Biochar amendment improves crop production in problem soils: A review

Rhizosphere dissolved organic matter and iron plaque modified by organic amendments and its relations to cadmium bioavailability and accumulation in rice

Organic amendments can modify rhizosphere dissolved organic matter (DOM) properties and Fe-plaque quantity, thereby affecting cadmium (Cd) bioavailability and uptake by rice. Pot experiments were conducted to investigate effects of biochar (BC) and vermicompost (VC) at different rates (0, 1%, and 5%) on rhizosphere DOM characteristics and Fe-plaque quantity, and their impacts on Cd bioavailability and accumulation in high and low Cd-accumulation rice cultivars (HAC and LAC). Soil DOM was characterized by ultraviolet-visible (UV-Vis) and fluorescence excitation-emission matrix (EEM) spectrum analyses. Hydroponic experiments were conducted to investigate effects of BC- or VC-derived DOM combined Fe-plaque on Cd uptake by rice. Results showed that increasing rates of organic amendments increased DOM concentration while decreased Cd availability in rhizosphere and bulk soils and Cd contents in rice tissues. The Cd reduction in LAC grains (31.9%-72.7%) was better than that in HAC grains (6.3%-25.4%) after organic amendment addition. Soil DOM properties were modified by organic amendments towards higher aromaticity, molecular weight, and stability. VC resulted in a greater increase of humic-like fractions but reduced protein-like proportions in rhizosphere DOM over BC. Negative correlations were observed between humic-like fractions and available Cd in the rhizosphere. Likewise, VC (especially 5%VC) promoted the formation of Fe-plaque and limited Cd soil-to-root transport, while BC groups showed a reverse trend. The results of hydroponic experiments confirmed BC- and VC-derived DOM and Fe-plaque further inhibited Cd uptake by rice via the complexation with Cd and the sequestration of Cd, respectively. Hence, VC application combined with low Cd-accumulation rice could be an effective strategy for the safe utilization of Cd-contamination soils.

Effects of Biochar and Biochar–Compost Mix on Growth, Performance and Physiological Responses of Potted Alpinia zerumbet

Container crop production has become increasingly popular over the last 50 years. A major component of container or potting media is peat. Peatlands are a natural carbon sink, and peat is a nonrenewable natural resource. Peat harvesting has become an important environmental issue. There is a growing effort to explore alternative organic materials to completely or partially replace peat as a medium component. Biochar is a carbon-rich product that has gained increasing interest as a component of growing media. In the present study, biochar was produced from rice straw. Peat/perlite/biochar (PPB; 40/30/30 v/v) and peat/perlite/biochar/vermicompost (PPBC; 30/30/35/5 v/v) were evaluated relative to a basal or control medium of peat/perlite (PP; 70:30 v/v). Alpinia (Alpinia zerumbet ‘Variegata Dwarf’) was used as a test plant. Amending biochar and biochar–compost mix increased the pH of the growing media. Hydrophysical properties including container capacity, bulk density, air space and total porosity were all within or near the standard ranges for soilless growing media. Chlorophyll a and b contents of A. zerumbet plants grown in PPB medium were reduced by more than 20% and 28%, respectively, compared to those grown in PP or PPBC media. The net photosynthetic rate of PPB-grown plants was more than 28% lower than those grown in PP and PPBC media. As a result, shoot and root dry weights of plants produced in PPB medium were more than 42% and 22% less, respectively, than those grown in PP and PPBC media. Although visual quality of PPB-grown plants was lower, they still exhibited marketable quality, which was largely due to the fact that their side shoots, leaf numbers, leaf areas, leaf thickness, and shoot diameters were comparable to those produced in PP and PPBC media. The present study showed that in a peat/perlite basal medium, substitution of peat by biochar derived from rice straw at 30% affected the growth of A. zerumbet plants, mainly in dry matter accumulation, but the plants were still marketable. On the other hand, plants grown in the same basal medium with peat replaced by the biochar at 35% plus an amendment of compost at 5% were comparable to those grown in the control medium. As the value of ornamental plants depends on their aesthetic appearance, a potting medium comprised of peat/perlite/biochar/vermicompost at 30/30/35/5 by volume is recommended for the production of A. zerumbet plants. The substitution of peat at 35% suggests that peat use can be reduced in the formulation of potting media, thus contributing to the conservation of peatlands.

Mechanisms and adsorption capacities of hydrogen peroxide modified ball milled biochar for the removal of methylene blue from aqueous solutions

In this work, hickory chip biochars developed at distinctive pyrolysis temperatures were ball milled (BMHC) and then post-modified with a 10% hydrogen peroxide (H₂O₂) solution to obtain a set of novel sorbents (BMHC-H₂O₂). The specific surface area (SSA) was dramatically increased after ball-milling while the hydroxyl and carboxyl groups on the surface of the biochars were further increased through H₂O₂ modification. Additionally, thermal stability of the biochar treated with ball-milling was not greatly reduced by H₂O₂ modification and hydrodynamic radius was decreased. Ball milling enhanced the adsorption efficiency to methylene blue (MB) by the biochar, and this ability was further increased by H₂O₂ modification, because of the increasing in oxygen-containing functional groups (OCFG) to interact with MB. The rate of MB adsorption to BMHC-H₂O₂ was faster than that of BMHC, reaching equilibrium after about 6 h. Among adsorbents tested, the 450 °C BMHC-H₂O₂ had the greatest MB adsorption capacity (310 mg g^-1).

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.

Effect of calcium and iron-enriched biochar on arsenic and cadmium accumulation from soil to rice paddy tissues

Arsenic (As) and cadmium (Cd) are nonessential toxic metal(loids) that are carcinogenic to humans. Hence, reducing the bioavailability of these metal(loids) in soils and decreasing their accumulation in rice grains is essential for agroecology, food safety, and human health. Iron (Fe)-enriched corncob biochar (FCB), Fe-enriched charred eggshell (FEB), and Fe-enriched corncob-eggshell biochar (FCEB) were prepared for soil amelioration. The amendment materials were applied at 1% and 2% application rates to observe their alleviation effects on As and Cd loads in rice paddy tissues and yield improvements using pot trials. The FCEB treatment increased paddy yields compared to those of FCB (9-12%) and FEB (3-36%); this could be because it contains more plant essential nutrients than FCB and a lower calcite content than that of FEB. In addition, FCEB significantly reduced brown rice As (As_BR, 29-60%) and Cd (Cd_BR, 57-81%) contents compared to those of the untreated control (CON). At a 2% application rate, FCEB reduced the average mobility of As (56%) and Cd (62%) in rhizosphere porewater and enhanced root Fe-plaque formation (76%) compared to those of CON. Moreover, the enhanced Fe-plaque sequestered a substantial amount of As (171.4%) and Cd (90.8%) in the 2% FCEB amendment compared to that of CON. Pearson correlation coefficients and regression analysis indicated that two key mechanisms likely control As_BR and Cd_BR accumulations. First, rhizosphere soil pH and Eh controlled As and Cd availabilities in porewaters and their speciation in the soil. Second, greater Fe-plaque formation in paddy roots grown in the amended soils provided a barrier for plant uptake of the metal(loids). These observations demonstrate that soil amendment with Fe-enriched corncob-eggshell biochar (e.g., 2% FCEB) is a prospective approach for the remediation of metal accumulation from the soil to grain system while simultaneously increasing paddy yield.

