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• We quantified biochar-C in biochar-soil mixtures from six industrial biochars and four cultivated soils. • PyC was mainly emitted as CO 2 between 410 and 610 °C, during the oxidation stage of the Rock-Eval® analysis. • The Rock-Eval® thermal method was a good tool for the quantification of biochar-C enrichment in agricultural soils. • A precise char-C quantification with the Rock-Eval® method requires the use of a reference soil sample. • When no reference soil sample is available, the Rock-Eval® method allows quantification of thermo-resistant organic C. Pyrogenic carbon (PyC) constitutes an important pool of soil organic carbon and may remain in soil over millennia. Its accurate quantification in soil is necessary to monitor the evolution of soil carbon stocks and fluxes. This study tested new direct approaches to quantify PyC enrichment in soil, using three protocols based on the Rock-Eval® thermal method. Six industrial biochars and four cultivated soils were mixed at five different biochar/soil ratios from 0.05 % to 1 % (w/w). Biochar-C emissions could be identified in the CO 2 signal from the oxidation stage (CO 2 oxi) between 410 °C and 610 °C, independently from carbon and carbonate contents from the original unamended soil. Based on this signal and using a reference sample, the protocol 3 allowed for a good estimation of the PyC enrichment relatively to the reference sample. This protocol is thus well adapted to monitor biochar addition in agricultural soils. However, the use of a reference sample, chosen as the sample with the lowest value of thermo-resistant organic carbon (Corg TR), may be tricky for heterogeneous surface areas and soil profiles. In the latter context, both protocols 1 and 2 are alternative methods to quantify Corg TR from biochar and soil without the need of a reference sample, although less accurate than protocol 3. Protocol 2, based on a more precise identification of the biochar-derived peak of CO 2 oxi, resulted in more accurate values than protocol 1. However, the use of protocol 2 is suitable when the biochar-derived peak is easily distinguishable from the peaks derived from both thermo-resistant SOM and PyC present in the original unamended soil. In conclusion, the Rock-Eval® thermal method turns out to be a good tool to quantify biochar-C in cultivated soil and is fully adapted in field experiments – in which, the initial content in biochar is controlled – aiming to decipher the potential benefits of biochar on soil functioning and related ecosystem services. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe-modified biochar addition enhanced the total gross NH 4 + immobilization while decreasing the autotrophic nitrification. • AOB dominated N 2 O emissions in paddy soils with or without biochar or Fe-modified biochar amendment under aerobic conditions. • Fe-modified biochar addition decreased total N 2 O emissions mainly by inhibiting AOB activity. We investigated the potential of ferric iron-modified biochar to lessen autotrophic nitrification and lower nitrous oxide (N 2 O) emissions in paddy soils. A 15N tracing incubation was conducted to investigate the changes in soil gross nitrogen (N) transformations under various biochar amendments (control, unmodified biochar, and Fe-modified biochar). Acetylene and 1-octyne were used to assess the relative contributions of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) to N 2 O emission from paddy soil. The Fe-modified biochar increased the rate of NH 4 + immobilization by 26 % and 383 % compared to the control and unmodified biochar treatments, respectively. The gross rate of autotrophic nitrification was reduced to 5.43 μg N g−1 d−1 in the Fe-modified biochar treatment, compared to 6.74 μg N g−1 d−1 in the control treatment and 9.38 μg N g−1 d−1 in the unmodified biochar treatment. Soil pH had varying effects on N 2 O emissions involving AOB and AOA. The N 2 O yields of AOA were more sensitive to Fe-modified biochar applications. AOB, specifically the Nitrosopira -AOB genus, dominated N 2 O production in all treatments. Overall, this study suggests that Fe-modified biochar holds greater potential than unmodified biochar in reducing N 2 O emissions from paddy soils by stimulating NH 4 + adsorption, restraining autotrophic nitrification rates, and AOB-dominant N 2 O production pathways. [ABSTRACT FROM AUTHOR]

[Display omitted] • Root penetration into soils result in increased gas permeability. • Biochar addition alters pore-filling and increases soil capillarity. • Gas permeability function is dependent on root length density. Biochar amendment have been explored recently for improving hydro-mechanical properties of landfill cover system and enhancing the vegetation for the ecological restoration of post closure landfills. Existing studies have predominantly focused on the hydro-mechanical properties of biochar-amended rooted soils and yet few studies have comprehensively investigated their gas permeability functions in response to unsaturated conditions. The objective of this study is to experimentally and theoretically investigate the coupled effects of biochar and root intensity on CO 2 gas permeability in unsaturated soil. Biochar-amended rooted soil was prepared by growing Chrysopogon zizanioides on granite residual soils with biochar at a mas ratio of 5 %. Gas permeability and unsaturated soil properties (i.e., suction and degree of saturation) were monitored simultaneously. Due to the presence of roots, the maximum gas permeability, hydraulic conductivity, and suction increased by 200 %, 600 %, and 50 %, respectively, compared with bare soil. This was attributed to preferential flow, micropore increasement and negative pressure induced by root growth. However, biochar addition decreased the maximum gas permeability and hydraulic conductivity by 21 % and 33 %, respectively. This was attributed to the pore filling function of biochar, increased capillarity due to intrapore of biochar, and presence of surface functional groups in biochar promoting CO 2 adsorption. A newly developed model was proposed to predict gas permeability with respected to unsaturated soil properties. It was revealed that the gas permeability function of rooted soils showed a strong dependence on the measured root length density. This study highlights the significance of adopting biochar in mitigation of gas emissions in vegetated landfill cover system. [ABSTRACT FROM AUTHOR]

• Biochar can alleviate soil salinity stress. • Biochar amendment does not modify the soil pH in salt-affected soils. • Biochar increases cation exchange capacity by 17.0% in salt-affected soils. • The impact of biochar addition on ECe depends on biochar feedstock and soil initial salinization level. Salinization remains a major issue in soil degradation, for which biochar is a potential solution. In this meta -analysis, using 660 paired observations from 99 peer-reviewed articles, we evaluated biochar's effect on salt-affected soils and identified the initial soil properties, biochar properties and experimental factors influencing its efficacy. The results showed that the addition of biochar had a significant ameliorating effect on salt-affected soils. The soil electrical conductivity of saturated paste extract (ECe) was significantly reduced by 13.2%, and such effect was significant in severe salinization soil (rather than slight and moderate salinization). Meanwhile, the soil cation exchange capacity was significantly increased by 17.0%. However, the addition of biochar had no significant impact on soil pH. Model selection analyses further indicated that the level of initial salinity and the type of biochar feedstock were the most important factors regulating the response of soil ECe to biochar addition. In summary, while our study highlights the potential of biochar in ameliorating salt-affected soils, particularly in severely salinized soils, it also underscores the need for more comprehensive research in this field. Additional research is necessary to comprehensively address the significant heterogeneity of biochars, including their thorough characterization. In addition, more studies are required to explore the impact of biochar on both salt-tolerant and non-salt-tolerant plants in salt-affected soils. [ABSTRACT FROM AUTHOR]

[Display omitted] • N addition increased the relative abundances of lignins or lipids in soil DOM. • Biochar application reduced the relative biomass of roots of Chinese fir seedlings. • Increase in pH after biochar amendment promoted the occurrence of labile DOM. Soil dissolved organic matter (DOM) is the most reactive pool of soil organic matter. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) is a powerful tool for obtaining molecular-level DOM information. The ongoing atmospheric nitrogen (N) deposition could cause some negative effects on tropical and subtropical forest ecosystems, and biochar is considered to be an effective soil ameliorator. However, few studies have evaluated the effects of biochar and N deposition, either separately or in combination, on the molecular composition of soil DOM. In this study, we conducted a pot experiment using Chinese fir seedlings amended with biochar (0, 12, and 36 t biochar ha−1, prepared from corn stover at 450 °C) and inorganic N (NH 4 NO 3 : 0, 40, and 80 kg N ha−1 y-1) in a full factorial design (four replications per treatment) and characterized soil DOM using FT-ICR-MS. A total of 6084 types of formulas were identified in this study. All 36 samples had 2109 types of formulas in common, which had much lower N/C and P/C ratios than the bulk DOM samples. Permutation-based multivariate analysis of variance revealed that both N addition and biochar application had a significant impact on DOM chemodiversity. N addition increased the relative abundance of lignins and lipids, which may be a way for Chinese fir to acclimate to an acidic environment by expanding roots and fixing N. Biochar amendment increased the relative abundance of carbohydrates and tannins in soil DOM at each N application level. Soil pH is a key soil variable controlling DOM composition, and an increase in pH after biochar amendment contributed greatly to the occurrence of DOM compounds with an O/C > 0.5, which are easily degradable. In particular, lignins associated with low N/C were more abundant at higher pH. Biochar application also improved the efficiency of roots in acquiring nutrients, reduced the relative biomass of roots, and decreased the relative content of lignins or lipids, which primarily originated from the roots. In summary, biochar amendment effectively alleviated the negative effects of N addition by investing more N into the production of easily degradable DOM compounds and stimulating the biogeochemical cycle of N. [ABSTRACT FROM AUTHOR]

• Maize-based organic amendments were examined after seven years of annual application. • All organic amendments increased SOM in bulk soil and all physical fractions. • Biochar exerted the strongest positive effect on SOC contents and thermal stability. • The majority of the accumulated C and N occurred in the silt + clay fractions. Application of organic amendments and N fertilizer can affect C and N sequestration, however, the degree to which diverse organic amendments and optimal N fertilization for matching demand for high crop productivity contributes to soil organic matter (SOM) of Cambisol in the North China Plain is not fully known. The objective was to evaluate the combined effects of annual maize straw-derived organic amendments (straw, manure, compost, biogas residue, or biochar) and in-season mineral N fertilizer amendment on soil organic carbon (SOC) and total N (TN) accumulation and thermal stability in bulk soils and physically isolated soil aggregate fractions in a long-term field experiment on the North China Plain. Application of organic amendments either alone or with N increased the proportion of macroaggregates (+62 to 137 %), aggregate mean weight diameter (+50 to 106 %), SOC (+38 to 206 %) and TN (+13 to 52 %) contents in bulk soil. The organic amendments and N fertilizer additions also increased SOC and TN contents in each of the isolated fractions: macroaggregates (+119 to 851 % for SOC, +109 to 237 % for TN) and microaggregates (+42 to 192 % for SOC and +30 to 145 % for TN), total fine particulate organic matter (T fPOM, +143 to 891 % for T fPOM-SOC, +129 to 549 % for T fPOM-TN) and total silt + clay within aggregates (53–139 % for SOC and 20–106 % for TN). Biochar resulted in the largest increase in SOC contents and improved soil aggregation without N fertilization, but fertilization greatly decreased these responses. The majority of the accumulated C and N occurred in the total silt + clay fractions, making up 50–90 % of total SOC and 79–96 % of total TN. Total fine POM and total silt + clay within aggregates contributed to 40–78 % and 10–56 % of SOC, 28–60 % and 37–71 % of TN increase between soil with and without organic amendments. Our results suggested that C and N retained in T fPOM and silt + clay fractions within aggregates were important mechanisms for C and N stabilization. Substitution of annual above-ground litter with biochar with or without mineral N fertilizer was the most effective way for SOM build up and stabilization under a wheat/maize system in the North China Plain, while manure, compost and biogas residue resulted in little to no increases of SOM in bulk soils and physically isolated aggregate fractions compared to straw amendment. Besides the effects of each amendment type on SOC, the different recovery rates of the various amendments, which determines the total quantity of each amendment that can be produced, should be taken into consideration in decisions about maize residue management at the regional scale in the North China Plain. [ABSTRACT FROM AUTHOR]

