Biochar-manure compost in conjunction with pyroligneous solution alleviated salt stress and improved leaf bioactivity of maize in a saline soil from central China: a 2-year field experiment

Differential response of biochar in mitigating salinity stress in periwinkle (Catharanthus roseus L.) as an ornamental-medicinal plant species

To investigate the effect of various levels of salinity and biochar on the growth and biochemical traits of Catharanthus roseus L., a medicinal plant, a factorial experiment with three levels of biochar (0, 2, and 4%) and four levels of salinity (0, 1,000, 2,000, and 3,000 mg/kg soil) was conducted in pots under greenhouse conditions, in three replications, 36 pots, and 6 plants/plot. Salinity reduced the vegetative and reproductive growth and Ca and K uptake, and chlorophyll content of the plants, and increased the Na+, Cl-, electrolyte leakage, and antioxidant enzyme (SOD, CAT, GPX) activities. Biochar improved all the vegetative and reproductive growth and biochemical traits of Catharanthus roseus L. and enhanced soil fertility. The application of biochar at the rate of 2% at all four levels of NaCl reduced the activity of antioxidants and decreased electrolyte leakage, reflecting the alleviation of salinity effects and the retention of cell health for survival. The application of biochar 2% was more effective than biochar 4% in alleviating salinity stress. Therefore, by using 2% biochar, it is possible to improve saline soils (soils containing 1,000 or 2,000 mg/kg NaCl) and grow periwinkle ornamental-medicinal plant in it. The plants showed acceptable performance at salinity levels of 1,000 or 2,000 mg/kg with biochar 2%.

Gel-Embedded Biochar and Hydroxyapatite Composite for the Improvement of Saline-Alkali Soil and Plant Growth Promotion

Soil amendments play a crucial role in modern agriculture, as they effectively enhance the planting environment. This study innovatively proposes the use of gel as a crosslinking agent to embed biochar and hydroxyapatite (HAP), thereby preparing a novel soil amendment. Furthermore, this study investigates the soil improvement effects of this amendment as well as its influence on plant growth. This study employed a hydrothermal method to combine corn stalk (CB) or sludge (SB) biochar with HAP at different ratios (0-20%). Subsequently, sodium alginate gel (SA) was utilized to encapsulate the biochar and minerals, successfully forming a ternary composite gel material (corn stalk biochar/sludge biochar-sodium alginate gel-hydroxyapatite: CB/SB-SA-HAP). Finally, the practical effectiveness of this amendment was verified through potted soil experiments. The results indicate that the CB/SB-SA-HAP composite materials exhibited a micrometre-scale spherical structure with well-developed micropores and possess the functional groups of CB/SB, SA, and HAP, along with unique mineral properties. Through pot experiments, it was verified that the composite material effectively enhances multiple soil properties. After 21 days of cultivation, the soil pH values stabilized within the neutral range (pH = 7 ± 0.3) across all treatment groups. Except for the CB0 (CB:HAP = 1:0) and CB2.0 (CB:HAP = 1:2) treatments, the remaining treatments significantly reduced the soil EC values by 3.27% to 47.92%. All treatments significantly increased the contents of alkali-hydrolysable nitrogen (AHN) (34.89~57.91%), available phosphorus (AP) (35.93~56.55%), and available potassium (AK) (36.41~56.80%) in the soil. In comparison, although the SB treatment was more effective in regulating the pH and electrical conductivity (EC) of saline-alkali soil than the CB treatment, it was less effective in promoting plant growth in the short term. Through correlation analysis and redundancy analysis, a significant positive correlation was found between soil pH and ryegrass germination rate and plant height, particularly with the most pronounced impact on soil pH observed in the CB1.0 and SB0 (SB:HAP = 1:0) treatments. This study underscores the potential of CB/SB-SA-HAP composite materials in soil improvement and plant growth promotion, providing valuable insights for soil remediation, enhancement, and plant cultivation advancements in the agricultural sector.

Biochar-based organic fertilizers: Influence on yield and concentration of antioxidants in the stigma of saffron and rhizosphere bacterial diversity of slightly saline and non-saline soils

Being the most expensive spice, saffron has great economic importance. This crop grows well in cold arid deserts. Salinity is one of the important limiting factors for the cultivation of this crop. However, the use of composted manured and co-composted biochar and fertilizers can play a role in attenuating the salinity stress on this crop. In this two-year field study, manures from three sources: sheep and goat (SG), cow and buffalo (FYM), and poultry (PM) farms, and their co-compost with slow-pyrolyzed wood-derived biochar (B) were used for saffron cultivation in slightly saline (electrical conductivity 1.95 dS m-1) and non-saline soils. Yield and concentration of antioxidants of stigma and bacterial diversity in the rhizosphere of this crop, under salinity and non-salinity conditions, were evaluated. Results revealed that in non-saline soil of first-year crops, all fertilizers decreased the yield of stigma than control by 15-49 % (P ≤ 0.05) but increased the concentration of carotenoids and total polyphenolics (P ≤ 0.05). In saline soil, no difference in yield was observed between treatments for the first-year crop; however, for the second-year crop, as compared to control, PM and FYM significantly increased yield by 41 % and 44 % respectively, whereas FYM also increased the concentration of total polyphenolics (P ≤ 0.05). The FYM fertilizer was found suitable for the yield and quality of saffron stigma for second-year crops in both soils (non-saline and saline). The observed OTUs, Chao1, Fischer, and ACE indexes based on 16 s rRNA metagenomic analysis revealed 2-4 times greater bacterial diversity in the rhizosphere soil of PM-B and SG-B treatments than in the control. Furthermore, 347 bacterial species were found in PM-B- or SG-B-amended soils absent in control treatments.

Can lettuce plants grow in saline soils supplemented with biochar?

Salt stress is presently a major environmental concern, given the huge number of soils affected by the presence of dissolved salts. Therefore, it is necessary to find solutions, preferably nature-based ones, to deal with this problem. In this study, biochar, a product made from plant biomass residues through the process of pyrolysis, was tested to alleviate salt stress on lettuce (Lactuca sativa L.) plants. Six different concentrations of NaCl were tested: 0, 50, 100, 200, 300 and 400 mM with and without the addition of 5% (w/w) biochar. Biochar ability to mitigate salinity damage was assessed by means of both biometric (fresh weight), physiological (chlorophyll content), and biochemical (i.e., electrolyte leakage, total antioxidant power, total soluble proteins, free amino acids, and mineral content) parameters. The experiment lasted four weeks. The results showed that NaCl has a negative effect from the concentration of 100-200 mM and that biochar was to some extent effective in mitigating the negative effects of salt on plant physiology; nevertheless, biochar failed to counteract Na accumulation. Similarly, biochar did not influence the content of free amino acids in lettuce leaves, but enhanced the expression of several parameters, such as total antioxidant power, fresh weight, chlorophyll content, total soluble protein, K content, although only clearly evident in some cases. Overall, the present study showed that biochar is a viable solution to counteract the damage caused by high salt concentrations on plant growth.

Straw Soil Conditioner Modulates Key Soil Microbes and Nutrient Dynamics across Different Maize Developmental Stages

Soil amendments may enhance crop yield and quality by increasing soil nutrient levels and improving nutrient absorption efficiency, potentially through beneficial microbial interactions. In this work, the effects of amending soil with straw-based carbon substrate (SCS), a novel biochar material, on soil nutrients, soil microbial communities, and maize yield were compared with those of soil amendment with conventional straw. The diversity and abundance of soil bacterial and fungal communities were significantly influenced by both the maize growth period and the treatment used. Regression analysis of microbial community variation indicated that Rhizobiales, Saccharimonadales, and Eurotiales were the bacterial and fungal taxa that exhibited a positive response to SCS amendment during the growth stages of maize. Members of these taxa break down organic matter to release nutrients that promote plant growth and yield. In the seedling and vegetative stages of maize growth, the abundance of Rhizobiales is positively correlated with the total nitrogen (TN) content in the soil. During the tasseling and physiological maturity stages of corn, the abundance of Saccharimonadales and Eurotiales is positively correlated with the content of total carbon (TC), total phosphorus (TP), and available phosphorus (AP) in the soil. The results suggest that specific beneficial microorganisms are recruited at different stages of maize growth to supply the nutrients required at each stage. This targeted recruitment strategy optimizes the availability of nutrients to plants and ultimately leads to higher yields. The identification of these key beneficial microorganisms may provide a theoretical basis for the targeted improvement of crop yield and soil quality. This study demonstrates that SCS amendment enhances soil nutrient content and crop yield compared with conventional straw incorporation and sheds light on the response of soil microorganisms to SCS amendment, providing valuable insights for the future implementation of this material.

