine the relationship between bedrock exposure rates and SLOCFs and to identify the most limiting factors for SLOCFs in karst rocky desertification areas. We found that (1) the concentrations and stocks of SLOCFs declined with increasing soil depth. SOC, DOC and MBC showed IBE &gt; LBE &gt; MBE &gt; SF; LFOC decreased with increasing bedrock exposure rate, and EOC did not show obvious regularity. (2) The carbon pool management index and sensitivity index had significant differences under different bedrock exposure rates. Redundancy analysis and linear regression showed that the increase in bedrock exposure rate had a great impact on MBC, DOC, EOC and SOC. In conclusion, the increase of bedrock exposure rate has no side impact on the DOC, EOC and MBC of the soil, but side effects are exhibited by LFOC. Secondary forest improves the integrity of karst landscapes, and does not change the soil properties as well as the concentrations and stocks of SLOCFs in karst rocky desertification areas.

Effects of Warming and Increased Precipitation on Soil Respiration of Abandoned Grassland in the Loess-Hilly Regions

Clarifying the changing trends and driving factors of soil respiration in fragile habitats under the background of climate change is of great significance for understanding the regional carbon cycle and the conversion of ecosystem carbon source and sink functions. This research focused on grasslands that had been naturally abandoned and restored for 12 years in the loess hilly region of northern Shaanxi, using an open top chamber (OTC) and artificially increased natural rainfall to simulate climate warming and precipitation increase and their interaction. Furthermore, we used a combination of field monitoring and indoor analysis to explore soil water content, temperature, and nutrient characteristics and the response characteristics of soil respiration rate to warming and increased precipitation and further analyzed the key factors driving changes in soil respiration. The results showed that:① warming (W) significantly increased the 5 cm soil temperature, with an average increase of 1.34℃ throughout the sampling year, whereas the increased precipitation (P50%) treatment significantly reduced the 5 cm soil temperature, reducing the average 5 cm soil temperature during the entire sampling year by 0.88℃ and increasing the soil water content (SWC) at the same time. The SWC was 13.12% and 16.45% higher than that in the control (CK), respectively. In addition, compared with that in the CK, the treatment of warming and increased precipitation (WP50%) not only increased soil temperature but also increased SWC; in general, the increase in temperature and precipitation played an antagonistic effect on the influence of soil temperature and humidity. ② P50% significantly increased the content of soil organic carbon, dissolved organic carbon, and labile organic carbon, causing changes in the soil stoichiometric ratio and the distribution characteristics of labile-recalcitrant carbon components, whereas W did not have a significant impact on organic carbon. In addition, soil total nitrogen and phosphorus and available nitrogen and phosphorus nutrients were not significantly different between treatments. ③ P50% significantly increased the Rs rate, and the effect of W on the soil respiration rate mainly depended on the seasonal precipitation and temperature. It was demonstrated that warming in winter and seasons with abundant rainfall had a significant promotion effect on the soil respiration rate. The exponential fitting of soil respiration rate and 5 cm soil temperature found that the soil respiration temperature sensitivity (Q10) was the highest under the precipitation treatment, reaching 1.68, whereas the Q10 was the lowest under the warming treatment (1.50). ④ Linear regression analysis showed that soil organic carbon, dissolved organic carbon, and labile organic carbon were all significantly positively correlated with soil respiration rate. Variation partitioning analysis showed that soil temperature, SWC, and nutrient characteristics explained 64.43% of the variation in soil respiration rate. The soil temperature and SWC were the main controlling factors of the change in soil respiration rate, with an explanation degree of 31.16%. Correlation analysis also showed that there was a significant correlation between SWC, soil temperature and respiration rate, soil organic carbon, dissolved organic carbon, labile organic carbon, C:N, and C:P. In summary, the climate prediction of abandoned grassland tending toward warm temperatures and high humidity in the loess hilly region will significantly affect the regional hydrothermal environment and nutrient characteristics, change the distribution ratio of soil labile and recalcitrant carbon, and promote regional soil carbon emissions. The analysis results showed that the key factor driving the change in soil respiration rate of abandoned grassland in the loess hilly region was soil temperature and SWC characteristics.

Restoration of organic-matter-impoverished arable soils through the application of soil conditioner prepared via short-time hydrothermal fermentation.

