Biochar as a carbonaceous material to enhance soil quality in drylands ecosystems: A review

Synthesis and Characterization of N-Doped Seaweed Biochar and Removal of Cationic Dyes

The development of functional porous carbon materials has attracted great attention in various fields. In this work, N-doped algal biochar (NABc) materials were successfully prepared by an impregnation and calcination methods using Dicyandiamide as a modifier. The specific surface area, average pore volume, and average pore diameter of NABc1%, were 693.92 m2·g-1, 0.162 cm3·g-1 and 6.76 nm, respectively. The high efficiency of NABc1% in adsorbing the cationic dyes rhodamine B and methylene blue from water may be attributed to the rich pore structure of NABc1%. The adsorption experiments show that the removal rates of rhodamine B and methylene blue by NABc1% in 90 min are 99.4 and 96.2%, respectively, which are obviously higher than those before modification. The experimental results of adsorption kinetics show that the adsorption process is more consistent with the quasi-second-order kinetic fitting equation (R 2 = 0.961, 0.998). The results of isothermal adsorption experiments show that the adsorption process is more consistent with the Langmuir equation (R 2 = 0.919, 0.916), indicating that the adsorption of rhodamine B and methylene blue by NABc1% is dominated by a monolayer adsorption process. In addition, the fitting of the intraparticle diffusion model shows that internal diffusion is not the only rate-limiting step. Hence, NABc1% has great potential for practical application as an efficient adsorbent in the field of cationic dye wastewater treatment.

Unraveling the synergistic effect of biochar and potassium solubilizing bacteria on potassium availability and rapeseed growth in acidic soil

Potassium (K) is an essential macronutrient for plant growth. However, its bioavailability is low in acidic soils. Excessive K fertilization deteriorates the soil health, thus highlighting the need for sustainable alternatives. In previous studies, biochar application has been proven to be an effective amendment. Meanwhile, various potassium solubilizing bacteria (KSB) have been identified in soil that contributes to K bioavailability. However, their interaction under combine (co) application in acidic soil and its effects on K availability remain poorly understood. Therefore, a pot experiment was conducted to investigate the synergistic effect of co-application of rice straw biochar (BC) and KSB consortium on K availability to promote rapeseed growth. The treatment plan consisted of CK (control), recommended K fertilizer, 2 % BC (2 % w/w), KSB consortium, KSB consortium + 2 % BC (2 % w/w). Results of soil analysis conducted after crop maturity showed that co-application of 2 % BC and KSB consortium significantly improved the soil pH and organic matter contents by 0.62 and 12.52 units respectively, relative to CK. Meanwhile, soil available nutrients were greatly enhanced, as available K content increased by 52.1 %, which indicated that co-application of 2 % BC and KSB consortium could facilitate the better conversion of different forms of soil K and make it available for plant uptake. Furthermore, it also improved extracellular enzymatic activities (26.7-71.6 %) and soil bacterial community (Actinobacteriota and Firmicutes). These improvements greatly enhanced plant biomass (46 %) and yield (31 %). Overall results proved that co-application of 2 % BC and KSB effectively enhanced K availability for sustainable plant growth. Still, there is a need to identify the most efficient KSB strains that, in conjugation with BC, reduce the K fertilizer usage.

Integrated enzyme activities and untargeted metabolome to reveal the mechanism that allow long-term biochar-based fertilizer substitution improves soil quality and maize yield