Potential of yak dung-derived hydrochar as fertilizer: Mechanism and model of controlled release of nitrogen

Improving fertilizer efficiency with assistance of biochar has drawn much attention in sustainable agriculture. Promoting slow-release properties of biochar itself with cost-effective production technology is a pressing demand. In this study, hydrochar derived from nutrition-enriched yak dung (HC) and corresponding controlled release nitrogen fertilizer (HCRNF) via HCl modifying were studied, and the slow release performance as well as mechanisms were investigated. The results show that HCRNF presents a better N controlled-release performance with cumulative N release amounts of 56.01%-70.30% compared with 72.60%-78.45% of HC. The specific surface area reached highest 47.161 m²·g^-1 in HCRNFs with the pore volume of 0.098 cm³·g^-1. Hydrochloric acid modification treatment increases the surface acid group contents such as phenolic hydroxyl group content increasing to 1.48 mmol·g^-1 in HCRNF250. Because the porous structure and stable internal force between N and O-containing functional groups are improved, the N desorption from HCRNF is retarded, which shows a controlled release behavior. We concluded that the HCRNF via HCl modification in this work has a great application potential as slow released N fertilizer in sustainable green agriculture.

After-effects of straw and straw-derived biochar application on crop growth, yield, and soil properties in wheat (Triticum aestivum L.) -maize (Zea mays L.) rotations: A four-year field experiment

Research on the after-effects of straw and straw-derived biochar applications on crop growth, yield, and retention of carbon (C) and nitrogen (N) in soil in wheat-maize rotation systems is limited, and has presented inconsistent conclusions. The purpose of this research was to compare the after-effects of straw and straw-derived biochar on wheat (Triticum aestivum L.) and maize (Zea mays L.) growth and yield, and on soil properties. A field experiment was conducted in four consecutive wheat-maize rotation cycles in the Loess Plateau of China under five treatments: CK (control without nitrogen and phosphate fertilizer, straw, or biochar); NP (conventional single application of nitrogen and phosphate chemical fertilizers); SNP (8 t ha^-1 wheat straw returned to the field plus fertilizer); B1NP (8 t ha^-1 straw-derived biochar plus fertilizer); B2NP (16 t ha^-1 straw-derived biochar plus fertilizer). The highest plant height and aboveground biomass for both wheat and maize always occurred with the B2NP treatment for the four study years. Grains per spike/ear and 1000-grain weight for both wheat and maize in B2NP and B1NP were significantly higher than observed for the other treatments. The four-year average wheat yields for NP, SNP, B1NP, and B2NP were 50.5%, 63.1%, 66.3%, and 81.7% greater than for CK, respectively, and the four-year average maize yields were 45.0%, 49.8%, 65.4%, and 72.1% greater than for CK, respectively. The application of straw-derived biochar significantly increased soil organic carbon, total nitrogen, microbial biomass carbon, and nitrogen in the soil surface layer compared with returning straw to the field. Both straw and straw-derived biochar reduced nitrate N leaching. Therefore, using straw-derived biochar to amend soil could be an appropriate practice for sustaining soil fertility and crop yield in wheat-maize rotation systems in the Loess Plateau of China.

Biochar and fertilizer improved the growth and quality of the ice plant (Mesembryanthemum crystallinum L.) shoots in a coastal soil of Yellow River Delta, China

Coastal soil is an important land reserve that may be used to alleviate the shortage of cultivated land; however, this soil is stressed by saline conditions and nutrient deficiency. Biochar offers the potential to reclaim coastal soil, but the response of plant growth to biochar addition in salt-affected soil is species-dependent. In this study, the response of ice plant (Mesembryanthemum crystallinum L.), an economically valuable halophyte that grows in the coastal soil of the Yellow River Delta, to wood chip biochar (WBC) either alone or in combination with chemical fertilizer was investigated using a 90-day pot experiment. The WBC enhanced the growth of ice plants in the coastal soil, but combining it with chemical fertilizer did not increase its effect. The nutritional quality of the plants was improved by the addition of WBC, regardless of whether chemical fertilizer was applied; moreover, WBC amendment enhanced photosynthesis and reduced the oxidative stress of the plants. The ameliorated soil properties (e.g., soil organic matter and water holding capacity) and increased contents of available macronutrients (e.g., P and K) and micronutrients (e.g., Mg, Mn, B and Zn) resulting from soil amendment with WBC may have contributed to the enhanced growth and quality of the ice plants. Additionally, in soil modified with WBC, an increased abundance of beneficial taxa (e.g., Erythrobacter, Sphingomonas and Lysobacter) and a shift in the microbial community may also have helped to improve the growth and quality of the ice plants. The results of our study provide useful information for developing a biochar-based technology to use in combination with valuable halophytes to reclaim degraded coastal soil and enhance food security.

Distinctive in-planta acclimation responses to basal growth and acute heat stress were induced in Arabidopsis by cattle manure biochar

In-planta mechanisms of biochar (BC)-mediated improved growth were evaluated by examining oxidative stress, metabolic, and hormonal changes of Arabidopsis wild-type plants under basal or acute heat stress (-HS/ + HS) conditions with or without BC (+ BC/-BC). The oxidative stress was evaluated by using Arabidopsis expressing redox-sensitive green fluorescent protein in the plastids (pla-roGFP2). Fresh biomass and inflorescence height were greater in + BC(‒HS) plants than in the -BC(‒HS) plants, despite similar leaf nutrient levels, photosystem II (PSII) maximal efficiencies and similar oxidative poise. Endogenous levels of jasmonic and abscisic acids were higher in the + BC(‒HS) treatment, suggesting their role in growth improvement. HS in ‒BC plants caused reductions in inflorescence height and PSII maximum quantum yield, as well as significant oxidative stress symptoms manifested by increased lipid peroxidation, greater chloroplast redox poise (oxidized form of roGFP), increased expression of DNAJ heat shock proteins and Zn-finger genes, and reduced expression of glutathione-S-transferase gene in addition to higher abscisic acid and salicylic acid levels. Oxidative stress symptoms were significantly reduced by BC. Results suggest that growth improvements by BC occurring under basal and HS conditions are induced by acclimation mechanisms to 'microstresses' associated with basal growth and to oxidative stress of HS, respectively.

Biochar application modified growth and physiological parameters of Ocimum ciliatum L. and reduced human risk assessment under cadmium stress

Biochar (BC) is prepared from waste organic material that can improve soil health in the contaminated area. Soil pollution with cadmium (Cd) is one of the worldwide problems. The present study aimed to evaluate the BC influence on some morphophysiological and biochemical characteristics, also Cd concentration of Ocimum ciliatum L. leaves under Cd stress as well as human risk assessment. Therefore, a pot factorial arrangement based on a completely randomized design was done which included three levels of BC (non-BC, 1%, and 2% of the pot soil) and three Cd levels (0, 20, and 40 mg/kg soil) with three replications. The results of the present study indicated that BC application improved morphological traits, photosynthetic pigments, relative water content (RWC), and catalase (CAT) activity of O. ciliatum under Cd stress and reduced total soluble sugars, total phenol, antioxidant activity, proline content, electrolyte leakage (EL), soluble protein content, ascorbate peroxidase (APX), and guaiacol peroxidase (GPX) activities, and Cd concentration as well as target hazard quotient (THQ). In conclusion, based on the findings of this study, BC could be applied as an environmental friendly amendment in Cd-polluted soil to ameliorate the negative influences of Cd stress on O. ciliatum and reduces Cd levels and THQ in the plants due to the absorption properties of BC. This means that BC usage in contaminated soil helps to reduce pollutions and decreases the human risk assessment.

Biochar Tablets with and without Embedded Fertilizer on the Soil Chemical Characteristics and Nutrient Use Efficiency of Zea mays

Densification of ashy biochar into tablet can enhance the handling and conveyance efficiencies of biochar. It was hypothesized that fertilizer-embedded biochar tablets can slowly release embedded nutrients in synchrony with optimum nutrient uptake by crops. The objectives of this research were to determine the effects of biochar tablets with and without embedded fertilizer on soil chemical properties and nutrient use efficiency of Zea mays (sweet corn). The biochar tablet (BT) was produced by blending a biochar mixture with starch followed by densification using a single punch tablet press whereas the fertilizer embedded biochar tablet (BF) was prepared using the same procedure except that NPK fertilizer was added during blending. A pot experiment with five fertilization treatments including control was carried out in an open field located in Perlis, Malaysia. Co-application of biochar and fertilizer increased soil total carbon, nitrogen, but it reduced soil electrical conductivity (EC). Additionally, the BF significantly increased leaf chlorophyll content, dry root weight, and total plant nutrient use efficiency of sweet corn. The findings suggest that BF can serve as a slow release fertilizer to improve crop nutrient use efficiency. Therefore, embedding fertilizer in biochar tablets is recommended for sweet corn production following a long term field study to confirm the findings of this pot study.