• A dataset of biochar incubations is made available along with code to analyse it. • Curve fitting and data selection are key steps in biochar persistence modelling. • The H/C ratio remains the main indicator of biochar persistence. • Non-linear models improved correlations between BC 100 estimates and properties. The climate change mitigation benefits of biochar systems arise largely from carbon storage in biochar. However, while biochar is increasingly recognized as a carbon dioxide removal technology, there are on-going scientific discussions on how to estimate the persistence of biochar carbon when biochar is used in soils. Estimates vary from decades to millennia, building on different modelling approaches and evidence. Here, we revisited the persistence estimates derived from extrapolation of biochar incubation experiments, with the aims of making incubation data available, modelling choices transparent, and results reproducible. An extensive dataset of biochar incubations, including 129 biochar decomposition time series, was compiled and is made available alongside code for its analysis. Biochar persistence correlations were sensitive to data selection procedures and to the curve fitting modelling step, while soil temperature adjustments methods had less impact. Biochar H/C ratio remained the main predictor of biochar persistence, in line with previous research, regardless of the extrapolation assumptions (multi-pool exponential functions or power function) used in curve fitting. The relation between H/C and percentage of biochar carbon remaining after 100 years (BC 100) was better explained by a power model than a linear model, with R2 values between 0.5 and 0.9. Using multi-pool exponential functions, estimated BC 100 varied between 90 % and 60 % for H/C from 0 to 0.7. However, using power functions, BC 100 was constrained between 90 % and 80 % for the same H/C range. Additional information about the biochar, the pyrolysis conditions or the environmental incubation conditions did not significantly increase explained variance. Notably, the dataset lacks observations at H/C ratios below 0.2, of biochar made from manure and biosolids, biochar from processes other than slow pyrolysis, field studies, and incubation temperatures below 10 °C, which should guide future experimental work. The detailed analysis performed in this study does not cast doubts on the longevity of biochar carbon storage; rather, it confirms previous knowledge by critically examining the modelling, elucidating the assumptions and limitations, and making the analysis fully reproducible. There is a need for further interdisciplinary work on integration of various theories and approaches to biochar persistence, ultimately leading to the formulation of policy-relevant conclusions. [ABSTRACT FROM AUTHOR]

[Display omitted] • K d of lanthanides show similar pattern when varying the initial Ln concentration. • Linear, strong correlations between K d (Ln) pairs confirm lanthanide analogy. • Data analyses show statistically similar K d (Ln) distributions within each matrix. • Best-estimates of sorption K d (Ln) useful for risk assessment models are proposed. Examining the effect of lanthanide-contaminated wastes, which have the potential to impact to other environmental compartments, requires conducting interaction studies with soils, as feasible first receptors of lanthanide leachates, and, if necessary, with sorbent materials, such as clay minerals and carbon-rich materials, which can serve as natural barriers and immobilisation agents used in remediation strategies. In this context, it is relevant to have available and reliable data on solid–liquid distribution coefficients (K d) to understand the lanthanide sorption in these environmental matrices. Moreover, confirming lanthanide sorption analogies permits filling data gaps and data extrapolation among different contaminated scenarios, and thus facilitate to have available input data for decision-making related to the impact of a contaminated site. In this study, we demonstrate for the first time an analogous sorption of La, Sm, and Lu in carbon-rich materials (i.e., biochar and activated charcoal), clay minerals and soils, through laboratory batch experiments. The obtained sorption K d values revealed similar sorption patterns among the three lanthanides for each matrix tested, even at different initial lanthanide concentrations. In all matrices, the maximum K d values exceeded 104 L kg−1, with a significant decrease when testing high lanthanide concentrations. The analogy was first confirmed by examining the K d correlations for the La-Sm, Lu-Sm, and La-Lu pairs within each matrix, for which strong linear correlations were obtained in all cases. Data compilations were built with own and literature data, and derived cumulative distribution functions revealed statistically equal lanthanide distributions and K d best estimates. In addition to this, K d variability decreased when grouping the data according to significant material properties. For the first time, K d (Ln) best-estimates for different scenarios and materials were proposed as input data for risk assessment models. [ABSTRACT FROM AUTHOR]

• Century-old kiln sites stored 54 t ha−1 more carbon than reference soils in 0–100 cm. • Century-old biochar accumulation increased subsoil C pool compared to reference soil. • Particulate organic matter dominated pyrogenic organic C pool in subsoil. • Pyrogenic organic C was associated with minerals of the clay and silt fraction. • Dissolved organic matter in century-old kiln sites was more aromatic than reference. Soil organic carbon (C) is a key component of the global C budget. As soil organic C turnover rates decrease with depth, agricultural practices favoring deep organic C storage will gain importance as long-term climate change mitigation strategies. In addition, amendment of pyrogenic organic matter (biochar) is considered a promising practice for sequestering C in croplands. However, so far the >30 cm depth soil organic C pool, and subsoil biochar dynamics in particular, has been understudied. To address this, we focused on leftovers from pre-industrial charcoal kilns as a proxy to study the accrual of century-old biochar in the subsoil (30–100 cm) in comparison to adjacent control soil. Using thermal and elemental analyses as well as size and density fractionations (i.e., separating particulate and mineral-associated organic matter), we determined the distribution of pyrogenic organic C within the soil profile and investigated its stabilization in depth. We measured the dissolved organic carbon (DOC) concentrations as well as absorbance and fluorescence properties of dissolved organic matter (DOM) at different depths to characterize the effects of century-old biochar accumulation on the current leaching of DOM. Our results showed that the presence of century-old biochar resulted in an increase of 53.8 ± 25.1 t C ha−1 in 0–100 cm, and 12 % of the pyrogenic organic C was stored in 30–60 cm. No difference in C stocks was observed in 60–100 cm between kiln sites and reference soils. Most of the pyrogenic organic C has been translocated as particulate organic matter, either free or occluded, to subsoils. This led to a change in the dominant fraction of organic matter in the E horizon; in reference soils 64.7 % of the total C was associated with mineral phases as opposed to only 42.3 % in soils enriched with biochar. The thermal analysis of the mineral-associated organic matter revealed that pyrogenic organic C was associated with mineral phases. With depth, DOC concentrations decreased and the relative contribution of microbial byproducts to fluorescent DOM increased. The soils enriched with century-old biochar displayed lower DOC concentrations and more aromatic DOM in the Ap horizon, which suggests biochar dissolution is still an on-going process. Our results suggest that the vertical transfers of century-old biochar mainly occurred as particle leaching in macroporosity and bioturbation but continuous dissolution has also contributed in these fine-textured cropland soils. In conclusion, the association of pyrogenic organic C with mineral phases as well as its migration in subsoil horizons promoted its physical disconnection from abiotic and biotic degrading agents, which likely contribute to the long-term stability of biochar. [ABSTRACT FROM AUTHOR]

Freeze-thaw cycles (FTCs) affect the nitrogen cycling process in the non-growing season. To explore the effects of biochar application combined with soil moisture on nitrogen mineralization under FTCs, a laboratory FTC test of simulated soil columns was conducted. In this laboratory study, black soil from the Songnen Plain, China, was subjected to different biochar application rates (0%, 2% and 4%), moisture contents (15%, 20% and 25%) and numbers of FTCs (each FTC consisted of freezing at −20 °C for 48 h and thawing at 10 °C for 48 h). We explored the changes in soil moisture and aggregates as well as the effects of biochar application and different moisture contents on nitrogen availability under FTCs. The results showed that FTCs promoted the fragmentation and decomposition of soil aggregates, processes that are also related to the moisture content and biochar application rate. Moreover, the application of biochar increased the soil water holding capacity. The ammonium nitrogen and nitrate nitrogen contents in the soil first increased and then decreased during the FTCs and peaked after the third FTC. However, influenced by transfer and transformation processes, the inorganic nitrogen contents were higher than the initial levels after freezing and thawing. In addition, the content of ammonium nitrogen increased with increasing initial soil moisture content but decreased with increasing biochar application rate. However, the content of nitrate nitrogen increased with increasing initial soil moisture content and biochar application rate. Analysis of variance showed that FTCs and moisture content are the major driving factors that affect nitrogen mineralization (p < 0.05). This study provides guidance for the regulation of farmland soil nitrogen and the efficient utilization of agricultural resources in areas with seasonally frozen soil. • Freeze-thaw cycle decreased the stability of soil aggregate. • Biochar inhibited the water migration, but improved soil nitrogen fixation ability. • Biochar promoted the increase of NO 3 −-N, but inhibited the increase of NH 4 +-N. • Freeze-thaw cycle and moisture content affected the N mineralization significantly. [ABSTRACT FROM AUTHOR]

Biochar's potential in improving crop performance, soil quality and functioning has been extensively studied with promising results reported. This study addressed research gaps and updated existing knowledge on long term effect of single biochar application on soil physicochemical properties. A three year field trial was set up on an acidic Alfisol testing the effect of rice husk biochar on select soil quality indicators viz.; soil pH, electrical conductivity, bulk density, water stable aggregates, water holding capacity, soil organic carbon, total nitrogen, CEC and C:N ratio sampled at two soil depth (0–10 cm and 10–20 cm). A soil quality index was estimated to provide a quantitative tool for assessing the long term effects of biochar amendment on Alfisol productivity. Biochar amendment at 6–12 t ha−1 proved more efficient at improving soil quality index (SQI = 1.00) on a long term basis. Further, biochar amendment significantly enhanced all determined soil quality indicators after one year of biochar amendment at sampled soil depths. However, the effect of biochar on some soil quality indicators such as electrical conductivity, organic carbon, total nitrogen and C:N ratio diminished after three years, while soil pH, CEC, bulk density – (decreased), water stable aggregates and water holding capacity remained consistently enhanced. Biochar showed more positive long term effect on improving soil physical quality indicators than chemical indicators. Particularly, decreasing soil electrical conductivity, organic carbon, total nitrogen and C/N ratio after three years suggest increased uptake of soluble ions by plants, carbon mineralization and nitrogen flux with plausible soil organic carbon and nitrogen losses. To mitigate these accelerated carbon and nitrogen flux and increase the efficiency of aged biochar in sequestering carbon and nitrogen, re-application of biochar after three years is recommended. Overall, biochar amendment at the dosage of 6–12 t ha−1 is recommended for long term soil quality improvement in the study area and regions of the world with similar soil type and climatic conditions. • Biochar effects on soil quality indicators diminished after three years. • Biochar showed more positive long term effect on soil physical quality indicators. • Biochar amendment at high dosage enhanced soil quality index (SQI = 1.00). • Re-application of biochar is necessary to increase aged biochar efficiency. [ABSTRACT FROM AUTHOR]

Biochar is used as a soil amendment to improve soil quality and fertility. The performance of biochar changes as it ages in fields. Artificial biochar aging methods (i.e. chemical oxidation) are considered proxies for natural biochar aging and help to evaluate the long-term effects of biochar amendment in soil. However, few studies have focused on how close artificial biochar aging methods are to biochar aging in fields. A meta-analysis of 42-studies was conducted to quantitatively compare the effects of soil incubation (natural field biochar aging), chemical oxidation (chemical biochar aging) and freeze-thaw cycling (freeze-thaw biochar aging) on biochar properties, including surface and bulk element compositions (C, H, O, N), specific surface area, cation exchange capacity and pH. The results showed that the artificial biochar aging methods cannot yet simulate biochar aging in the soil. In comparison with natural field aging, chemical aging tended to have a higher degree of oxidation at the surface of the aged biochar and posed the problems of oxidation inside the biochar and the import of exogenous elements from oxidants to the biochar. Freeze-thaw aging changed only the porous structure of the biochar with no significant alterations to element compositions, in contrast with natural aging. • Effects of artificial and natural biochar aging methods on biochar properties were studied using a meta-analysis. • Chemical oxidation aging had a higher degree of oxidation at the surface of the aged biochar. • Chemical oxidation aging posed the problems of oxidized biochar interior. • Chemical oxidation aging imported exogenous elements from oxidants to biochar. • Freeze-thaw cycling aging changed only biochar porous structure. [ABSTRACT FROM AUTHOR]

