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Biochar and modified biochar have gained wide attention for Cd-contaminated soil remediation. This study investigates the effects of rape straw biochar (RSB), sulfur-iron modified biochar (S–FeBC), and nitrogen-iron modified biochar (N–FeBC) on soil Fe oxide transformation and Cd immobilization. The mediated electrochemical analysis results showed that Fe modification effectively enhanced the electron exchange capacity (EEC) of biochar. After 40 days of anaerobic incubation, compared to the treatment without biochar (CK), the concentrations of CaCl 2 -extractable Cd in N–FeBC, S–FeBC, and RSB treatments decreased by 79%, 53%, and 23%, respectively. Compared with S–FeBC, N–FeBC significantly decreased the soil Eh and increased soil pH within the first 15 days, which could be attributed to its higher EEC and alkalinity. There is a negative correlation between the concentration of CaCl 2 -extractable Cd and soil pH (p < 0.01). The sequential extraction results showed that both N–FeBC and S–FeBC promoted Cd transfer from acid-soluble to Fe/Mn oxides bound fraction (Fe/Mn–Cd). N–FeBC significantly increased the concentration of amorphous Fe oxides (amFeox) from 4.0 g kg−1 in day 1 to 4.6 g kg−1 in day 15 by promoting the NO 3 −-reducing Fe(II) oxidation process, while S–FeBC significantly increased amFeox from 4.0 g kg−1 in day 15 to 4.8 g kg−1 in day 40 by promoting the Fe(II) recrystallization. There is a positive correlation between the concentration of amFeox and Fe/Mn–Cd (p < 0.01). The scanning electron microscopy analysis showed that Cd was bound to the amFeox coating on the surface of Fe-modified biochar. By acting as an electron shuttle, the active surface of Fe-modified biochar may serve as a hotspot for Fe transformation, which promotes amFeox formation and Cd immobilization. This study highlights the potential of Fe-modified biochar for the remediation of Cd-contaminated soils and provides valuable insights into the development of effective remediation approaches for Cd-contaminated soils. [Display omitted] • Fe modification significantly increased the EEC of biochar, especially for N–FeBC. • Fe-modified biochar promoted the amFeox formation and thus enhanced Cd immobilization. • N–FeBC increased amFeox by promoting the NRFO process. • S–FeBC increased amFeox by promoting the Fe(II) recrystallization process. [ABSTRACT FROM AUTHOR]

Abstract While biochar on metal immobilization was well understood, a small pool of dissolvable organic matter (DOM) from biochar was recently recognized as a bioactive agent for plant growth promotion. However, how the molecular composition and plant effects of this fraction and the performance for metal immobilization of the DOM-removed biochar could vary with pyrolysis temperature had been not well addressed. In this study, wheat straw biochar pyrolyzed at a temperature of 350 °C, 450 °C, 550 °C were extracted with hot water to separate the DOM fraction. The obtained biochar extracts (BE350, BE450, and BE550) were tested as foliar amendment to Chinese cabbage while the extracted (DOM-removed) biochars were tested for heavy metal immobilization in a contaminated soil. The results showed that BE350 was higher in organic matter content, abundance of organic molecules and mineral nutrients than BE450 and BE550. Compared to control, foliar application of BE350 significantly enhanced the shoot biomass (by 89%), increased leaf soluble sugar content (by 83%) but reduced leaf content of nitrate (by 34%) and of potential toxic metals (by 49% for Cd and by 30% for Pb). Moreover, BE350 treatment increased gene expression of nitrate reductase and glutamine synthetase enzyme activity of the tested plant. Meanwhile, soil amendment of DOM-extracted biochars significantly decreased soil CaCl 2 extractable pool of Cd, Pb, Cu and Zn in a range of 27%–78%. Thus, the performance of DOM extract of biochar on plant growth promotion was indeed dependent of pyrolysis temperature, being greater at 350 °C than at higher temperatures. In contrast, metal immobilizing capacity of biochar was regardless of pyrolysis temperature and DOM removal. Therefore, pyrolyzing wheat straw at low temperature could produce a biochar for valorized separation of a significant DOM pool for use in vegetable production, leaving the residual biochar for amendment to metal contaminated soil. Graphical abstract Unlabelled Image Highlights • DOM and nutrients content in BE was varied with the pyrolysis temperature. • Spraying BE350 showed greatest value for plant yield and quality promotion. • DOM may regulate gene expression and stimulate nitrogen assimilation in cabbage. • DOM-free biochar can be used for metal immobilization in soil. • Biochar can be recycled with value-added applications in agriculture. [ABSTRACT FROM AUTHOR]

Abstract Minimizing potential environmental risks of toxic metals is a prerequisite for recycling crop straw from contaminated farmlands. In this study, feedstocks of wheat straw were collected from paddy fields with low and high level of metal contamination and pyrolysed at temperature of 350 °C and of 550 °C, respectively. The produced biochars were subsequently extracted with hot water and potassium hydroxide solution. Contents of potentially toxic metals (PTEs), polycyclic aromatic hydrocarbons (PAHs) and mineral nutrients were analyzed both of the biochars and their extracts. To test the effect of the biochar extracts on plant growth and quality, a pot experiment was carried out with foliar amendment to Chinese cabbage. The results showed that contents of nutrients, PTEs and PAHs of both the biochars and their extracts differed significantly both between feedstocks and between pyrolysis temperatures. Total concentrations of PTEs and PAHs of the biochars were well under the recommended quality limits with their negligible presence in the biochar extracts. The pot experiment revealed a very significant promotion for cabbage yield and quality by the extracts of biochar pyrolysed at 350 °C, regardless of the feedstock. Thus, pyrolysing crop straw from metal contaminated fields at 350 °C could be an option to stabilize toxic metals in biochar as soil amendment but to recycle the biochar extract as foliar fertilizer to off-site crop production. Therefore, a viable mechanism is urged to develop in China where direct crop residue return has been state-funded under a policy of strict ban of straw burning. Graphical abstract Image 1 Highlights • Comparative pyrolysis of wheat straw of contrasting metal contamination. • Chemicals level of biochars depend rather on pyrolysis temperature than on feedstock. • Biochar extracts high in nutrients but low in toxic metals and PAHs. • Extracts of low temperature biochar induced promotion of Cabbage growth and quality. [ABSTRACT FROM AUTHOR]