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.

Biochar Improves Maize Growth but Has a Limited Effect on Soil Properties: Evidence from a Three-Year Field Experiment

Biochar application is reported as a method for improving physical and chemical soil properties, with a still questionable impact on the crop yields and quality. Plant productivity can be affected by biochar properties and soil conditions. High efficiency of biochar application was reported many times for plant cultivation in tropical and arid climates; however, the knowledge of how the biochar affects soils in temperate climate zones exhibiting different properties is still limited. Therefore, a three-year-long field experiment was conducted on a loamy Haplic Luvisol, a common arable soil in Central Europe, to extend the laboratory-scale experiments on biochar effectiveness. A low-temperature pinewood biochar was applied at the rate of 50 t h−1, and maize was selected as a tested crop. Biochar application did not significantly impact the chemical soil properties and fertility of tested soil. However, biochar improved soil physical properties and water retention, reducing plant water stress during hot dry summers, and thus resulting in better maize growth and higher yields. Limited influence of the low-temperature biochar on soil properties suggests the crucial importance of biochar-production technology and biochar properties on the effectiveness and validity of its application in agriculture.

Biochar application to rice with 15N-labelled fertilizers, enhanced leaf nitrogen concentration and assimilation by improving morpho-physiological traits and soil quality

Leaf nitrogen (N) concentration plays an important role in biochemical and physiological functions, and N availability directly influences rice yield. However, excessive N fertilization is considered to be a root cause of environmental issues and low nitrogen use efficiency. Therefore, the selection of appropriate nutrient management practices and organic amendments is key to maximizing nitrogen uptake and maintaining high and sustainable rice production. Here, we evaluated the effects of different ¹⁵N-labelled nitrogen sources (urea, ammonium nitrate, and ammonium sulfate at 315 kg ha^-1) with or without biochar (30 t ha^-1) on paddy soil properties, root growth, leaf gas exchange, N metabolism enzymes, and N uptake in the early and late seasons of 2019. We found significant differences among N fertilizer sources applied with or without biochar (P < 0.05). Across the seasons, the combination of biochar with N fertilizers significantly increased soil organic carbon by 51.21% and nitrogen availability by 27.51% compared with N fertilizers alone. Correlation analysis showed that rice root morphological traits were strongly related to soil chemical properties, and higher root growth was measured in the biochar treatments. Similarly, net leaf photosynthetic rate averaged 9.34% higher, chlorophyll (Chl) a concentration 12.91% higher, and Chl b concentration 10.05% higher in the biochar treatments than in the biochar-free treatments across the seasons. Notably, leaf ¹⁵N concentration was 23.19% higher in the biochar treatments in both seasons. These results illustrated higher activities of N metabolism enzymes such as NR, GS, and GOGAT by an average 23.44%, 11.26% and 18.16% in the biochar treatments across the seasons, respectively. The addition of biochar with synthetic N fertilizers is an ecological nutrient management strategy that can increase N uptake and assimilation by ameliorating soil properties and improving the morpho-physiological factors of rice.

Influence of plastic film mulch with biochar application on crop yield, evapotranspiration, and water use efficiency in northern China: A meta-analysis

Background

China is the leading consumer of plastic film worldwide. Plastic film mulched ridge-furrow is one of the most widely adopted agronomic and field management practices in rain-fed agriculture in dry-land areas of China. The efficiency of plastic film mulching as a viable method to decrease evapotranspiration (ET), increase crop yields, and water use efficiency (WUE), has been demonstrated extensively by earlier studies.

Methods

A comprehensive evaluation of how co-application of plastic-film mulch and biochar in different agro-environments under varying climatic conditions influence ET, crop yield, WUE, and soil microbial activity were assessed. We performed a meta-analysis using the PRISMA guideline to assess the effect of plastic-film mulched ridge-furrow and biochar on ET, yield, and WUE of wheat (Triticum aestivum L.), potato (Solanum tuberosum L.), and maize (Zea mays L.) in northern China.

Results

The use of plastic film increased average yields of wheat (75.7%), potato (20.2%), and maize (12.9%) in Gansu, Ningxia, Shaanxi, and Shanxi provinces, respectively due to the reduction in ET by 12.8% in Gansu, 0.5% in Ningxia, and 4.1% in Shanxi, but increased in Shaanxi by 0.5% compared to no-mulching. These changes may be attributed to the effect of plastic film mulch application which simultaneously increased WUE by 68.5% in Gansu, 23.9% in Ningxia, 16.2% in Shaanxi, and 12.8% in Shanxi, respectively. Compared to flat planting without mulching, in three years, the yield of maize increased with the co-application of plastic film and biochar by 22.86% in the Shanxi and Shaanxi regions.

Conclusion

Our analysis revealed co-application of plastic film with biochar is integral for improving soil and water conservation in rain-fed agriculture and as an integrated practice to avert drought while simultaneously mitigating runoff and erosion.

Successive biochar amendment affected crop yield by regulating soil nitrogen functional microbes in wheat-maize rotation farmland

Biochar has attracted increased attention because of its potential benefits for carbon sequestration, soil fertility, and contaminant immobilization. However, mechanism of long-term successive biochar amendment affected crop yield by regulating soil properties and nitrogen (N) functional microbes is still unclear by now. A field fixed experiment was carried out from 2011 to 2018 that aimed to study the effects of successive biochar on soil properties, soil nitrogen functional microbial genes, and grain yield in wheat and maize rotation farmland in Northern China. Four straw biochar treatments were tested in this study: 0 (BC0, CK), 2.25 (BC2.25), 6.75 (BC6.75), and 11.25 (BC11.25) Mg ha^-1. The results showed that, after seven wheat-maize rotations, the total organic carbon (TOC), total N (TN), NO₃^-, available potassium (AK), and the C/N ratio in 0-20 cm topsoil were increased significantly following biochar application; however, there were no obvious differences in available phosphorus (AP) and NH₄⁺ among biochar treatments. Biochar also resulted in a significant increase in crop yield and NO₃^- accumulation in 0-200 cm soil layer, with the highest yield in BC6.75. Furthermore, a marked increase was found in the amoA gene abundance in topsoil; however, it decreased significantly with excessive biochar application (BC11.25). At wheat maturity, the nirS gene abundance consistently decreased following biochar application, whereas the nosZ gene abundance initially increased and then decreased (peaking in BC6.75); however, no obvious changes in the nirK gene were observed. At maize maturity, biochar significantly increased the nirS and nosZ gene abundance in topsoil, especially in BC6.75. In addition, redundancy analysis indicated that the soil moisture content, AP, AK, TN, TOC, NO₃^-, NH₄⁺, pH, and C/N ratio had markedly effects on the abundance of the amoA, nirK, nirS, and nosZ genes. In general, biochar-induced alterations of soil properties resulted in changes of gene abundance of soil nitrifying and denitrifying bacteria, and eventually affecting crop yields.

