Labile Carbon Content Research Articles

Labile carbon content and nutrient availability determines microbial composition in topsoil and subsoil following land‐use change in subtropical China

AbstractEvaluating the impact of land‐use intensification on soil microbial communities is essential for recognizing the implications on microbiome stability and ecosystem function. The microbial biomass and enzyme activity in the topsoil have been found to decrease as a consequence of natural forest conversion; however, the impact of land‐use conversion on the microbes in subsoil remains largely unclear. Here, we examined the effect of primary forest conversion to plantations and cultivated lands on microbial communities at three sites with similar soil, climate, and landform. The forest conversion was set as the experimental treatment, and the primary forest as the control. A linear mixed‐effect model was applied to investigate the role of environmental parameters in shaping the soil microbial biomass and community determined by the phospholipid fatty acids analysis in both the topsoil (0–20 cm) and subsoil (20–40 cm). Compared to the primary forest, the total microbial biomass, β‐1,4‐N‐acetylglucosaminidase, leucine aminopeptidase, acid phosphatase activities, and labile organic C fraction contents in both topsoil and subsoil were reduced in cultivated lands. The ratios of gram‐positive bacteria to gram‐negative bacteria and arbuscular mycorrhizal fungi to saprotrophic fungi in subsoil decreased by 45%–53% and increased by 29%–151%, respectively, following the primary forest conversion to cultivated lands. The response ratio (the percentage of microbial and enzyme indicator response to the primary forest conversion) ranged from −80% to 140% depending on the soil depth, specific microbial group, and converted land‐use type. Microbial biomass and enzyme activity are primarily controlled by the labile organic C content and nutrients availability in both topsoil and subsoil. This study suggests that the primary forest conversion exerts an adverse effect on the microbial biomass, enzyme activity, and substrate availability in both topsoil and subsoil, highlighting the degradation of subsoil health in subtropical China.

Influence of biodestructors on sequestration of labile carbon compounds in the soil

Ukraine stands as a testament to agricultural wealth due to its fertile soils, most notably, its significant share of the world’s chornozem. Rich soil is fundemantal to agricultural production, and therefore the success of the agricultural industry heavily relies on the fertility of the soil. However, modern agricultural practices in Ukraine, have led to increased anthropogenic impact on soils, affecting their biodiversity and humus content. In this regard, it is becoming increasingly important to perform comprehensive studies of microbiological, biochemical and chemical processes in the soil in response to different agricultural interventions. The urgent need to restore natural ecosystems to preserve their biodiversity and ensure ecological stability poses new scientific challenges, emphasizing the importance of urgent measures aimed at protecting the environment from pollution and degradation. This research aims to explore the effects of biodestructors on the deposition of labile carbon compounds in the soil during long-term consistent corn cultivation. The research was conducted during 2020–2023 within the framework of a stationary field experiment of the scientific research department of the «Druzhba Nova» in Varva village, Chernihiv region. The soil is a typical low-humus chornozem with the experiment focusing on a monoculture corn crop rotation. The DKC 4351 corn hybrid was sown at a density of 82 thousand units per hectare, employing a three-part experiment design: 1) a UAN control at 32–28 l/ha, 2) Ecostern Classic at 2 l/ha combined with UAN 32–28 l/ha, and 3) Ecostern Bacterial at 2 l/ha alongside Ecostern Trichoderma at 1 l/ha and UAN 32–28 l/ha. In the present study, the influence of biodestructors on soil’s agrochemical and microbiological indicators, as well as corn yield was evaluated. In a long-term stationary field experiment conducted on a typical low-humus chornozem, we investigated the influence of microbial preparations — plant residue biodestructors — on the deposition of labile carbon compounds in the soil under continuos corn cultivation. The application of Ecostern Classic and a combination of Ecostern Bacterial + Ecostern Trichoderma biodestructors resulted in an increase of labile carbon content by 0.11% and 0.18%, respectively, compared to the control. The aim of further analysis was to determinate the dynamics of the organic matter transformation coefficient, which is a marker of enhanced microbiological activity in the soil and a predominance of organic matter synthesis over its mineralization. In treatments utilizing biodestructors, this indicator was significantly higher than control values throughout the study. The survival of the fungal bioagent from Ecostern Classic and Ecostern Trichoderma bioproducts in the soil was monitored by assessing the population dynamics of the Trichoderma genus species. Results demonstrated an increase by an average of 19 thousand CFU/g with Ecostern Classic and by 34 thousand CFU/g with the combined use of Ecostern Bacterial with Ecostern Trichoderma, compared to 28 thousand CFU/g in control soil samples. This may indirectly indicate a successful colonization of the bioagent in treated soils. Using BIOTREX technology to evaluate the soil’s ecophysiological diversity, we found that the diversity index increased from 3.66 in control samples to between 4.87 and 5.61 in treatments with biodestructors. According to the further BIOTREX assessment, the use of biodestructors not only increased soil biodiversity, but also improved soil health. The application of these biodestructors also significantly boosted corn grain yield with an increase of 0.32 t/ha with Ecostern Classic treatment and 0.18 t/ha with the combined use of Ecostern Bacterial with Ecostern Trichoderma, compared to control.