In this study, we applied coconut fiber-derived biochar (CFB) to a lead (Pb)-contaminated soil (at 600 mg kg−1) at 2% and 4% (w/w), in order to explore the efficacy and mechanism of CFB to immobilize Pb in soil during a 150-day incubation experiment. Our approach integrated various techniques namely micro-X-ray fluorescence, sequential extraction, X-ray absorption fine structure, scanning electron microscopy combined with energy dispersive X-ray spectroscopy to evaluate the Pb immobilization. Results indicated that the distribution of Pb in the studied soil was significantly affected by CFB application. The Pb content in organic matter bound fraction of the studied soil increased by 29.5% and 33.5% with 2% and 4% CFB, respectively, compared to control soil after 150-day of incubation. Lead-loaded humic acid (HA) and Pb 3 (PO 4) 2 were higher in the biochar-amended soil (2% CFB) as compared with the control soil. The CFB particles possibly offer more binding sites of PO 4 3− and carboxylic functional groups than the binding sites of –FeO(OH), SiO 3 2−, −Al 2 O 3 and organic functional groups provided by the original soil particles alone (no biochar) for Pb. Overall, this study highlights that CFB can be a potential candidate to immobilize Pb for the restoration and remediation of Pb-contaminated soils. Unlabelled Image • Binding of Pb by organic matter in soil increased by 29.5% with 2% biochar addition. • Pb distribution was mainly on biochar surface in the soil amended with 2% biochar. • Biochar particles offered binding sites of PO3–4 and carboxylic groups for Pb. • Pb was grabbed by biochar as Pb carboxylate and Pb 3 (PO 4) 2 in biochar-amended soil. [ABSTRACT FROM AUTHOR]

• More mineral-bound organic carbon in weathered coal- than in biochar-amended soils. • Weathered coal was more effective than biochar in improving soil structure. • Weathered coal could improve the soil organic carbon stability more than biochar. Soil carbon pool stability plays an important role in reaching carbon neutrality and mitigating global warming. Applying soil amendments is a practical strategy in agricultural production to improve soil environment. Weathered coal (WC) is an organic amendment that can be used to improve soil quality. However, the effects of WC application on soil organic carbon pool stability, and its differences from the effects of biochar (BC, a common amendment) application remains unclear. In this study, BC was selected as a comparison to further evaluate the potential of WC based on a 3-year field experiment, in which WC and BC were individually applied into a loamy clay soil at 0%, 1%, and 3% (w/w) rates. Soil organic carbon and its fractions (including particulate organic carbon and mineral-bound organic carbon), soil aggregate fractions and its stability, and the organic carbon content in aggregates were examined. The results showed that both WC and BC significantly increased soil total organic carbon, particulate and mineral-bound organic carbon (P < 0.05). The mineral-bound organic carbon content in WC treatment was significantly higher than that in BC treatment (by 32% under the 3% rate) (P < 0.05), whereas, there were no significant differences in soil total organic carbon content. Both WC and BC increased the soil organic carbon content in all aggregate fractions. While only the WC improved the soil aggregate stability, and which was 15% (under 1% rate) and 28% (under 3% rate) higher in WC treatments than in BC treatments (P < 0.05). The proportion of mineral-bound organic carbon to soil total organic carbon content and the soil aggregate stability were obviously related the soil C/N, and the WC treatments had a higher proportion of mineral-bound organic carbon and soil aggregate stability than BC treatments under the same soil C/N. The results indicated that the application of WC may be more effective than BC in increasing mineral and aggregate protection for soil organic carbon and thus improving soil carbon pool stability. Additionally, the purchase cost of WC was clearly lower than that of BC. Combined with the low cost and the benefits in soil structure and carbon pool stability, the application of WC appeared to have advantages over BC. Our findings provide robust evidence that WC is more effective than BC in improving soil carbon pool stability. [ABSTRACT FROM AUTHOR]

• Pyroligneous vinegar improved azalea growth and increased flower numbers. • Pyroligneous vinegar increased bacterial abundances but decreased fungal abundances. • The more concentrated vinegar increased amoA genes abundances, along with an increase nitrate concentration. • N 2 O production potential was decreased with the higher ratio of nosZ /(nirS + nirK) under vinegar treatments. • Nitrogen use efficiency was negatively correlated with nirS and nirK abundance. Excessive chemical fertilization in protected horticulture has caused nutrient accumulation, reduction of soil biodiversity, and subsequently soil degradation. Pyroligneous vinegar is a byproduct of pyrolysis for biochar production. While there has been an increase in interest in using pyroligneous vinegar as an amendment to improve soil quality, a paucity of data exists of its effect on the growth of acidophilous plants such as azalea (Rhododendron). To address this, we investigated the changes in the growth of azalea and soil microbial abundance, specifically those involved in nitrogen cycling in the rhizosphere with amendment of conventional inorganic NPK fertilizer (NPK) and four dilutions of pyroligneous vinegar each with matched NPK content. The results showed that the treatments of pyroligneous vinegar increased plant biomass (51%-99%), root length (29%-81%) and surface area (63%-151%), and nitrogen use efficiency (83%-299%) compared to NPK alone. The pyroligneous vinegar treatments decreased soil pH and increased the contents of rhizosphere soil dissolved organic carbon and nitrate, and changed potential denitrification activity. Compared with NPK, pyroligneous vinegar increased archaeal and bacterial amoA genes (AOA and AOB) abundances (45% − 79% and 39% − 75%, respectively) in nitrification, but inhibited the denitrification gene abundances (i.e. nirS and nirK abundance up to 21% lower). Pyroligneous vinegar increased the ratio of nosZ /(nirS + nirK), suggesting an increased potential to lower nitrous oxide emissions. Correlation analysis indicated that nitrogen use efficiency correlated positively with AOA and AOB, but negatively with nirS and nirK abundance. Therefore, our study suggests that pyroligneous vinegar could improve the growth of acidophilous plants and increase their nitrogen use efficiency by changing nitrogen cycling related functional genes, and could be a potential soil amendment in protected horticulture. [ABSTRACT FROM AUTHOR]

[Display omitted] • The main factor that increased AWC was the reduction of PWP in medium-textured soils. • The long-term effect of biochar on AWC was strongest in fine-textured soils. • FC was not always the main driver of AWC increase under biochar treatment. Biochar has been widely applied as a soil modifier to improve the physical properties and increase the water content of the soil. Although the response of soil hydrological properties to biochar has been extensively studied, the effect of biochar on soil hydrological properties in different soil textures has not been comprehensively quantified. Here, we performed a meta-analysis of 939 observations to quantify the effects of biochar on the water retention capacity of soil with different textures. The effect of biochar on field capacity (FC) and available water capacity (AWC) of the soil was greater in coarse-textured soils (23.8%, 25.6%) than those in medium- (5.0%, 20.9%) and fine-textured soils (7.2%, 11.5%). The permanent wilting point increased in coarse-textured soils (19.9%), decreased in medium-textured soils (−4.2%), and did not change considerably in fine-textured soils as affected by biochar. We demonstrated that FC is not always the main driver of increased AWC. In coarse-textured soils, there is a high correlation between hydrological properties. In addition, the specific surface area, surface functional groups, and cation exchange capacity of biochar are important factors affecting the water retention of soils with different textures. Our study establishes that the differences in soil texture cause heterogeneity in the mechanisms by which biochar improves soil water retention. [ABSTRACT FROM AUTHOR]

Biochar application has been shown to be effective in mitigating soil N 2 O emission in agricultural soils. However, the effect of biochar on soil N 2 O emission in subtropical plantations and the underlining mechanisms are poorly understood. The objective of this study was to investigate the effect of biochar application rates (0, 5 and 15 t ha−1) on soil properties and N 2 O emissions within a Moso bamboo (Phyllostachys edulis) plantation in a 24-month field trial. Biochar application significantly (P < 0.05) decreased soil N 2 O emission, with the reduction rate positively related to the biochar application rate. The reduction in N 2 O emission by biochar application diminished over time. Biochar did not affect soil temperature (at 5 cm depth), and there were no significant relationships between N 2 O emission and either soil moisture content or soil microbial biomass C. However, biochar application significantly (P < 0.05) increased the water soluble organic C but decreased soil NH 4 +-N, NO 3 −-N and water soluble organic N (WSON) concentrations, soil urease and protease activities, and soil gross nitrification and denitrification rates. Soil N 2 O flux was positively (P < 0.05) correlated with soil NH 4 +-N, NO 3 −-N and WSON concentrations, soil urease and protease activities, and soil gross nitrification and denitrification rates, regardless of the treatment. Structural equation modeling suggests that biochar application decreased soil N 2 O emissions directly by decreasing soil gross nitrification and denitrification rates, and indirectly by decreasing concentrations of NH 4 +-N, NO 3 −-N and WSON, and the activities of urease and protease. We conclude that biochar application decreased soil N 2 O emission in the Moso bamboo plantation by decreasing labile N concentrations, N-cycling enzyme activities and nitrification/denitrification rates. Our findings suggest that biochar application can be an effective method to mitigate soil N 2 O emission in subtropical plantations. • Biochar decreased soil N 2 O emission in a bamboo plantation. • Biochar application did not affect soil temperature but increased moisture content. • Biochar application decreased N availability and enzyme activities. • Biochar decreased N 2 O emission via reducing nitrification/denitrification rates. [ABSTRACT FROM AUTHOR]

Biochar has been reported to reduce emission of nitrous oxide (N 2 O) from soils, but the mechanisms responsible remain fragmentary. For example, it is unclear how biochar effects on N 2 O emissions are mediated through biochar effects on soil gross N turnover rates. Hence, we conducted an incubation study with three contrasting agricultural soils from Kenya (an Acrisol cultivated for 10-years (Acrisol10); an Acrisol cultivated for over 100-years (Acrisol100); a Ferralsol cultivated for over 100 years (Ferralsol)). The soils were amended with biochar at either 2% or 4% w/w. The 15N pool dilution technique was used to quantify gross N mineralization and nitrification and microbial consumption of extractable N over a 20-day incubation period at 25 °C and 70% water holding capacity of the soil, accompanied by N 2 O emissions measurements. Direct measurements of N 2 emissions were conducted using the helium gas flow soil core method. N 2 O emissions varied across soils with higher emissions in Acrisols than in Ferralsols. Addition of 2% biochar reduced N 2 O emissions in all soils by 53 to 78% with no significant further reduction induced by addition at 4%. Biochar effects on soil nitrate concentrations were highly variable across soils, ranging from a reduction, no effect and an increase. Biochar addition stimulated gross N mineralization in Acrisol-10 and Acrisol-100 soils at both addition rates with no effect observed for the Ferralsol. In contrast, gross nitrification was stimulated in only one soil but only at a 4% application rate. Also, biochar effects on increased NH 4 + immobilization and NO 3 −consumption strongly varied across the three investigated soils. The variable and bidirectional biochar effects on gross N turnover in conjunction with the unambiguous and consistent reduction of N 2 O emissions suggested that the inhibiting effect of biochar on soil N 2 O emission seemed to be decoupled from gross microbial N turnover processes. With biochar application, N 2 emissions were about an order of magnitude higher for Acrisol-10 soils compared to Acrisol-100 and Ferralsol-100 soils. Our N 2 O and N 2 flux data thus support an explanation of direct promotion of gross N 2 O reduction by biochar rather than effects on soil extractable N dynamics. Effects of biochar on soil extractable N and gross N turnover, however, might be highly variable across different soils as found here for three typical agricultural soils of Kenya. Unlabelled Image • Biochar application consistently reduced N 2 O emissions from all soils. • Biochar effects on gross N turnover were highly variable across soils. • Biochar effects on N 2 O were decoupled from effects on mineral N availability. • Kenyan Acrisols showed higher N 2 O emissions than Ferralsols. [ABSTRACT FROM AUTHOR]

