Acid-Modified Biochar Impacts on Soil Properties and Biochemical Characteristics of Crops Grown in Saline-Sodic Soils

Agricultural waste-based modified biochars differentially affected the soil properties, growth, and nutrient accumulation by maize (Zea mays L.) plants

Biochar (BC) is an organic compound formed by the pyrolysis of organic wastes. Application of BCs as soil amendments has many benefits including carbon sequestration, enhanced soil fertility and sustainable agriculture production. In the present study, we acidified the different BCs prepared from rice straw, rice husk, wheat straw, cotton stalk, poultry manure, sugarcane press mud and vegetable waste; following which, we applied them in a series of pot experiments. Comparisons were made between acidified and non- acidified BCs for their effects on seed germination, soil properties (EC, pH) nutrient contents (P, K, Na) and organic matter. The treatments comprised of a control, and all above-described BCs (acidified as well as non-acidified) applied to soil at the rate of 1% (w/w). The maize crop was selected as a test crop. The results showed that acidified poultry manure BC significantly improved germination percentage, shoot length, and biomass of maize seedlings as compared to other BCs and their respective control plants. However, acidified BCs caused a significant decrease in nutrient contents (P, K, Na) of soil,maize seedlings, and the soil organic matter contents as compared to non- acidified BCs. But when compared with control treatments, all BCs treatments (acidified and non-acidified) delivered higher levels of nutrients and organic matter contents. It was concluded that none of the BCs (acidified and non-acidified) had caused negative effect on soil conditions and growth of maize. In addition, the acidification of BC prior to its application to alkaline soils might had altered soil chemistry and delivered better maize growth. Moving forward, more research is needed to understand the long-term effects of modified BCs on nutrient dynamics in different soils. In addition, the possible effects of BC application timings, application rates, particle size, and crop species have to be evaluated systemtically.

Effects of biochar types on seed germination, growth, chlorophyll contents, grain yield, sodium, and potassium uptake by wheat (Triticum aestivum L.) under salt stress

Soil salinity is a significant challenge in agriculture, particularly in arid and semi-arid regions such as Pakistan, leading to soil degradation and reduced crop yields. The present study assessed the impact of different salinity levels (0, 25, and 50 mmol NaCl) and biochar treatments (control, wheat-straw biochar, rice-husk biochar, and sawdust biochar applied @ 1% w/w) on the germination and growth performance of wheat. Two experiments: a germination study and a pot experiment (grown up to maturity), were performed. The results showed that NaCl-stress negatively impacted the germination parameters, grain, and straw yield, and agronomic and soil parameters. Biochar treatments restored these parameters compared to control (no biochar), but the effects were inconsistent across NaCl levels. Among the different biochars, wheat-straw biochar performed better than rice-husk and sawdust-derived biochar regarding germination and agronomic parameters. Biochar application notably increased soil pHs and electrical conductivity (ECe). Imposing NaCl stress reduced K concentrations in the wheat shoot and grains with concomitant higher Na concentrations in both parts. Parameters like foliar chlorophyll content (a, b, and total), stomatal and sub-stomatal conductance, and transpiration rate were also positively influenced by biochar addition. The study confirmed that biochar, particularly wheat-straw biochar, effectively mitigated the adverse effects of soil salinity, enhancing both soil quality and wheat growth. The study highlighted that biochar application can minimize the negative effects of salinity stress on wheat. Specifically, the types and dosages of biochar have to be optimized for different salinity levels under field conditions.

Biochar pH reduction using elemental sulfur and biological activation using compost or vermicompost

This study aimed to improve biochar's quality for arid land applications by using elemental sulfur as a pH reducer agent co-applied with compost or vermicompost as biological activators. Biochar pH was decreased by the addition of elemental sulfur, with the highest reduction from 8.1 to 7.2 occurring when co-amended with vermicompost. Elemental sulfur increased the water-soluble concentrations of calcium, magnesium, and many other elements, and stimulated substrate-induced respiration, especially when co-amended with vermicompost. The bacterial diversity community structure were significantly affected by all treatments. The Shannon index significantly increased in response to compost and sulfur treatments, while the vermicompost treatments showed higher microbial evenness and equitability diversity indices. Multivariate analyses indicated that elemental sulfur oxidation was associated with specific sulfur-oxidizing bacterial clusters. Integrating biochar with sulfur and (vermi)compost was found to be a promising sustainable technology for managing excessive biochar alkalinity, increasing its fertility and potential for application in aridlands.