Successful remediation of soils with mixed contamination of chromium and lindane: Integration of biological and physico-chemical strategies

Soils contaminated by organic and inorganic pollutants like Cr(VI) and lindane, is currently a main environmental challenge. Biological strategies, such as biostimulation, bioaugmentation, phytoremediation and vermiremediation, and nanoremediation with nanoscale zero-valent iron (nZVI) are promising approaches for polluted soil health recovery. The combination of different remediation strategies might be key to address this problem. For this reason, a greenhouse experiment was performed using soil without or with an organic amendment. Both soils were contaminated with lindane (15 mg kg^-1) and Cr(VI) (100 or 300 mg kg^-1). After one month of aging, the following treatments were applied: (i) combination of bioaugmentation (actinobacteria), phytoremediation (Brassica napus), and vermiremediation (Eisenia fetida), or (ii) nanoremediation with nZVI, or (iii) combination of biological treatments and nanoremediation. After 60 days, the wellness of plants and earthworms was assessed, also, soil health was evaluated through physico-chemical parameters and biological indicators. Cr(VI) was more toxic and decreased soil health, however, it was reduced to Cr(III) by the amendment and nZVI and, to a lesser extent, by the biological treatment. Lindane was more effectively degraded through bioremediation. In non-polluted soils, nZVI had strong deleterious effects on soil biota when combined with the organic matter, but this effect was reverted in soils with a high concentration of Cr(VI). Therefore, under our experimental conditions bioremediation might be the best for soils with a moderate concentration of Cr(VI) and organic matter. The application of nZVI in soils with a high content of organic matter should be avoided except for soils with very high concentrations of Cr(VI). According to our study, among the treatments tested, the combination of an organic amendment, biological treatment, and nZVI was shown to be the strategy of choice in soils with high concentrations of Cr(VI) and lindane, while for moderate levels of chromium, the organic amendment plus biological treatment is the most profitable treatment.

Environmental-friendly coal gangue-biochar composites reclaiming phosphate from water as a slow-release fertilizer

To solve the problem of limited adsorption efficiency of pristine biochar for phosphate, a novel biochar composite was prepared from different feedstocks and coal gangue by one facile-step pyrolysis method. The effects of pyrolysis temperature, adsorbent dosage, pH of the solution, and coexisting ions on phosphate adsorption were analyzed. The adsorption performance and mechanism of phosphate in water were investigated. The application of the phosphorus-laden (P-laden) composite as slow-release fertilizer was evaluated by a germination test. The results showed that the maximum phosphate adsorption capacity of coal gangue modified oilseed rape straw biochar prepared at 700 °C (CG-OR700) was 7.9 mg/g at pH 4.0, which is 4.6 times that of pristine biochar. The adsorption process can be well fitted by the pseudo-second-order kinetic and Langmuir isotherm adsorption model. The mechanism of phosphate adsorption mainly includes surface precipitation, ligand exchange, and electrostatic attraction. The P-laden biochar can be used as a slow-release fertilizer to promote seed germination and growth. This study shows that the coal gangue modified biochar composite can not only be used to remove phosphate from wastewater, but also be used as a slow-release fertilizer, providing a new way for the phosphorus recovery and resource utilization of solid wastes.

Biochar Role in the Sustainability of Agriculture and Environment

The exercise of biochar in agribusiness has increased proportionally in recent years. It has been indicated that biochar application could strengthen soil fertility benefits, such as improvement in soil microbial activity, abatement of bulk density, amelioration of nutrient and water-holding capacity and immutability of soil organic matter. Additionally, biochar amendment could also improve nutrient availability such as phosphorus and nitrogen in different types of soil. Most interestingly, the locally available wastes are pyrolyzed to biochar to improve the relationship among plants, soil and the environment. This can also be of higher importance to small-scale farming, and the biochar produced can be utilized in farms for the improvement of crop productivity. Thus, biochar could be a potential amendment to a soil that could help in achieving sustainable agriculture and environment. However, before mainstream formulation and renowned biochar use, several challenges must be taken into consideration, as the beneficial impacts and potential use of biochar seem highly appealing. This review is based on confined knowledge taken from different field-, laboratory- and greenhouse-based studies. It is well known that the properties of biochar vary with feedstock, pyrolysis temperature (300, 350, 400, 500, and 600 °C) and methodology of preparation. It is of high concern to further investigate the negative consequences: hydrophobicity; large scale application in farmland; production cost, primarily energy demand; and environmental threat, as well as affordability of feedstock. Nonetheless, the current literature reflects that biochar could be a significant amendment to the agroecosystem in order to tackle the challenges and threats observed in sustainable agriculture (crop production and soil fertility) and the environment (reducing greenhouse gas emission).

Biochar production from Cypress sawdust and olive mill wastewater: Agronomic approach

Olive mill wastewater (OMW) is nowadays considered as a serious source pollution. At the same time, it contains high amounts of nutrients, especially potassium and phosphorus that could be recovered for agricultural purposes. The aim of the current experimental research work is to investigate the agronomic potential use of OMW based biochar produced from the slow pyrolysis at 500 °C of raw cypress sawdust (CS) impregnated with OMW (ICS-OMW-B). In order to understand the contribution of OMW, two additional biochars were produced from raw cypress sawdust (RCS-B) and cypress sawdust pretreated with potassium chloride (ICS-K-B). Results indicated that RCS impregnation by OMW significantly improved the produced biochar's chemical properties, especially its nutrients contents. Furthermore, in comparison with the other biochars, ICS-OMW-B application as an organic fertilizer showed promising results in terms of produced fresh and dry masses, as well as potassium bioavailability as assessed in test experiments with ryegrass. For instance, the dry matter masses of the rye-grass treated with ICS-OMW-B were about 23, 34 and 50 wt% higher than the ones measured for the tests using RCS-B, ICS-K-B and synthetic K-fertilizer as amendments, respectively. Besides, this biochar has a potential effect on the suppression of various pathogens existing in the tested agricultural soil. All these results demonstrated that the biochar generated from the slow pyrolysis of impregnated sawdust with OMW could be considered as attractive and promising organic fertilizer for acidic agricultural soils.

Modification on biochars for applications: A research update

Biochars are the solid product of biomass under pyrolysis or gasification treatment, whose wholesale prices are lower than commercial activated carbons and other fine materials now in use. The employment of biochars as a renewable resource for field applications, if feasible, would gain apparent economic niche. Modification using physical or chemical protocol to revise the surface properties of biochar for reaching enhanced performances of target application has attracted great research interests. This article provided an overview of biochar application, particularly with the respect to the use of modified biochar as preferred soil amendment, adsorbent, electrochemical material, anaerobic digestion promotor, and catalyst. Based on literature works the current research trends and the prospects and research needs were outlined.

Chemical speciation and distribution of potentially toxic elements in soilless cultivation of cucumber with sewage sludge biochar addition

Potentially toxic elements in municipal sewage sludge can be effectively immobilized during biochar production via pyrolysis. However, the bioavailability of these elements when biochar is applied in soilless cultivation to improve substrate quality has yet to be sufficiently established. In this study, we investigated the chemical speciation and cucumber plant uptake of potentially toxic elements in soilless cultivation when the growth substrate was amended with sewage sludge biochar (0, 5, 10, 15, and 20 wt%). It was found that the addition of 10 wt% biochar was optimal with respect to obtaining a high cucumber biomass and achieving low environmental risk considering the occurrence of hormesis. When the substrate was amended with 10 wt% biochar, cucumber fruit contained lower concentrations of As, Cr, and Zn and smaller bioavailable fractions of As, Cd, Cr, Ni, Cu, and Zn compared with the fruit of control plants, thereby meeting national safety requirements (standard GB 2762-2012, China). Most of the As and Cd taken up by cucumbers accumulated in the leaves and fruit, whereas Cr was found primarily in the roots, and most Ni, Cu, and Zn was detected in the fruit. Importantly, only small proportions of the potentially toxic elements in biochar were taken up by cucumber plants (As: 0.0075%; Cd: 0.038%; Ni: 0.0064%; Cu: 0.0016%; and Zn: 0.0015%). Given that the As, Cd, Ni, and Zn speciation in sewage sludge biochar was effectively immobilized after cultivation, the findings of this study indicate that sewage sludge biochar is a suitable substrate amendment in terms of the risk posed by potentially toxic elements.

