Wood Biochar Research Articles

Biochar Addition to a Mediterranean Agroecosystem: Short-Term Divergent Priming Effects

The goal of this study was to evaluate biochar’s resistance to microbial decomposition and its impact on native soil organic matter (SOM) decomposition. Conducted in a vineyard with a sandy loam Mediterranean soil with neutral pH and low organic carbon content, the experiment involved the application of 6.5 g biochar kg−1 derived from pine (PB) and corn cob (ZB). The monitoring period spanned two years, with soil samples collected at short- and medium-term timepoints (2 and 26 months post-application) and incubated in the lab for an additional 250 days. Soil respiration, the CO2-C isotopic signature, and dissolved organic carbon (DOChw) were assessed to identify potential priming effects (PE) and evaluate their persistence over two years. In the short term, biochar-induced priming effects were feedstock and pyrolysis temperature dependent, exhibiting negative priming in high-temperature wood biochar and positive priming in low-temperature grass biochar. The mechanism behind short-term positive priming was attributed to the higher labile organic carbon (OC) content in ZB compared to PB. In the medium term, initial strong priming effects shifted to slightly negative priming effects in both biochars, indicating the depletion of labile carbon fractions and the emergence of physical protection processes that mitigated priming.

Meso-Microporous Carbon Nanofibrous Aerogel Electrode Material with Fluorine-Treated Wood Biochar for High-Performance Supercapacitor.

A supercapacitor is an electrical energy storage system with high power output. With worldwide awareness of sustainable development, developing cost-effective, environmentally friendly, and high-performance supercapacitors is an important research direction. The use of sustainable components like wood biochar in the electrode materials for supercapacitor uses holds great promise for sustainable supercapacitor development. In this study, we demonstrated a facile and powerful approach to prepare meso-microporous carbon electrode materials for sustainable and high-performance supercapacitor development by electrospinning polyacrylonitrile (PAN) with F-treated biochar and subsequent aerogel construction followed by stabilization, carbonization, and carbon activation. The resultant carbon nanofibrous aerogel electrode material (ENFA-FBa) exhibited exceptional specific capacitance, attributing to enormously increased micropore and mesopore volumes, much more activated sites to charge storage, and significantly greater electrochemical interaction with electrolyte. This electrode material achieved a specific capacitance of 407 F/g at current density of 0.5 A/g in 1 M H2SO4 electrolyte, which outperformed the state-of-the-art specific capacitance of biochar-containing electrospun carbon nanofibrous aerogel electrode materials (<300 F/g). A symmetric two-electrode cell with ENFA-FBa as electrode material showed an energy density of 11.2 Wh/kg at 125 W/kg power density. Even after 10,000 cycles of charging-discharging at current density of 10 A/g, the device maintained a consistent coulombic efficiency of 53.5% and an outstanding capacitance retention of 91%. Our research pointed out a promising direction to develop sustainable electrode materials for future high-performance supercapacitors.

Combined lime and biochar application enhances cowpea growth and yield in tropical Alfisol

It is essential to increase the pH of tropical soils in order to reduce acidity and promote soil and crop productivity. Therefore, experiments were carried out in 2020 and 2021 to assess the impacts of biochar and lime on the chemical properties, growth, nodulation, and yield of cowpea (Vigna unguiculata). The study involved various levels of lime (CaCO3) and wood biochar (ranging from 0 to 10 t ha−1), organized in a factorial combination. The treatments were arranged in a randomized complete block design and replicated three times. The application of lime and biochar, either separately or in combination, led to improvements in soil chemical properties such as pH, nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), magnesium (Mg), and cation exchange capacity (CEC), as well as enhancements in the growth, nodulation, and yield of cowpea when compared to the control. Lime and biochar alone and combined reduced exchangeable acidity (Al + H) relative to the control. Cowpea yield increased with lime rate up to a point, but then decreases. The highest cowpea yield is achieved at a lime rate of 2.5 t ha−1, whereas cowpea yield increased as the Biochar rate increased from 0 up to 10 t ha−1. There was a significant correlation between pH and cowpea pod weight in both years (2020 and 2021). The R values were − 0.615 and − 0.444 for years 2020 and year 2021 respectively at P < 0.05. At higher lime levels combined with biochar, there were considerable reductions in cowpea yield, and this decrease can be attributed to unfavorable soil pH conditions. Relative to 2.5 t ha−1 lime + 5 t ha−1 biochar, 10 t ha−1 lime + 10 t ha−1 biochar, reduced cowpea grain yield by 853% in 2020 and 845% in 2021. Since there were no significant differences between the effects of 2.5 t ha−1 lime + 5 t ha−1 biochar, 2.5 t ha−1 lime + 7.5 t ha−1 biochar, and 2.5 t ha−1 lime + 10 t ha−1 biochar applications on cowpea yield, therefore to prevent waste of Biochar, 2.5 t ha−1 lime + 5 t ha−1 biochar is recommended for production of cowpea.