Effects of biochar treatments on the elemental composition of tobacco (Nicotiana tabacum L.) leaves based on the priming period

This study determined the effects of different doses of biochars (B) on Virginia tobacco (Nicotiana tabacum L.) cultivar, on first and second harvest dependent change in plant nutrients (N, P, K, Ca, Mg, Cl, Zn, Fe, Mn, Cu, and B), leaf color parameters (L*, a*, and b*), chlorophyll value (SPAD), electrolyte leakage (EL), crude ash, number of leaves, and plant height. Pot experiments were conducted with biochar treatments of 10 tons ha-1 (B1), 20 tons ha-1 (B2), 40 tons ha-1 (B3), and 80 tons ha-1 (B4). Tobacco leaf macroelement (N, P, K, Ca, and Mg) levels increased with increasing biochar doses. The highest values were obtained for B4 treatments (80 tons ha-1) and the lowest for control (B0) treatments. Microelements (Fe, Zn, Mn, and B) exhibited a non linear change, while Cl and Cu exhibited a linear change. Color parameters (L*, a*, and b*) for the first and second priming showed the highest L* and b* values for B2 and B3 treatments, respectively, and the highest a* values for the B2 treatment. Leaf SPAD values increased with increasing biochar doses; further, the obtained SPAD values were ordered as B4 > B3 > B2 > B1 > B0. Leaf electrolyte leakage values were 25.90 %-37.25 % in the first priming and 26.90 %-40.59 % in the second priming. For both the primings, the highest crude ash values (21.94 % and 19.05 %) were observed for the B4 treatments, whereas the lowest values (17.89 % and 17.01 %) were observed for the B0 treatments. the tallest plant height (121.9 cm) and the highest number of leaves (45.3) were determined in B4 applications. Overall, considering the nutrition and quality of tobacco, B2 application is recommended.

Synergistic effect of biochar-based compounds from vegetable wastes and gibberellic acid on wheat growth under salinity stress

Soil salinization is a prevalent form of land degradation particularly in water-deficient regions threatening agricultural sustainability. Present desalinization methods demand excessive water use. Biochar has been recognized as a potential remedy for saline soils and Gibberellic acids (GA3) are known to mediate various biochemical processes aiding in stress mitigation. This study was undertaken at The Islamia University of Bahawalpur during winter 2022-23 to explore the combined effect of biochar and GA3 on wheat (Triticum aestivum L.) in saline conditions. Employing a fully randomized design wheat seeds in 24 pots were subjected to two salinity levels with three replications across eight treatments: T1 to T8 ranging from controls with different soil electrical conductivities (ECs) to treatments involving combinations of GA3, biochar and varying soil ECs. These treatments included T1 (control with soil EC of 2.43dS/m), T2 (salinity stress with soil EC of 5.11dS/m), T3 (10 ppm GA3 with soil EC of 2.43dS/m), T4 (10 ppm GA3 with soil EC of 5.11dS/m), T5 (0.75% Biochar with soil EC of 2.43dS/m), T6 (0.75% Biochar with soil EC of 5.11dS/m), T7 (10 ppm GA3 combined with 0.75% biochar at soil EC of 2.43dS/m) and T8 (10 ppm GA3 plus 0.75% biochar at soil EC of 5.11dS/m). The results indicated that the combined applications of GA3 and biochar significantly enhanced plant growth in saline conditions viz. germination rate by 73%, shoot length of 15.54 cm, root length of 4.96 cm, plant height of 16.89 cm, shoot fresh weight 43.18 g, shoot dry weight 11.57 g, root fresh weight 24.26 g, root dry weight 9.31 g, plant water content 60.77%, photosynthetic rate 18.58(CO2 m-2 s-1) carotenoid 3.03 g, chlorophyll a 1.01 g, chlorophyll b 0.69 g, total chlorophyll contents by 1.9 g as compared to the control. The findings suggest that the combined application of these agents offers a sustainable and effective strategy for cultivating wheat in saline soils. The synergy between biochar and GA3 presents a promising avenue for sustainable wheat cultivation in saline conditions. This combined approach not only improves plant growth but also offers an innovative, water-efficient solution for enhancing agricultural productivity in saline-affected regions.

Biochar improves the growth and physiological traits of alfalfa, amaranth and maize grown under salt stress

Purpose

Salinity is a main factor in decreasing seed germination, plant growth and yield. Salinity stress is a major problem for economic crops, as it can reduce crop yields and quality. Salinity stress occurs when the soil or water in which a crop is grown has a high salt content. Biochar improve plant growth and physiological traits under salt stress. The aim of the present study, the impact of biochar on growth, root morphological traits and physiological properties of alfalfa, amaranth and maize and soil enzyme activities under saline sands.

Methods

We studied the impact of biochar on plant growth and the physiological properties of alfalfa, amaranth and maize under salt stress conditions. After 40 days, plant growth parameters (plant height, shoot and root fresh weights), root morphological traits and physiological properties were measured. Soil nutrients such as the P, K and total N contents in soil and soil enzyme activities were analyzed.

Results

The results showed that the maize, alfalfa, and amaranth under biochar treatments significantly enhanced the plant height and root morphological traits over the control. The biochar on significantly increased the total root length, root diameter, and root volume. Compared to the control, the biochar significantly increased the chlorophyll a and b content, total chlorophyll and carotenoid content under salt stress. Furthermore, the biochar significantly increased enzyme activities of soil under salt stress in the three crops.

Conclusions

Biochar treatments promote plant growth and physiological traits of alfalfa, amaranth, and maize under the salt stress condition. Overall, biochar is an effective way to mitigate salinity stress in crops. It can help to reduce the amount of salt in the soil, improve the soil structure, and increase the availability of essential nutrients, which can all help to improve crop yields.

Calcium-modified biochar rather than original biochar decreases salinization indexes of saline-alkaline soil

We investigated the improvement effects of herbaceous (corn) and woody (oak sawdust) biochar with their calcium modification on saline alkali soil. The addition of unmodified biochar regardless of types had no significant effect on the soluble cations (Na⁺, Ca²⁺, and Mg²⁺) and the main indicators of soil salinity and alkalinity (pH, sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP), and total alkalinity (TA)), but the addition of calcium modified biochar decreased these soluble cations and indicators, especially the addition of modified woody biochar (PBM). Compared to CK, TA decreased by 70.02% and 89.25% in PBM with 2% and 4% addition, respectively. Soil ESP and SAR showed a significantly positive correlation with pH and TA, which indicated that soil salinization and alkalization were synchronized. These results showed that the calcium modified biochar, especially the modified woody biochar, instead of the original biochar could be potential soil amendments for the improvement of saline-alkali soil.

The critical role of biochar to mitigate the adverse impacts of drought and salinity stress in plants

Drought stress (DS) is a potential abiotic stress that is substantially reducing crop productivity across the globe. Likewise, salinity stress (SS) is another serious abiotic stress that is also a major threat to global crop productivity. The rapid climate change increased the intensity of both stresses which pose a serious threat to global food security; therefore, it is urgently needed to tackle both stresses to ensure better crop production. Globally, different measures are being used to improve crop productivity under stress conditions. Among these measures, biochar (BC) has been widely used to improve soil health and promote crop yield under stress conditions. The application of BC improves soil organic matter, soil structure, soil aggregate stability, water and nutrient holding capacity, and the activity of both beneficial microbes and fungi, which leads to an appreciable increase in tolerance to both damaging and abiotic stresses. BC biochar protects membrane stability, improves water uptake, maintains nutrient homeostasis, and reduces reactive oxygen species production (ROS) through enhanced antioxidant activities, thereby substantially improving tolerance to both stresses. Moreover, BC-mediated improvements in soil properties also substantially improve photosynthetic activity, chlorophyll synthesis, gene expression, the activity of stress-responsive proteins, and maintain the osmolytes and hormonal balance, which in turn improve tolerance against osmotic and ionic stresses. In conclusion, BC could be a promising amendment to bring tolerance against both drought and salinity stresses. Therefore, in the present review, we have discussed various mechanisms through which BC improves drought and salt tolerance. This review will help readers to learn more about the role of biochar in causing drought and salinity stress in plants, and it will also provide new suggestions on how this current knowledge about biochar can be used to develop drought and salinity tolerance.

Biochar-compost as a new option for soil improvement: Application in various problem soils

Due to the synergistic effects of biochar and compost/composting, the combined application of biochar and compost (biochar-compost) has been recognized as a highly promising and efficient method of soil improvement. However, the willingness to apply biochar-compost for soil improvement is still low compared to the use of biochar or compost alone. This paper collects data on the application of biochar-compost in several problem soils that are well-known and extensively investigated by agronomists and scientists, and summarizes the effects of biochar-compost application in common problem soils. These typical problem soils are classified based on three different characteristics: climatic zones, abiotic stresses, and contaminants. The improvement effect of biochar-compost in different soils is assessed and directions for further research and suggestions for application are made. Generally, biochar-compost mitigates the high mineralization rate of soil organic matter, phosphorus deficiency and aluminum toxicity, and significantly improves crop yields in most tropical soils. Biochar-compost can help to achieve long-term sustainable management of temperate agricultural soils by sequestering carbon and improving soil physicochemical properties. Biochar-compost has shown positive performance in the remediation of both dry and saline soils by reducing the threat of soil water scarcity or high salinity and improving the consequent deterioration of soil conditions. By combining different mechanisms of biochar and compost to immobilize or remove contaminants, biochar-compost tends to perform better than biochar or compost alone in soils contaminated with heavy metals (HMs) or organic pollutants (OPs). This review aims to improve the practicality and acceptability of biochar-compost and to promote its application in soil. Additionally, the prospects, challenges and future directions for the application of biochar-compost in problem soil improvement were foreseen.