Biodegradable microplastics pose greater risks than conventional microplastics to soil properties, microbial community and plant growth, especially under flooded conditions

Biodegradable plastics (bio-plastics) are often viewed as viable option for mitigating plastic pollution. Nevertheless, the information regarding the potential risks of microplastics (MPs) released from bio-plastics in soil, particularly in flooded soils, is lacking. Here, our objective was to investigate the effect of polylactic acid MPs (PLA-MPs) and polyethylene MPs (PE-MPs) on soil properties, microbial community and plant growth under both non-flooded and flooded conditions. Our results demonstrated that PLA-MPs dramatically increased soil labile carbon (C) content and altered its composition and chemodiversity. The enrichment of labile C stimulated microbial N immobilization, resulting in a depletion of soil mineral nitrogen (N). This specialized environment created by PLA-MPs further filtered out specific microbial species, resulting in a low diversity and simplified microbial community. PLA-MPs caused an increase in denitrifiers (Noviherbaspirillum and Clostridium sensu stricto) and a decrease in nitrifiers (Nitrospira, MND1, and Ellin6067), potentially exacerbating the mineral N deficiency. The mineral N deficit caused by PLA-MPs inhibited wheatgrass growth. Conversely, PE-MPs had less effect on soil ecosystems, including soil properties, microbial community and wheatgrass growth. Overall, our study emphasizes that PLA-MPs cause more adverse effect on the ecosystem than PE-MPs in the short term, and that flooded conditions exacerbate and prolong these adverse effects. These results offer valuable insights for evaluating the potential threats of bio-MPs in both uplands and wetlands.

Modern arable and diverse ley farming systems can increase soil organic matter faster than global targets

Abstract Agriculture can be pivotal in mitigating climate change through soil carbon sequestration. Land conversion to pasture has been identified as the most effective method to achieve this. Yet, it creates a perceived trade-off between increasing soil carbon and maintaining arable food crop production. In this on-farm study, we assessed the potential of incorporating a 2-year diverse ley (consisting of 23 species of legumes, herbs, and grasses) within a 7-year arable crop rotation for soil organic matter accumulation. We established upper and lower boundaries of soil organic matter accumulation by comparing this approach to positive (permanent ley, akin to conversion to permanent pasture) and negative (bare soil) references. Our findings in the 2-year diverse ley treatment show greater soil organic matter accumulation in plots with lower baseline levels, suggesting a potential plateau of carbon sequestration under this management practice. In contrast, the positive reference consistently showed a steady rate of organic matter accumulation regardless of baseline levels. Moreover, we observed a concurrent increase in labile carbon content in the 2-year ley treatment and positive reference, indicating improved soil nutrient cycling and ecological processes that facilitate soil carbon sequestration. Our results demonstrate that incorporating a 2-year diverse ley within arable rotations surpasses the COP21 global target of a 0.4% annual increase in soil organic carbon. These findings, derived from a working farm's practical and economic constraints, provide compelling evidence that productive arable agriculture can contribute to climate change mitigation efforts.