Intrinsic electrical conductivity of monolithic biochar

While biochar is an effective and viable tool for alleviating climate change, monolithic biochar is emerging as a functional material for applications that enhance sustainability, such as renewable energy storage and low-cost, high-efficiency water purification. Its performance depends on its physical and chemical characteristics, including electrical conductivity. Monolithic biochar's bulk conductivity is expected to rely on the porosity and conductivity of its carbon matrix - intrinsic conductivity – a fundamental property that has not been systematically studied. The work discerns intrinsic conductivity and its dependence on biomass species and carbonization temperature. We carbonized four hardwoods, three softwoods, and bamboo following an ultra-slow pyrolysis procedure and characterized biochar's chemical and structural properties. We modified the two-probe method and measured bulk conductivity along the axial direction. The bulk conductivity and density followed the linear and the Reynolds-Hough relationships, allowing the determination of intrinsic conductivity. The intrinsic conductivity increased with pyrolysis temperatures and became independent of wood species at 1500 °C.According to the linear model, the highest value of wood biochar produced at 1500 °C was 14,600 S/m. Bamboo biochar had a higher intrinsic conductivity (21,000 S/m), attributed to bamboo's high cellulose content and large graphite nanocrystal size in its biochar. Moreover, the modified two-probe method minimized measurement uncertainty and enabled the quantification of natural variation in biochar conductivity, which was less than 10% for the same wood species. These findings will help strengthen monolithic biochar's potential as a low-cost, high-performance functional material.

Growth and Reproduction of Eudrilus eugeniae in Parthenium hysterophorus Biomass and Mixed Leaf Litter Substrates Amended with Wood Biochar

Growth and Reproduction of Eudrilus eugeniae in Parthenium hysterophorus Biomass and Mixed Leaf Litter Substrates Amended with Wood Biochar

Soil hydrophysical and chemical attributes in ferralsol amended with wood biochar

Soil hydrophysical and chemical attributes in ferralsol amended with wood biochar

Improvement of N, P, and K availability of post-brick mining soil to increase maize yield by applying different types of biochar

The low fertility of post-brick mining soil may be improved by applying biochar to the soil because biochar is an excellent soil amendment, although its quality varies depending on the raw materials used. Therefore, soil fertility, nutrient availability, and crop yields are affected by the type and amount of biochar added to soils. This study examined the effect of types and dosages of biochar on nitrogen, phosphorus, and potassium availability of post-brick mining soil to increase maize yield. The treatment combinations of biochar dosages (0 t ha-1, 15 t ha-1, 30 t ha-1, and 45 t ha-1) and biochar types (coconut shell, wood, and rice husk biochars) were arranged in randomized block design with three replications. Each treatment plot measuring 4 m x 4.5 m was planted with maize seeds with a planting space of 80 cm x 25 cm. Urea (135 kg N ha-1), SP36 (36 kg P2O5 ha-1), and KCl (110 kg K2O ha-1) were applied as basal fertilizers. The results showed that at eight weeks after biochar application, the amount and type of biochar positively affected maize yield. The application of rice-husk biochar at 30 t ha-1 resulted in the highest maize yield. The application of each type of biochar at 45 t ha-1 yielded the highest increase in the availability of nitrogen, phosphorus, and potassium in the soil.