Moderation of nitrogen availability through the application of pyrolyzed and unpyrolyzed organic materials in saline water irrigated soil

Soil application of pyrolyzed biomass (biochar) has been proposed as an effective strategy for managing degraded land, but its limitations as a sole nutrient supplier discourage its widespread application as a soil amendment. Excessive use of saline water for irrigation leads to buildup of salts and other toxic ions, which cause a decline in the availability of essential nutrients due to negative effects on the mineralization process. Therefore, a long-term incubation experiment was conducted for 52 weeks to study the individual or combined impact of pyrolyzed [biochar derived from rice residue (RB)] and unpyrolyzed organic materials [rice residue (RR) and animal manure (AM)] on nitrogen (N) dynamics in soil irrigated with water of varying electrical conductivity (EC) (EC_0.3 [non-saline canal water), EC₁₀, and EC₁₅ dS m^-1 (saline)]. Increasing salinity had an adverse effect on N mineralization, reducing it by 20-70% during the incubation period. Irrespective of the EC, soil amended with AM showed greater and faster N mineralization than unamended control, while individual application of RB or RR showed immobilization of N during the early period of incubation. However, conjoint application of pyrolyzed (RB) and unpyrolyzed organic materials (RR or AM) showed enhanced mineralized N content (26-96%) compared with the sole biochar-amended soil irrigated with water of different EC levels. It was most likely due to the synergic effect of unpyrolyzed materials on the mineralization rate of biochar. On the other hand, the high cation exchange capacity, large surface area, and greater total porosity of the biochar may cause stronger adsorption of free NH₄⁺-N released from the labile organic amendments, thereby moderating the N mineralization process under saline conditions. Therefore, it is recommended that biochar be used in conjunction with AM or RR to ensure the prolonged availability of N in a saline environment.

Combined effect of Zinc lysine and biochar on growth and physiology of wheat (Triticum aestivum L.) to alleviate salinity stress

Globally, Food security main threaten by abiotic stress like salinity and levels amongst the majority serious environmental stressors which reduce crop yield mass production. Biochar application has received much attention in agricultural practices as it enhances crop quality and production. The present study was carried out to analyze the role of lysine zinc and biochar on growth enhancement of wheat (Triticum aestivum L. cv. PU-2011) under saline stress (EC 7.17 dSm^-1). Seeds were sown in pots containing saline soil with and without 2% biochar, and foliar application of Zn-lysine (0, 1.0, and 2.0 mM) was made at different time intervals during plant growth. A combined application of biochar and Zn-lysine 2.0 mM highly improved the physiological attributes such as chlorophyll a (37%), chlorophyll b (60%), total chlorophyll (37%), carotenoids (16%), photosynthesis rate (Pn) 45%, stomatal conductance (gs) 53%, transpiration rate (Tr) 56%, and water use efficiency (WUE) 55%. The levels of malondialdehyde (MDA) 38%, hydrogen peroxide (H₂O₂) 62%, and electrolyte leakage (EL) 48% were decreased with the combined application of biochar and Zn-lysine 2.0 mM as compared with other treatments. The activities of catalase (CAT) 67%, superoxide dismutase (SOD) 70%, and ascorbate peroxidase (APX) 61% as well as catalase (CAT) 67% were regulated with the combined biochar and Zn-lysine 2.0 mM treatment. Similarly, the combined application of biochar and zinc-lysine (2.0 mM) enhanced the growth and yield attributes such as shoot length (79%), root fresh weight (62%), shoot fresh weight (36%), root dry weight (86%), shoot dry weight (39%), grain weight (57%), and spike length (43%) as compared with untreated control. The concentrations of sodium (Na) decreased whereas potassium (K), iron (Fe), and zinc (Zn) concentrations were enhanced in plants with the combined application of Zn-lysine and biochar. Overall, results showed that the combined application of Zn-lysine (2.0 mM) and biochar significantly inhibited the negative effect of salinity and improved the growth and physiological performance of wheat plants. The combined use of Zn-lysine and biochar might be a practical solution to tackle salt stress in plants, but field studies by growing various crops under varied environmental conditions are needed before any recommendation to farmers.

Biochar-plant interaction and detoxification strategies under abiotic stresses for achieving agricultural resilience: A critical review

The unpredictable climatic perturbations, the expanding industrial and mining sectors, excessive agrochemicals, greater reliance on wastewater usage in cultivation, and landfill leachates, are collectively causing land degradation and affecting cultivation, thereby reducing food production globally. Biochar can generally mitigate the unfavourable effects brought about by climatic perturbations (drought, waterlogging) and degraded soils to sustain crop production. It can also reduce the bioavailability and phytotoxicity of pollutants in contaminated soils via the immobilization of inorganic and/or organic contaminants, commonly through surface complexation, electrostatic attraction, ion exchange, adsorption, and co-precipitation. When biochar is applied to soil, it typically neutralizes soil acidity, enhances cation exchange capacity, water holding capacity, soil aeration, and microbial activity. Thus, biochar has been was widely used as an amendment to ameliorate crop abiotic/biotic stress. This review discusses the effects of biochar addition under certain unfavourable conditions (salinity, drought, flooding and heavy metal stress) to improve plant resilience undergoing these perturbations. Biochar applied with other stimulants like compost, humic acid, phytohormones, microbes and nanoparticles could be synergistic in some situation to enhance plant resilience and survivorship in especially saline, waterlogged and arid conditions. Overall, biochar can provide an effective and low-cost solution, especially in nutrient-poor and highly degraded soils to sustain plant cultivation.

Soil and Foliar Applications of Wood Distillate Differently Affect Soil Properties and Field Bean Traits in Preliminary Field Tests

Natural products such as wood distillate (WD) are promising alternatives to xenobiotic products in conventional agriculture and are necessary in organic farming. A field study gave insight into the effectiveness of WD applied as foliar spray (F-WD), soil irrigation (S-WD), and their combination as growth promoters for field beans. The soil fertility and quality parameters, plant growth, nutrient uptake, and resource partitioning within plants were evaluated. In a pot trial, we tested the effect of S-WD on root nodule initiation and growth. S-WD increased DOC and microbial biomass by approximately 10%, prompted enzyme activities, and increased nitrate and available phosphorus in soil, without affecting the number and growth of nodules in field beans. In contrast, the F-WD slightly reduced the DOC, exerted a lower stimulation on soil enzymes, and lowered the soil effect in the combined distribution. In field beans, the F-WD reduced the stem height but increased the number of pods per stem; S-WD increased the N and P concentrations of leaves and the N concentration of the pods. Moreover, all WD treatments retarded plant senescence. The WD revealed itself to be promising as a growth promoter for grain legumes, but further research is needed to understand the interference between the combined soil and foliar applications.

Biochar application for greenhouse gas mitigation, contaminants immobilization and soil fertility enhancement: A state-of-the-art review

Rising global temperature, pollution load, and energy crises are serious problems, recently facing the world. Scientists around the world are ambitious to find eco-friendly and cost-effective routes for resolving these problems. Biochar has emerged as an agent for environmental remediation and has proven to be the effective sorbent to inorganic and organic pollutants in water and soil. Endowed with unique attributes such as porous structure, larger specific surface area (SSA), abundant surface functional groups, better cation exchange capacity (CEC), strong adsorption capacity, high environmental stability, embedded minerals, and micronutrients, biochar is presented as a promising material for environmental management, reduction in greenhouse gases (GHGs) emissions, soil management, and soil fertility enhancement. Therefore, the current review covers the influence of key factors (pyrolysis temperature, retention time, gas flow rate, and reactor design) on the production yield and property of biochar. Furthermore, this review emphasizes the diverse application of biochar such as waste management, construction material, adsorptive removal of petroleum and oil from aqueous media, immobilization of contaminants, carbon sequestration, and their role in climate change mitigation, soil conditioner, along with opportunities and challenges. Finally, this review discusses the evaluation of biochar standardization by different international agencies and their economic perspective.