The Concurrent Application of Phosphogypsum and Modified Biochar as Soil Amendments Influence Sandy Soil Quality and Wheat Productivity

Sandy soil covers a significant portion of Egypt's total land area, representing a crucial agricultural resource for future food security and economic growth. This research adopts the hypothesis of maximizing the utilization of secondary products for soil improvement to reduce ecosystem pollution. The study focuses on assessing the impact of combining phosphogypsum and modified biochar as environmentally friendly soil amendments on loamy sand soil quality parameters such as soil organic carbon, cation exchange capacity, nutrient levels, and wheat yield. The treatments were T1: the recommended NPK fertilizer (control); T2: 2.5 kg phosphogypsum m-2 soil; T3: 2.5 kg rice straw biochar m-2 soil; T4: 2.5 kg cotton stalk biochar m-2 soil; T5: 2.5 kg rice-straw-modified biochar m-2 soil; T6: 2.5 kg cotton-stalk-modified biochar m-2 soil; and T7 to T10: mixed phosphogypsum and biochar treatments. The results revealed that the combined use of phosphogypsum and modified cotton stalk biochar (T10) significantly enhanced soil organic carbon (SOC) by 73.66% and 99.46% in both seasons, the soil available N both seasons by 130.12 and 161.45%, the available P by 89.49% and 102.02%, and the available K by 39.84 and 70.45% when compared to the control treatment. Additionally, this treatment led to the highest grain yield of wheat (2.72 and 2.92 Mg ha-1), along with a significant increase in straw yield (52.69% and 59.32%) compared to the control treatment. Overall, the findings suggest that the combined use of phosphogypsum and modified biochar, particularly cotton-stalk biochar, holds promise for improving loamy sand-soil quality and wheat productivity.

Alterations in the composition and metabolite profiles of the saline-alkali soil microbial community through biochar application

Saline-alkali soil poses significant chanllenges to sustainable development of agriculture. Although biochar is commonly used as a soil organic amendment, its microbial remediation mechanism on saline-alkali soil requires further confirmation. To address this, we conducted a pot experiment using cotton seedlings to explore the potential remediation mechanism of rice straw biochar (BC) at three different levels on saline-alkaline soil. The results showed that adding of 2% biochar greatly improved the quality of saline-alkaline soil by reducing pH levels, electrical conductivity (EC), and water-soluble ions. Moreover, biochar increased the soil organic matter (SOM), nutrient availability and extracellular enzyme activity. Interestingly, it also reduced soil salinity and salt content in various cotton plant tissues. Additionally, biochar had a notable impact on the composition of the microbial community, causing changes in soil metabolic pathways. Notably, the addition of biochar promoted the growth and metabolism of dominant salt-tolerant bacteria, such as Proteobacteria, Bacteroidota, Acidobacteriota, and Actinobacteriota. By enhancing the positive correlation between microorganisms and metabolites, biochar alleviated the inhibitory effect of salt ions on microorganisms. In conclusion, the incorporation of biochar significantly improves the soil microenvironment, reduces soil salinity, and shows promise in ameliorating saline-alkaline soil conditions.

Unlocking the potential of biochar in the remediation of soils contaminated with heavy metals for sustainable agriculture

Agricultural soils contaminated with heavy metals (HMs) impose a threat to the environmental and to human health. Amendment with biochar could be an eco-friendly and cost-effective option to decrease HMs in contaminated soil. This paper reviews the application of biochar as a soil amendment to immobilise HMs in contaminated soil. We discuss the technologies of its preparation, their specific properties, and effect on the bioavailability of HMs. Biochar stabilises HMs in contaminated soil, enhance the overall quality of the contaminated soil, and significantly reduce HM uptake by plants, making it an option in soil remediation for HM contamination. Biochar enhances the physical (e.g. bulk density, soil structure, water holding capacity), chemical (e.g. cation exchange capacity, pH, nutrient availability, ion exchange, complexes), and biological properties (e.g. microbial abundance, enzymatic activities) of contaminated soil. Biochar also enhances soil fertility, improves plant growth, and reduces the plant availability of HMs. Various field studies have shown that biochar application reduces the bioavailability of HMs from contaminated soil while increasing crop yield. The review highlights the positive effects of biochar by reducing HM bioavailability in contaminated soils. Future work is recommended to ensure that biochars offer a safe and sustainable solution to remediate soils contaminated with HMs.