There are growing trends of combined contaminations in agricultural soils, and therefore it is urgently needed to remediate contaminated soils with eco-friendly approaches. This study aimed to evaluate the effects of Medicago sativa L. (alfalfa) planting, alone or together with biochar additions, on contaminant removals and bacterial properties in an agricultural soil contaminated by heavy metal and organic fungicide. The treatments in this study included: the control (CK), alfalfa planting (AP), alfalfa planting +1.5% biochar addition (w/w) (AP + 1.5B), alfalfa planting +3.0% biochar addition (AP + 3.0B), and alfalfa planting +6.0% biochar addition (AP + 6.0B). Relative to the alfalfa planting only, extra biochar additions increased alfalfa biomass and heavy metal cadmium (Cd) phytoextraction. The alfalfa planting, alone or together with biochar additions, significantly decreased soil iprodione concentrations. After 90 days of remediation, bacterial 16S rRNA gene abundances of the AP, AP + 1.5B, AP + 3.0B and AP + 6.0B treatments were 1.69, 3.84, 3.34 and 3.13 times as great as that obtained from the CK treatment, respectively. The AP + 1.5B treatment had the highest richness estimators and Shannon diversity index, but the AP + 6.0B treatment had the lowest invsimpson diversity index among the five treatments. The relative abundances of Bacteroidetes and Nitrospirae were enhanced by the alfalfa phytoremediation, alone or together with biochar additions. Our results suggest that the alfalfa has promising potentials in the remediation of co-contaminated soil and in the increases of soil bacterial biomass and community diversity. Simultaneously, biochar is beneficial to enhance Cd phytoextraction, however, biochar addition rate would need to be optimized. The alfalfa, alone or together with the biochar addition, has promising potentials in the remediation of co-contaminated soil and in the increase of soil bacterial biomass. Biochar is beneficial to enhance phytoremediation performance, however, biochar addition rates would need to be optimized. Unlabelled Image • Relative to alfalfa planting only, biochar additions increased Cd phytoextraction • Alfalfa planting with/without biochar decreased soil iprodione concentrations • Soil bacterial biomass was increased by alfalfa planting with/without biochar. • Biochar addition at a higher rate tended to decrease bacterial community diversity • Alfalfa with/without biochar positively stimulated Bacteroidetes and Nitrospirae [ABSTRACT FROM AUTHOR]

Biochar application to agricultural soils has been proposed as a way to increase crop production by improving soil chemical and physical properties. Liming potential and improved nutrient exchange on biochar surfaces are the most reported mechanisms. Wherever crops experience drought stress, improvements in soil water holding capacity (WHC) might also be an important mechanism. However, reported effects on soil structure and WHC are mixed. Therefore, we studied the effects of biochar on soil bulk density (BD) and WHC in a laboratory column study using two agricultural soils from Portugal: a sandy and a sandy loam soil. Mixed woody feedstock was pyrolysed at 620 °C, creating a wettable biochar that was used unsorted as well as sieved into large (2–4 mm) and small (0.05–1.00 mm) particles, mixed into the soils at 1, 5, 10 and 20% (by volume), and incubated for 10 days at field capacity to allow aggregation. Soil samples were analysed for BD and WHC using soil columns. We found biochar to decrease soil BD and increase maximum WHC, expressed as gravity-drained equilibrium water content, for both soils. The sandy soil was more responsive with significant effects at the lowest application rate (1%), while the sandy loam soil started to show significant effects at 5% biochar. Small biochar particles reduced the BD of sandy soil more, while large biochar particles caused a greater reduction in the BD of the sandy loam soil. The effect of biochar particle size on WHC was less clear, except for small particles at 20% volumetric concentration, which showed a 60% increase in gravimetric WHC. When expressed as total soil water storage (SWS), 20% biochar incorporation to 15 cm depth would increase the total SWS of sandy soil from 0.56 mm (control) to 0.83–0.91 (mm), and of the sandy loam soil from 0.56 to 0.79–0.96 (mm), depending on biochar particle size. Our results suggest that biochar particle sizes can be used to achieve specific effects in soils, while mechanisms and trade-offs (agro-economic and environmental) need further exploration. Unlabelled Image • Small biochar particles reduced bulk density more for sandy than sandy loam soil. • Large biochar particles reduced bulk density more for sandy loam than sandy soil. • Small particles at 20% increased gravimetric water holding capacity by 60%. • The total soil water storage of sandy soil increased from 56 to 83–91 (mm). • The total soil water storage of sandy loam soil increased from 56 (mm) to 79–96 (mm). [ABSTRACT FROM AUTHOR]

Phosphorus (P) is a vital element for plant growth, especially in mudflat-reclaimed soil due to its extra alleviation of adverse effect by salt stress. P availability in mudflat-reclaimed soil is a critical factor for crop yield. In this study, cerium-modified straw biochar (Ce-MSB) derived from maize straw was prepared and characterized and its influence on P availability of the paddy soil was evaluated. The results indicated that the cerium elements were chemically bound to the functional groups of the biochar surface through SEM, EDX and FTIR techniques. The equilibrium process of P by Ce-MSB was described well by the Langmuir isotherm model (R 2 > 0.99). The maximal P adsorption capacity of Ce-MSB was influenced remarkably by temperature. Accordingly, the addition of Ce-MSB significantly decreased the P content of surface water in paddy system after 3 months, while increasing the soil P availability. Furthermore, the incorporation of both common biochar and Ce-MSB into the soil increased the SOM content, while decreased soil pH and EC. Biolog EcoPlateTM trials indicated that Ce-MSB has no significantly negative effects on soil microbial diversity. This study provides valuable information for the source-reduction of P discharge from paddy system and improvement of P availability. Phosphorus (P) is a vital element for plant growth, especially in coastal reclaimed mudflat due to its extra alleviation of adverse effect by salt stress. P availability in mudflat-reclaimed soil is a critical factor for crop yield. In this study, cerium-modified straw biochar (Ce-MSB) derived from maize straw was prepared and characterized and its influence on P availability of the paddy soil was evaluated. The results indicated that the cerium elements were chemically bound to the functional groups of the biochar surface through scanning electron microscopy (SEM), energy dispersive X-ray spectrum scanning (EDX), and fourier transform infrared spectroscopy (FTIR) techniques. The equilibrium process of P (PO 4 3−) by Ce-MSB was described well by the Langmuir isotherm model (R 2 > 0.99). The maximal P adsorption capacity of Ce-MSB was influenced remarkably by temperature, which was 58, 69, and 78 mg g−1 under 5, 25, and 40 °C, respectively. Under laboratory simulation, the addition of Ce-MSB significantly decreased the P content of surface water in paddy system after 3 months, while increasing the P availability of soil. Furthermore, the incorporation of both common biochar and Ce-MSB into the soil increased the SOM content, while decreased soil pH and EC. Biolog EcoPlateTM trials indicated that Ce-MSB has no significantly negative effects on soil microbial diversity. This study provides valuable information for the source-reduction of P discharge from paddy system and improvement of P availability. • Cerium was successfully loaded on the surface of maize straw biochar. • The maximum P adsorption capacity of Ce-MSB was about 78 mg g−1. • Ce-MSB decreased pH and EC of mudflat-reclaimed paddy soil. • Ce-MSB increased P availability and SOM of mudflat-reclaimed paddy soil. • Ce-MSB addition has no significant effect on carbon metabolism of soil microbes. [ABSTRACT FROM AUTHOR]

Abstract Recently biochar has attracted attention as a soil amendment and soil organic carbon source which can be used to modify soil quality. Although the effects of biochar on individual soil quality parameters are well established, the impacts on soil quality indexes are rather limited or less known. Soil samples were collected from a two year controlled experiment treated with various levels of biochars (0, 4 and 8 Mg ha−1) obtained from three locally available materials (cotton straws, pistachio shells and corn cobs) and two different irrigation regimes 100% (FC100) and 65% of field capacity (FC65). Soil samples were collected and analyzed for important soil quality indicators; soil organic matter, aggregate stability, bulk density, porosity, available water content, hydraulic conductivity and total nitrogen. A Soil Quality Index (SQI) of multiple measured soil parameters for each parcel was obtained using both linear and non-linear scoring functions. Biochar application improved all soil quality parameters investigated and soil quality indexes and these improvements were more prominent in FC65 parcels than those in FC100 parcels. Soil quality indexes were significantly increased with a synergistic impact of biochar applications with a range from 3.9% to 138.5% depending on treatments and scoring function used. The results from these field studies showed that carbon rich biochars obtained from locally available plant residues can be applied to improve soil qualities on the degraded, low organic matter soils of the Harran Plain. Highlights • Biochars obtained from the residues of locally grown crops can improve the quality of field soils • Biochars obtained from pistachio shells were more effective in impacting soil quality parameters • Improvements of soil quality variables in soils with deficit irrigation were more pronounced • Biochar application can increase the soil quality index of degraded soils • Soil quality indexes are useful for demonstrating the synergistic effects of biochar on multiple soil quality parameters [ABSTRACT FROM AUTHOR]

Abstract The agronomic management of vineyards, aimed at the maximization of grape yields, is intensive and includes repeated tillage, crop residues removal, strict weed and pest control treatments. In viticulture, healthy soils and a suitable climate are the key factors that influence the quality of the produced wine. Even under intensive agronomic practices, typical of conventional viticulture, the choice of appropriate soil management strategies can preserve soil quality in the long term. The use of biochar as soil amendment has been suggested as a potential practice that allows restoration of the functionality of degraded soils in terms of water retention, chemical and biological fertility. In this paper we report the results of a long field trial on biochar amendment of a vineyard, assessing the impact on soil functionality, VOC emission and fertility. Our results show that biochar effects on soil functions and fertility are maintained in the long term (seven years) after a one-time application. Highlights • Biochar application is an effective practice for restoration of the functionality of degraded soils. • Changes in soil fertility after a single application of biochar persist after seven years • Biochar incorporation into soil caused substantial changes in the metabolic pathways of soil microbial activity. • Biochar is an environmentally-friendly solution for soil management in vineyards. [ABSTRACT FROM AUTHOR]

Abstract The production of biochar is a technological alternative to transform sewage sludge (SS) into a useful product for agro-environmental purposes. Despite an increased knowledge on the role of sewage sludge biochar (SSB) for improving soil quality and crop productivity, some concerns remain regarding the accumulation of total and available heavy metals (HM) in soils amended with SSB. Particularly, there is a dearth of studies under field conditions and in tropical latitudes. Therefore, the objective of this study was to evaluate the effect of applying SS biochars, prepared at different pyrolysis temperatures, on the accumulation and availability of heavy metals (HM). To do so, 15 Mg ha−1 of SS biochar produced at 300 °C (BC300) and 500 °C (BC500) were applied to a soil cultivated with corn. Total and available levels of HM in SS, biochars and post-harvest soil were determined. Pyrolysis concentrated total HM in the biochars in relation to the SS. However, HM availability was reduced with increasing pyrolysis temperature due to an increase in pH, pore volume, specific surface area, P and K content, and reduction of the H/C ratio. Biochar did not alter the total HM contents, with the exception of Mn. Available levels of all HM in the soil were <1.2% of the total contents. In addition, the available levels of Zn and Mn, when evaluated as micronutrients, were considered low. Therefore, the results of the present study indicate that biochar produced from SS of a sewage treatment plant processing predominantly domestic sewage can be used in agriculture, without risk of soil contamination by HM. Moreover, in some tropical soils, with a low value of micronutrients, biochar can provide a source of these elements. Highlights • Total and available heavy metals in sewage sludge, biochars and soil were determined. • Heavy metal (HM) availability was reduced with increasing pyrolysis temperature. • Available levels of all HM in the soil were <1.2% of the total contents. • In relation to HMs, biochar represents a better alternative for land use of sludges. [ABSTRACT FROM AUTHOR]