Performance of the emerging biochar on the stabilization of potentially toxic metals in smelter- and mining-contaminated soils

Soil potentially toxic metals (PTMs) pollution caused by anthropogenic activities has become serious concern with respect to the crop safety production. In this study, an emerging biochar derived from kiwi pruning branches waste was employed as amendment aiming to evaluate its remediation potential on smelter- and mining-contaminated soils. The effect of biochar on the soil physicochemical properties, leachability, and chemical fractions acted on stabilization practice of PTMs in soil was investigated. The results showed that the addition of biochar increased the soil pH, cation exchange capacity, organic matter, and enzymatic activities (dehydrogenase, urease, and sucrase) but reduced the extraction toxicity of PTMs in both smelter (Fengxian, FX) and mining (Tongguan, TG) soils. The fraction analysis showed that the maximum reduction of exchangeable fraction of Cd, Zn, and Pb in the 4% biochar amended soils decreased by 11.1, 13.3, and 24.7% in FX soil and 7.67, 22.8, and 7.89% in TG soil, respectively, in comparison with to control (no biochar added). Additionally, the residual fraction of Cd, Zn, and Pb increased by 55.9, 7.14, and 11.0% in FX soil and 23.7, 5.86, and 10.0% in TG soil, respectively. The further greenhouse experiment showed that the Indian mustard (Brassica juncea) production increased with the increasing application dosages of biochar, while the PTMs uptakes in plant notably decreased after amendments. Conversion of kiwi pruning branches waste into emerging biochar benefits the agricultural waste recycling utilization and enhances PTMs-contaminated soil remediation in practice. Graphical abstract.

Mitigating arsenic accumulation in rice (Oryza sativa L.) using Fe-Mn-La-impregnated biochar composites in arsenic-contaminated paddy soil

Arsenic (As) is a prominent metal contaminant of the soil in China. Pot experiments were conducted to examine the effects of corn stem powder biochar (BC) and Fe-Mn-La-impregnated biochar composites (FMLBC₁, FMLBC₂, and FMLBC₃; BC:Fe:Mn:La at different weight ratios) on As accumulation in an indica cultivar of rice (Oryza sativa L.). The application of FMLBCs and BC improved the dry weight of the grains, leaves, stems, and roots of rice. The As uptake in different rice organs was significantly reduced in the FMLBC-amended soils (FMLBC₃ > FMLBC₂ > FMLBC₁) compared with the BC treatment. Compared to the concentration of As in the control, the concentration of As in rice grains decreased by 56.0-89.4% with the addition of 2% FMLBC₃. The application of FMLBCs significantly increased the ratio of essential amino acids in grains and the contents of Fe and Mn plaques on root surfaces. The reduction in As accumulation can be ascribed to the Fe, Mn, and La oxides that enhance the adsorption and retention of As, as well as the FMLBCs that provide nutrients and create a rhizosphere environment, promoting rice growth. This study demonstrated that applications of 2% FMLBC₂ and FMLBC₃ have the potential to remediate As-contaminated soils, reduce As accumulation in rice plants, and improve rice grain quality.

Exploration of the potential capacity of fly ash and bottom ash derived from wood pellet-based thermal power plant for heavy metal removal

This study was conducted to explore the potential capacity for the removal of heavy metals from the fly ash (FA) and bottom ash (BA) emitted by wood pellet thermal power plants. Fly ash consists of inorganic compounds such as CaSiO₃, P₂O₅, and K₂O, whereas BA shows properties very similar to the biochar derived from organic biomass. The adsorption properties of both FA and BA for Cd were described well by the Langmuir and pseudo-second-order models, and the maximum adsorption capacity of FA for Cd was 4.2 times higher than that of BA. The results indicate that FA can be applied to the treatment of wastewater that contains heavy metals over pH range from 2-6; however, BA is considered to be most effective for application with wastewater that contains heavy metals at a pH of 5-6. Study of the mechanism concluded that the adsorption of Cd by FA is dominated by the formation of Cd₂SiO₄ complexes by chemical reactions between CaSiO₃ and Cd ions as well as via the precipitation of Cd(OH)₂ in the neutral and alkaline solutions that is caused by the dissolution of K. It was found that the adsorption of Cd by BA was influenced by the binding of functional groups (CC and COH), coupled CaCO₃ dissolution-CdCO₃ precipitation reaction and ion exchange between some minerals with Si and Cd ions in weakly acidic conditions. Results indicate that the FA and BA emitted from wood pellet thermal power plants have high potential for heavy metal removal, and their practical use in the purification and restoration of heavy metals could be an effective way to reduce the waste produced by power plants and clean the environment.

Can biochar reclaim coal mine spoil?

Surface coal mining activities completely destroy vegetation cover, soil and biodiversity. The aftermaths include huge coal mine spoil dumps, changed topography, drainage and landscape, deteriorated aesthetics and increased pollution load. These coal mine spoils are characterised by high rock fragments, extremely low water holding capacity, compacted and high bulk density, lack of organic carbon and plant nutrients, low cation exchange capacity, acidic pH and toxic metal contamination, which poses difficulties in reclamation. An array of studies has been focused on the sustainable use of biochar for restoration of degraded agricultural soil by improving the soil physicochemical, nutritional and biological properties. Although a volume of studies has been done on biochar application, its specialised application in reclamation of coal mine spoils is still atypical, also a systematic review on the mechanism by which biochar amends the mine spoil is lacking. This review focuses on i) factors affecting the biochar properties, ii) the mechanism involved in altering the physical, chemical and biological properties by biochar, (iii) remediation of potentially toxic elements in soil and restoration of degraded land using biochar, and, iv) highlighting the important aspects to be considered while using biochar for reclamation of coal mine spoil. Biochar prepared at 450 °C from a lignocellulosic rich biomass can be an alternative for reclamation for coal mine spoil. Review also suggested suitable methodologies for bulk production, application and economics of biochar in coal mine spoil reclamation.

Biochar-fertilizer interaction modifies N-sorption, enzyme activities and microbial functional abundance regulating nitrogen retention in rhizosphere soil

The impact of the excessive use of N fertilizer remains an environmental problem of global concern. The effect of biochar on soil N retention is still unclear, and knowledge on how a mixture of biochar and fertilizer (B-F) influence N-sorption, N-cycling enzymes activities, diversity and functional abundance of organisms regulating N-retention in rhizosphere soil is poorly understood. Therefore, biochars derived from bamboo, rice straw, cow and pig manure were characterized, and their interactions with NPK fertilizer were evaluated. Results showed that while the effect of biochar on N retention varied among biochar types, such variations increased after B-F. Unlike NH₄⁺ retention, NO₃^- retention by biochar in fertilized soil was poor (<8 weeks), but were however increased after longer periods (15 weeks) in B-F due to plant uptake, sorption and stimulation of N-cycling enzymes activities. This stimulation proved that N-fertilizer provided substrates for N-cycling organisms which was confirmed by the dominance of Proteobacteria, Chloroflexi, Actinobacteria, and Gemmatimonadetes which are important in soil N-cycling, despite the reductions in total diversity, class, phyla and genera abundance of bacterial 16SrRNA genes by B-F. This suggested that B-F induced specific organisms involved in N-cycling, which out-competed other organisms not involved in N-cycling. The provision of substrates by N-fertilizer in B-F for bacterial groups involved in N-cycling modified the rhizosphere microbial structure. The abundance of N-cycling organisms was regulated by the persistence among dominant groups, soil pH, total N, and microbial colonization induced by different biochars interacting with fertilizer which led to enhanced N-retention.

