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Both biochar and layered double hydroxide (LDH) have drawbacks in regard to the removal of heavy metals. The combined application of biochar and LDH not only solved the problem of the easy agglomeration of LDH but also effectively improved the heavy metal adsorption capacity of biochar. In this work, a MgFe–LDH banana straw biochar composite (MgFe–LDH@BB), with a regular hydrotalcite structure, was synthesized by employing a simple hydrothermal method. The composite showed an ultra-high adsorption capacity for lead (Pb), cadmium (Cd), and zinc (Zn) in water. A series of experiments were conducted to investigate the adsorption characteristics of MgFe–LDH@BB. At pH = 6.0, MgFe–LDH@BB demonstrated the effective adsorption of Pb, Cd, and Zn. In addition, the results showed that the adsorption of Pb, Cd, and Zn by MgFe–LDH@BB was rapid and conformed to pseudo-second-order kinetic and Langmuir models, indicating single-layer chemical adsorption. The maximum adsorption capacity of MgFe–LDH@BB for Pb, Cd, and Zn was 1112.6, 869.6, and 414.9 mg·g−1, respectively. Moreover, the adsorption mechanisms of MgFe–LDH@BB mainly included metal hydroxide/carbonate precipitation, complex formation with hydroxyl groups, and ion exchange. Meanwhile, MgFe–LDH@BB had the ability to immobilize heavy metals in soil. The surface-rich functional groups and cation exchange promoted the transformation of active heavy metal ions into a more stable form. [ABSTRACT FROM AUTHOR]

Introduction: Susbtantial agricultural wastes are produced globally which need urgent management policies. To explore the effective utilization of agricultural waste in enhancing soil quality and carbon sequestration capacity, straw and its biochar can be applied as soil ameliorants. Methods: This study was designed to investigate the impact of different return-to-field methods of rice straw on the transformation between different carbon components in the soil of Siraitia grosvenori i fields. We hypothesize that rice straw and its biochar, as soil amendments, can influence the transformation and cycling of different carbon components in the soil of S. grosvenorii fields through various return-to-field methods. Rice straw, rice straw biochar, and "rice straw + rice straw biochar" were applied as additives in a 2-year field experiment. Results: The results showed that the field application of rice straw and its biochar increased the content of soil organic carbon, the amount of organic carbon mineralization, particulate organic carbon, mineral-associated organic carbon, dissolved organic carbon, and readily oxidizable organic carbon content, while reducing the content of soil microbial biomass carbon. The combined application of rice straw and biochar in S. grosvenorii cultivation fields had a more significant effect on various soil carbon fractions compared to the use of either rice straw or biochar alone. The co-application of rice straw and its biochar to the soil increased the content of soil organic carbon by 117.4%, enhanced the mineralization of organic carbon by 100.0%, and reduced the content of soil microbial biomass carbon by 61.6%. The metabolic entropy and microbial entropy of rice straw and its biochar mixed application in the field were 5.2 and 0.18 times higher than of the control group, respectively. Discussion: In summary, the return of rice straw and biochar to the field improves soil structure and the content of recalcitrant organic carbon, providing a habitat for microorganisms, thereby promoting the stability and cycling of soil organic carbon. [ABSTRACT FROM AUTHOR]

To examine the mechanisms of organic carbon transformation and sequestration by biochar in citrus orchard soil, a 100-day organic carbon mineralization test was conducted using citrus orchard soil from a 5-year-old forest. Calcium-modified citrus peel biochar (OBC-Ca) was applied at rates of 0%, 1%, 2%, and 4%. The results indicated that different percentages of OBC-Ca significantly influenced the mineralization processes in citrus orchards. Specifically, the cumulative mineralization of soil organic carbon was notably reduced by 8.68% and 17.00% with the application of 2% and 4% OBC-Ca, respectively, compared to the control group. Random forest analysis revealed that microbial biomass carbon (MBC), readily oxidizable carbon (ROC), and dissolved organic carbon (DOC) were critical indicators for predicting the cumulative mineralization of soil organic carbon. MBC and ROC were found to inhibit the cumulative mineralization, while DOC promoted it. As the proportion of OBC-Ca applications increased, MBC rose by 2.63% to 10.46%, ROC increased by 16.41% to 108.59%, and DOC increased by 0.48% to 11.67%. Correlation analysis demonstrated a significant negative correlation between the cumulative mineralization rate of soil organic carbon and soil enzyme activity, with soil sucrase content increasing significantly by 216.42% to 393.44% compared to the control. The application of calcium-modified biochar effectively reduces carbon dioxide emissions from citrus orchard soils, with a 4% application yielding the most favorable outcomes for enhancing soil carbon sinks, thereby positively impacting the carbon sequestration potential of citrus orchard soil. [ABSTRACT FROM AUTHOR]

