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Greenhouse gaseous (GHGs) emissions from cropland soils are one of the major contributors to global warming. However, the extent and pattern of these climatic breakdowns are usally determined by the management practices in-place. The use of biochar on cropland soils holds a great promise for increasing the overall crop productivity. Nevertheless, biochar application to agricultural soils has grown in popularity as a strategy to off-set the negative feedback associated with agriculture GHGs emissions, i.e., CO 2 (carbon dioxide), CH 4 (methane), and N 2 O (nitrous oxide). Despite increasing efforts to uncover the potential of biochar to mitigate the farmland GHGs effects, there has been little synthesis of how different types of biochar affect GHGs fluxes from cropland soils under varied experimental conditions. Here, we presented a meta-analysis of the interactions between biochar and GHGs emissions across global cropland soils, with field experiments showing the strongest GHG mitigation potential, i.e. CO 2 (RR = −0.108) and CH 4 (RR = −0.399). The biochar pyrolysis temperature, feedstock, C: N ratio, and pH were also found to be important factors influencing GHGs emissions. A prominent reduction in N 2 O (RR = −0.13) and CH 4 (RR = −1.035) emissions was observed in neutral soils (pH = 6.6–7.3), whereas acidic soils (pH ≤ 6.5) accounted for the strongest mitigation effect on CO 2 compared to N 2 O and CH 4 emissions. We also found that a biochar application rate of 30 t ha−1 was best for mitigating GHGs emissions while achieving optimal crop yield. According to our meta-analysis, maize crop receiving biochar amendment showed a significant mitigation potential for CO 2 , N 2 O, and CH 4 emissions. On the other hand, the use of biochar had shown significant impact on the global warming potential (GWP) of total GHGs emissions. The current data synthesis takes the lead in analyzing emissions status and mitigation potential for three of the most common GHGs from cropland soils and demonstrates that biochar application can significantly reduce the emissions budget from agriculture. [Display omitted] • Biochar effects on croplands GHGs emissions were evaluated using a meta-analysis of 45 research articles. • Effectiveness of biochar to mitigate GHGs emissions from croplands relied on soil types and biochar properties. • Maize was the most responsive crop to biochar related GHGs mitigation. • Maximum mitigation effects were observed when biochar was applied at the rate of 30 t ha−1. [ABSTRACT FROM AUTHOR]

Pollution from potentially toxic metals (PTMs) is one of the most pressing global environmental challenge with soaring human health concerns. It is now critical to seek out effective remediation technologies to control PTMs in the terrestrial environment. Biochar has piqued the interest of researchers due to its ability to immobilize PTMs, particularly in soil, with the assumption that biochar having unique physico-chemical properties may influence PTM mobility. A meta-analysis was performed using 1503 observations extracted from 80 peer-reviewed articles to determine: (a) the effects of various physico-chemical properties of biochar on the bioavailability of PTMs (As, Cd, Cu, Ni, Pb, Zn) in soil and plants, and (b) the best specification of physico-chemical properties of biochar for effective remediation of these PTMs. The findings revealed that the reduction rate of PTM bioavailability is heavily influenced by the physico-chemical properties of both biochar and soil. The physico-chemical parameters of biochar that have effective response to PTMs immobilization were as; 101–500 m2 g−1 surface area, neutral to alkaline pH, pyrolysis temperature > 500 °C, with best application rate of 1.1–3%. However, overall results indicate that the biochar, with given specification of physico-chemical attributes, can decrease the bioavailability of PTMs by 40% in soil and 22% in plants. Moreover, edaphic factors such as soil pH, texture, and crop type can also influence the biochar mediated PTMs adsorption and transformation under field or pot conditions. Furthermore, research gaps remain to be filled in order to investigate the efficiency, high specificity, and secondary pollution aspects of biochar, particularly on large-scale applications as an amendment for PTM remediation. [Display omitted] • Eighty peer reviewed publications were used to conduct this meta-analysis. • Biochar addition can reduce PTMs concentration in soil by 40% and in plants by 22%. • Biochar pyrolyzed at >500 °C with 101–500 m2 g−1 surface area showed effective results. • Immobilization of PTMs can be a function of physicochemical properties of biochar. • Criteria should be established for uniform classification of biochar. [ABSTRACT FROM AUTHOR]

Biochar amendments are widely recognized to improve crop productivity and soil biogeochemical quality, however, their effects on vegetable crops are less studied. This pot study investigated the effects of cotton stick, corncob and rice straw biochars alone and with farmyard manure (FYM) on tomato growth, soil physico–chemical and biological characteristics, soil organic carbon (SOC) content and amount of soil nutrients under recommended mineral fertilizer conditions in a nutrient-depleted alkaline soil. Biochars were applied at 0, 1.5 and 3% (w/w, basis) rates and FYM was added at 0 and 30 t ha−1 rates. Biochars were developed at 450 °C pyrolysis temperature and varied in total organic C, nitrogen (N), phosphorus (P) and potassium (K) contents. The results showed that biochars, their amounts and FYM significantly improved tomato growth which varied strongly among the biochar types, amounts and FYM. With FYM, the addition of 3% corncob biochar resulted in the highest total chlorophyll contents (9.55 ug g−1), shoot (76.1 cm) and root lengths (44.7 cm), and biomass production. Biochars with and without FYM significantly increased soil pH, electrical conductivity (EC) and cation exchange capacity (CEC). The soil basal respiration increased with biochar for all biochars but not consistently after FYM addition. The water-extractable organic C (WEOC) and soil organic C (SOC) contents increased significantly with biochar amount and FYM, with the highest SOC found in the soil that received 3% corncob biochar with FYM. Microbial biomass C (MBC), N (MBN) and P (MBP) were the highest in corncob biochar treated soils followed by cotton stick and rice straw biochars. The addition of 3% biochars along with FYM also showed significant positive effects on soil mineral N, P and K contents. The addition of 3% corncob biochar with and without FYM always resulted in higher soil N, P and K contents at the 3% rate. The results further revealed that the positive effects of biochars on above-ground plant responses were primarily due to the improvements in below-ground soil properties, nutrients' availability and SOC; however, these effects varied strongly between biochar types. Our study concludes that various biochars can enhance tomato production, soil biochemical quality and SOC in nutrient poor soil under greenhouse conditions. However, we emphasize that these findings need further investigations using long-term studies before adopting biochar for sustainable vegetable production systems. [ABSTRACT FROM AUTHOR]