Soil Properties and Maize Yield Improvement with Biochar-Enriched Poultry Litter-Based Fertilizer

Conversion of poultry litter into fertilizer presents an environmentally friendly way for its disposal. The amendment of stabilizing sorption materials (e.g., biochar) to broiler chicken rearing seems promising, as it protects produced litter from nutrient losses and improves fertilizing efficacy. Thus, a pot experiment was carried out with maize and organic fertilizers produced from biochar-amended chicken bedding. The properties of three types of poultry-matured litter, amended with biochar at 0%, 10% and 20% dose, were analyzed. These matured litters were added to soil and physicochemical, biological properties and dry aboveground crop biomass yield were determined. Both biochar doses improved matured litter dry matter (+29%, +68% compared to unamended litter) and organic carbon (+5%, +9%). All three fertilizers significantly increased dry plant aboveground biomass yield (+3% and +42% compared to control litter-treated variant) and N-acetyl-β-D-glucosaminidase activity (+51%, +57%) compared to unamended control soil. The 20% biochar poultry-matured litter derived the highest dry plant aboveground biomass, highest respiration induced by D-glucose (+53%) and D-mannose (+35%, compared to control litter-treated variant), and decreased pH (-6% compared to unamended control). Biochar-derived modification of poultry litter maturation process led to organic fertilizer which enhanced degradation of soil organic matter in the subsequently amended soil. Furthermore, this type of fertilizer, compared to conventional unamended litter-based type, increased microbial activity, nutrient availability, and biomass yield of maize in selected biochar doses, even under conditions of significant soil acidification.

Organic Amendments for Mitigation of Salinity Stress in Plants: A Review

Natural and/or human-caused salinization of soils has become a growing problem in the world, and salinization endangers agro-ecosystems by causing salt stress in most cultivated plants, which has a direct effect on food quality and quantity. Several techniques, as well as numerous strategies, have been developed in recent years to help plants cope with the negative consequences of salt stress and mitigate the impacts of salt stress on agricultural plants. Some of them are not environmentally friendly. In this regard, it is crucial to develop long-term solutions that boost saline soil productivity while also protecting the ecosystem. Organic amendments, such as vermicompost (VC), vermiwash (VW), biochar (BC), bio-fertilizer (BF), and plant growth promoting rhizobacteria (PGPR) are gaining attention in research. The organic amendment reduces salt stress and improves crops growth, development and yield. The literature shows that organic amendment enhances salinity tolerance and improves the growth and yield of plants by modifying ionic homeostasis, photosynthetic apparatus, antioxidant machineries, and reducing oxidative damages. However, the positive regulatory role of organic amendments in plants and their stress mitigation mechanisms is not reviewed adequately. Therefore, the present review discusses the recent reports of organic amendments in plants under salt stress and how stress is mitigated by organic amendments. The current assessment also analyzes the limitations of applying organic amendments and their future potential.

Comparative study of pyrochar and hydrochar on peanut seedling growth in a coastal salt-affected soil of Yellow River Delta, China

Biochar (i.e., pyrochar and hydrochar) application is a promising strategy to improve soil quality and productivity. However, the comparison of biochars with different carbonization methods and feedstocks for the plant growth in the coastal salt-affected soil remains limited. In this study, a 30-day microcosmic experiment was conducted to compare the effects of pyrochars and hydrochars derived from reed straw (RPC and RHC) and cow manure (CPC and CHC) on the peanut (Arachis hypogaea L.) seedling growth in a coastal salt-affected soil of Yellow River Delta, China. The results showed that RPC, CHC and CPC significantly elevated fresh shoot weight by 67.77%-89.37%, whereas the RHC amendment showed little effect. The malondialdehyde contents in peanut seedling leaves were significantly declined by 25.28%-35.51% with pyrochar and hydrochar amendments, which might be associated with the enhanced proline contents and K/Na ratios. The stimulation of certain phytohormones (i.e., indole-3-acetic acid, zeatin riboside, gibberellic acid 3) in peanut seedlings with pyrochar and hydrochar amendments might be attributed to the growth enhancement. RPC, CPC and CHC improved the soil properties and fertility such as cation-exchange capacity (CEC), total nitrogen, and available potassium and water holding capacity (WHC) of the coastal salt-affected soil. However, RHC not only significantly decreased soil CEC and WHC, but also increased soil exchangeable sodium percentage. The abundances of soil beneficial bacteria, such as f_Gemmatimonadacea, Sphingomonas, Blastococcus and Lysobacter were enhanced by RPC, CHC and CPC amendments, which were mainly associated with the increased WHC and CEC. Fungal community was less sensitive to pyrochar and hydrochar amendments than bacterial community according to the relative abundance and diversity, and beneficial fungi, such as Oidiodendron and Sarocladium were enriched in the CHC soil. Overall, the application of RPC, CHC and CPC showed greater potentials for the enhancement of peanut growth in a coastal salt-affected soil.

Wood vinegar facilitated growth and Cd/Zn phytoextraction of Sedum alfredii Hance by improving rhizosphere chemical properties and regulating bacterial community

Soil Cd and Zn contamination has become a serious environmental problem. This work explored the performance of wood vinegar (WV) in enhancing the phytoextraction of Cd/Zn by hyperaccumulator Sedum alfredii Hance. Rhizosphere chemical properties, enzyme activities and bacterial community were analyzed to determine the mechanisms of metal accumulation in this process. Results demonstrated that, after 120 days growth, different times dilution of WV increased the shoot biomass of S. alfredii by 85.2%-148%. In addition, WV application significantly increased soil available Cd and Zn by lowing soil pH, which facilitated plant uptake. The optimal Cd and Zn phytoextraction occurred from the 100 times diluted WV (D100), which increased the Cd and Zn extraction by 188% and 164%, compared to CK. The 100 and 50 times diluted WV significantly increased soil total and available carbon, nitrogen and phosphorus, and enhancing enzyme activities of urease, acid phosphatase, invertase and protease by 10.1-21.4%, 29.1-42.7%,12.2-38.3% and 26.8-85.7%, respectively, compared to CK. High-throughput sequencing revealed that the D 100 significantly increased the bacterial diversity compared to CK. Soil bacterial compositions at phylum, family and genera level were changed by WV addition. Compared to CK, WV application increased the relative abundances of genus with plant growth promotion and metal mobilization function such as, Bacillus, Gemmatimonas, Streptomyces, Sphingomonas and Polycyclovorans, which was positively correlated to biomass, Cd/Zn concentrations and extractions by S. alfredii. Structural equation modeling analysis showed that, soil chemical properties, enzyme activities and bacterial abundance directly or indirectly contributed to the biomass promotion, Cd, and Zn extraction by S. alfredii. To sum up, WV improved phytoextraction efficiency by enhancing plant growth, Cd and Zn extraction and increasing soil nutrients, enzyme activities, and modifying bacterial community.

Novel maricultural-solid-waste derived biochar for removing eutrophic nutrients and enrofloxacin: Property, mechanism, and application assessment

Land-based seawater aquaculture accompanied by high stocking density usually involves producing excess eutrophic nutrients, residual baits, excrement, and antibiotics. Because of limited technology and salinity, proper and efficient treatment of these wastes is still an unsolved issue. In this study, the feasibility of maricultural fish residual bait and excrement-derived biochar as water pollutant remover and saline-alkaline soil amendment were firstly assessed. The biochar was pyrolyzed at 300, 500, 700, 800, 900 ℃ (marked as BC300, BC500, BC700, BC800, BC900) and modified by zirconium or iron (BC700-Zr or BC700-Fe). BC700-Zr had the highest specific surface area. BC700-Zr and BC700-Fe exhibited higher nitrogen removal efficiency. The biochars exhibited nitrogen and phosphate desorption, while we observed no obvious phosphate desorption in BC700-Zr or BC700-Fe. Adsorption kinetics analysis indicated that adsorption processes of nitrate, nitrite and enrofloxacin were consistent with pseudo-second-order model, while ammonium and phosphate adsorption processes fitted pseudo-first-order model better. The biochar showed nitrogen and phosphate nutrients release effects, indicating potential application in saline-alkaline soil improvement. Multi-linear regression analysis indicated that nitrogen release was closely related to biochar nitrogen content, pH and average pore width. Phosphate release was inversely related to pH and positively related to average pore width.

Recent Trends in Microbial Approaches for Soil Desalination

Soil salinization has become a major problem for agriculture worldwide, especially because this phenomenon is continuously expanding in different regions of the world. Salinity is a complex mechanism, and in the soil ecosystem, it affects both microorganisms and plants, some of which have developed efficient strategies to alleviate salt stress conditions. Currently, various methods can be used to reduce the negative effects of this problem. However, the use of biological methods, such as plant-growth-promoting bacteria (PGPB), phytoremediation, and amendment, seems to be very advantageous and promising as a remedy for sustainable and ecological agriculture. Other approaches aim to combine different techniques, as well as the utilization of genetic engineering methods. These techniques alone or combined can effectively contribute to the development of sustainable and eco-friendly agriculture.

Soil Amendment with Arbuscular Mycorrhizal Fungi and Biochar Improves Salinity Tolerance, Growth, and Lipid Metabolism of Common Wheat (Triticum aestivum L.)