Engineered Biochar Production and Its Potential Benefits in a Closed-Loop Water-Reuse Agriculture System

Biochar’s potential to remove various contaminants from aqueous solutions has been widely discussed. The rapid development of engineered biochar produced using different feedstock materials via various methods for wastewater treatment in recent years urges an up-to-date review on this topic. This article centers on summarizing state-of-the-art methods for engineered biochar production and discussing the multidimensional benefits of applying biochar for water reuse and soil amendment in a closed-loop agriculture system. Based on numerous recent articles (<5 years) published in journals indexed in the Web of Science, engineered biochar’s production methods, modification techniques, physicochemical properties, and performance in removing inorganic, organic, and emerging contaminants from wastewater are reviewed in this study. It is concluded that biochar-based technologies have great potential to be used for treating both point-source and diffuse-source wastewater in agricultural systems, thus decreasing water demand while improving crop yields. As biochar can be produced using crop residues and other biomass wastes, its on-farm production and subsequent applications in a closed-loop agriculture system will not only eliminate expensive transportation costs, but also create a circular flow of materials and energy that promotes additional environmental and economic benefits.

Influences of rice straw biochar and organic manure on forage soybean nutrient and Cd uptake

This pot experiment aimed to investigate the influence of rice straw biochar (BC 0, 1, and 3%, w/w) and organic manure (OM 0, 1, and 2%, w/w) addition on the growth, nutrient and cadmium (Cd) uptake of forage soybean in 10 mg Cd kg-1 contaminated soils. Compared with non-biochar treatments, biochar decreased shoot biomass, height and nitrogen (N) contents. Organic manure markedly increased the shoot biomass, shoot phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) concentration, and root N, P, Ca contents without biochar addition treatments, while in the case of 3% biochar, there were no significant effects on N, K, Ca, and Mg contents of shoot and root among organic manure treatments. In comparison with other treatments, the minimum Cd content of shoots and roots both occurred in the treatment of BC3%+OM2%, while shoot Cd content reached the maximum value in OM2% treatment. Thus, these results suggested that organic manure addition can elevate forage soybean yield and nutrient content, while biochar had no positive effects. High biochar (3%) addition in combination with highest dose of organic manure (2%) can decline the Cd content of soybean and contribute to the agricultural product safety.

Colloidal interactions of micro-sized biochar and a kaolinitic soil clay

Fine-sized biochars and clay minerals co-present in various circumstances, e.g., agricultural land and water treatment. Because both of these materials are scavengers for nutrients, agrochemicals and other toxicants, their dispersibility and transportability have received much attention. However, little is documented about their colloidal interactions and to what extent biochar particles can stimulate the dispersion of clay minerals. Here, the effect of engineered micro-sized biochar amendment on the surface charge (SC) and colloidal dynamics of the clay fraction of a kaolinite-rich soil was determined. The engineered biochars showed distinctive SC and colloidal properties depending on their pyrolysis conditions (e.g., oxygen level and temperature) and solution chemistry (i.e., pH and cation type). Two types of biochars prepared under non-biochar-oriented pyrolysis (open heating, 'O-biochar') and biochar-oriented pyrolysis (N₂-supported heating, 'N₂-biochar') showed contrasting effects on the colloidal dynamics of clay. The O-biochars provoked aggregation due to their higher content of soluble salts, which increased ionic strength and provided multivalent cations, inducing bridging between negatively charged colloids. In contrast, the N₂ biochars low in soluble salts and rich in negatively charged burned organic matter compounds favoured the dispersion of clay. The adjustment of biochar production methods can therefore be highlighted as the way to customize biochar for specific uses or to reduce the risk of clay loss from soils in the short term. In the long term, when soluble salts are removed by leaching, it is likely that dispersion is facilitated and the risk for erosion increases.

Are there environmental or agricultural benefits in using forest residue biochar in boreal agricultural clay soil?

Short-term agronomic and environmental benefits are fundamental factors in encouraging farmers to use biochar on a broad scale. The short-term impacts of forest residue biochar (BC) on the productivity and carbon (C) storage of arable boreal clay soil were studied in a field experiment. In addition, rain simulations and aggregate stability tests were carried out to investigate the potential of BC to reduce nutrient export to surface waters. A BC addition of 30 t ha^-1 increased soil test phosphorus and decreased bulk density in the surface soil but did not significantly change pH or water retention properties, and most importantly, did not increase the yield. There were no changes in the bacterial or fungal communities, or biomasses. Soil basal respiration was higher in BC-amended plots in the spring, but no differences in respiration rates were detected in the fall two years after the application. Rain simulation experiments did not support the use of BC in reducing erosion or the export of nutrients from the field. Of the C added, on average 80% was discovered in the 0-45 cm soil layer one year after the application. Amendment of boreal clay soil with a high rate of BC characterized by a moderately alkaline pH, low surface functionalities, and a recalcitrant nature, did not induce such positive impacts that would unambiguously motivate farmers to invest in BC. BC use seems unviable from the farmer's perspective but could play a role in climate change mitigation, as it will likely serve as long-term C storage.

Effects of pyrolysis temperature on soil-plant-microbe responses to Solidago canadensis L.-derived biochar in coastal saline-alkali soil

Because salinity of coastal soils is drastically increasing, the application of biochars to saline-alkali soil amendments has attracted considerable attention. Various Solidago-canadensis-L.-derived biochars prepared through pyrolysis from 400 to 600 °C were applied to coastal saline-alkali soil samples to optimise the biochar pyrolysis temperature and investigate its actual ecological responses. All biochars reduced the soil bulk density and exchangeable sodium stress and increased soil water-holding capacity, cation exchange capacity, and organic matter content. Principal-component-analysis results showed that pyrolysis temperature played an important role in the potential application of biochars to improve the coastal saline-alkali soil, mainly contributed to ameliorating exchangeable sodium stress and decreasing biochar-soluble toxic compounds. Furthermore, soil bulk density and organic matter, as well as carboxylic acids, phenolic acids and amines of biochar were major driving factors for bacterial community composition. Compared to low-temperature biochar (pyrolyzed below 550 °C), which showed higher toxicity for Brassica chinensis L. growth due to the higher content of carboxylic acids, phenols and amines, high-temperature biochar (pyrolyzed at or above 550 °C) possessed less amounts of these toxic functional groups, more beneficial soil bacteria and healthier for plant growth. Therefore, high-temperature biochar could be applied as an effective soil amendment to ameliorate the coastal saline-alkali soil with acceptable environmental risk.

Popular wood and sugarcane bagasse biochars reduced uptake of chromium and lead by lettuce from mine-contaminated soil

As a result of metal mining activities in Pakistan, toxic heavy metals (HMs) such as chromium (Cr) and lead (Pb) often enter the soil ecosystem, accumulate in food crops and cause serious human health and environmental issues. Therefore, this study examined the efficacy of biochar for contaminated soil remediation. Poplar wood biochar (PWB) and sugarcane bagasse biochar (SCBB) were amended to mine-contaminated agricultural soil at 3% and 7% (wt/wt) application rates. Lactuca sativa (Lettuce) was cultivated in these soils in a greenhouse, and uptake of HMs (Cr and Pb) as well as biomass produced were measured. Subsequently, health risks were estimated from uptake data. When amended at 7%, both biochars significantly (P<0.01) reduced plant uptake of Cr and Pb in amended soil with significant (P<0.01) increase in biomass of lettuce as compared to the control. Risk assessment results showed that both biochars decreased the daily intake of metals (DIM) and associated health risk due to consumption of lettuce as compared to the control. The Pb human health risk index (HRI) for adults and children significantly (P<0.01) decreased with sugarcane bagasse biochar applied at 7% rate relative to other treatments (including the control). Relative to controls, the SCBB and PWB reduced Cr and Pb uptake in lettuce by 69%, 73.7%, respectively, and Pb by 57% and 47.4%, respectively. For both amendments, HRI values for Cr were within safe limits for adults and children. HRI values for Pb were not within safe limits except for the sugarcane bagasse biochar applied at 7%. Results of the study indicated that application of SCBB at 7% rate to mine impacted agricultural soil effectively increased plant biomass and reduced bioaccumulation, DIM and associated HRI of Cr and Pb as compared to other treatments and the control.