The understanding of the carbon (C) and nitrogen (N) mineralization is essential to mitigate the climate change and improve the soil quality for agricultural sustainability. An incubation study was carried out to investigate the effects of corncob-derived biochar with and without the corncob residues, as added organic matter (AOM), on C and N mineralization in an organic C deficient alkaline soil. The study used biochar produced from corncobs by pyrolysing the biomass at 400 °C and consisted of four treatments: unamended control soil, soil + 2% biochar (45 tons ha − 1 ), soil + 2% corncob residue (45 tons ha − 1 ) and soil + 1% corncob residue + 1% biochar (22.5 tons ha − 1 each of biochar and residue). Soil C mineralization was quantified by measuring soil respiration periodically throughout the experiment over the 54 d incubation period. Soils were analyzed for microbial biomass C (MBC), water extractable organic C (WEOC) and N mineralization. We also calculated microbial metabolic quotient ( q CO 2 ), net C mineralization (NCM), net CO 2 efflux and priming effect values. The results revealed that only a very little fraction of biochar was respired whereas a high proportion of corncob was decomposed. Biochar addition suppressed decomposition of native and AOM by 16.31% and 30.13% respectively through negative priming effect (− 40.01%). Compared to the corncob residue alone, addition of biochar with corncob residue significantly increased MBC but decreased WEOC, q CO 2 , NCM and net CO 2 efflux. Moreover, residue significantly increased the net CO 2 efflux, NCM and q CO 2 and, at the same time, decreased net N mineralization. Extractable NH 4 + -N, NO 3 − -N and mineral-N contents were the highest in the biochar and biochar + residue treatments. In addition, biochar alone and in combination with residue resulted in higher negative net N mineralization/immobilization. Enhanced MBC contents and reduced q CO 2 indicated efficient C utilization by microorganisms. The results of this study conclude that biochar could decrease C mineralization but enhanced microbial C use efficiency and, therefore, offer an important management strategy to improve C sequestration in nutrient and organic C deficient alkaline soil. The results also imply that the amendment of corncob residue with biochar had a potential to reduce the rate of the soil N leaching and N 2 O emission by N immobilization and sorption to biochar. [ABSTRACT FROM AUTHOR]

Organic amendments (animal manure and biochar) to agricultural soils may enhance soil organic carbon (SOC) contents, improve soil fertility and crop productivity but also contribute to global warming through nitrous oxide (N 2 O) emission. However, the effects of organic amendments on N 2 O emissions from agricultural soils seem variable among numerous research studies and remains uncertain. Here, eighty-five publications (peer-reviewed) were selected to perform a meta-analysis study. The results of this meta-analysis study show that the application of animal manure enhanced N 2 O emissions by 17.7%, whereas, biochar amendment significantly mitigated N 2 O emissions by 19.7%. Moreover, coarse textured soils increased [ l n R R ‾ = 182.6%, 95% confidence interval (CI) = 151.4%, 217.7%] N 2 O emission after animal manure, in contrast, N 2 O emission mitigated by 7.0% from coarse textured soils after biochar amendment. In addition, this study found that 121–320 kg N ha−1 and ⩽ 30 T ha−1 application rates of animal manure and biochar mitigated N 2 O emissions by 72.3% and 22.5%, respectively. Soil pH also played a vital role in regulating the N 2 O emissions after organic amendments. Furthermore, > 10 soil C: N ratios increased N 2 O emissions by 121.4% and 27.6% after animal and biochar amendments, respectively. Overall, animal manure C: N ratios significantly enhanced N 2 O emissions, while, biochar C: N ratio had not shown any effect on N 2 O emissions. Overall, average N 2 O emission factors (EFs) for animal manure and biochar amendments were 0.46% and −0.08%, respectively. Thus, the results of this meta-analysis study provide scientific evidence about how organic amendments such as animal manure and biochar regulating the N 2 O emission from agricultural soils. [Display omitted] • Organic amendments (animal manure and biochar) may increase SOC stocks but also influence N 2 O emissions. • Animal manure significantly increased N 2 O emission by 17.7%. • Biochar amendment significantly mitigated N 2 O emissions by 19.7%. • Maximum reduction was observed with medium doses of animal manure (121–320 kg N ha-1) and biochar (⩽ 30 T ha−1). [ABSTRACT FROM AUTHOR]