Quantifying direct CO2 emissions from organic manure fertilizer and maize residual roots using 13C labeling technique: A field study

Organic manure compost offers benefits like enhanced crop yield, improved soil health, and increased soil carbon storage. However, its application might elevate direct CO2 emissions from organic matter decomposition. Beyond manure compost, significant sources of CO2 emissions in agricultural settings are from residual roots and root exudates of pre-crops, and soil carbon. Quantifying the contribution of these sources to CO2 emissions is crucial for maximizing carbon reduction in crop-livestock systems, yet field studies have not assessed this contribution. Our study at the Yucheng field station in Shandong Province, China employed 13C labeling on summer maize to generate 13C-labeled manure compost and maize root, which is used to differentiate CO2 emissions from these sources. Our results revealed novel insights into the magnitude and patterns of CO2 emissions from these sources. The emission pattern of 13C-CO2 derived from manure compost, root and root exudates was similar, but the magnitude differed. Specifically, manure compost accounted for 5 % of the total CO2 emissions, while residual roots and root exudates contributed 2 % and 57 %, respectively, suggesting a higher labile carbon content in root exudates. The remaining 36 % of CO2 emissions was derived from the soil and other sources. CO2 emission factors were 6 % for manure compost, 12 % for roots, and 2 % for root exudates. By quantifying the direct emissions from manure compost, residual roots, root exudates, and soil, our study highlights the dominant role of managing root exudates in overall CO2 emissions. These findings can guide targeted carbon reduction strategies, emphasizing the importance of managing root exudates and understanding the relative innocuousness of manure compost applications in the context of CO2 emissions. This novel research quantifies the direct contribution of individual manure compost to CO2 emissions, providing valuable data for carbon cycle models and improving understanding of CO2 contributions from new carbon inputs.

Microbial attributes as structural quality index for physical health of an Oxisol under compaction levels

Microbial activity is a sensitive indicator of soil structure improvement provided by plant species in the physical recovery of compacted soils. This study aimed to assess the impacts of crop species on soil aggregate classes for soil recovery after compaction and identify which microbial attributes best describe the structural quality index for soil physical health in an Oxisol under no-tillage. The experiment comprised three crop species—maize, ruzigrass, and black oats—cultivated under four degrees of compactness produced by chiseling or machine traffic under long-term no-tillage. Soil aggregates were separated by dry sieving into five diameter classes to assess the basal respiration, microbial biomass carbon, metabolic quotient for CO2 (qCO2), labile carbon, cellulase activity, and total organic carbon. The values of microbial indicators for the bulk soil were estimated as a weighted mean of each attribute using aggregate size distribution. The lowest values for total organic carbon, labile carbon, and microbial biomass carbon were observed in aggregates > 4 mm. The basal respiration values increased from 8.2 µg C-CO2 g d−1 in the aggregates > 4 mm, to 22.1 µg C-CO2 g soil d−1 in the aggregates < 0.5 mm (+170%). Similarly, the cellulase activity increased approximately four times comparing aggregates > 4 mm (38 µg glucose g−1 d−1) to those < 1 mm (181 µg glucose g−1 d−1). The total organic carbon and microbial biomass carbon were found to be little affected by crops. However, the plots cultivated with black oats or ruzigrass exhibited higher cellulase activity, basal respiration, and qCO2 in comparison with maize, primarily due to the greater content of labile carbon. Increasing the mean weight diameter from 3 mm to 8 mm led to a decrease in the labile carbon (−27.4%), microbial biomass carbon (−25.5%), cellulase activity (−70%), and basal respiration (−21.6%), thereby revealing negative effects of soil compaction on microbial attributes. The degree of compactness did not influence the values of total organic carbon and qCO2. The response of the microbial indicators depends on the aggregate diameter classes. The results of this study indicate that cultivation of cover crops decreases the negative impacts of soil structure degradation on soil microbial quality. Cellulase activity and labile carbon were considered as new potential indicators of soil compaction for soil physical health studies—highly sensitive and quickly responsive to managements that induce soil structure changes in an Oxisol.