Abstract The reactive nature of phosphorus (P) leads to the formation of insoluble Fe, Al and Ca phosphates in highly weathered tropical soils, thus reducing P availability for plant uptake. Biochar with its heterogeneous surface properties as influenced by feedstock and pyrolysis temperature can affect P retention and availability in tropical soils. In the present study, incubation studies were conducted for 90 days to investigate the effect of corn cob and rice husk biochar on P sorption and desorption in two acid (Typic Plinthustult-A & Plinthic Acrudox-B) and one neutral soil (Quartzipsamment-C). The biochars were pyrolyzed at varying temperatures (300 °C, 450 °C and 650 °C) and applied at a rate of 1% (w/w) to the soils. Phosphorus sorption data were fitted to Langmuir and Freundlich models. Phosphorus desorption was done on the residual samples that received initial P concentrations of 21.5 mg L−1, 43.0 mg L−1 and 86.0 mg L−1 solution using 10 mM KCl. The P sorption capacity of the two acid soils i.e. A (395 mg kg−1) and B (296 mg kg−1) were more than two fold that of the neutral soil (C) (105 mg kg−1). Addition of the biochar types to soil A raised the equilibrium P concentration in solution at decreasing pyrolysis temperature. Similar trend was observed in soil B with the exception of corn cob and rice husk biochar at 650 °C which increased the soil's (B) P sorption capacity. In soil C, both biochar types increased P sorption capacity with increasing pyrolysis temperatures. Phosphorus desorbability increased with increasing initial P concentrations in the three soils. Generally, P desorbability increased in the acid soils but decreased in the neutral soil upon biochar amendment. Decreases in P adsorption and consequently increases in P desorption were more pronounced when the 300 °C biochar types were amended with the soils. The study thus showed that biochar pyrolyzed at 300–450 °C could be used to reduce P sorption and increase P bioavailability especially in acid soils. The addition of biochar to neutral or alkaline soils might increase P retention possibly in the short-term, reducing P bioavailability. Highlights • Phosphorus bioavailability in soil solution is dependent on soil type, feedstock used and pyrolysis temperature. • Addition of biochar to acid soils decreases P retention at decreasing pyrolysis temperature. • Biochar amendment in neutral soil raises P sorption capacity at increasing pyrolysis temperature. • Phosphorus desorbability in biochar amended acid soils increases while in neutral soil it decreases. [ABSTRACT FROM AUTHOR]

Abstract The ability of soil to retain water under drought and other extreme hydrological events is critical to the sustainability of food production systems and preserving soil ecosystem services. We investigated the impact of biochar on water retention properties in California agricultural soils in a series of column, lab incubation, and field studies. Results from studies based on similar variables (soil, biochar) were used to demonstrate the impact of biochar on soil-water relations at different scales. The influences of biochar type (softwood, 600–700 °C, low surface area; walnut shell, 900 °C, high surface area), application rate (0, 0.5, 1% wt.), and particle diameter (0–0.25, 0.25–0.5, 0.5–1, 1–2 mm) were investigated. Only the higher surface area biochar increased the field capacity of a sandy soil. Neither biochar, altered the field capacity of the higher clay content soil. The walnut shell biochar with 1–2 mm particle diameter was more effective at increasing field capacity in sandy soils compare to smaller biochar size fractions. Neither biochar affected the wilting point in either soil. Neutron imaging was used to explore potential mechanisms involved in water retention by observing the spatial and temporal distribution of water in and surrounding biochar particles (~ 2 mm diameter). After wetting, water retained in the internal pores of biochar was continuously released to surrounding space (~ 2.2 mm sphere) during a 7-day air drying at room temperature, suggesting that soil water retention is improved via the biochar's intraparticle structure. In the field trial, (6 yr., corn-tomato rotation), neither walnut shell biochar amendment (10 t/ ha, equivalent to 0.5% wt. in lab scale experiments) nor agricultural management practices (organic, conventional) altered the water retention capacity of a silty clay loam soil. These data suggest that biochars with a high pore volume can temporarily increase the field capacity and plant available water in a coarse-textured soil, until biochar internal pores are filled by clay and soil organic matter. Our results suggest that biochar can have a limited impact on soil water retention when biochar pore volume is low, or soil texture is fine. High dosage (≥10 t/ha) of high pore volume biochar with bulky particle size (≥1 mm) can improve water retention of coarse-textured soil with limited capacity of water storage and may improve soil's resilience during hydrological extremes. Highlights • High porosity biochar particles improved water retention of coarse-textured soils. • Water release from biochar particle to sand was observed using neutron imaging. • Biochar didn't impact soil water retention in a 6-year field trial (silty clay loam). [ABSTRACT FROM AUTHOR]

Abstract The effects of biochar on soil properties including nutrients have been reported in previous studies, but few studies targeted on soil nitrogen. Moreover, there remains a lack of studies considering the liberation of ammonia during the ammonium (N-NH 4 +) adsorption process. Our study aimed to fill this research gap. A pot incubation experiment was conducted for 84 days, with ten different soils and four rates of wood chip-based biochar (0.5, 2, 4, and 8%). Biochar's effect on soil ammonium was inconsistent and insignificant in most of the incubated soils at all biochar rates. This finding contradicted our Langmuir model, which estimated maximum ammonium adsorption capacity of biochar as 6.66 mg of N-NH 4 + per g of biochar. Soil response in nitrate (N-NO 3 −) and dissolved organic carbon (DOC) followed a similar declining trend in all soils in both incubation periods, with the effect boosted according to the biochar application rate. The Langmuir isotherm estimated the maximum N-NO 3 − adsorption capacity of our biochar as 11.3 mg g−1. Soil original properties determined amount of nitrate and DOC reduction after biochar addition. Our result also indicated poor estimation of ammonium adsorption by biochar due to the liberation of ammonia. As a result, we strongly recommend that ammonia liberation should be considered during adsorption experiments and more studies in this field. Highlights • Wide range of soils included in the experiment. • Biochar amendment reduces soil N ‐ NO 3 − and soil dissolved organic carbon content. • Soil original properties determine amount of biochar induced N ‐ NO 3 − reduction. • Ammonia loose has effect on estimation of N ‐ NH 4 + adsorption by biochar. [ABSTRACT FROM AUTHOR]

Abstract Biochar amendment has been proposed as a strategy to improve soil quality and mitigate climate change. Yet the extent and regulating mechanisms of soil nitrous oxide (N 2 O) emission in response to amendment of biochars derived from different feedstock have not been clearly demonstrated. A 12-month field trial was conducted to study the impact of two distinct biochar feedstocks (pine chip and peanut shell, at 10 and 30 t ha−1) with (+N) and without nitrogen (N) (−N) fertilization on soil N dynamics, N 2 O emissions, plant performance and microbial gene abundance. The cumulative N 2 O emissions varied greatly with biochar feedstock and application rate, and N fertilization. Pine biochar (at 30 t ha−1) significantly increased N 2 O emissions (by 48%) compared to control under −N, while peanut shell biochar (at 30 t ha−1) significantly increased N 2 O emissions (by 131%) compared to control under +N. Overall, biochar amendments had no impact on soil mineral N (NH 4 + and NO 3 −) under both −N and +N. Under −N, biochar amendments showed no effect on plant yield, whereas under +N yield was significantly improved by 25–27% from pine biochar treatments. Under +N, only pine biochar (at 10 t ha−1) significantly increased plant N uptake (by 47%), and only peanut shell biochar (at 30 t ha−1) significantly enhanced soil AOB, narG , nirS and nosZ gene abundance. Increased soil N 2 O emission under −N from pine biochar amendment is likely to be regulated by improved water retention. However, increases in N 2 O emission from peanut shell biochar under +N could be driven by its large N inputs, labile organic C concentration and the increased soil pH which might largely facilitate biotic processes as evidenced by higher narG , nirS and AOB gene abundance. Positive feedback to N 2 O emission by biochar application revealed from this study is inconsistent with many current biochar studies, showing that caution should be exercised when considering use of biochar to mitigate N 2 O emission. Highlights • Peanut shell biochar plus N fertilizer significantly increased N 2 O emission. • Stimulated N 2 O emissions were involved with different mechanisms. • Pine biochar significantly increased water retention in studied sandy loam soil. • High rate peanut shell biochar enhanced AOB, narG , nirS and nosZ in +N treatments. • Woody biochars with high C:N are not recommended if no fertilization is available. [ABSTRACT FROM AUTHOR]

Abstract Karst ecosystems are vulnerable to degradation and constitute a significant proportion of southwestern China. Here, we explored the amendment of karst soils with biochar in combination with swine manure compost and chemical fertilizer with the aim of improving the microbial community structure and soil nutrient status of these soils. A pot experiment with eight treatments including CK, F, M, MF, B, BF, BM and BMF were set up, where CK was the control, F was chemical fertilizer, M was swine manure compost, and B was wood-derived biochar. The results showed that biochar and biochar-based fertilizer treatments (B, BF, BM and BMF) had higher bacterial diversity (Simpson and Shannon), microbial biomass and soil nutrient content compared to the corresponding no-biochar treatments (CK, F, M, MF), and treatments with compost (M, MF, BM and BMF) had higher values than no-compost treatments (CK, F, B and BF). The cluster and LEfSe analyses showed that different treatments had distinct bacterial community structure and composition; the biochar network (B, BF, BM and BMF) had a higher number of nodes, links and modules than the no-biochar network (CK, F, M and MF), and the compost network (M, MF, BM and BMF) had more complexity than the no-compost network (CK, F, B and BF). Soil variables significantly influenced the biochar and the no-biochar networks, whereas there was no significant correlation with compost or no-compost networks. In conclusion, additions of both biochar and organic compost induced microbial correlation network complexity increases and improved the soil nutrients, indicating biochar-based fertilizer had great benefits on restoration of karst degraded soil. Highlights • Biochar-based fertilizer induced bacterial community structure and composition shifts and increased microbial correlation complexity. • Biochar-based fertilizer significantly increased soil nutrients content. [ABSTRACT FROM AUTHOR]

Abstract Rapid industrial development and human activities have caused a degradation of soil quality and fertility. There is increasing interest in rehabilitating low fertility soils to improve crop yield and sustainability. Biochar, a carbonaceous material intentionally produced from biomass, is widely used as an amendment to improve soil fertility by retaining nutrients and, potentially, enhancing nutrient bioavailability. But, biochar is not a simple carbon material with uniform properties, so appropriate biochar selection must consider soil type and target crop. In this respect, many recent studies have evaluated several modification methods to maximize the effectiveness of biochar such as optimizing the pyrolysis process, mixing with other soil amendments, composting with other additives, activating by physicochemical processes, and coating with other organic materials. However, the economic feasibility of biochar application cannot be neglected. Strategies for reducing biochar losses and its application costs, and increasing its use efficiency need to be developed. This review synthesized current understanding and introduces holistic and practical approaches for biochar application to low fertility soils, with consideration of economic aspects. Highlights • Biochar has potential to be the best management practice for low fertility soils. • Biochar coating with organic materials can result in enhanced crop nutrient supply. • Biochar may accelerate the composting process and improve the end-product quality. • The influence of biochar varies strongly according to the types of feedstock/soil. [ABSTRACT FROM AUTHOR]