Biochar-based fertilizer has potential benefits in improving soil quality and crop yield, but the biological mechanisms of soil microbial enzymes interacting with related metabolisms still need to be further investigated. In this study, we combined enzymology and untargeted metabolomics to investigate how biochar-based fertilizer substitution affects soil quality and crop yield by regulating soil enzymes and metabolites in dry-crop farmland. Our findings showed that biochar-based fertilizer substitution enhanced the activities of enzymes related to carbon, nitrogen, and phosphorus cycling, as well as influenced metabolite composition. The identified differential metabolites were enriched into 10 metabolic pathways including linoleic acid metabolism, fatty acid biosynthesis, styrene degradation, ABC transporters, biosynthesis of unsaturated fatty acids, glutathione metabolism, glycine, serine and threonine metabolism, phenylalanine metabolism, pyrimidine metabolism, and arachidonic acid metabolism. Substantial soil quality index improvement was demonstrated, with at least 63.46% increased, under biochar-based fertilizer application, while maize yield was increased by at least 11.16%, compared to conventional fertilizer. Model analysis elucidated mechanisms underlying soil quality and maize yield enhancement, emphasizing the importance of intrinsic regulation through the release of carbon- and nitrogen-related enzymes (e.g., α-glucosidase (α-GC), N-acetyl-β-D-glucosidase (NAG), and leucine aminopeptidase (LAP)) and specific metabolites (e.g., stearic acid, arachidonic acid, and melibiose). Moreover, the key role of soil quality factors was highlighted, with soil organic carbon (SOC), microbial biomass, and available nutrients playing a fundamental role in contributing to the increase in maize yield. The above findings illustrated that biochar-based fertilizer is crucial in modulating soil microbial activity and their metabolites, and their interactions in the soil are essential for promoting improved soil quality and crop yield.

Potential of biochar to restoration of microbial biomass and enzymatic activity in a highly degraded semiarid soil

Biochar is an effective material for enhancing soil ecosystem services. However, the specific impacts of biochar on microbial indicators, particularly in degraded soils, remain poorly understood. This study aimed to evaluate the effects of biochar produced from cashew residues and sewage sludge, in a highly degraded soil, on microbial indicators. We analyzed soil chemical composition and microbial biomass C and N, enzyme activity, and stoichiometry. Cashew biochar increased soil respiration, indicating a higher availability of C to microorganisms compared to sewage sludge biochar and a better adaptation of soil microbial communities to C-rich organic material obtained from a native plant. Although the biochar differentially impacted microbial biomass C, both significantly increased N in the microbial biomass. Arylsulphatase activity did not respond to biochar application, while β-glucosidase, urease, and phosphatases showed significant changes with biochar treatments. Importantly, stoichiometry and vector analysis revealed that both types of biochar increased P limitation for soil microbes. Conversely, both biochar alleviated C and N limitations for the soil microbes. Thus, biochar applications in highly degraded soils should be supplemented with external P sources to maintain soil functions, mainly for cashew residues. Our results provide evidence that biochar can restore soil biological properties and enhance the availability of C and N to microorganisms. These findings have significant implications for restoration practices in degraded lands of semiarid regions.

Biochar aided priming of carbon and nutrient availability in three soil orders of India

In recent years biochar (BC) has gained importance for its huge carbon (C) sequestration potential and positive effects on various soil functions. However, there is a paucity of information on the long-term impact of BC on the priming effect and nutrient availability in soil with different properties. This study investigates the effects of BC prepared from rice husk (RBC4, RBC6), sugarcane bagasse (SBC4, SBC6) and mustard stalk (MBC4, MBC6) at 400 and 600 °C on soil C priming and nitrogen (N), phosphorus (P), and potassium (K) availability in an Alfisol, Inceptisol, and Mollisol. BC properties were analyzed, and its decomposition in three soil orders was studied for 290 days in an incubation experiment. Post-incubation, available N, P, and K in soil were estimated. CO2 evolution from BC and soil alone was also studied to determine the direction of priming effect on native soil C. Increasing pyrolysis temperature enhanced pH and EC of most of the BC. The pyrolysis temperature did not show clear trend with respect to priming effect and nutrient availability across feedstock and soil type. MBC6 increased C mineralization in all the soil orders while RBC6 in Alfisol and SBC6 in both Inceptisol and Mollisol demonstrated high negative priming, making them potential amendments for preserving native soil C. Most of the BC showed negative priming of native SOC in long run (290 days) but all these BC enhanced the available N, P, and K in soil. SBC4 enhanced N availability in Alfisol and Inceptisol, RBC4 improved N and P availability in Mollisol and P in Alfisol and MBC6 increased K availability in all the soils. Thus, based on management goals, tailored BC or blending different BC can efficiently improve C sequestration and boost soil fertility.