Biochar Aged for Five Years Altered Carbon Fractions and Enzyme Activities of Sandy Soil

Biochar applied to soil has been considered as an effective tool for mitigation of atmospheric carbon dioxide emission and enhancement of carbon storage in soil, which may also enhance soil quality. However, the effect of biochar aged for 5 years on the different carbon fractions and enzyme activities as well as its changes, is not well understood in the cropland sandy soil of northern China. Therefore, a field trial was carried out in 2014 with biochar applied once at 0, 5.25, 10.50, 21.00 and 42.00 g·kg−1 (BC0, BC1, BC2, BC3, and BC4, respectively). We evaluated the influence of biochar addition to the changes in soil organic carbon (SOC), labile carbon pools (readily oxidized carbon, dissolved organic carbon, and microbial biomass carbon) and enzyme activities (invertase, urease, and catalase). Biochar significantly increased SOC (122.00%) and altered the content of labile carbon (increased ROC, DOC and MBC by 71.29%, 10.35%, and 900.00%, respectively). Soil urease and invertase activities increased by 55.81% and 46.76%, respectively, with an increase in biochar application rate, but catalase activity significantly decreased by 31.79%. The values of the geometric means of labile carbon (0.88) and enzyme activities (2.39) for the BC3 treatment were higher than others, which indicated that the biochar application rate of 21.00 g·kg−1 is suggested for the sandy soil. Our results suggest that the application of biochar in sandy soil for five years increased soil carbon sequestration, changed enzyme activities and ameliorated soil quality.

Variations in composition and stability of biochars derived from different feedstock types at varying pyrolysis temperature

Feedstock type and pyrolysis temperature primarily affect the properties of resultant biochar. Therefore, the effects of several different feedstock types and various pyrolysis temperatures on structural, chemical, proximate, morphological, and elemental compositional characteristics of the resultant biochars were explored. Nine types of wastes (date palm fiber waste (DF), date palm leaf waste (DL), date palm petiole waste (DP), tomato plant waste (TM), cucumber plant waste (CC), poultry litter (PL), chicken feather waste (CH), cow dung (CD), and conocarpus waste (CN) were collected and pyrolyzed at varying temperatures (300, 400, 500, and 600 °C) to produce different types of biochar, which were subjected to physio-chemical, proximate, and ultimate analyses. Distinctive variations were observed in the characteristics of the used feedstock types and their derived biochars. The biochars derived from CC exhibited the highest pH (8.41–11.02), while the biochars derived from CH demonstrated the minimum pH (7.99–8.40). Overall, the biochars derived from PL, CC, TM, and DL showed higher contents of C as compared to the other biochars, suggesting higher stability. Contrarily, the biochars derived from CH and CD exhibited a higher labile C fraction, indicating its lower recalcitrance than other tested biochars. The biochars produced at low pyrolysis temperatures showed a comparatively amorphous surface with lower alkalinity and electrical conductivity, while higher moisture, net negative charge, labile carbon, and volatile contents. Contrarily, the higher pyrolysis temperature demonstrated the higher ash and fixed carbon contents with more surface porosity and comparatively higher non-labile carbon fraction. Biochar produced at 600 °C exhibited H/C and O/C atomic ratios of <0.2, suggesting higher stability and recalcitrant potential against biochars produced below 500 °C, which showed H/C and O/C atomic ratios in the range of 0.2–0.4.

Constraints on the spatial variations of soil carbon fractions in a mangrove forest in Southeast China

Mangroves, carbon-rich ecosystems, store significant amounts of carbon in the soil to mitigate climate change. For better mangrove carbon management, the spatial distributions and driving factors of distinct soil carbon fractions, notably soil inorganic carbon (IC) and labile carbon, require clarification. Here, we quantified variations in the soil carbon fractions (total organic carbon (TOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), permanganate-oxidizable carbon (POC), and IC) with landward distance and soil depth, and identified the means by which edaphic and biotic factors affect soil carbon fractions in a mangrove forest in Southeast China. Average TOC, IC, POC, DOC, and MBC densities were 15.22 kg/m3, 1.39 kg/m3, 4.23 kg/m3, 43.49 g/m3, and 63.25 g/m3, respectively. Soil total nitrogen was the most important factor affecting TOC, POC, and MBC. Soil IC was found to be controlled by pH, and plant biomass was the main factor explaining soil DOC variation. Except for MBC, landward distance was negatively correlated with organic carbon fractions and positively correlated with IC via soil nutrients, pH, bulk density, and plant biomass. Soil depth directly or indirectly altered soil carbon fractions via soil nutrients, pH, clay, and salinity, resulting in negative relationships with TOC, POC, and MBC and a positive relationship with IC. Collectively, our results indicate that future changes in soil total nitrogen content and pH are likely to impact carbon storage in mangroves, and that the conservation of landward mangroves is important with respect to their high labile carbon contents.