Salt stress in soils impacts grain crop yield. Soil amendment with biochar and arbuscular mycorrhizal alone has been analyzed to improve the growth of several crops under salinity stress. However, the combined application of biochar and arbuscular mycorrhizal fungi for the remediation of salinity and improvement of crop productivity in wheat are rarely discussed and have remained unclear. Therefore, this experiment was performed to investigate the effect with biochar (150 g biochar per each treated pot containing 3 kg soil) and/or arbuscular mycorrhizal fungi (20 g AMF inoculum containing 80% mycorrhizal roots, 100–160 spores, and extraradical hyphae per each treated pot) on the productivity of wheat (Triticum aestivum L.) under four salt stress gradients; 0, 50, 100, and 150 mM NaCl. The results show salinity significantly reduced plant height (9.9% to 22.9%), shoot fresh weight (35.6% to 64.4%), enzymatic activities (34.1% to 39.3%), and photosynthetic pigments—i.e., total chlorophyll contents (75.0%) and carotenoids contents (56.2%) of plants—as compared with control. Under exclusive biochar application, the plants were moderately tolerant to salinity stress, which was evident in their growth, moderately reduced fatty acid content, partially impaired enzymatic activity, and photosynthetic pigments, while under the exclusive AMF application, the wheat plants were relatively sensitive to salinity stress, resulting in impaired growth rate, decreased unsaturated fatty acid composition, enzymatic activity, and photosynthetic pigments. Conversely, under the co-application of biochar and AMF, wheat plants partially increased plant height (14.1%), shoot fresh biomass (75.7%), root fresh biomass (24.9%), partially increased enzymatic activity (49.5%), and unimpaired photosynthetic pigments (30.2% to 54.8%) of wheat under salinity stress. Current findings concluded that exclusive incorporation of biochar, and the synergistic application of AMF and biochar, could be utilized as a promising way to reduce the deleterious effects of salinity stress in wheat production.

Bio-Based Solutions for Agriculture: Foliar Application of Wood Distillate Alone and in Combination with Other Plant-Derived Corroborants Results in Different Effects on Lettuce (Lactuca Sativa L.)

Bio-stimulants are showing growing success and are gradually replacing synthetic fertilizers in agriculture. Wood distillate (WD), also known as wood vinegar or pyroligneous acid, is a by-product of biomass pyrolysis and is increasingly used as a bio-stimulant for crop production. This study investigated whether weekly foliar applications of 0.25% and 0.50% WD have a differential effect on the chlorophyll and sugar content as well as biomass production in lettuce (Lactuca sativa L.). Moreover, the additional beneficial effect from the addition of corroborants of plant origin such as 3% soy lecithin and 5% flavonoid-rich wood glycolic extract to WD (BF) was investigated. Moreover, the possible toxicological concern from some potentially toxic elements (PTEs), namely Cd, Cu, Fe, Pb, and Zn, which may be abundant in WD was verified. After four weeks, we found that 0.25% WD not only increases lettuce biomass, which has an economic value, but also has beneficial effects on other qualitative parameters such as sugars and total sweetness. On the other hand, the use of 0.5% WD decreased the content of soluble sugars, suggesting a hormetic-type effect. We did not find evidence of further beneficial effects from the addition to WD of plant-derived corroborants, nor of any enrichment in the content of the investigated PTEs.

Positive Effects on Alfalfa Productivity and Soil Nutrient Status in Coastal Wetlands Driven by Biochar and Microorganisms Mixtures

Biochar application in reclaiming degraded soils and improving plant productivity has been recognized as a promising technology. Yet, the impacts of biochar and mixtures with compound effective microorganisms (CEM) on alfalfa growth and soil quality in coastal wetlands are poorly understood. A greenhouse experiment was set to systematically reveal the impacts of biochar and biochar combined with CEM on alfalfa growth traits, nutrient uptake, biomass, soil quality, and enzyme activities. Eight treatments were included: (1) control (CK−CEM), (2) 10-g/kg biochar (B10−CEM); (3) 20-g/kg biochar (B20−CEM); (4) 30-g/kg biochar (B30−CEM), (5) CEM without biochar (CK + CEM); (6) 10-g/kg biochar with CEM (B10 + CEM), (7) 20-g/kg biochar with CEM (B20 + CEM), (8) 30-g/kg biochar with CEM (B30 + CEM). The utilization of biochar promoted seed germination, height, and tissue nutrient contents of alfalfa, and the combined biochar with CEM showed greater effects. Alfalfa biomass showed the maximum value in the B20 + CEM treatment, and the biomass of root, shoot, leaf in the B20 + CEM treatment increased by 200, 117.3, 144.6%, respectively, relative to the CK−CEM treatment. Alfalfa yield in the CK + CEM, B10 + CEM, B20 + CEM, B30 + CEM treatments was 71.91, 84.11, 138.5, and 120.5% higher than those in the CK−CEM treatment. The use of biochar and CEM decreased soil salinity and elevated soil nutrient content effectively. Biochar elevated soil organic carbon (SOC) and microbial biomass carbon (MBC), NH4+, NO3–, and enzymatic activities, and the positive impacts of biochar combined with CEM were additive. The combined addition of 20-g/kg biochar with CEM showed the pronounced improvement effects on improving soil fertility and nutrient availability as well as soil enzyme activities. Path analysis indicated that the application of biochar mixture with CEM promoted alfalfa biomass by regulating plant nutrient uptake, soil quality (soil nitrogen, SOC, MBC, NH4+, NO3–), and soil enzymatic activities (sucrase, urease, and alkaline phosphatases). Thus, incorporation of suitable biochar and CEM can serve as an effective measure to promote alfalfa productivity and restore coastal wetlands soils.

Effect of Organic Amendments in Soil on Physiological and Biochemical Attributes of Vachellia nilotica and Dalbergia sissoo under Saline Stress

Vachellia nilotica (L.) P.J.H. Hurther & Mabb. and Dalbergia sissoo Roxb. are two of the most important multipurpose agroforestry tree species of the Indian sub-continent, but their growth in saline soils is greatly reduced. Recently, organic amendments have showed the potential to increase plant growth in salt-affected soils; however, the influence of using these amendments for growing the above-mentioned tree species under saline conditions is not yet quantified. Therefore, an experiment was devised to analyze the interactive effects of organic amendments in saline soils on the growth of V. nilotica and D. sissoo. Under controlled conditions, a pot experiment was conducted in sandy loam saline soils (EC = 20.5 dSm⁻¹). Organic amendments from four diverse sources: farmyard manure (FYM), poultry manure (PM), slurry (SL), and farmyard manure biochar (FYMB) were employed in this study. At the harvesting time, data regarding morphological, physiological, ionic, and biochemical parameters were obtained. The current study results indicated that both tree species reacted differently, but positively, to diverse applied amendments. The maximum increment in total above-ground biomass, total below-ground biomass, and shoot length for V. nilotica (163.8%, 116.3%, and 68.2%, respectively) was observed in FYM amended soils, while the maximum increment for D. sissoo (128%, 86%, and 107%, respectively) was observed in FYMB amended soils, as compared to control. Minimum plant growth of both species was observed in untreated soils (saline soils). Likewise, the maximum potassium ion and minimum sodium ion concentrations were present in the root and shoots of plants (both species) treated with FYMB. The use of organic amendments resulted in decreased concentrations of malondialdehyde and hydrogen peroxide, and increased concentrations of antioxidant enzymes such as SOD, POD, and CAT. Moreover, higher photosynthetic rates and stomatal conductance were observed in the plants grown in amended soils. The findings of this study can be used to include the above-mentioned high-value tree species for future afforestation programs under saline conditions.

Rice straw biochar application to soil irrigated with saline water in a cotton-wheat system improves crop performance and soil functionality in north-west India

Applications of biochar to degraded soils have attracted considerable interest because of its capacity to enhance nutrients availability to the plants, sequester C and immobilize organic and inorganic pollutants. A five-year field experiment was conducted in a cotton-wheat system to investigate the effect of different levels of irrigation water salinity (0.3, 5, 10, and 15 dS m^-1) and rice straw biochar (0, 2, 4, and 8 t ha^-1) on the crop yield and soil functions. Rice straw-derived biochar was applied every year to cotton and its residual effect was observed on wheat. Results of the study indicated that regular irrigation with saline water (5-15 dS m^-1) reduced both seed cotton (12-44%) and wheat grain (7-27%) yield. However, application of biochar (2-8 t ha^-1) to plots irrigated with saline water showed 6-23% and 13-27% greater seed cotton and wheat grain yield compared with unamended plots, respectively. Likewise, biochar application to soil irrigated with canal or saline water showed significant beneficial effects on soil pH, EC, nutrient metabolism and availability, bulk density, infiltration rate and microbial biomass carbon. Our results indicated that biochar amendment especially at the optimum rate of 4 t ha^-1 effectively promoted crop performance by ameliorating soil physical, chemical, and biological properties. In the absence of any chemical amendment for alleviating salinity stress, the results of the present study established that the biochar holds promising potential as a soil amendment in ameliorating soil functions and promoting plant productivity under saline water irrigated conditions.