Production and characterization of wood biochar from energetic forests by pyrolysis in a horizontal screw reactor

Production and characterization of wood biochar from energetic forests by pyrolysis in a horizontal screw reactor

Development of biochar/HDPE composites and characterization of the effects of carbon loadings on the electromagnetic shielding properties

The aim of this research is to develop high carbon-yielding biochar from pinewood, coffee husk, sugarcane bagasse, and maize cob and to characterize the biochar/HDPE composites for electromagnetic (EM) shielding application. During the biochar/HDPE composites fabrication, slow pyrolysis and compression molding manufacturing were used. The enhanced properties characterizations were conducted by using thermogravimetric analysis (TGA), scanning electron microscopy (SEM), differential thermal analysis (DTA), Fourier transform spectrometry (FTIR), Brunauer-Emmet-Teller (BET) analysis, digital multi-meter, and proximity analysis. The results of biochar pyrolysis showed the maximum carbon yield of 74.6 %, 68.9 %, 68.4 %, and 40 % for pine wood, maize cob, sugarcane bagasse, and coffee husk respectively. The BET analysis showed the maximum specific surface area (734.5 m2/g), pore volume (0.2364 cm3/g), and pore radius (9.897 Å) from the pine wood biochar. The biochar loading analysis results showed that the 30 % and 40 % pine wood biochar significantly enhanced the electrical conductivity, thermal conductivity, thermal stability, crystallinity, and EM shielding effectiveness (SE) of the biochar/HDPE composites. In particular, the biochar/HDPE composite with 30 wt% pine wood biochar showed the highest thermal conductivity of 2.219 W/mK, and the 40 wt% pine wood biochar/HDPE composite achieved the highest electrical conductivity of 4.67 × 10−7 S/cm and EM SE of 44.03 dB at 2.1 GHz.

Ameliorative Effect of Wood Biochar for Cadmium Stress on Soybean (Glycine Max L. Merrill) Growth and Yield

Cadmium (Cd) is a heavy metal that affects plant growth and yield. Biochar can mitigate the detrimental effect of Cd on plants. To assess effectiveness of wood biochar (WB) in mitigating Cd stress, a pot experiment was conducted with six treatments in Soyabean crop viz., control (0% biochar and no Cd stress), 1.5% WB, 3% WB, 100 mg CdCl2 Kg-1 soil, 100 mg CdCl2 Kg-1 soil +1.5% WB, 100 mg CdCl2 Kg-1 soil +3% WB. The impact of Cd on the growth, physiological status, yield and yield-contributing characters of Soybean were found to be significant (p&lt;0.05). The application of 1.5% and 3% WB significantly (p &lt; 0.05) alleviated Cd toxicity to Soybean under Cd stress conditions. There was no significant difference in the effect of two rates of wood biochar’s (1.5% and 3% WB) on growth, physiological status and yield of Soybean. Therefore, it can be concluded that 1.5% WB is sufficient to reduce toxicity caused by Cd stress in Soybean. SAARC J. Agric., 21(2): 157-168 (2023)

The Influence of Rubberwood Biochar Size on the Effectiveness of Using Urea Fertilizer in the Cultivation of Pakcoy (Brassica chinensis L.)

The effectiveness of fertilizer and crop production can be increased through the provision of biochar as a soil amendment. This research aims to evaluate the effect of the combination of varying sizes of rubber wood biochar with doses of urea fertilizer on the growth of pak choy mustard plants. The research was conducted with two factors arranged in a completely randomized design. The first factor is the size of the rubber wood biochar and the second factor is the dose of Urea fertilizer, each consisting of 4 levels. All treatment combinations were carried out with 3 repetitions. The response variables observed include soil pH, plant height, number of leaves, canopy area, and fresh plant production. The results showed biochar size factor had a significant effect on soil pH and fresh weight. The urea fertilizer dosage factor shows a significant influence on the plant height and fresh weight. The treatment with the most optimal growth was 1 mm biochar produced yield of 19.03 g/plant, while Urea dose of 2 g/plant produced pak choy plants of 20.72 g/plant. Keywords: Biochar, Pakchoy, rubberwood, size, Urea.

Wood biochar as a point source CO2 adsorbent-impact of humidity on performance

Adsorption of carbon using biobased materials is a sustainable approach to point source carbon capture and storage, particularly if the biomass is a “waste” and the adsorbent can then be re-used in soils. In this work, biochar derived from fast pyrolysis of softwood residues (sawdust) was investigated as a CO2 adsorbent under humid conditions to determine the effect of water on biochar adsorption performance. Dry and wet adsorption experiments were run at concentrations of CO2 between 20–80 vol.% (balanced with N2) at 20 °C. Water concentrations were set by saturating the N2 stream and resulted in 0.5–1.8 vol.% (relative humidity of 20%–80%). For the dry gas experiments, the adsorption capacities doubled (0.83–1.98 mmol/g) as the CO2 concentration increased from 20% to 80%. The capacity did not change between wet and dry experiments for 20, 40, and 60 vol.% CO2; however, at 80 vol.% CO2, the adsorption capacity increased by 38% for the “wet” gas from the dry gas. This is potentially due to carbonates formed due to CO2 dissolution/reaction in water. The adsorption time was not impacted by the range of water concentrations studied. The Avrami kinetic model best represented the rate of adsorption in both dry and wet conditions. The fact that neither the biochar adsorption capacity nor its adsorption rate was negatively impacted by water shows that biochar can be a promising option for stack gases, which contain water vapor. However, more experiments at higher temperatures are required.