Organic management enhances soil quality and drives microbial community diversity in cocoa production systems

Maintaining soil quality for agricultural production is a critical challenge, especially in the tropics. Due to the focus on environmental performance and the provision of soil ecosystem services, organic farming and agroforestry systems are proposed as alternative options to conventional monoculture farming. Soil processes underlying ecosystem services are strongly mediated by microbes; thus, increased understanding of the soil microbiome is crucial for the development of sustainable agricultural practices. Therefore, we measured and related soil quality indicators to bacterial and fungal community structures in five cocoa production systems, managed either organically or conventionally for 12 years, with varying crop diversity, from monoculture to agroforestry. In addition, a successional agroforestry system was included, which uses exclusively on-site pruning residues as soil inputs. Organic management increased soil organic carbon, nitrogen and labile carbon contents compared to conventional. Soil basal respiration and nitrogen mineralisation rates were highest in the successional agroforestry system. Across the field sites, fungal richness exceeded bacterial richness and fungal community composition was distinct between organic and conventional management, as well as between agroforestry and monoculture. Bacterial community composition differed mainly between organic and conventional management. Indicator species associated with organic management were taxonomically more diverse compared to taxa associated with conventionally managed systems. In conclusion, our results highlight the importance of organic management for maintaining soil quality in agroforestry systems for cocoa production.

Mollic soils situated in non-Chernozem regions in Slovakia

Abstract This study is focused on an evaluation of some important soil properties as a result of the genesis of mollic soils which are located outside of the main Chernozem regions in Slovakia. Several soil profiles selected from the Soil Monitoring Network in Slovakia were evaluated and interpreted. Unified analytical procedures used in soil monitoring system have been applied. Following soil indicators: pH, humus content, and qualitative components as humic acids (HA) and fulvic acids (FA) as well as the fractional composition of HA, the content of labile carbon (CL), potentially mineralisable nitrogen (Npot) have been analysed. Based on obtained results in more details, it may be said that the dark-coloured soils in non-Chernozem regions opposite dark-coloured soils in Chernozem regions have a higher content of labile carbon and higher index of lability as well as higher CL: Npot ratio. This indicator seems to be more significant than the often used C/N ratio. In addition, the darkcoloured soils in non-Chernozem regions are characteristic with higher content of aliphatic carbon as well as lower content of carboxylic groups (-COOH) and lower value of the optical parameter (E1% 6). These indicators in more detail are of higher interpretation value for a better evaluation of dark-coloured soils in non-Chernozem regions compared with similar soils in Chernozem regions.

Factors affecting ammonium capture by some Victorian lignites

ABSTRACT Nitrogen (N) loss from intensive animal husbandry leads to economic loss and environmental damage. Lignite has a demonstrated capacity to suppress ammonia (NH3) volatilisation from manure and this has been attributed to the pH, cation exchange capacity (CEC), pH buffer capacity and labile carbon (C) content of the lignite. Whilst lignite is effective in mitigating NH3 loss, the capacity for N retention and how this is influenced by the lignite's properties are not well studied. It is unclear if lignites from different mines will have comparable N retention under similar conditions. In this study, we characterised five Victorian lignites for their C-containing functional groups, surface morphology and chemical properties. These were then related to the ammonium () adsorption capacity of the lignites using a batch isotherm technique. The contribution of biological immobilisation to the N retention capacity of the lignites was determined using 15N tracing in an incubation study. All lignites were acidic (pHH2O: 3.3–5.8; pHCaCl2: 3.0–5.4). The lignite had similar patterns of distribution of C functional groups with the carboxyl C between 2.8% and 5.3%. The maximum adsorption capacity (Qmax ) varied with the composition of the lignite and correlated positively with the lignites’ CEC, pH and carboxyl groups. Increase in pH, especially from pH >5, resulted in up to 3-fold increase in Qmax (25.6 mg g−1), likely due to deprotonation of carboxyl groups. Compared to adsorption, the biological immobilisation of did not play a substantial role in the overall lignite's N retention capacity. Highlights Victorian lignites were assessed for their retention capacity using adsorption isotherms and 15N tracing. adsorption capacity of lignites increased (up to 3-fold) with pH, especially from pH 5 to 7. Biological immobilisation did not play a substantial role in the retention capacity of the lignites. pH-dependent adsorption was the dominant means by which lignite retained .