Agricultural Waste-Based Biochar for Agronomic Applications

Agricultural activities face several challenges due to the intensive increase in population growth and environmental issues. It has been established that biochar can be assigned a useful role in agriculture. Its agronomic application has therefore received increasing attention recently. The literature shows different applications, e.g., biochar serves as a soil ameliorant to optimize soil structure and composition, and it increases the availability of nutrients and the water retention capacity in the soil. If the biochar is buried in the soil, it decomposes very slowly and thus serves as a long-term store of carbon. Limiting the availability of pesticides and heavy metals increases soil health. Biochar addition also affects soil microbiology and enzyme activity and contributes to the improvement of plant growth and crop production. Biochar can be used as a compost additive and animal feed and simultaneously provides a contribution to minimizing greenhouse gas emissions. Several parameters, including biochar origin, pyrolysis temperature, soil type when biochar is used as soil amendment, and application rate, control biochar’s efficiency in different agricultural applications. Thus, special care should be given when using a specific biochar for a specific application to prevent any negative effects on the agricultural environment.

A Review on Current Status of Biochar Uses in Agriculture

In a time when climate change increases desertification and drought globally, novel and effective solutions are required in order to continue food production for the world's increasing population. Synthetic fertilizers have been long used to improve the productivity of agricultural soils, part of which leaches into the environment and emits greenhouse gasses (GHG). Some fundamental challenges within agricultural practices include the improvement of water retention and microbiota in soils, as well as boosting the efficiency of fertilizers. Biochar is a nutrient rich material produced from biomass, gaining attention for soil amendment purposes, improving crop yields as well as for carbon sequestration. This study summarizes the potential benefits of biochar applications, placing emphasis on its application in the agricultural sector. It seems biochar used for soil amendment improves nutrient density of soils, water holding capacity, reduces fertilizer requirements, enhances soil microbiota, and increases crop yields. Additionally, biochar usage has many environmental benefits, economic benefits, and a potential role to play in carbon credit systems. Biochar (also known as biocarbon) may hold the answer to these fundamental requirements.

Biochar and jasmonic acid application attenuates antioxidative systems and improves growth, physiology, nutrient uptake and productivity of faba bean (Vicia faba L.) irrigated with saline water

The effect of foliar treatment with jasmonic acid at 0.5 mM (JA) and biochar (15 ton ha^-1) as a soil amendment for the faba bean (Vicia faba L. Sakha 4) was studied under salinity conditions. Salt stress led to a significant decrease in leaf numbers, leaf areas and plants, chlorophyll content, relative water content, and yield parameters. In contrast, reactive oxygen species, the proline concentration, level of malondialdehyde, and amount of electrolyte leakage were noticeably increased during both seasons under salt levels of 1500 and 3000 ppm sodium chloride (NaCl). Also, enzyme activities (i.e., of superoxide dismutase, catalase, peroxidase, and glutathione reductase) were increased, especially under a high level of salinity stress (3000 ppm). Application of biochar, jasmonic acid, or biochar + jasmonic acid significantly reduced the catalase, superoxide dismutase, and glutathione reductase activities in salt-stressed plants to values approaching those of the control (unstressed) plants, especially under 1500 ppm of NaCl stress. Biochar and jasmonic acid treatments mitigated the damaging effects of salinity and improved the plant status as indicated by the plant height, leaf area, relative water content, and chlorophyll a and b concentrations. Moreover, biochar and jasmonic acid treatments of the salt-stressed plants enhanced plant productivity, number of flowers, number of seeds per plant, and weight of 100 seeds during two successive seasons. Overall, this study suggests that biochar or jasmonic acid treatments might be promising for mitigating the detrimental impact of salt stress on faba beans.

Biochar as a tool for effective management of drought and heavy metal toxicity

Drought and heavy metal stress undesirably disturb soil fertility and plant growth. Heavy metals pose severe biological toxic effects. Biochar, a carbon rich source application ameliorates this stress by increasing the plant growth, biomass, nutrient uptake and improves gaseous exchange in drought stress. Application of biochar reduces drought stress by increasing water holding capacity of soil through modification of soil physio-chemical properties that in turn increases water availability to plants and also enhances mineral uptake and regulation of stomatal conductance. Biochar mediates the retention of moisture, nutrients, inhibits harmful bacteria, absorbs heavy metals, pesticides, prevents soil erosion, increases soil pH, improves cationic exchange and boosts soil fertility. Drought and heavy metal stress often lead to production of reactive oxygen species. However, biochar significantly modifies the Reactive Oxygen Species (ROS) scavenging enzymes and provides an efficient electron transferring mechanism to tackle the toxic effects of ROS in plants. Biochar is regarded as a tool for the effective management of agricultural productivity and various environmental issues. This review provides insights on the potential role of biochar in ameliorating drought and heavy metal stress.

Effect of three different types of biochars on eco-physiological response of important agroforestry tree species under salt stress

Soil reclamation through afforestation along with soil amendments is one of the most suitable practices to combat soil salinity while the use of biochar may have potential to ameliorate salt-affected soils. This study was designed to check effects of different biochars on the physico-chemical properties of soil and characteristics of three important agroforestry trees species: Eucalyptus camaldulensis, Vachellia nilotica and Dalbergia sissoo, in saline soils. Farmyard manure biochar (FYMB), sugarcane bagasse biochar (SCB), woodchips biochar (WCB) were applied (6% w/w) to check their effects on plants under saline conditions. Results revealed that FYMB was the best for promoting all growth and physiological parameters of three tree species while E. camaldulensis was the best suited species. Different types of biochars influenced the growth of agroforestry species differently as SCB showed better results for D. sissoo as compared to WCB but for V. nilotica and WCB was more effective than SCB. Trend of growth and other physiological attributes for E. camaldulensis and V. nilotica was FYMB > WCB > SCB > control whereas D. sissoo showed trend as FYMB > SCB > WCB > control. Biochar was helpful in improving physicochemical characteristics of saline soils by lowering values of soil EC and SAR but type of biochar has a differential effect on tree growth.Novelty statement: Biochar may be a potential source for the amelioration of salt affected soils while less is known about the effects of different types of biochars on the soil and eco-physiological response of important agroforestry trees species in saline soils. In this study, although all types of biochar ameliorated the soil conditions and enhanced the plant growth, but farmyard manure biochar was the most efficient treatment among three types of used biochars.

Assessment of Acidic Biochar on the Growth, Physiology and Nutrients Uptake of Maize (Zea mays L.) Seedlings under Salinity Stress

The application of an acidic biochar can improve plant growth and soil properties in saline conditions. In this study, we investigated the effect of acidic biochar on plant growth and nutrients contents in saline soil. Seven treatments were arranged in a complete randomized design, including control (CK), 0, 30, and 45 g biochar added to a soil having 1% and 1.5% salts; these treatments were termed as B0S1, B30S1, B45S1 and B0S1.5, B30S1.5, B45S1.5 respectively. Experimental results showed that the plant height, leaves plant−1, leaf area, and shoot fresh and dry biomass, and root fresh and dry biomass were increased for the B45S1.5, respectively. Similarly, the highest total nitrogen (TN), total phosphorus (TP), total potassium (TK), and total sodium (Na) concentration in maize shoot were observed for B30S1, B0S1.5, CK, and B0S1.5, respectively. The highest concentrations of TN, TP, TK, and Na in root were obtained with the treatments B0S1, B0S1, B45S1, and B0S1, respectively. Soil pH, and EC decreased and nutrients concentration improved by the addition of acidic biochar. We conclude that the use of acidic biochar can be a potential source for the improvement of maize plant growth as well as mitigate the adverse effect of salt stress.

Soil salinity under climate change: Challenges for sustainable agriculture and food security

Soil salinity is one of the major and widespread challenges in the recent era that hinders global food security and environmental sustainability. Worsening the situation, the harmful impacts of climate change accelerate the development of soil salinity, potentially spreading the problem in the near future to currently unaffected regions. This paper aims to synthesise information from published literature about the extent, development mechanisms, and current mitigation strategies for tackling soil salinity, highlighting the opportunities and challenges under climate change situations. Mitigation approaches such as application of amendments, cultivation of tolerant genotypes, suitable irrigation, drainage and land use strategies, conservation agriculture, phytoremediation, and bioremediation techniques have successfully tackled the soil salinity issue, and offered associated benefits of soil carbon sequestration, and conservation and recycling of natural resources. These management practices further improve the socio-economic conditions of the rural farming community in salt-affected areas. We also discuss emerging reclamation strategies such as saline aquaculture integrated with sub surface drainage, tolerant microorganisms integrated with tolerant plant genotypes, integrated agro-farming systems that warrant future research attention to restore the agricultural sustainability and global food security under climate change scenarios.