Effect of acid-modified biochar coupled with alternate wetting and drying on P leaching, soil P retention and plant P uptake in paddy fields

H2SO4-modified biochar has been recognized as a means to achieve the advantages of carbon sequestration, and nitrogen loss reduction. However, little information is available on its effect on phosphorus (P) uptake, soil available P, and P leaching under alternate wetting and drying irrigation (IAWD). A split-plot experimental layout was carried out with two irrigation regimes (conventional continuous flooding, ICF, and alternate wetting and drying, IAWD) as main plots and three biochar additions (biochar-free control, B0, non-acidified biochar, B20, and acid-modified biochar, B20A) as subplots. Results indicated that IAWD decreased water percolation by 9.26%-14.74% and P leaching by 50.14%-106.64% and increased surface soil available P by 10.88-29.08%, resulting in 14.21-35.03% apparent phosphorus balance (APB) over the three years as compared with ICF. B20 produced a 6.23% lower grain yield in the 1st year and 5.06% and 11.02% higher yields in the 2nd and 3rd years, while B20A increased or tended to increase it throughout the three years. Both B20 and B20A significantly decreased total water percolation (9.68-28.37%), P leaching (18.26-152.00%), and increased soil available P (9.90-46.24%), dissolved P in surface soil (10.00-62.50%), and P uptake (4.31-49.71%), and thereafter enhanced apparent phosphorus balance (11.06-40.78%). Compared with B20, B20A achieved a better APB due to a 113% lower P leaching and 52.9% lower dissolved P at 60 cm soil profiles. IAWDB20A-M produced the highest APB, surface soil available and dissolved P, and the lowest P leaching, which increased grain yield, APB, surface soil available P, and dissolved P by 9.54%, 129.61%, and 53.19%, and decreased P leaching by 257% over ICFB0, respectively. Therefore, the use of H2SO4-modified biochar could produce higher grain yield with lower P leaching and higher APB for IAWD paddy systems, which is beneficial to enhancing plant P uptake, mitigating P leaching, and ensuring sustainable agricultural production.

The biochar-based nanocomposites improve seedling emergence and growth of dill by changing phytohormones and sugar signaling under salinity

Biochar-based nanocomposites (BNCs) with a high level of sodium sorption capacity may improve salinity tolerance and seedling establishment of dill. Thus, a pot experiment was conducted to evaluate the effects of solid biochar (30 g solid biochar kg^-1 soil) and biochar-based nanocomposites of iron (BNC-FeO) and zinc (BNC-ZnO) in individual (30 g BNC kg^-1 soil) and a combined form (15 g BNC-FeO + 15 g BNC-ZnO kg^-1 soil) on dill seedling growth in different levels of salt stress (non-saline, 6 and 12 dSm^-1). Salinity caused a decrease in emergence percentage and emergence rate of seedlings. Increasing salinity of soil up to 12 dSm^-1 decreased the biomass of dill seedlings by about 77%. Application of biochar and particularly BNCs increased the content of potassium, calcium, magnesium, iron, and zinc, reducing and non-reducing sugars, total sugars, invertase and sucrose synthase activities, leaf water content, gibberellic acid, and indole-3-acetic acid in dill plants, leading to an improvement in seedling growth (shoot length, root length, and dry weight) under saline conditions. Sodium content was noticeably decreased by BNC treatments (9-21%), which reduced mean emergence rate and stress phytohormones such as abscisic acid (31-43%), jasmonic acid (21-42%), and salicylic acid (16-23%). Therefore, BNCs especially in combined form can potentially improve emergence and growth of dill seedlings under salt stress, through reducing sodium content and endogenous stress hormones, and enhancing sugars and growth promoting hormones.