Abstract Knowledge of long-term pesticide behavior in biochar (BC) amended soil is still contradictory. In this work, we compared the sorption of three highly persistent and ionizable pesticides [two anionic (imazamox and picloram) and one weak base (terbuthylazine)] on both fresh and field-aged BC as well as on a soil amended with these biochars. The aging process was performed by burying the biochar at 10 cm in a silt loam soil [Upper Midwest USA (Wisconsin)] for six months. Field aged BC removed the three pesticides from solution to a higher extent (>85%) than the fresh BC (<16%). This removal was attributed to water-soluble components on the biochar. Laboratory incubation experiments demonstrated that dissipation in soil and biochar mixtures were both a function of pesticide and biochar type. The amounts of soil extractable (i.e, bioavailable) pesticide were inversely related to the extent of sorption. Similar dissipation and sorption of imazamox was observed in unamended and BC-amended soils. Terbuthylazine dissipated similarly in all treatments, but sorption increased with incubation time in the aged BC-amended soil. Conversely, picloram dissipated to a higher extent in aged BC-amended soil when compared to unamended or fresh BC-amended soil. This work demonstrates temporal variability of biochar sorption capacities due to soil exposure, which alters the efficacy and bioavailability of soil applied pesticides. Highlights • Aged biochar removed greater amounts of herbicides from solution than fresh biochar. • Herbicide sorption by aged biochar was attributed to a dissolvable surface coating. • Degradation of picloram in soil was accelerated by the presence of aged biochar. • Slow sorption occurred for terbuthylazine and imazamox in aged biochar amended soil. [ABSTRACT FROM AUTHOR]

Abstract Biochar addition to soil often increases the activity of alkaline phosphatase (ALP) involved in phosphorus (P) cycling, but the underlying mechanisms of its effect is poorly understood. This study investigated the response of kinetic parameters including maximal velocity (V max) and Michaelis–Menten constant (K m), and thermodynamic parameters including activation energy (E a), enthalpy (ΔH a) and temperature coefficient (Q 10) of ALP to addition of two maize biochars (400 and 600 °C) in two calcareous (Typic Haplocalcid) soils with clayey and sandy loam texture. The biochars were added to the soils at 1% (w/w) and the mixtures were incubated for 90 days under laboratory conditions (25 ± 1 °C and 70% of water holding capacity). Soils with addition of raw residue were used as positive controls and soils without biochar and raw residue were included as negative controls. The potential activity of ALP was assayed at the end of incubation period. The kinetic parameters of ALP were estimated using non-linear regression techniques and the thermodynamic characteristics were determined at different incubation temperatures (17, 27, 37, 47 and 57 °C) using the Arrhenius equation. Compared with the negative control, the addition of raw residue and biochars increased ALP activity (3.1- to 4.4-fold) after the 90-day incubation, depending upon the pyrolysis temperature and soil texture. The positive effect of biochar addition on soil ALP was greater with low than high temperature biochars and in sandy loam than clayey soils. Biochar addition increased the K m and V max values of ALP in the clayey soil but decreased these parameters in the sandy loam soil compared with the corresponding negative controls. Generally, application of maize raw residue and biochars increased the E a , ΔH a and Q 10 values of ALP compared with the negative controls, and the increases were similar for the two pyrolysis temperatures. Soil ALP can be strongly adsorbed by biochar particles; increasing its thermal stability and decreasing its sensitivity to elevated temperatures. In conclusion, application of maize biochar to arid-soils has a high potential to improve the ALP activity, with implications for organic P mineralization and availability. Biochar would change ALP kinetic and thermodynamic characteristics differently, depending mainly on soil texture, through the surface adsorption of this enzyme on biochar particles. These changes will be useful for modeling P mineralization and biochemical processes in biochar-amended calcareous soils. Highlights • Maize biochar application increased soil alkaline phosphatase (ALP) activity. • Biochar particles strongly adsorbed soil ALP and increased its thermal stability. • Biochar affected K m and V max of ALP in clayey and sandy loam soils differently. • Maize biochars increased E a , ΔH a and Q 10 values of soil ALP at 17–37 °C. • Biochar effect on ALP kinetics and thermodynamics is critical for soil P cycling. [ABSTRACT FROM AUTHOR]

Abstract The use of biochar as a soil amendment is being widely studied, whereas clay addition to meliorate soils has only been considered in a few studies. However, there is a limited understanding of the impact of biochar and clay on nutrient retention under field conditions, especially in seasonally dry tropical forests in semi-arid regions. In this study, biochar and clay were added to a tropical Arenosol to quantify nutrient leaching as a measure of nutrient retention to test the potential of both amendments for soil amelioration. In a field experiment, planting holes were prepared with 5 vol% medium-temperature biochar made of Prosopis juliflora (SW) DC, produced locally in the traditional manner in a kiln, or 10 vol% clayey sediment from a temporarily dry lake. Both amendments and control were tested as fertilised and unfertilised treatments. Then seedlings of the endemic tree Spondias tuberosa Arr. were planted. Self-integrating accumulators (SIAs) were used to quantify nutrient leaching at a depth of 0.7 m for ammonium-N (NH 4 + − N), nitrate-N (NO 3 − − N), and potassium (K+). Leaching was assessed for two consecutive periods of eight months each. In the fertilised treatments, biochar addition significantly reduced NO 3 − − N leaching by 46% in the first period; leaching of all other nutrients was reduced but remained non-significant. In contrast, clay addition significantly reduced NH 4 + − N leaching by 79% in the second period, K+ leaching by 51% in the first period, and by 45% in the second period, but significantly increased NO 3 − − N leaching by 57% in the second period. Both treatments showed pronouncedly different leaching patterns over time. Between the first and second period, the ability of biochar to reduce leaching relative to the control decreased by about half for the nutrients tested, whereas the ability of the clay treatment remained rather stable over 1.5 years for NH 4 + − N and K+. The reason for the distinct decrease in nutrient retention of biochar in the second period may be the rapid decomposition of biochar carbon by 51% within 16 months. Under the given conditions, only clay can be recommended as a sustainable land management strategy to enhance NH 4 + − N and K+ retention capacity of Arenosols in seasonally dry tropical forests. Highlights • Biochar and clay were added to an Arenosol in a seasonally dry tropical forest. • Biochar significantly decreased leaching of NO 3 − − N, but diminished over time. • Clay significantly increased NH 4 + − N and K+ retention, remaining stable over time. • Medium-temperature biochar applied in this study had only poor long-term efficacy. [ABSTRACT FROM AUTHOR]

Abstract The co-application of biochar and inorganic N fertilizer has been shown to be a sustainable and environmental friendly technology for the improvement of soil fertility and crop yield. However, their interactive effects on nutrient availability and rain-fed rice productivity in contrasting soil types in the tropics have been scarcely studied. A field study was set up to investigate the effects of rice husk biochar and N-fertilizer applications at different rates on rain-fed rice yield and soil nutrient distribution in the 0–20 cm soil layer. Biochar was applied at four rates; 0, 3, 6, and 12 t/ha−1, in combination with N fertilizer (urea) applied at four rates; 0, 30, 60 and 90 kg/ha−1 to two different soil types (sandy clay loam Oxic-Paleustalf and sandy loam Oxic-Paleustult). In the Oxic-Paleustaif, biochar × N-fertilizer interaction significantly (p < 0.05) enhanced rain-fed rice yield and yield components such as number of panicles/m2 by 71%, filled spikelet (%) by 24%, grain yield (t/ha−1) by 78%, straw yield (t/ha−1) by 74% and 1000 grain weight (g) by 16% when compared to the control. In the Oxic-Paleustult, interaction between biochar and N-fertilizer significantly (p < 0.05) increased number of panicles/m2 by 73%, filled spikelet (%) by 24%, grain yield (t/ha−1) by 83%, straw yield (t/ha1) by 68% and 1000 grain weight (g) by 13% in the when compared to the control. Leaching of soil nitrate (NO 3 -N) was mostly reduced in the Oxic-Paleustalf, while soil pH, soil organic carbon (SOC), total nitrogen (TN), available P and K content at the soil depth of 0–10 cm were significantly (p < 0.05) increased in both soil types. The result from this study suggest that biochar amendment and N fertilization have the potential to enhance rain-fed rice productivity and soil nutrient availability, while minimizing nitrate (NO 3 -N) leaching. Highlights • Combination of biochar and inorganic fertilizer enhanced rain-fed rice productivity. • Soil nutrient availability was increased by biochar and inorganic fertilizer interaction. • Soil Nitrate (NO 3 -N) leaching was reduced by biochar amendment. • These effects were more evident in the Alfisol than in the Ultisol. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) in biochars is critical to carbon dynamics and contaminant transport in soils. This study aimed to develop a robust and easy method to characterize and quantify the biochar-DOC, using water-, acid-, and base-extractable DOC samples (WEOC, AEOC, and BEOC respectively) from 46 biochars produced from diverse feedstocks and pyrolysis conditions. BEOC concentrations were the highest (2.3–139 mg-C/g-biochar), followed by WEOC (0.5–40 mg-C/g-biochar) and AEOC (0.2–23 mg-C/g-biochar). Fast-pyrolysis biochars generally had higher DOC concentrations than slow-pyrolysis biochars. DOC concentrations in slow-pyrolysis biochars decreased exponentially with increasing pyrolysis temperature from 300 to 600 °C. The solid-state 13 C NMR showed that biochar-DOC had abundant small fused-ring aromatics, aliphatic C, and carboxyl C. Biochar-DOC included an acid-precipitated (AP) fraction of higher molecular weight and aromaticity and an acid-soluble (AS) fraction of lower molecular weight and aromaticity. BEOC generally had a greater AP fraction than WEOC and AEOC. Molecular weight, aromaticity and composition of AEOC and BEOC differed from those of more environmentally-relevant WEOC, suggesting that the acid- and base-extraction may not produce the DOC released in real soils. Finally, a quick, easy and robust UV–vis spectrometric method was developed to measure the composition and concentrations of WEOC in diverse biochar samples ( R 2  = 0.96, n  = 46). [ABSTRACT FROM AUTHOR]

Burning of crop residues after harvest is a quick, cheap and an easy way to manage the large quantities of agricultural biomass for timely preparation of the field for next crop. Conversion of the crop harvest residues into biochars and incorporating them back in the same field can address the issue of land clearing, waste utilization and nutrient conservation but, any amendment to the soil changes its physico-chemical characteristics and can affect the fate of soil applied herbicides. The present study reports the effect of low (400 °C) and high (600 °C) temperature wheat (WBC) and rice (RBC) straw biochar's amendment on leaching, degradation and bioavailability of pyrazosulfuron-ethyl (PYRAZO) in a sandy loam soil. The PYRAZO was poorly retained in the control soil column where 78% of the soil-applied herbicide leached out of the control soil column. Biochars addition (0.02 and 0.05 g kg −1 ) significantly reduced the PYRAZO leaching by affecting herbicide's breakthrough time and its maximum concentration in leachate. The biochars reduced PYRAZO degradation, both in the flooded and the nonflooded soils; but, effect was more pronounced in the nonflooded soils. The effect of biochars on PYRAZO's leaching and degradation was the function of the nature of feedstock, biochar production temperature and its dose. The high temperature biochars were more effective in reducing the leaching and degradation of PYRAZO than the low temperature biochars and the rice biochars were better than the wheat biochars. The bioavailability of PYRAZO was assayed by its effect on mustard seedlings and results suggested that low temperature biochars, even at 0.05 g kg −1 level, had no negative effect on herbicide efficacy. However, high temperature biochars significantly reduced the herbicide bioavailability and higher concentration of PYRAZO was required for the desired effect. These findings are relevant in assaying the fate of PYRAZO in the biochar amended soils. [ABSTRACT FROM AUTHOR]