Comparison of various sustainable amendments on soil cracking in semi-arid regions

Soil desiccation is an important process that happens mainly in semi-arid regions especially in Central Asia. Soil desiccation leads to higher loss of moisture at shallower depths and also deeper penetration of water, which ultimately reduces water availability and hence impacts the growth of plants for the application of agriculture and green infrastructures. Therefore, minimizing soil desiccation will help maintain higher water availability for plants for agricultural productivity and green infrastructure in Central Asian Region. In literature, various amendments such as natural fibers, cementation, lime, vegetation and biochar have been used to suppress cracking of soil. There is rarely any study that analyses and compares mechanism of crack suppression among the above-mentioned methods. The objective of this study is to explore various sustainable methods of minimizing soil desiccation and compare their mechanisms. Further, the aim is to analyse the feasibility of these methods by revealing their advantages and disadvantages. In order to achieve this objective, 1-D columns were prepared with control soil and amended soil (with fibers, vegetation and biochar). The review also provides insights into their mechanism of suppression of soil cracking by proposing a new factor (i.e., normalized CIF). Based on the proposed factor, the efficiency of biochar and fiber amendments are higher than that of vegetation. Vegetation may or may not have positive impact on cracking of soil depending on their shoot length. Among various amendments, wood biochar (10% content) and coir fiber (at 0.75 % content) seems to have highest efficiency in reducing cracking in soil. Overall, the study aims to develop preliminary guidelines suppressing soil desiccation in semi-arid regions such as Central Asia.

Enhancing herbicides sorption in sodic soils through biochar amendment : A promising approach for sustainable agriculture

This study is essential for assessing the binding capacity of Prosopis wood biochar to commonly used herbicides, Pretilachlor and Pendimethalin. Understanding their sorption dynamics at varying biochar application rates and exposure times is crucial for sustainable and effective herbicide management in intensively farming agricultural fields and for reducing environmental contamination. The Prosopis wood biochar was produced in an earthen kiln at 300-350°C. The batch experiment was conducted to study the sorption potential of biochar additions at rates of 0, 5, and 10 t ha-1. The herbicides were added to the homogenized soil-biochar mixes at zero, whole, twice, and four times the recommended dose. The sorption of the herbicides by soil biochar mixture was studied for 12 and 24 hours. The result showed that Pendimethalin sorption increased with biochar application rate, requiring 24 hours for 95% sorption at 4X dose without biochar (77.95 mg/kg soil) and 12 hours with 10 t/ha biochar (75.82 mg/kg soil). The Kd value increased with biochar application (0.57-77.95 mg/kg soil) and decreased with pendimethalin application (77.95-3.04 mg/kg soil). Maximum sorption (95%) was attained within 12 hours for 1X and 2X rates and 24 hours for 4X rates when biochar was added. This demonstrated that although pendimethalin residue in the soil can be immobilized by adding biochar within 8 hours at lower rates, more than 24 hours were required when pendimethalin was applied at higher rates or repeatedly. Biochar can be used to reduce pendimethalin leaching in agricultural fields, especially sodic soils, at higher application rates.