THE INFLUENCE OF BIOLOGICAL PREPARATIONS AND THEIR MIXTURES ON SOIL AGROCHEMICAL PROPERTIES IN WINTER WHEAT

Intensive tillage accelerates soil erosion, reduces the content of organic matter and carbon in the soil. Scientists around the world talk extensively about soil conservation policies. The process of accumulation and maintenance of soil organic matter is important for the long-term preservation of agro-system productivity. Crop production technologies applied should increase carbon sequestration in the soil (Kaiser, Kalbitz, 2012; Baumhardt et al., 2015). The study was conducted in 2018–2019 in the winter wheat crop “Sailor”. An experiment with two factors was performed: preparations of biological origin and their mixtures were used with the application of different tillage technologies. The aim of this study is to determine the effect of biological preparations on soil agrochemical properties in winter wheat crop using different tillage technologies. The use of biological preparations and their mixtures, in many cases, increased the content of water-soluble (labile) carbon in the soil comparing compensatory nitrogen 8 kg t of straw, without biological preparations to stimulate straw mineralization . The content of labile carbon was particularly increased by mixtures of two preparations (Ruinex + Penergetic k, Ruinex + Azofix and Penergetic k + Azofix) using both tillage technologies: when applying no-tillage, the content of soluble carbon increased from 2.9% to 12.2%, and when using the mixtures in ploughless tillage – from 1.4% to 10.3. The combination of the three preparations increased the content of soluble carbon by 5.4% more in ploughless technology, in no-tillage – only 0.5%. The use of one-component biological preparations in ploughless tillage also increased the content of water-soluble carbon, and in no-tillage – reduced it but insignificantly.

Contrasting effects of warming and N deposition on soil microbial functional genes in a subtropical forest

Climate warming and nitrogen (N) deposition are expected to increase in the coming decades. The consequences of the interaction between warming and N deposition on forest ecosystems and their functions (i.e., carbon sequestration) remain uncertain. In this study, we examined the composition, diversities, and abundances of soil microbial functional genes in a subtropical forest after four years of exposure to warming and N addition. We found that warming alone did not have a significant effect on the composition, diversities, and abundances of functional genes, suggesting that four years were not long enough to reach the critical threshold that would activate a response to warming from soil functional genes in the subtropical forest. Conversely, warming significantly decreased soil labile carbon (C) content. The application of N in combination with warming significantly enhanced the diversities and abundances of functional genes associated with C and N cycling, leading to an accelerated loss of soil N. Interestingly, the interaction between warming and N addition did not have a significant effect on the diversities and abundances of functional genes associated with C and N cycling. Redundancy analysis indicated that a decrease in pH caused by N addition significantly affected the abundances of those functional genes. Overall, our study fills a research gap by examining the effect of simultaneous warming and N deposition on soil microbial functional genes in subtropical forests. Additionally, the study indicates that microbial functional genes are more sensitive to a combination of warming and N addition than to warming alone. Therefore, the effects of multi-factor global change on soil microbial functional genes cannot be underestimated.