Biochar has been considered a stable additive for long-term soil carbon (C) storage and climate change mitigation. However, our understanding of the long-term interactions between aged biochar, soil organic C (SOC), and fresh low molecular weight C compounds (LMW-C) is still limited. In addition to the changes in the chemical properties of biochar and the SOC after aging, biochar stability and C sequestration potentials might be affected by the LMW-C availability. After 3.5 years of incubation, aged soils and aged soil-biochar mixtures (4 atom‰ 13 C enriched grass-derived biochar, 10% addition rate) of two different soil types were used in this study, with or without the addition of LMW-C. The 13 C natural abundance of the LMW-C was manipulated by mixing cane sucrose (C4) and beet sugar (C3) to make it different from or equal to the native SOC isotopic signature of the two soil types, which allowed the partitioning of the LMW-C and biochar C from the SOC in non-biochar and biochar addition treatments, respectively. We traced the 13 C in the cumulative CO 2 , microbial biomass C (MBC), and dissolved organic C (DOC) at the beginning and the end of the 28 days of incubation. Results indicated that this aged biochar was not as effective for SOC protection as it was when fresh. Aged biochar caused significant increases in the native SOC-derived CO 2 compared to non-biochar treatment during the 3.5 years of aging. Within the 28 days of incubation, aged biochar not only promoted the total CO 2 emission but also did not limit the priming effect of LMW-C on native SOC mineralization. SOC-derived DOC in the aged soil-biochar mixture was significantly higher than that in the aged soil, which further increased the SOC loss. A decline in the SOC stability with aged biochar might be associated with the attenuated sorption of SOC on aged biochar, the decline in bulk density with the high biochar addition rate, and a modified microbial community. The priming of aged SOC mineralization with the addition of LMW-C might be associated with the enhanced microbial N demand in aged soils and soil-biochar mixtures. The effect of aged biochar on the soil DOC and the effect of LMW-C on the aged biochar and SOC stabilities should be further investigated in field conditions, under continuous fresh C inputs, to better evaluate the effects of biochar on long-term SOC storage. [ABSTRACT FROM AUTHOR]

The impact of biochar (BC) application on soil varies with BC feedstock and soil type. The objective of this study was to investigate the linkage between the properties and surface functionality of various BCs and their role in the rehabilitation of two infertile soils. Sandy loam (SL) and sandy (S) soils were collected from agricultural areas in Korea and Vietnam, respectively. The BCs of amur silvergrass residue (AB), paddy straw (PB), and umbrella tree (UB) were applied to the soils at a rate of 30 t ha −1 and incubated at 25 °C for 90 d. Soil carbon (C) mineralization was investigated by a periodic measurement of CO 2 efflux. Soil texture strongly influenced the CO 2 efflux more than the BC type as indicated by 2–4 folds increase in cumulative CO 2 -C efflux from the SL soil compared to that from the S soil. For the PB-, AB-, and UB-treated S soils, the values of cation exchange capacity (CEC) were increased by 906%, 180%, and 130%, respectively, compared to that of the control; however, for the PB-treated SL soil, only a 13% increase in CEC was found. The pH in the PB-treated S soil sharply increased by 4.5 units compared to that in the control, due to a high concentration of readily soluble compounds in the PB and the low buffering capacity of the S soil. The S soil was more sensitive to the addition of BCs than the SL soil. A more prominent improvement in soil fertility can be achieved by BC application to the sandy soil having low clay, nutrient, and organic matter contents. [ABSTRACT FROM AUTHOR]

Biochar is proposed as a soil amendment to improve soil physical-chemical properties and crop productivity. However, the effect of biochar on crop yield is not consistent and the mechanisms affecting plant growth are still not well-understood. In this paper, field experiments were carried out to investigate the impact of biochar addition on soil properties, water and fertilizer productivity of tomato in semi-arid area of Inner Mongolia, China. The tested biochar was made from maize straw by slow pyrolysis. Four biochar treatments were conducted including addition of 10, 20, 40 and 60 t ha −1 and no biochar as a control. Addition of biochar reduced the bulk density and increased the porosity of soil. Electrical conductivity of soil increased with increasing biochar application rate. Soil pH was not affected by addition of biochar in one growing season. Yield, crop water productivity and partial factor productivity for fertilizer were nonlinearly (quadratic) proportional to application rate of biochar. Highest water and fertilizer productivity obtained from the 40 t ha −1 biochar treatment. Comprehensive analysis of biochar impact on yield, water and nutrient productivity, and cost-benefit for the grower indicate that addition of approximate 30 t ha −1 is an appropriate rate for tomato production in the study area. This suggestion is based on the relatively short term effect and local market conditions. A prolonged experiment is desirable to understand the long term response of soil and crop to biochar addition. [ABSTRACT FROM AUTHOR]

Plant-residue derived biochars from walnut shell, corn cob, corn straw, and rice straw obtained at three heat treatment temperatures (HTTs) (250 °C, 400 °C, and 600 °C) were applied in an incubation experiment to investigate how feedstocks, HTTs, and biochar properties affect the quantity of microorganisms, microbial community shift, enzyme activity, and biodegradation of polycyclic aromatic hydrocarbons (PAHs) in an aged contaminated soil. The microbial quantities (bacteria and fungi) and enzyme activities (catechol 2,3-dioxygenase and ligninolytic enzymes) generally decreased with the increase in HTTs. Microbial quantities had significantly positive correlations with the aliphatic carbon (C) ( p  < 0.01) but negative correlations with the aromatic C of biochars ( p  < 0.01). Similar findings were observed with enzyme activities, which had significantly positive correlations with microbial quantities ( p  < 0.05). Meanwhile, there were significantly positive correlations between C23O activity and bacterial quantity ( p  < 0.01) and between ligninolytic enzyme activities and the quantity of fungi ( p  < 0.05). These results indicate that the increase in recalcitrant aromatic C in biochars that occurs with the increase in HTT is unfavorable for the microbial growth and enzyme activity in the soil studied. Generally, application of biochars had little influence on the biodegradation rates of total PAHs. However, the effects of biochars on the biodegradation rates of major individual PAH (e.g., Nap, Phe, Pyr, and Chr) depended on both the types of biochars and the PAH properties such as benzene ring number and angular pattern of the ring linkage. [ABSTRACT FROM AUTHOR]

Agriculture is one of the largest anthropogenic contributors of phosphorus (P) to surface waters and reducing these P loads is a target set by many countries. One potential mitigation strategy could be to utilize biochar, functionalized by co-precipitating metal ions onto its surface to adsorb phosphates. We evaluated such an approach in a series of laboratory experiments and a three-year field lysimeter study. Leached phosphates were trapped in a 3-cm layer of a commercially available 20% hardwood/80% Norway spruce biochar, coated with magnetite and placed under the soil root zone. Langmuir maximum adsorption potential (Qmax) was 3.38 mg P g −1 biochar, as determined from batch adsorption studies performed at pH 6.5. Further laboratory experiments revealed that adsorption was strongly negatively correlated with pH (R 2  = 0.995). In a laboratory column study using high flow rates, no difference was found in phosphate adsorption between coated biochar and the control (no biochar), after application of ammonium phosphate at a rate corresponding to 22 kg P ha −1 . However, differences were observed at higher application rates (285 or 570 kg P ha −1 ). Calculation of a Fe:P molar ratio to evaluate the magnetite treatment method from laboratory (2:1) to lysimeter (248:1) suggested a relatively effective laboratory performance, but overall poor field efficiency. Nevertheless, biochar in the lysimeter study still reduced phosphate leaching from two organic soils, by 62% (P < 0.05) and 35% (NS). This suggests that, even though the method of magnetite-coating biochar is not necessarily resource-efficient, it is effective in removing P from soil leachate. [ABSTRACT FROM AUTHOR]

Biochar production for soil amendment was recently proposed as a tool to mitigate climate change, reducing soil greenhouse gas (GHG) emissions and sequestrating carbon (C) in soil. The aim of this research project was to test the hypothesis that only biochars with specific requirements (low H/C org and O/C org ratios, high C/N ratio) can reduce soil N 2 O emissions without increasing CO 2 emissions in the short term. A 45-days incubation study was carried out, in which six engineered biochars made from the pyrolysis of wood, switchgrass and the solid fraction of pig manure (SFPM), were amended to two agricultural soils (loamy sand and silt loam) at a dose of 2% (w/w) in 1-liter jars. Soil moisture content was adjusted at 80% of water-filled pore space with a solution of ammonium nitrate that corresponds to 170 kg of nitrogen per hectare. N 2 O and CO 2 emissions were analysed on days 2, 3, and then weekly. Soil chemical properties and bacterial richness, composition and taxonomy were analysed after the incubation period. When compared to the control soils without biochar, N 2 O emissions were decreased by 42 to 90%, but only in the silt loam amended with biochars made from wood and switchgrass, these biochars having a high C/N ratio (>30). Lower N-NH 4 + and N-NO 3 − concentrations were observed in these biochar treatments than in control soil. Moreover, two bacterial classes ( Deltaproteobacteria and Thermoleophilia ) were correlated with a decrease in N 2 O emissions. For each type of biochar, those produced at the highest temperature with low O/C org and H/C org ratios resulted in the lowest increase in CO 2 emissions, which could indicate a higher biochar carbon stability. Overall, results of this study demonstrated that biochar can either increase or decrease soil GHG emissions depending on its properties, and that the effect can differ according to soil properties. Future long-term studies in the field in the presence of crop should be carried out in order to validate the conclusions of this study. [ABSTRACT FROM AUTHOR]