Carbon sequestration, kinetics of ammonia volatilization and nutrient availability in alkaline sandy soil as a function on applying calotropis biochar produced at different pyrolysis temperatures

This incubation study assessed the effects of unpyrolyzed Calotropis procera and its biochar produced at different pyrolysis temperatures as well as incubation periods on carbon (C) emission, ammonia (NH₃) volatilization, soil quality indicators and nutrient availability of alkaline sandy soil. Five treatments were studied in this experiment: unamended soil (CK), unpyrolyzed calotropis (UPC), calotropis biochar at 250 °C (CB250), calotropis biochar at 400 °C (CB400), and calotropis biochar at 650 °C (CB650). These amendments were applied to the soil at level of 4% (w/w). The results of this study showed that applying unpyrolyzed calotropis residues increased cumulative CO₂ emission from the soil by 117.3, 239.4 and 232.0% over CB250, CB400, and CB650, respectively, by the end of incubation. Compared to the unamended soil, applying CB250 reduced cumulative NH₃ volatilization in soil by 71.5%, which attributed to ammonia adsorption because of increased cation exchange capacity and decreased soil pH, but CB650 increased cumulative NH₃ volatilization by 73.3% after the 3-day incubation as a result of high soil pH. The available phosphorus in soil improved significantly (p ≤ 0.01) with adding unpyrolyzed calotropis residues and its biochar produced at different pyrolysis temperatures compared to the unamended soil. The values of available phosphorus in the soil under study influenced significantly by pyrolysis temperatures of produced biochar; this is due to the pyrolysis of feedstocks increases labile phosphorus. Thenceforth, using biochar is an important strategy for enhancing carbon sequestration, decreasing ammonia volatilization and improving soil quality parameters in arid regions.

Potential short-term negative versus positive effects of olive mill-derived biochar on nutrient availability in a calcareous loamy sand soil

In the present work, the olive mill solid waste (OMSW)-derived biochar (BC) was produced at various pyrolytic temperatures (300–700°C) and characterized to investigate its potential negative versus positive application effects on pH, electrical conductivity (EC), and nutrients (P, K, Na, Ca, Mg, Fe, Mn, Zn, and Cu) availability in a calcareous loamy sand soil. Therefore, a greenhouse pot experiment with maize (Zea mays L.) was conducted using treatments consisting of a control (CK), inorganic fertilizer of NPK (INF), and 1% and 3% (w/w) of OMSW-derived BCs. The results showed that BC yield, volatile matter, functional groups, and zeta potential decreased with pyrolytic temperature, whereas BC pH, EC, and its contents of ash and fixed carbon increased with pyrolytic temperature. The changes in the BC properties with increasing pyrolytic temperatures reflected on soil pH, EC and the performance of soil nutrients availability. The BC application, especially with increasing pyrolytic temperature and/or application rate, significantly increased soil pH, EC, NH₄OAc-extractable K, Na, Ca, and Mg, and ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA)-extractable Fe and Zn, while AB-DTPA-extractable Mn decreased. The application of 1% and 3% BC, respectively, increased the NH₄OAc-extractable K by 2.5 and 5.2-fold for BC300, by 3.2 and 8.0-fold for BC500, and by 3.3 and 8.9-fold for BC700 compared with that of untreated soil. The results also showed significant increase in shoot content of K, Na, and Zn, while there was significant decrease in shoot content of P, Ca, Mg, and Mn. Furthermore, no significant effects were observed for maize growth as a result of BC addition. In conclusion, OMSW-derived BC can potentially have positive effects on the enhancement of soil K availability and its plant content but it reduced shoot nutrients, especially for P, Ca, Mg, and Mn; therefore, application of OMSW-derived BC to calcareous soil might be restricted.

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.

Potential of Biochar to Alternate Soil Properties and Crop Yields 3 and 4 Years after the Application

Several studies have reported that biochar can improve soil properties which are linked with higher crop yields and this effect is long-term. This paper aimed to study the effects of biochar (0, 10 and 20 t ha−1) and its combinations with N-fertilization (zero, first and second level of N-fertilization) after 3 and 4 years of its application on improving soil characteristics of loamy Haplic Luvisol and crop yields (Dolná Malanta, Slovakia). The results indicated an increase in soil pH (+7%), improvement in sorption properties (hydrolytic acidity decreased by 11%, sum of basic cations and base saturation increased by 20% and 5%, respectively) and soil organic carbon rose by 27% with increasing biochar rate in the soil. N-fertilization applied to biochar treatments was a stabilizing moment in C sequestration even in the case of its labile forms. Overall, humus stability and quality were not significantly changed, however in biochar treatments without N-fertilization, the humus stability and quality decreased 3 and 4 years after biochar application. Yield parameters differed with relation to climate conditions during both vegetation crop seasons, however the combination of 20 t ha−1 of biochar with the first and second level of N-fertilization had the highest potential to increase the grain yield.

Balancing Waste and Nutrient Flows Between Urban Agglomerations and Rural Ecosystems: Biochar for Improving Crop Growth and Urban Air Quality in The Mediterranean Region

Mediterranean ecosystems are threatened by water and nutrient scarcity and continuous loss of soil organic carbon. Urban agglomerations and rural ecosystems in the Mediterranean region and globally are interlinked through the flows of resources/nutrients and wastes. Contributing to balancing these cycles, the present study advocates standardized biochar as a soil amendment, produced from Mediterranean suitable biowaste, for closing the nutrient loop in agriculture, with parallel greenhouse gas reduction, enhancing air quality in urban agglomerations, mitigating climate change. The study’s scope is the contextualization of pyrolytic conditions and biowaste type effects on the yield and properties of biochar and to shed light on biochar’s role in soil fertility and climate change mitigation. Mediterranean-type suitable feedstocks (biowaste) to produce biochar, in accordance with biomass feedstocks approved for use in producing biochar by the European Biochar Certificate, are screened. Data form large-scale and long-period field experiments are considered. The findings advocate the following: (a) pyrolytic biochar application in soils contributes to the retention of important nutrients for agricultural production, thereby reducing the use of fertilizers; (b) pyrolysis does not release carbon dioxide to the atmosphere, contributing positively to the balance of carbon dioxide emissions to the atmosphere, with carbon uptake by plant photosynthesis; (c) biochar stores carbon in soils, counterbalancing the effect of climate change by sequestering carbon; (d) there is an imperative need to identify the suitable feedstock for the production of sustainable and safe biochar from a range of biowaste, according to the European Biochar Certificate, for safe crop production.

Surface soil mixing is more beneficial than the plough layer mixing mode of biochar application for nitrogen retention in a paddy system

The benefits of biochar as a soil amendment have been investigated extensively, but few studies have considered the effects of different application modes on nitrogen (N) dynamics. In the present study, a pot experiment was conducted to evaluate the effects of two different biochar application modes [plough layer mixing (PLM) and surface soil mixing (SSM)] on the N dynamics in a paddy system. It was found that biochar application significantly reduced the total N (TN), NH₄⁺-N, and NO₃^--N contents of the paddy surface water after fertilization, and that the SSM mode of application was more effective in doing this, particularly for NH₄⁺-N, reducing TN by 11-76%, NH₄⁺-N by 31-77%, and NO₃^--N by 31-60% compared with the control at 7 days after fertilizer dressing. By contrast, the effect of biochar application on soil N varied with biochar application mode, N form, and rice growth period. In general, there was no significant effect of biochar type on soil N content, with both types of biochar resulting in a higher TN content of the soil after the tiller stage compared with the control. In addition, the SSM mode of application led to a higher TN content but lower NH₄⁺-N content of the soil than the PLM mode, while the two application modes had varying effects on the NO₃^--N content depending on the growing period of the rice. The rice grain yield increased by 25-36% with the SSM application mode and 11-14% with the PLM mode. These findings indicate that the SSM mode of biochar application in paddy soils is a more promising strategy for both reducing the risk of N loss and improving rice yield than PLM mode.