Environmental salinization processes: Detection, implications & solutions

A great portion of Earth's freshwater and land resources are salt-affected and thus have restricted use or may become unsuitable for most human activities. Some of the recent scenarios warn that environmental salinization processes will continue to be exacerbated due to global climate change. The most relevant implications and side-effects in ecosystems under excessive salinity are destructive and long lasting (e.g. soil dispersion, water/soil hypersalinity, desertification, ruined biodiversity), often with non-feasible on site remediation, especially at larger scales. Agro-ecosystems are very sensitive to salinization; after a certain threshold is reached, yields and food quality start to deteriorate sharply. Additionally, salinity often coincides with numerous other environmental constrains (drought, waterlogging, pollution, acidity, nutrient deficiency, etc.) that progressively aggravate the threat to food security and general ecosystem resilience. Some well-proven, widely-used and cost-effective traditional ameliorative strategies (e.g. conservation agriculture, application of natural conditioners) help against salinity and other constraints, especially in developing countries. Remotely-sensed and integrated data of salt-affected areas combined with in situ and lab-based observations have never been so easy and rapid to acquire, precise and applicable on huge scales, representing a valuable tool for policy-makers and other stakeholders in implementing targeted measures to control and prevent ecosystem degradation (top-to-bottom approach). Continued progress in biotechnology and ecoengineering offers some of the most advanced and effective solutions against salinity (e.g. nanomaterials, marker-assisted breeding, genome editing, plant-microbial associations), albeit many knowledge gaps and ethical frontiers remain to be overcome before a successful transfer of these potential solutions to the industrial-scale food production can be effective.

The roles of co-composted biochar (COMBI) in improving soil quality, crop productivity, and toxic metal amelioration

The use of co-composted biochar (COMBI) made by the addition of biochar at the beginning of the composting process has greatly increased in agriculture during the last decade. There are more benefits of using the co-composting end product COMBI than using compost and biochar separately or the mixture of the two products. We conducted an extensive review of the production of several COMBIs and their contribution to the composting process and biochar properties as well as the further use of COMBIs in agricultural lands to improve soil health and increase crop yields, and to remediate areas severely contaminated with potentially toxic metals (PTMs). Although the number of researches focused on COMBI production and its application is so far limited, there is enough evidence to elucidate the importance of creating such products to promote sustainable agriculture and environmental safety. Even if a few drawbacks or side effects are found, they are outweighed by the many benefits achieved with COMBIs production and application in comparison to other amendments. The quality of both biochar and compost is largely improved in so many ways during the co-composting process, which in turn improved soil health and crop yields of up to 300% in some particular cases. This work improved the overall understanding of COMBI production and application in agriculture. Based on the review, we suggested future researches to better understand the mechanisms of COMBI long-term application to promote awareness on its role over time through alterations in its surface chemistry, ionic nutrient adsorption, supply (aging effect), and environmental implications.

Biochar—A Panacea for Agriculture or Just Carbon?

The sustainable production of food faces formidable challenges. Foremost is the availability of arable soils, which have been ravaged by the overuse of fertilizers and detrimental soil management techniques. The maintenance of soil quality and reclamation of marginal soils are urgent priorities. The use of biochar, a carbon-rich, porous material thought to improve various soil properties, is gaining interest. Biochar (BC) is produced through the thermochemical decomposition of organic matter in a process known as pyrolysis. Importantly, the source of organic material, or ‘feedstock’, used in this process and different parameters of pyrolysis determine the chemical and physical properties of biochar. The incorporation of BC impacts soil–water relations and soil health, and it has been shown to have an overall positive impact on crop yield; however, pre-existing physical, chemical, and biological soil properties influence the outcome. The effects of long-term field application of BC and how it influences the soil microcosm also need to be understood. This literature review, including a focused meta-analysis, summarizes the key outcomes of BC studies and identifies critical research areas for future investigations. This knowledge will facilitate the predictable enhancement of crop productivity and meaningful carbon sequestration.

Biochar application for the improvement of water-soil environments and carbon emissions under freeze-thaw conditions: An in-situ field trial

There are few studies about biochar application in seasonally frozen soil areas. The regulatory mechanism of biochar on the water-soil environment and carbon emissions in seasonally frozen soil areas is unclear, which affects the study of nutrient migration and spring cropping systems under the control of biochar. For this purpose, we monitored the soil temperature (Ts), soil liquid moisture content (Ms) and soil respiration (Rs) rate during the freeze-thaw period under different application amounts of corn stover biochar (0 t∙ha^-1, 15 t∙ha^-1, 30 t∙ha^-1, 45 t∙ha^-1 and 60 t∙ha^-1). The results showed that biochar can reduce the thermal conductivity of soil, thus improving the thermal insulation effect of frozen thawed soil, and Ts increased by 1.8-5.7 °C. The Ts and Ms were more sensitive to the high biochar application amount than to the low application amount. At the same time, biochar changed the soil aggregate distribution, and Pearson correlation analysis indicated that the soil water retention capacity increased by increasing the macroaggregate content (>0.25 mm), and the Ms increased by 3.7-6.1%. Principal component regression (PCR) analysis showed that biochar can promote soil carbon emission, and Rs of soil treated with biochar was 0.01-0.58 μmol m^-2 s^-1 higher than that of the control. The Ms and Ts were the most important factors promoting the carbon emissions of freeze-thaw soil under the synergistic effect of biochar and freeze-thaw conditions. However, biochar may promote soil CO₂ emissions by affecting the water-soil environment. Considering the soil moisture, seed germination and growth conditions in spring, the suitable biochar application amount was determined to be 44-51 t∙ha^-1. This study provides theoretical support for determining reasonable and effective biochar control measures and improving the soil productivity of farmland soil in seasonally frozen soil areas.

Biochar production and applications in agro and forestry systems: A review

Biochar is a product of biomass thermochemical conversion. Its yield and quality vary significantly with the production technology and process parameters, which also affect its performance in agro and forestry systems. In this review, biochar production technologies including slow pyrolysis, fast pyrolysis, gasification, and torrefaction were compared. The yield of biochar was found to decrease with faster heating rate or more oxygen available. The benefits of biochar application to agro and forestry systems were discussed. Improvements in soil health, plant growth, carbon sequestration, and greenhouse gas mitigation are apparent in many cases, but opposite results do exist, indicating that the beneficial aspect of biochar are limited to particular conditions such as the type of biochar used, the rate of application, soil type, climate, and crop species. Limitations of current studies and future research needed on biochar are also discussed. Specifically, the relationships among biochar production technologies, biochar properties, and biochar performance in agro and forestry systems must be better understood.

Biochar and fulvic acid amendments mitigate negative effects of coastal saline soil and improve crop yields in a three year field trial

China with large area of land planted with crops are suffering secondary salinization in coastal area for the lack of fresh water and saltwater intrusion to the groundwater. The purpose of this study was to investigate the effects of biochar (BC) and fulvic acid (FA) on the amelioration of coastal saline soil and their impact on crop yields under maize-barley rotation system. A three year field experiment was conducted in a saline soil on a farm in coastal area of east Jiangsu Province, China. A maize-barley rotation system had been carried out for ten years with local conventional management before the experiment. The saline soil was amended with BC at rates of 0, 7.5 t ha⁻¹ (BC1), 15 t ha⁻¹ (BC2) and 30 t ha⁻¹ (BC3) alone or combined with fulvic acid (1.5 t ha⁻¹) compared with control. Fertilizers were applied under normal planting strategies. The BC was added only once during the four growing seasons, and the FA was applied before each sowing. Soil salinity changed significantly during the three year field experiment. This was mainly due to the great quantity of rain during the period of maize cultivation. Although Na⁺, Cl⁻ and SO₄²⁻ in BC and /or FA treatments significantly decreased, the pH value increased up to 9.0 as the CO₃²⁻ + HCO₃⁻content increased. Total organic carbon (TOC) and phosphorus (TP) responded positively to biochar addition rate. BC applied with appropriate rate at 15 t ha⁻¹ (BC2) in combination with FA showed optimal effects on soil salinity amelioration, soil physics properties regulation, soil nutrition improvement and crop yields increase. The TOC and TP was 5.2 g kg⁻¹ and 507 mg kg⁻¹ in BC2 + FA treatment, which were lower than BC3 and BC3 + FA treatments. However, the highest total grain yield was obtained in the BC2 + FA treatment, and the total yield was increased by 62.9% over the CK. This study emphasizes that using combined organic amendment of BC with FA for profitable and sustainable use of salt-affected soils would be practicable.