Optimization of tillage rotation and fertilization increased the soil organic carbon pool and crop yield in a semiarid region

AbstractTillage and mineral fertilization are important strategies for maintaining crop production, but their effects on soil organic carbon (SOC) and labile fractions in semiarid regions are controversial. A 10‐year field experiment was conducted to evaluate the effects of fertilization and tillage on SOC stock, labile fractions, soil quality and crop yields in a wheat–maize cropping system at the Loess Plateau. Results showed that balanced fertilization could provide comprehensive nutrition for crops and increase the crop residue input carbon, thereby increasing the SOC, readily oxidizable carbon, particulate organic carbon and dissolved organic carbon contents. In 0–50 cm layers, the SOC stock was increased by 3% under balanced fertilization compared to conventional fertilization. For tillage, no‐tillage (zero tillage) and subsoiling rotation with less soil disturbance and higher stabilization rate of input carbon was the most effective tillage practice for increasing SOC stock. This tillage technique increased the labile carbon contents by 41%–63%, 5%–19% and 26%–67% compared to ploughing in 0–10 cm, 20–35 cm and 35–50 cm layers, respectively. Balanced fertilization combined with no‐tillage and subsoiling rotation (BF + NS) increased carbon pool management index due to higher SOC and labile carbon contents, which contributed to the improvement of soil quality and the promotion of crop growth. Among all treatments, BF + NS treatment produced the highest SOC stock as well as wheat and maize yields. Therefore, BF + NS is the best strategy to increase SOC sequestration and to improve soil quality and productivity in semiarid regions.

Excellent excrement? Frass impacts on a soil's microbial community, processes and metal bioavailability

The commercial rearing of insects is a growing economic sector. Therefore, an assessment was made of the potential of its by-product, frass, to be a soil improver. Essential plant nutrients were extracted (using 0.01 M CaCl2 or Mehlich 3) from frass of mealworms (Tenebrio molitor), black soldier flies (Hermetia illucens) and buffalo worms (Alphitobius diaperinus). A 28-day incubation, in which frass was added to a sandy loam soil at application rates of 2.5% or 5% (w/w), assessed its effects on soil microbial biomass, abundance of bacteria, archaea and fungi, carbon mineralisation and nitrification. In a separate 56-day incubation, the impact of frass on heavy metal bioavailability in an artificially contaminated, carbon-poor substrate was tested. All frass types featured high electrical conductivity, a mildly acidic to neutral pH and C: N ratios between 11 and 16. Black soldier fly frass (BSFF) was richer in extractable ammonium, phosphorus, potassium and magnesium than mealworm frass (MWF) and buffalo worm frass (BWF) but poorer in extractable calcium. All frass types stimulated carbon mineralisation, nitrification, bacterial and archaeal 16S rRNA gene copy numbers, and fungal biomass as determined by ergosterol concentrations. Bacterial and particularly fungal abundances were stimulated by the 5% frass application rate whereas archaeal abundances were greater in the 2.5% application rate regimes. The 2.5% application rate of MWF and BWF led to a profound build-up of soil extractable nitrite. Correspondingly, these treatments featured the highest 16S rRNA gene copy numbers of archaea, a domain encompassing organisms which oxidise ammonium to nitrite. No nitrite was detectable in soil amended with BSFF. The 5% application rates induced microbial biomass growth (as determined by extractable DNA concentrations) only when BSFF was applied. This was possibly due to differences in the frass types' extractable nutrient or labile carbon contents. BSFF and BWF amendment led to significantly higher microbial biomass in a metal-contaminated substrate. This was likely due to frass providing nutrients, energy and reduced metal bioavailability: extractable zinc, copper, cadmium and nickel concentrations fell due to increased metal sorption and complexation. All frass types could be used as ameliorants in metal-contaminated soils, while BSFF shows most promise as an organic fertiliser as its use did not cause soil nitrite build-up.

Assessment of soil organic carbon stocks in relation to variation in physiography under sub-mountainous Shiwalik ranges of lower Himalayas, India

A study was conducted in lower Shiwaliks of Punjab, India to study the soil organic carbon (SOC) stock variation in hill, piedmont plain and alluvial plain regions of Punjab, and further to investigate the SOC variability down the slope in the lower Shiwaliks region of Punjab. The SOC fractions viz. very labile carbon, labile carbon, less labile carbon and recalcitrant were determined using standard methodologies. The total SOC stock in 0–60 cm soil depth was highest in plain region (31.81 Mg ha−1), followed by piedmont (23.43 Mg ha−1) and lowest in hill region (22.86 Mg ha−1). Whereas, the SOC concentration in surface layer was highest in foot slope (5.76 g kg−1) followed by mid slope (4.14 g kg−1) and lowest in up slope (2.32 g kg−1). Among the SOC fractions the average labile carbon content in soil samples was found in the order, hills (0.81 g kg−1) > piedmonts (0.73 g kg−1) > plains (0.50 g kg−1). The soil bulk density (Db) was higher in the plain than that of piedmont and hills. Moreover, a similar trend is observed in case of water holding capacity. Regression analysis has revealed significant relationship between Db and SOC stock at p < 0.05. Further, analysis of variance (ANOVA) at p < 0.05 has indicated significant differences among concentration of SOC and stock influenced by land use and soil depths. Thus, an understanding of the effect of physiography on SOC via such studies is important for soil quality management.