The primary ecological challenges in citrus orchards include soil acidification, nutrient depletion, and significant carbon dioxide emissions resulting from conventional cultivation practices. To address these challenges, citrus peel residues and cassava stalks underwent pyrolysis at 500 °C to generate biochars. Different proportions of these biochars (1%, 2%, and 4%) were applied under controlled laboratory conditions to assess their impact on the mineralization of soil organic carbon in citrus orchards. The results indicated that both types of biochar effectively regulated the soil pH to approximately 5.5. Significantly, the addition of 4% cassava stalk biochar significantly increased the levels of available phosphorus and potassium. The phosphorus levels rose by 512.55%, and the potassium levels surged by 1434.01%. Additionally, the soil organic carbon increased to 16.7 g/kg. Conversely, the citrus peel biochar decreased the availability of phosphorus but resulted in the highest increase in available potassium, at 1523.75%, and elevated the soil organic carbon content to 13 g/kg. Both types of biochar enhanced the soil organic carbon mineralization rate to varying extents with increasing application ratios, simultaneously boosting the cumulative amount of organic carbon mineralized. Among the treatments, cassava stalk biochar displayed the lowest C0/SOC ratio, of 0.169, indicating its superior carbon retention capacity. Furthermore, cassava stalk biochar showed inhibitory effects on soil catalase and urease activities within the citrus orchard. Overall, the application of 4% cassava stalk biochar appears to be more beneficial for nutrient regulation and carbon sequestration in citrus orchard soils, while also contributing to the reduction in soil acidification by adjusting pH levels. [ABSTRACT FROM AUTHOR]

In order to study the effects of wildfires on soil carbon dioxide (CO2) emissions and microbial communities in planted forests, Pinus massoniana Lamb. and Cunninghamia lanceolata (Lamb.) Hook. forests were selected as the research subjects. Through a culture test with 60 days of indoor constant temperature, the soil physical and chemical properties, organic carbon mineralization, organic carbon components, enzyme activity, and microbial community structure changes of the two plantations after fire were analyzed. The results showed that wildfires significantly reduced soil CO2 emissions from the Pinus massoniana forests and Cunninghamia lanceolata forests by 270.67 mg·kg−1 and 470.40 mg·kg−1, respectively, with Cunninghamia lanceolata forests exhibiting the greatest reduction in soil CO2 emissions compared to unburned soils. Bioinformatics analysis revealed that the abundance of soil Proteobacteria in the Pinus massoniana and Cunninghamia lanceolata forests decreased by 6.00% and 4.55%, respectively, after wildfires. Additionally, redundancy analysis indicated a significant positive correlation between Proteobacteria and soil CO2 emissions, suggesting that the decrease in Proteobacteria may inhibit soil CO2 emissions. The Cunninghamia lanceolata forests exhibited a significant increase in soil available nutrients and inhibition of enzyme activities after the wildfire. Additionally, soil CO2 emissions decreased more, indicating a stronger adaptive capacity to environmental changes following the wildfire. In summary, wildfire in the Cunninghamia lanceolata forests led to the most pronounced reduction in soil CO2 emissions, thereby mitigating soil carbon emissions in the region. [ABSTRACT FROM AUTHOR]

In this study, the feasibility and mechanism of Pb2+ and malachite green (MG) adsorption from wastewater using KMnO4-modified bamboo biochar (KBC) was evaluated. The KBC was characterized by SEM–EDS, XRD, FTIR and XPS. The adsorption results for Pb2+ conformed to pseudo-second-order kinetics and the Langmuir model theory. Unlike the case for Pb2+, the Freundlich model better described the adsorption behaviour of MG, indicating that adsorption occurred within multiple molecular layers. Both pseudo-first-order kinetics and pseudo-second-order kinetics fit the MG adsorption data well, indicating that physical adsorption was involved in the adsorption process. In addition, the maximum adsorption capacity for Pb2+/MG was 123.47/1111.11 mg·g−1, KBC had high adsorption capacities for Pb2+ and MG, and the mechanisms of Pb2+ adsorption were mineral precipitation, functional group complexation, and cation-π interactions, while the main mechanisms for MG adsorption were pore filling, π–π interactions, and functional group complexation. In this study, KMnO4-modified biochar was prepared and used as an efficient adsorbent, and showed good application prospects for treatment of wastewater containing MG and Pb2+. [ABSTRACT FROM AUTHOR]

Background: Organic substrates and calcium are important factors controlling organic matter turnover in Karst soils. To understand their effects on soil organic carbon (SOC) mineralization, an incubation experiment was conducted involving a control treatment (CK), the addition of a (14)C-labeled rice straw (T1), CaCO(3) (T2), and both (14)C-labeled rice straw and CaCO(3) (T3) to two types of Karst soils (terra fusca and rendzina) and a red soil from southwestern China., Results: Cumulative mineralization of the rice straw over 100 days in rendzina (22.96 mg kg(-1)) and terra fusca (23.19 mg kg(-1)) was higher than in the red soil (15.48 mg kg(-1); P < 0.05). Cumulative mineralization of native SOC decreased following addition of (14)C-labeled rice straw in the rendzina and terra fusca but increased in the red soil (negative and positive priming effects on native SOC). The turnover times of (14)C-labeled microbial biomass C (MBC) in the red soil, terra fusca and rendzina were 71 ± 2, 243 ± 20 and 254 ± 45 days, respectively. By adding CaCO(3), the accumulation of SOC was greater in the Karst soils than in the red soil., Conclusion: Although the interactions between rice straw decomposition and priming effects on native SOC are not yet understood, there was considerable variation between Karst and red soils. Soil calcium was a positive factor in maintaining SOC stability. MBC from rice straws was stable in terra fusca and rendzina, whereas it was active in the red soil. The Karst soils (terra fusca and rendzina) used in this study benefited SOC accumulation., (Copyright © 2011 Society of Chemical Industry.)