Comparative study of individual and Co-Application of biochar and wood vinegar on blueberry fruit yield and nutritional quality

Biochar and its by-product, wood vinegar, have attracted extensive attention owing to their great potentials in improving degraded soil, which is a global concern because of the threats to soil productivity and food security. However, the effect of biochar or wood vinegar on blueberry production is unknown. Therefore, a field trial was conducted to investigate the effects of individual and co-application of biochar (BC450) and wood vinegar (WV450) derived from blended wood waste on the blueberry tree (Vaccinium corymbosum L.) growth, fruit yield, appearance, and nutritional quality as well as the soil properties and nutrient availability. Regardless of individual or co-application, all the amendments had little effect on tree growth. Although BC450 and WV450 increased the fruit yield, the differences between the amended treatments were non-significant. Both the amendments had little effect on the apparent fruit quality, but improved the nutritional quality has been improved (e.g., increased vitamin C and decreased titratable acidity). Additionally, the individual or co-application of BC450 and WV450 had little effect on soil properties (except for soil organic matter), but increased the soil nutrient availability (e.g., NH₄⁺-N, NO₃⁻-N, and Mg). The enhancement in the nutritional quality of the blueberry fruit can be mainly attributed to the increased nutrient availability. This is the first preliminary study that demonstrates that the individual or co-application of biochar and wood vinegar can be a potential strategy for reclaiming degraded soil and enhancing blueberry production.

Responses of ammonia volatilization from rice paddy soil to application of wood vinegar alone or combined with biochar

Wood vinegar (WV) was applied alone or combined with biochar (BC) to observe their efficiency on suppressing the ammonia (NH₃) volatilization from rice paddy soil. Five treatments, i.e., control (240 kg N ha^-1 applied in urea), WV-5 and WV-10 (240 kg N ha^-1 plus 5 and 10 t WV ha^-1, respectively), and their counterparts WV-5-BC and WV-10-BC (WV-5 and WV-10 plus 7 t BC ha^-1), were evaluated by a soil columns experiment. The N fertilizer was split applied as basal and two supplementary fertilizations (named BF, SF1 and SF2, respectively). The results showed that WV-5 treatment increased rice grain yield up to 11.2% compared to the control. Compared with the control, four WV-amended treatments, exhibited lower pH values of the floodwater (7.94-8.18 vs 8.47 and 7.85-7.91 vs 7.98) and the topsoil (6.52-6.76 vs 6.82 and 6.82-6.92 vs 6.99) during the BF and SF1 periods. Both WV-5 and WV-10 increased the NH₄⁺-N contents of topsoil by 10.9-17.8% and 16.1-36.2% after BF and SF1, respectively, than control treatment. Additionally, the floodwater of the WV-amended treatments had higher NH₄⁺-N concentration than control during the first three days after N fertilization, which can be attributed to the stimulating effect of WV on soil urease enzyme activity. WV did not effectively reduce NH₃ volatilization as hypothesized. Interestingly, four WV-amended had relatively reduced the yield-scale NH₃ volatilization by 13.6% than the control. It is suggested that WV needs to be applied with BC at a moderate rate to achieve optimum rice yield and mitigate NH₃ volatilization.

Biochar Type and Ratio as a Peat Additive/Partial Peat Replacement in Growing Media for Cabbage Seedling Production

Biochar has been proposed mainly as a soil amendment, positively affecting plant growth/yield, and to a lesser degree for growing media. In this study, four commercial grade biochars (A-forest wood; B-husks and paper fiber; C-bamboo and D-fresh wood screening), mostly wood-based materials, were selected. Initial mixtures of peat (P) with different Biochar type and ratios (0-5-10-15-20%) were selected for cabbage seedling production. Biochar material had high K content and pH ≥ 8.64 which resulted in increased pH of the growing media. Biochar A and C at 20% reduced cabbage seed emergence. Biochar A, B and D maintained or improved plant growth at low ratio (i.e., 5–10%) while all Biochars increased N, K and P content in leaves. Biochars A and D were further examined at 7.5% and 15% with the addition of two doses of minerals (1-fold and 1.5-fold). Biochar A and D, initially stimulated seed emergence when compared to the control. High dose of fertilizer favored plant growth in Biochar A at 7.5% and Biochar D at 15%. Leaf stomatal conductance was decreased at Biochar A+Fert at 7.5% and Chlorophyll b content was decreased at Biochar A+Fert at 15%. The presence of Biochar A increased the antioxidant activity (as assayed by 2,2-diphenyl-1-picrylhydrazyl-DPPH). Lipid peroxidation was higher in plants grown with fertilized peat and Biochar A at 15%, activating antioxidant enzymatic metabolisms. Potassium, phosphorous and copper accumulation and magnesium deficiency in cabbage leaves were related to the Biochar presence. Wooden biochar of beech, spruce and pine species (Biochar A) at 7.5% and fertilized biochar of fruit trees and hedges (Biochar D) were more promising for peat replacement for cabbage seedling production.

A quantitative understanding of the role of co-composted biochar in plant growth using meta-analysis

The combined use of biochar and compost as a soil amendment presents benefits to crops and nutrient cycling. Although there are literature reviews regarding biochar and biochar-compost mixtures, a quantitative literature review on the role of co-composted biochar (hereby called COMBI) in plant productivity is currently missing. The goal of this review paper is to find evidence-based measures of the effects of application rates, soil pH, plant types, biochar feedstock, and compost materials, on plant productivity. Plant productivity covers a variety of measurements but mostly refers to grain yield and above-ground biomass. Response ratio was selected as the effect size. Funnel plot showed that the studies were reasonably symmetrically distributed around the mean effect size. Results showed that application rates of <20 t/ha and >30 t/ha significantly increased plant productivity by 48.3 and 15.7%, respectively, while no significant yield increases were found for the application rates between 20 and 30 t/ha. When data was grouped based on the soil pH, the greatest increase in plant productivity was found to be at acidic soil pH values (pH 4-5), which was expected because the liming effect of biochar is often reported as one of the main mechanisms behind the increased crop yields. When different plant species were compared, cereal grasses grown with COMBI yielded significantly higher grain yields (39.7%). Rice husk biochar yielded the highest increase in productivity but this result was based on only one study. The second highest increase was obtained with wood-based biochars (29.4%) based on ten studies. The effect sizes found with our meta-analyses are based on 14 research works worldwide and represent the most updated information regarding the effects of COMBI on plant production. As more data on COMBI become available, data analyses can be updated to make more robust comparisons.

Soil nutrients status affected by simple and enriched biochar application under salinity conditions

In order to study the effect of biochar application as simple and enriched, on the soil nutrients status in the salinity conditions, a research was conducted as a factorial arrangement based on completely randomized design (CRD) with three replicates. The biochar (grape pruning residues) was applied in three levels (0, 2% biochar, and 2% enriched biochar by rock phosphate and cow manure). Also, the salinity treatment was considered in three levels (2, 4.5, and 9 dSm^-1). After treating the soil, it was incubated in polyethylene containers for a 70-day period at 25 °C and 70% field capacity moisture regime. The results showed that salinity significantly affected the soil pH, electrical conductivity (EC), calcium, magnesium, sodium, basal respiration, and nitrifying bacteria frequency (P < 0.001) and chloride concentration (P < 0.01). Also, the biochar significantly affected the pH, organic carbon, concentration of total nitrogen, phosphorous, solution potassium, sodium, iron, zinc, copper, basal respiration, and nitrifying bacteria frequency (P < 0.001) of the soil. The interaction effect of biochar and salinity levels was significant on soil sodium concentration (P < 0.01) and pH (P < 0.05). In comparison with the control treatment, the enriched biochar, decreased soil pH (about 1.4%) and increased the phosphorous, iron, and zinc up to 36%, 29%, and 36%, respectively and simple biochar increased the Nitrogen and Potassium up to 46% and 48%, respectively. In general, it was concluded that both types of the biochars lowered the sodium concentration of the soil in different salinity levels due to high potential of biochar for sodium absorption which this ability may be considered in saline soils remediation.

Biochar amendment improves crop production in problem soils: A review

Problem soils are referred to as those with poor physical, chemical, and biological properties that inhibit or prevent plant growth. These poor properties may be a result of soil formation processes but are largely due to inappropriate farming practices or anthropogenic pollution. The world has lost a third of its arable land due to erosion and pollution in the past 40 years. Thus, there is an urgent need for improving and remediating problem soils. As a novel multifunctional carbon material, biochar has been widely used as a soil amendment for improving soil quality. Previous reviews have summarized the characteristics of biochar, the interactions with various soil contaminants, and the effects on soil quality, soil productivity, and carbon sequestration. Relatively limited attention has been focused on the effects of biochar amendment on plant growth in problem soils. As a result, a comprehensive review of literature in the Web of Science was conducted with a focus on the effects of biochar amendment on plant growth in problems soils. The review is intended to present an overview about problem soils, biochars as functional materials for soil amendment, how amended biochars interact with soils, soil microbes, and plant roots in remediation of problem soil and improve plant growth. Additionally, existing knowledge gaps and future directions are discussed. Information gathered from this review suggests that biochar amendment is a viable way of improving the quality of problem soils and enhancing crop production. It is anticipated that further research on biochar amendment will increase our understanding on the interactions of biochar with components of problem soils, speed up our effort on soil remediation, and improve crop production in problem soils.