Effects of planting broadleaf trees and Moso bamboo on soil carbon mineralization and microbial community structure

We conducted a pot experiment to investigate the effects of planting broadleaf tree species (i.e., Cinnamomum camphora, Schima superba, and Quercus glauca) and Moso bamboo (Phyllostachys edulis) on soil carbon mineralization and microbial community structure. The rates of soil carbon mineralization were measured via alkali trapping method. The structural and functional diversity of soil bacterial and fungal communities were analyzed by terminal restriction fragment length polymorphism (T-RFLP) and real-time quantitative PCR techniques. The soil planted with Moso bamboo exhibited a significantly higher carbon mineralization rate and labile carbon content than those in the soils planted with broadleaf tree species. The underground biomass of Moso bamboo was higher than that of broadleaf tree species. The soil bacterial communities were more sensitive than fungal communities to the planting of different plant species . Moreover, soil fungal diversity of Moso bamboo was distinctly different from that of broadleaf tree species. Compared to the diversity of soil bacterial communities, the diversity of soil fungal communities was more closely related with soil pH, organic carbon content, and carbon mineralization. In comparison to the broadleaf tree species, the Moso bamboo planting could substantially increase soil organic carbon minera-lization, which was affected mainly by the soil fungal community structure.

Quantification of soil labile carbon content in lowland rice ecology amended by different bio-wastes

Soil organic carbon (SOC) plays a critical role in terrestrial carbon cycling and is central to preserving soil quality. The effects of bio-wastes on soil carbon storage were investigated. The SOC has different pools and fractions including microbial biomass carbon (MBC), readily mineralizable carbon (RMC), and water soluble carbon (WSC). Each has a varying degree of decomposition rate and stability. The rice straw + RDF treatment was more effective in increasing WSC, MBC, RMC concentrations than the RDF treatment alone. Therefore, it could be the best option for improving carbon storage and soil health while emerging as best bio-waste management technology in the rice–rice cropping system.

Soil trace gas fluxes in living mulch and conventional agricultural systems

AbstractRow crop agriculture is a significant source of two major greenhouse gases (GHGs) (carbon dioxide [CO2] and nitrous oxide [N2O]) and the air pollutant precursor ammonia (NH3). Fluxes of these naturally occurring trace gases are often augmented by agricultural practices, such as fertilizer application and crop systems management. A living mulch system (LMS) maintains a live cover crop year‐round and is an emerging agricultural system that can reduce pesticide and fertilizer use while maintaining yields. Multiple trace gas fluxes of GHGs and NH3 had not previously been measured together in an LMS of corn (Zea mays L.) and white clover (Trifolium repens L.). This study compared soil gas fluxes in a white clover LMS with two other cover crop systems and a no‐cover‐crop system. Infrared and gas chromatography measurements were taken over 2 yr in northern Georgia. Mean soil CO2 and N2O fluxes (159.7 kg ha−1 d−1 and 0.027 kg N ha−1 d−1, respectively) observed in LMS plots exceeded those from other treatments. Soil temperature, moisture, potentially mineralizable nitrogen (N), and nitrate partially explained these differences. Mean soil NH3 emissions were greater in LMS (0.089 kg N ha−1 d−1) compared with no cover crop (0.038 kg N ha−1 d−1). Increased N2O and NH3 fluxes could be from release of N from decomposition of clover and from release of N into the soil as the corn shades the clover. Although LMS plots did not reduce trace gas emissions, labile carbon content was at least 100 mg kg−1 greater than other treatments after 2 yr, improving soil health.