The diversity and stability of critical microbial communities are of great importance for ensuring soil fertility. From the perspective of stimulating microbial diversity in organic-matter-impoverished arable soils, soil conditioner with a certain proportion of labile organic carbon was prepared by short-time hydrothermal fermentation (SHF). The effects of applying SHF, along with soil conditioner derived from traditional aerobic fermentation (TF) and heterogeneous fertilizer (HF), on soil texture, dissolved organic matter evolution, the structure of humic acid, and the succession of dominant microbial taxa were evaluated. SHF enhanced the storage capacity of soil organic carbon and nitrogen retention, and increased the relative abundance of Proteobacteria, Firmicutes and Nitrospirae in organic-matter-impoverished arable soil, with Lysobacter as its significant difference species. In conclusion, the proposed soil conditioner and the positive effects observed in this study indicate that it could be used to solve dual problems of food waste recycling and arable soil improvement.

Changes in soil organic carbon stocks from reducing irrigation can be offset by applying organic fertilizer in the North China Plain

Elaborate water and fertilization management to increase soil organic carbon (SOC) accumulation is important in maintaining high agricultural productivity and a sound ecological environment. Here, a field experiment was conducted for eight years to investigate the effects of irrigation regimes and fertilizer types on SOC stocks and labile organic carbon concentrations (particulate organic carbon, POC; dissolved organic carbon, DOC; and microbial biomass carbon, MBC). The irrigation regimes were no irrigation (W0); presowing irrigation (W1); presowing and jointing irrigation (W2); and presowing, jointing, and anthesis irrigation (W3). The fertilizer types were no fertilizer (C0), mineral fertilizer only (C1), half mineral plus half cattle manure (C2), and cattle manure only (C3). Thus, sixteen treatments were created and laid out in a split block design with triplicates. Both irrigation and manure application distinctly enhanced SOC accumulation. POC, DOC, and MBC were mainly affected by manure application in surface soil (0–20 cm) and by irrigation in deep soil (40–60 cm). The interaction between irrigation and fertilization on SOC and labile organic carbon concentrations was not significant in the 0–60 cm soil layer. The SOC stocks and relative SOC sequestration rate increased with increasing irrigation and cattle manure inputs. There was no significant difference in SOC stocks between W2C2 (108.15 Mg C ha−1) and W3C1 (109.05 Mg C ha−1), as well as between W1C2 (90.25 Mg C ha−1) and W2C1 (87.07 Mg C ha−1), indicating that in W2 and W1, replacing half of the nitrogen with organic manure can result in equal SOC stocks caused by increasing irrigation under mineral fertilizer alone. This study emphasizes the important role that irrigation plays in SOC management and provides theoretical support to improve the SOC stock by reducing irrigation and applying cattle manure in the North China Plain.

Land Use, Landform, and Soil Management as Determinants of Soil Physicochemical Properties and Microbial Abundance of Lower Brahmaputra Valley, India

Due to the shifting course of the Brahmaputra River, the fluvial landforms of the Brahmaputra Valley of Assam, India, are prone to changes in landform and land use. For sustainable soil management under such conditions, it is crucial to have information about soil physicochemical and biological properties for different land uses. Therefore, the present study was conducted to investigate the soil physicochemical properties and soil microbial population across five major land uses under different landforms, such as paddy fields, banana systems, and arecanut cultivations in the alluvial plains; and rubber plantations and sal forests in the uplands, with varying slope gradients and soil depths (0–25 cm and 25–50 cm) in the lower Brahmaputra Valley. The results of the analysis of variance revealed that the effects of different landforms and land uses were found to be statistically significant on very labile soil organic carbon (VLSOC), available K, B, Fe, Mn, Zn, and Cu, and soil moisture content across two different soil depths. Paddy cultivated systems recorded the highest (1.23%) soil organic carbon (SOC), but these levels were statistically at par with other land use scenarios except for banana systems; whereas, forests and rubber plantations showed the highest VLSOC (0.38% and 0.34%, respectively,) and were significantly different from other land use scenarios. All soil microbial populations (bacteria, fungi, and actinomycetes) studied varied significantly in different land uses across varying soil depths. Perennial land uses under arecanut, rubber, and forest cultivations showed significantly higher microbial populations than paddy and banana systems. The principal component analysis (PCA) identified SOC, VLSOC, Cu, K, B, P, and the bacteria count as the major soil quality parameters of the study area. The results showed that landforms, land use, and management practices collectively affect soil properties. Therefore, soil management choices should take into consideration the landforms and land use for maintaining soil health and its sustainability.