Biopolymer as an additive for effective biochar-based rhizobial inoculant

Biochar is an efficient and inexpensive carrier for bacteria that stimulate plant development and growth. In this study, different biopolymer additives (cellulose, xanthan gum, chitin and tryptone) were tested with different addition ratios (1:0.1, 1:0.5 and 1:1) on further enhancing biochar capacity for supporting the growth and activity of Bradyrhizobium japonicum (CB1809). We utilized pine wood biochar (PWBC) pyrolyzed at 400 °C as the base inoculum carrier. The shelf life and survival rate of CB1809 were counted using the colony-forming unit (CFU) method for up to 120 days. Peat served as a standard reference material against which all treatments were compared. Subsequent experiments evaluated the ability of carrier inoculants to promote Glycine max L. (soybean) plant growth and nodulation under different watering regimes, i.e., 55 % water holding capacity (WHC) (D0), 30 % WHC (D1) and, 15 % WHC (D2) using sandy loam soil. Results revealed that among different additives; xanthan gum with 1:0.5 to PWBC [PWBC-xanthan gum(1:0.5)] was observed as a superior formulation in supporting rhizobial shelf life and survival rate of CB1809. In pot experiments, plants with PWBC-xanthan gum(1:0.5) formulation showed significant increase in various physiological characteristics (nitrogenase activity, chlorophyll pigments, membrane stability index, and relative water content), root architecture (root surface area, root average diameter, root volume, root tips, root forks and root crossings), and plant growth attributes (shoot/root dry biomass, shoot/root length, and number of nodules). Additionally, a reduced enrichment of isotopic signatures (δ13C, δ15N) was observed in plants treated with PWBC-xanthan gum(1:0.5), less enrichment of δ15N indicates an inverse link to nodulation and nitrogenase activity, while lower δ13C values indicates effective water use efficiency by plants during drought stress. These results suggest that biopolymers supplementation of the PWBC is useful in promoting shelf life or survival rate of CB1809.

Impact of biochar and compost amendment on corn yield and greenhouse gas emissions under waterlogged conditions

Biochar, widely recognized for its capacity to counteract climate change impacts, has demonstrated substantial benefits in agricultural ecosystems. Nevertheless, empirical studies exploring its efficacy during climatic aberrations such as heavy rainfall are limited. This study investigated the effects of compost and biochar addition on corn growth attributes, yield, and soil CO2 and N2O fluxes under heavy rain (exceeding 5-yr average) and waterlogging conditions. Here, treatments included compost (CP, 7.6 t ha−1); rice husk biochar (RB, 7.6 t ha−1); wood biochar (WB, 7.6 t ha−1); and control (Cn). Under high rainfall and waterlogging, the CP treatment manifested a pronounced enhancement in corn biomass and productivity, exceeding biomass and productivity of Cn treatment by 12.6 and 32.2%, RB treatment by 120 and 195%, and WB treatment by 86.1 and 111%, respectively. Corn yield increased in the order: CP > Cn > WB > RB. Intriguingly, negligible disparity occurred between the RB and WB treatments in straw yield, grain yield, grain index, and corn productivity but both treatments recorded distinctively lower values than CP treatment. Also, the CO2 and N2O fluxes remained largely similar for two biochar treatments but lower than CP treatment. Overall, CP increased corn yield, straw, and grain yield whereas biochars reduced N2O flux during waterlogging. Although derived from a short-term experimental window, these pivotal findings furnish invaluable insights for devising soil amendments for yield and environmental benefits in contexts of extreme climatic perturbations. Our findings offer a robust foundation for refining nutrient management strategies confronted with waterlogging challenges, but long-term studies are necessary for definitive conclusions.

Agronomic amendments drive a diversity of real and apparent priming responses within a grassland soil

Soil carbon (C) sequestration is often viewed as a nature-based solution to help mitigate climate change. Key to realising this potential is a better understanding of which C inputs promote greater long-term C storage. The priming effect (PE) is the change in rates of microbial soil organic matter (SOM) decomposition caused by the addition of organic or mineral amendments to soil. The apparent PE (changes in CO2 from microbial biomass turnover) of substrates is often studied as a confounding factor, however, the real PE (decomposition of native SOM) is rarely measured due to uncertainties in C pool differentiation. Here, we used a 50-day mesocosm study to compare the effect of various common soil amendments (wood biochar and ash, protein, amino acids, glucose, cellulose, cattle farmyard manure (FYM), cattle slurry, inorganic N fertiliser, and different ratios of wheat straw:shoot mixes) on the real and apparent PEs of soil, using 5-year old quasi-stable 14C-labelled SOM and 14C-labelled active microbial biomass, respectively. Our results show that there are often significant differences in the real and apparent PE, for the same amendment, with variance in magnitude and, in some case, direction. We identified few consistent drivers of PE across the two assays, however, there was a negative relationship between the initial C:N ratio of the treatment and PEs, suggesting that while the nutrient stoichiometry of the C amendment is important, the usability and quality of the substrate for the microbial community are key to determining its priming response. Equally, context is important for interpretation, as treatments that elicit positive priming may still be replenishing or increasing soil C stocks.

Biochar enhances root development and aloin content of mature leaves in containerized Aloe arborescens Mill.