Recent advances in biochar application for water and wastewater treatment: a review

In the past decade, researchers have carried out a massive amount of research on the application of biochar for contaminants removal from aqueous solutions. As an emerging sorbent with great potential, biochar has shown significant advantages such as the broad sources of feedstocks, easy preparation process, and favorable surface and structural properties. This review provides an overview of recent advances in biochar application in water and wastewater treatment, including a brief discussion of the involved sorption mechanisms of contaminants removal, as well as the biochar modification methods. Furthermore, environmental concerns of biochar that need to be paid attention to and future research directions are put forward to promote the further application of biochar in practical water and wastewater treatment.

Goethite-modified biochar ameliorates the growth of rice (Oryza sativa L.) plants by suppressing Cd and As-induced oxidative stress in Cd and As co-contaminated paddy soil

Co-contamination of soils with cadmium (Cd) and arsenic (As) in rice growing areas is a serious threat to environment and human health. Increase in soil Cd and As levels curtail the growth and development of rice plants by causing oxidative stress and reduction in photosynthetic activity. Therefore, it is necessary to formulate and evaluate different strategies for minimizing the Cd and As uptake in rice plant. We modified biochar (BC) with goethite and assessed the effects of goethite-modified biochar (GB) application on mitigating Cd and As stress in rice plant. Although BC supply to rice plants enhanced their performance in contaminated soil but application of different GB levels i.e.1.5% GB to the soil resulted in prominent improvements in physiological and biochemical attributes of rice plants grown in Cd and As co-contaminated paddy soil. It was observed that soil amendment with GB increased the plant growth, biomass, photosynthetic pigments, gas exchange attribute of rice plant and suppressed the oxidative stress in rice leaves and roots by increased antioxidant enzymes activities. Supplementing the soil with 1.5% GB incremented the iron plaque (Fe-plaque) formation and enhanced the Cd and As sequestration by Fe-plaque. Application of GB (1.5%) significantly improved the Fe content of Fe-plaque by 68.7%. Maximum Cd (1.57 mg kg^-1) and As (0.85 mg kg^-1) sequestration by Fe-plaque was observed with 1.5% GB treatment. Compared to the control, 1.5% GB treatment application prominently reduced the Cd content in the rice roots and shoots by 42.9%, and 56.7%, respectively and As content in the rice roots and shoots declined by 32.2%, 46.6%, respectively, compared to the control. These findings demonstrate that amending the soil with 1.5% GB can be a potential remediation strategy for checking Cd and As accumulation, reducing oxidative stress and increasing the growth of rice plant.

Two-year study of biochar: Achieving excellent capability of potassium supply via alter clay mineral composition and potassium-dissolving bacteria activity

At present, there has been renewed interest in biochar research, but most of them were focused on the short-term effects of biochar and the information of long-term application of biochar is still lacking. In addition, the nutrient mechanism of biochar has rarely been the subject of research. This research explored the effect of potassium (K) nutrient and the response of bacterial communities to biochar in yellow-brown soil based on two-year experiment. In this study, we used peanut shell biochar obtained by pyrolysis at 400 °C, and at the same time, 0%, 20%, 40%, 100% conventional potassium fertilizer were used. The results indicated that the effective improvement of biochar on acidic soil was long-term and 2% biochar replaced 40% conventional potassium fertilizer. Biochar accelerated the conversion of slowly-available K to available K by changing the composition of clay minerals and promoting the growth of K-dissolving bacteria. From the perspective of bacterial community, biochar significantly increased the relative abundance of Sphingomonas, Gaiella, and Elev-16S-1332, which improved the potential ability of soil to degrade pollutants and inhibit pathogens. The pH, organic matter, cation exchange capacity (CEC), and available phosphorus and potassium were important environmental factors that caused significant effects in the bacterial community of yellow-brown soil. Overall, the study demonstrates that biochar is not only an effective alternative to potash fertilizer but also improves soil bacterial communities.

Biochar and nitrogen application rates effect on phosphorus removal from a mixed grass sward irrigated with reclaimed wastewater

This 2-year (2017 and 2018) field study evaluated biochar and nitrogen application rates effect on herbage phosphorus (P) and nitrogen (N) removal from a mixed-grass sward of tall fescue [Schedonorus arundinaceus (Schreb.) Dumort] and Kentucky bluegrass (Poa pratensis L.) irrigated with treated wastewater. Treatments used in this study carried out at the Main Station Field Laboratory, Reno, NV were three biochar application rates (0, 8.9, and 17.8 Mg/ha), and three N rates (0, 80, and 120 kg N/ha) arranged in a 3 × 3 factorial in a randomized complete block design experiment with four replications of each treatment combination. Responses were considered different P < 0.05. There was a linear increased in soil volumetric water content as biochar rate increased from 0 to 17.9 Mg/ha. However, biochar application rate did not affect the quantity of biomass produced, forage tissue P and N concentrations, P and N removal or interact with the other experimental variables of N rate and year to influence the response variables. There was, however, an N rate effect (P < 0.05) on biomass production and it was greater for the 80 and 120 kg N rate (average = 8.3 Mg DM/ha) relative to the 0 kg N/ha rate (6.0 Mg DM/ha). Further, cumulative P removal for the 80 and 120 kg N rate (average = 48.9 kg/ha) was greater than the 0 kg N/ha rate (38.1 kg/ha), and cumulative N removal was in the order 120 kg N/ha (321.1 kg/ha) > 80 kg N/ha (267.4 kg/ha) > 0 kg N/ha (187.8 kg/ha). There was a trend for a biochar × N rate interaction on soil P concentration and it tended to be greater for the combinations 8.9 and 17.8 Mg/ha biochar rates and 80 and 120 kg N/ha rates compared to the unamended control. Even though our study did not reveal a definitive effect of biochar on the major response parameters (biomass, tissue P and N concentrations) evaluated, the trend for a biochar × N rate interaction on soil P concentration offers hope that biochar-amended soils coupled with appropriate N fertilization will be effective in P retention on agricultural landscapes irrigated with treated wastewater.

Preparation, environmental application and prospect of biochar-supported metal nanoparticles: A review

Biochar is a low-cost, porous, and carbon-rich material and it exhibits a great potential as an adsorbent and a supporting matrix due to its high surface activity, high specific surface area, and high ion exchange capacity. Metal nanomaterials are nanometer-sized solid particles which have high reactivity, high surface area, and high surface energy. Owing to their aggregation and passivation, metal nanomaterials will lose excellent physiochemical properties. Carbon-enriched biochar can be applied to overcome these drawbacks of metal nanomaterials. Combining the advantages of biochar and metal nanomaterials, supporting metal nanomaterials on porous and stable biochar creates a new biochar-supported metal nanoparticles (MNPs@BC). Therefore, MNPs@BC can be used to design the properties of metal nanoparticles, stabilize the anchored metal nanoparticles, and facilitate the catalytic/redox reactions at the biochar-metal interfaces, which maximizes the efficiency of biochar and metal nanoparticles in environmental application. This work detailedly reviews the synthesis methods of MNPs@BC and the effects of preparation conditions on the properties of MNPs@BC during the preparation processes. The characterization methods of MNPs@BC, the removal/remediation performance of MNPs@BC for organic contaminants, heavy metals and other inorganic contaminants in water and soil, and the effect of MNPs@BC properties on the remediation efficiency were discussed. In addition, this paper summarizes the effect of various parameters on the removal of contaminants from water, the effect of MNPs@BC remediation on soil properties, and the removal/remediation mechanisms of the contaminants by MNPs@BC in water and soil. Moreover, the potential directions for future research and development of MNPs@BC have also been discussed.