To investigate the effects of biochar on soil carbon composition and transformation, the effects of 1%, 2%, and 5% mass ratios of banana and cassava straw biochar on carbon dioxide release, total organic carbon (TOC), soluble organic carbon (SOC), and enzyme activity in soil were studied in incubation experiments at a constant temperature in the laboratory. The results showed that the cumulative CO₂ emissions from cassava straw were 15.82 (1% addition ratio) and 28.14 μg·kg⁻¹ (2%), which were lower than those from banana straw, i.e., 46.77 (1%) and 59.26 μg·kg⁻¹ (2%). After culture, the total organic carbon contents of cassava straw were 8.55 (5%), 5.27 (2%), and 3.98 μg·kg⁻¹ (1%), which were higher than those of banana straw, i.e., 6.31 (5%), 4.23 (2%), and 3.16 μg·kg⁻¹ (1%). The organic carbon mineralization rate in each treatment showed a trend of increasing first, then decreasing, and finally stabilizing. There was a very significant positive correlation between catalase and urease activity in soil with cassava straw biochar and between catalase activity and SOC mineralization with banana straw biochar. It plays an important role in the transformation and decomposition of organic carbon. These results show that the application of biomass carbon can significantly improve the organic carbon content and enzyme activity of farmland soil, increase the cumulative mineralization amount and mineralization rate of SOC, and thus increase the carbon sequestration capacity of soil.

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.

In order to maintain soil stability, improve soil productivity and optimize planting patterns, the distribution characteristics of soil aggregates in sugarcane fields under different intercropping methods were studied. We investigated the differences in organic carbon content of different particle size aggregates and the effects of intercropping on soil organic carbon, aggregates stability, sugarcane water content and nutrients content. The results showed that intercropping could effectively improve soil physicochemical properties, increase soil organic carbon (SOC) content, but such an approach had little effect on soil stability. After intercropping, the content of SOC, readily oxidized organic carbon (ROC), dissolved organic carbon (DOC) in soil increased significantly. The content of SOC increased with the decrease in aggregate size, and the organic carbon is more stable in the aggregates with the particle size of R>2 mm and R<0.154 mm. The selection of soybean and mucuna pruriens as intercropping crops in both OS//M and OM treatments was less damaging to soil stability and soil performance was significantly improved than the other groups, making them more suitable for intercropping in sugarcane fields. Intercropping increased the water content and N, P and K content of sugarcane plants.

In this study, banana biochar (BB) and cassava biochar (CB) were roasted in a tube furnace at 400℃ for 2 h, and their adsorption effects on malachite green (MG) were studied. The removal of MG with respect to the solution concentration and reaction time was also investigated. The results show that the optimal amount of biochar is 2 g/L. Studies of the adsorption kinetics and adsorption isotherms show that the pseudo-second-order kinetics can most accurately reflect the adsorption process. Freundlich model fits the experimental data well. The theoretical saturated adsorption capacities of BB and CB are 1,092.80 mg/g and 261.42 mg/g, respectively. SEM-EDS, TGA, BET, FTIR, XRD, element analysis and other characterization techniques were used to explore the adsorption mechanism. Based on the characterization results, it is speculated that the adsorption of BB and CB for MG mainly includes chemical adsorption and physical adsorption.

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 grosvenorii 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.

Plants associated with symbiotic nitrogen-fixers and soil free-living nitrogen-fixing bacteria are good indicators for detecting the source of nitrogen in natural ecosystems. However, the community composition and diversity of plants associated with symbiotic nitrogen-fixers and soil free-living nitrogen-fixing bacteria in karst shrub ecosystems remain poorly known. The community composition and diversity of soil free-living nitrogen-fixing bacteria and plants, as well as the soil physical–chemical properties were investigated in 21 shrub plots (including different topographies and plant types). The frequency of plants associated with symbiotic nitrogen-fixers was found to be low in the 21 shrub plots. The soil free-living nitrogen-fixing bacterial community structure varied among the 21 shrub soils. Based on a variance partitioning analysis, topography, plant type, and soil pH explained 48.5% of the observed variation in bacterial community structure. Plant type had a predominant effect on community structure, and topography (aspect and ascent) and soil pH had minor effects. A negative correlation between the abundance of the soil free-living nitrogen-fixing bacterial community and the richness index for plants associated with symbiotic nitrogen-fixers was observed. The result of the low frequency of plants associated with symbiotic nitrogen-fixers highlights the importance of sources of fixed nitrogen by soil free-living nitrogen-fixing bacteria in the nitrogen limitation shrub ecosystem of the karst regions.