The leaves of the medicinal plant Aloe arborescens Mill. (Asphodelaceae) contain significant amounts of bioactive metabolites, including aloin (a mixture of the two diastereoisomers, aloin A and aloin B), aloesin, isoaloeresin D, and aloenin A. The presence of these metabolites varies considerably depending on the plant's growth conditions, including the used growing substrate. In recent years, there has been growing interest in using biochar for potted plants cultivation. However, there is currently no available information regarding the suitability of biochar for the containerized cultivation of A. arborescens. A pot experiment was conducted with the hypothesis that biochar could influence the growth and phytochemistry of A. arborescens. The growing medium was supplied with increasing proportions of biochar (1: 100 % commercial substrate; 2: mixed 50 % (v/v) substrate; 3: 100 % conifers wood biochar). Over the course of three years, the plants were closely monitored, and several key growth parameters were measured, including plant height, stem diameter, number and weight of leaves, and the number of suckers. After the first year, the content of selected active metabolites was assessed. This evaluation also involved a comparison of the respective levels in the leaves taken from the apical, median, and basal sections of the stem. The leaves collected from the median section of plants were found to be larger and exhibited the highest percentage of spikes, epidermis, and gel on fresh weight. As a general trend, it was observed that in plants cultivated within the highest amount of biochar, the leaves collected from the intermediate stem portion contained the highest quantity of secondary metabolites.

Tiered Approach for Assessing the Effective and Safe Applicability of Beech Wood Biochar for Soil Improvement

The soil degradation processes may cause long-term serious problems in various areas of life on Earth, thus mitigation of these processes by environmental-friendly, innovative soil protection methods is necessary. Biochar produced from organic wastes or by-products by pyrolysis may have several positive properties as additive in soil improvement technologies. In our complex research applying a tiered approach we assessed the main properties of a beech-wood biochar produced from a high volume by-product of a food industry technology. Then we studied in 4-months microcosm experiments the applicability of this biochar as amendment mixed into an acidic, degraded sandy soil. In addition, to forecast the long-term effects of the biochar, artificial physical and biological aging experiments were conducted.Based on the results, the beech-wood biochar was able to shift the acidic pH of the soil to the alkaline range and the electric conductivity of the soil increased with incremental biochar doses. Biochar addition significantly increased the microbial activity, as well. The results had clearly shown that during the mid-term experiment not even the highest biochar dose (15%) had inhibitive effect, but it rather improved several soil parameters. Furthermore, the biochar had positive effect on the soil water holding capacity, and the available soil nutrient and organic matter content. The results of the aging experiments generally showed also favourable effects and demonstrated that the aging-mediated changes differed according to the soil types. Therefore, we have concluded that biochar application requires a char by char and soil by soil testing prior to field application.

Combined application of biochar and partial root-zone drying irrigation improves water relations and water use efficiency of cotton plants under salt stress

Reduced irrigation in combination with biochar application can improve stomatal anatomy, water relations and intrinsic water use efficiency (WUEi), thus having a positive effect on the alleviation of salinity and drought stresses. A split-root pot experiment was executed to explore the effects of two biochar applications (WSP: wheat straw biochar; SWP: soft wood biochar) in combination with three irrigation strategies (FI: full irrigation; DI: deficit irrigation, PRD: partial root-zone drying irrigation) on stomatal anatomy, water relations and WUEi of cotton plants under normal soil (S0, EC=0.36 dS m-1) and saline soil (S1, EC=16.55 dS m-1). The results revealed that both salinity and drought stresses negatively affected plant water relations and reduced stomatal conductance, carbon isotope discrimination (Δ13C), stomatal size (SS) and hydraulic conductance (Kl) while increased leaf abscisic acid (ABA) concentration ([ABA]leaf). However, biochar amendment under salt stress significantly decreased [ABA]leaf while improved leaf water relations, increased Kl, stomatal density (SD), SS, Δ13C and maximum stomatal conductance (gsmax). Meanwhile, compared with FI and DI, PRD plants had greater SD, gsmax, and WUEi but lowered stomatal conductance (gs). Among all treatments, the combined application of WSP and PRD significantly increased SD and gsmax, improved leaf water relations, Kl and [ABA]leaf and WUEi. It is concluded that the altered stomatal features caused by the biochar and irrigation treatments are associated with changes in [ABA]leaf and Kl, and have a major role in affecting plant hydraulic integrity and water use efficiency of cotton exposed to salinity stress.