Land degradation reduces soil productivity and exacerbates the problem of food security. Thus, there is an increasing need to look for sustainable farming practices aimed to water and soil conservation. In this regards, conditioning the soil with biochar has been identified as a possible means on improving water conservation and soil biochemical, physical, i.e. mechanical and hydraulic characteristics. Many studies demonstrate these effects of biochar. However, the extended number of variables influencing its impact require further measurements. The objective of this study is to determine the effect of wood-based biochar on two different textured soils and to evaluate their influence on some hydrological properties: water retention, shrinkage behavior and the effect of wetting and drying periods on the hydraulic conductivity. Test samples were prepared by adding 2.5 and 5% (by dry mass) of pyrolyzed mango-wood biochar to a sand and a sandy loam. Soil water retention and soil shrinkage curves were measured. Additionally, extra core samples were exposed to four intense cycles of wetting and drying, by drying the samples at 30 °C for three consecutive days. Biochar amendments increased water retention in the coarse textured sand compared to the unamended soil. Pore size distribution was significantly altered in the sandy substrate, reducing the fraction of wide coarse pores and increasing meso porosity. Repeated wetting and drying cycles enhanced the structural stability of the pore system increasing the saturated hydraulic conductivity. Soil rigidity, especially in the sandy mixtures, was enhanced by the addition of biochar, forming an internal pore structure able to resist better hydraulic deformation due to drying. These results confirm the suitability of biochar to overcome extreme hydrological conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biochar decreased Acidobacteria abundance while increasing Gemmatimonadetes. • Biochar increased the genetic richness and diversity of soil microbes. • Experiment types played a role in shaping microbial response to biochar addition. • Biochar and soil properties were related to the changes of phyla abundance. • Selecting key biochar properties can improve soil microbial functions. Biochar has gained global attention due to its potential for climate change mitigation and soil quality improvement. Yet, the consequences of biochar additions for soil microbes -the major biotic drivers of soil function- remain unknown across global environmental gradients. We aimed to explore the responses of soil bacterial communities to biochar addition, and further investigate how biochar and soil properties impact these responses. We conducted a global meta -analysis and found that, in general, biochar has a limited impact on the proportion of major bacterial phyla, with only Acidobacteria and Gemmatimonadetes being largely impacted: the relative abundance of Acidobacteria decreased by 14.6%, while that of Gemmatimonadetes increased by 19.8%. Also, the experimental type played a role in shaping the response of microbial community to biochar application. In addition, biochar significantly promoted the diversity of soil bacteria, i.e., genetic richness and diversity. These changes were significantly associated with biochar load, C/N ratio, pyrolysis temperature, biochar pH, as well as soil C/N ratio and pH. We further found that the impacts of biochar on functional diversity, i.e., C substrate richness consumed by soil microbes increased with the biochar load, which might relate to increased genetic richness. Our work suggests that selecting key biochar properties can improve soil quality, microbial function, and climate change mitigation while maintaining the positive impacts of biochar on soil microbial diversity. Further research is needed to link the response of soil microbial composition at the genus level to biochar addition, with microbial functions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biochar reduced CH 4 , N 2 O and NO emissions by 20.1%, 36.3%, 28.4%, respectively. • Biochar decreased the aggregate GHGs by 25.2% and yield-scaled GHGs by 31.5%. • Biochar decreased N-oxides by 35.7% on average and yield-scaled N-oxides by 41.0%. • Similar mitigation was observed between biochar single application and reapplication. Biochar application to soil has been proposed as a promising tool for sequestering carbon, ensuring food security, mitigating greenhouse gases (GHGs), and lowering nitrous oxide (N 2 O) and nitric oxide (NO) emissions. Efforts and observations to determine whether biochar can be repeatedly amended to soil to further sequester carbon while meeting those targets from long term and practical perspective are limited. A three-year field experiment was conducted to observe simultaneous methane (CH 4), N 2 O, and NO emissions in a rice–wheat rotation system, where six treatments were established as follows: control plot without biochar (B0), biochar-enriched soil with biochar applied once in 2012 at 20 t ha−1 (B20−) and 40 t ha−1 (B40−), reapplication of half rate biochar in 2015 at 10 t ha−1 (B20+) and 20 t ha−1 (B40+) to the above described biochar-enriched soils, single application of biochar in 2015 to the control soil at 40 t ha−1 (B40). Then a series of incubation experiments explored the mechanism for mitigating trace gases. The results showed that compared with nonamended soils, the soils with the single biochar application and the biochar reapplication had similar effects on CH 4 , N 2 O, and NO emissions, significantly decreasing them by 14.5%–27.1%, 31.5%–43.4%, and 22.4%–33.6%, respectively, when compared with non-amended soils. The decrease in CH 4 emissions was largely due to the decrease in CH 4 production and the increase in CH 4 oxidation in the biochar application treatments. Biochar single and reapplication significantly decreased yield-scaled GHGs by an average of 31.5% and yield-scaled N-oxides by an average of 41.0%. Nonetheless, the effectiveness of biochar in decreasing yield-scaled GHGs and yield-scaled N-oxides did not increase with the biochar reapplication at the two different application rates. Both single and reapplied biochar appeared to be promising practices to mitigate GHG and N-oxide emissions from the rice–wheat rotation system. Biochar can be repeatedly applied for further carbon sequestration while not hindering improvements in crop yield or mitigation of other GHGs and N-oxides. [ABSTRACT FROM AUTHOR]

• Pore structure of macroaggregates was studied using X-ray computed tomography (CT). • Straw biochars increased total porosity and pore heterogeneity in macroaggregates. • Porosity and pore connectivity are positively correlated with SOC in macroaggregates. • Straw biochars significantly enhanced the permeability of macroaggregates. • Biochar potentially enhanced the SOC storage and hydraulic properties of macroaggregates. The addition of biochars produced by different feedstocks to soil affects soil aggregation, which has been shown to be critical for soil carbon sequestration, water holding capacity and plant growth. In this study, rice stalk biochar (RB) and canola stalk biochar (CB) produced at 350℃ were added to a Ultisol at the 1% rate. After a three-year incubation, the macroaggregates (5–6 mm) in soils were separated for quantification of pore structure using industrial X-ray computed tomography (CT) scanning. The RB and CB treatments significantly increased the total porosity and the ratio of connectivity to isolated porosity(C/I) in macroaggregates relative to CK treatments. The addition of biochars decreased the proportion of equant pores in the macroaggregates, while increased the proportion of irregular pores such as prolate and acircular pores, resulting in the high porosity heterogeneity in macroaggregates. The canola stalk biochar had a larger effect on the improvement of pore structure than rice stalk biochar, while having the opposite effect on pore throat structure. There was a positive correlation between porosity, connectivity and SOC in macroaggregates. Simulation results on water flow showed that the permeability for RB and CB treatments were 25.16 μm2 and 28.62 μm2, respectively, which were 116.7% and 146.5% higher than that of CK treatment (11.61 μm2). The results indicated that the biochars altered the pore structure of macroaggregates, potentially enhancing the functional services of macroaggregates such as SOC storage and hydraulic properties. The findings provided the detailed information on the effect of different biochar additions on pore structure in macroaggregates and simulated soil water movement within the macroaggregates, which is important for understanding the mechanism of biochars affecting soil aggregation and its functions. [ABSTRACT FROM AUTHOR]

Soil thermal properties play crucial roles in governing heat storage and conduction across soil profiles and affect various soil processes by determining soil microclimate. Biochar has gained wide attention as a soil amendment to affect a series of soil physiochemical properties. However, little information is available on the integrated effects of biochar application on soil thermal properties. Disturbed soil columns with consistent bulk density (1.3 g cm −3 ) were packed using clayey red soil and wheat straw biochar at application rates (w/w) of 0%, 0.5%, 1.0%, 1.5%, 2.0% and 2.5%. Besides, a 2-year field experiment of biochar application at the same application rates with crop rotation was performed in a red soil region in south China. Soil thermal properties, i.e. thermal capacity, conductivity and diffusivity, were measured with heat pulse method for disturbed soil columns and undisturbed soil cores from the field at controlled soil water contents ranging from 0% to 40% at an interval of 5%. Furthermore, soil thermal properties were measured in situ for different biochar treatments under field conditions. For the disturbed soil columns, no significant effect of biochar application on soil thermal properties was detected at most of the soil water content levels. Additionally, it indicated that biochar application cannot directly affect soil thermal properties by changing soil solid substances composition at application rates up to 2.5% w/w. The results from undisturbed soil cores showed significant decreasing effects of biochar application on soil thermal capacity and diffusivity at most of the soil water content levels. The results from in situ measurement showed significant decreasing effect of biochar application on soil thermal capacity, conductivity and diffusivity. Two main underlying mechanisms were identified for the effects of biochar application on soil thermal properties. One is the negative effect of biochar application on soil thermal capacity and conductivity by increasing the soil total porosity, mainly by increase in the meso- and macro-porosity. The other is the positive effects of biochar application on soil thermal properties by increasing the soil water content through improved soil water retention ability. The negative effects through change in the soil structure were the dominant effect under field condition. [ABSTRACT FROM AUTHOR]

Biochar is a carbon-rich porous material intensively studied for its agronomic benefits, such as decrease of greenhouse gases emission and nutrient losses via leaching, increased crop production and improved soil physical and chemical properties. We investigated the effect of holm oak biochar produced at 600 °C on mineral nitrogen (N) leaching from two contrasting soils (Acrisol and Calcisol). Biochar was applied at three rates (0%, 1% and 2% w/w) with (B0-F, B1-F and B2-F, respectively) and without (B0, B1 and B2, respectively) ammonium-based fertilizer. Soil columns were leached with deionized water and mineral N in leachate was monitored during ten weeks after each fertilization. Sorption behavior of biochar-amended soils was assessed in batch experiments before and after leaching. Biochar increased ammonium (NH 4 + -N) sorption in sandy Acrisol but had no effect on nitrate (NO 3 − -N) sorption. Furthermore, sorption properties of soil decreased by up to 25% during the study. In Acrisol, biochar affected NH 4 + -N leaching, which was increased by both doses of biochar without fertilization, but decreased by the lower biochar application rate when fertilizer was added. The leaching of NO 3 − -N was not affected by biochar in Acrisol. The ability of Calcisol to adsorb NH 4 + -N was high and was not further increased by biochar, which corresponds to no NH 4 + -N leaching from Calcisol regardless the biochar application rate. Moreover, biochar had no effect on NO 3 − -N leaching from Calcisol. Our results demonstrate that biochar effect on leaching of inorganic N forms is inconsistent, evolves in time and is highly dependent on soil properties. Alleviation of soil acidity by biochar application to Acrisol resulted in short-term stimulation organic N mineralization, which resulted in enhanced amount of NH 4 + -N being leached. Furthermore, the fact that biochar lost its effect on N leaching already after the second fertilizer application could cast a doubt on the efficiency of biochar application to soil in order to increase N retention and decrease N leaching. [ABSTRACT FROM AUTHOR]

Bio-based alternative Si fertilizers were developed by pyrolyzing Si-rich agricultural crop residue biomass of rice straw, sugarcane harvest residue, miscanthus, and switchgrass with KOH pretreatment at 0:100, 1:100, 5:100, 10:100, 25:100 and 50:100 KOH:Feedstock biomass ratios (termed 0 KB, 1 KB, 5 KB, 10 KB, 25 KB and 50 KB) and were evaluated for enhancing bioavailable Si in soils. KOH pretreatment enhanced plant-available Si in all feedstocks-derived biochars with rice straw-derived 10 KB biochar exhibiting the highest Si release. SEM-EDX mapping images showed morphological and structural changes of phytoliths in KOH-enhanced biochars which contributed to the increased bioavailable Si. Application of 1% KOH-enhanced biochars to soils significantly increased plant-available Si in soils with minimum effect on soil pH. Perennial ryegrass grown in 10 KB rice straw biochar treated soil increased Si uptake by 31% over 0 KB treated soil and was comparable with mineral Si treatment. Overall, KOH-enhanced biochar as alternative Si source could provide multiple functions in disease control, K nutrition, and C sequestration. [ABSTRACT FROM AUTHOR]

Numerous studies have been conducted worldwide and more specifically in Brazil assessing the consequences of biochar amendments on the soil properties and on the agronomical production. The present study aimed to evaluate the effects of biochar of coffee residues on the physicochemical characteristics of an Entisol and water use efficiency of maize ( Zea mays ). Two types of biochar were produced with both coffee ground (CG) and coffee husk (CH) and their physicochemical properties were characterized. A greenhouse pot experiment, quantifying the growth of maize, with different rates of biochar amendments and fertilizing procedures was conducted in a completely randomized design. Treatments consisted in four replications of (i) control (native soil), (ii) synthetic fertilization and (iii) organic fertilization with cow manure, and (iv) the two types of biochar in four doses (4, 8, 12 and 16 Mg ha − 1 ). Specific surface area (SSA) of CH was significantly higher than CG biochar but both types of biochar had higher SSA than soil. Nutrient and water retention properties of soil and maize growth were significantly improved with increasing biochar doses. The water use efficiency was 50% higher for the treatment with the highest dose of biochar. This is a significant found considering the potential of growing maize on a sandy soil in a dry regions of Brazil. Nutrient use efficiency as well as the C content in Entisol were largely improved by the use of biochar. Determination of SSA was a quick and robust method to anticipate the benefits of biochar on water retention of soil. [ABSTRACT FROM AUTHOR]