Worldwide, massive amounts of food waste have been generated at increasingly accelerated rates, posing potentially great risks to the environment. Shifting traditional waste treatment to a sustainable bioeconomy thus challenges food chain management worldwide. In this study, food waste was copyrolyzed with rice husk to produce biochar with a pilot-scale industrialized system. The efficiency of the material conversion and the properties and functions of the produced biochars as well as the potential environmental impacts of pyrolysis were evaluated using in situ measurements, physico-chemical characterization and in vitro (pot) experiments with biochar. The results showed that the emissions of potential toxic compounds and metals from the pyrolysis system were within the guideline limits under the legislation of China or the EU commission. On average, biochar yielded approximately 20% of feedstock and contained a total organic carbon content of 433 g kg−1. In the pot experiment, Chinese cabbage yield and quality were significantly improved, and the plant uptake of heavy metals was significantly reduced in soil amended with food waste biochar compared to no biochar amendment. Furthermore, the food waste biochar was blended with mineral nutrients to create a biochar based compounded N-P-K fertilizer. Application of the biochar based compound fertilizer exerted a significant positive effect on cabbage growth and nutrient use efficiency relative to a conventional mineral compound fertilizer. For per tonne of dry mass of food waste, copyrolysis costed less than 60 USD but gained a gross profit of more than 30 USD. Therefore, the copyrolysis of food waste with crop residues could be applicable to the safe recycling of food waste into value added products to raise agricultural production. [Display omitted] • A pilot-scale copyrolysis system was used to convert food waste into biochar. • The concentrations of potential toxic elements in flue gas was negligible. • Food waste biochar (BC) and biochar compound fertilizer (BCF) was analyzed. • BC and BCF significantly improved the yield and quality of Chinese cabbage. • The average cost and gross profit were 54.5 and 32.9 USD per tonne. [ABSTRACT FROM AUTHOR]

Highlights: [•] Biochar treatment at 20–40tha−1 reduced rice Cd by 20%–90% from metal polluted rice fields. [•] Grain Cd under biochar treatment fell in a safe level by 0.4mgkg−1 in soils with Cd in range 0.16–4.83mgkg−1. [•] Biochar amendment caused Cd immobilization primarily due to the liming effect by biochar. [Copyright &y& Elsevier]

Highlights: [•] No increase in soil respiration and variable changes in crop yield with biochar amendment in a rice and wheat rotation year. [•] N2O emission greatly decreased consistently with biochar treatments and crop seasons, CH4 emission from rice season increased only at 20tha−1 amendment. [•] An overall net reduction in GHGI of the whole rotation cycle by 10–20% was consistent across the biochar treatments. [Copyright &y& Elsevier]

Abstract: Biochar production and application from crop straw had been proposed as one effective countermeasure to mitigate climate change. We conducted a 2-year consecutive field experiment in 2009 and 2010 in rice paddy to gain insight into the consistency over years of biochar effects on rice production and greenhouse gases emissions. Biochar was amended in 2009 before rice transplanting at rates of 0, 10, 20 and 40tha−1, soil emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were monitored with closed chamber method at 7 days interval throughout the whole rice growing season (WRGS) both in 2009 and 2010. The results showed that biochar amendment increased rice productivity, soil pH, soil organic carbon, total nitrogen but decreased soil bulk density in both cycles of rice growth. Soil respiration observed no significant difference between biochar amendment and the corresponding control both in the first and second cycle, respectively. However, biochar amendment decreased nitrous oxide emission but increased methane emission in both cycles. No significant difference in carbon intensity of rice production (GHGI) and global warming potential (GWP) were observed between the biochar amendment at the rate of 10tha−1 and 40tha−1 and control though the GWP and GHGI was increased by 39% and 26% at the rate of 20tha−1 respectively, in the first cycle. However, in the second cycle, both of overall GWP and GHGI were observed significantly decreased under biochar amendment as compared to control, ranging from 7.1% to 18.7% and from 12.4% to 34.8%, respectively. The biochar effect intensity on global warming potential were observed from −2.5% to 39.2% in the first cycle, and from −18.7% to −7.1% in the second cycle. However, the biochar effect intensity on C intensity of rice production was observed from −10.2% to 25.8% in the first cycle, and from −36.9% to −18.6% in the second cycle. Therefore, biochar effect on reducing the overall C intensity of rice production could become stronger in the subsequent cycles than that in the first cycle though a consistently strong effect on reducing N2O emission in a single crop cycle after biochar amendment. Nevertheless, these effects were not found in proportional to biochar amendment rates and a high rice yield but lowest C intensity was achieved under biochar amendment at 10tha−1 in both cycles of the rice paddy in the present study. [Copyright &y& Elsevier]

• Rice fields of a clayey paddy without and with biochar 6 years compared in a farm. • Soil carbon increased and soil aggregation enhanced in biochar field. • Microbial growth and enzyme activities promoted greatly in biochar field. • Beneficiary by microbial community composition changes in biochar field. • Legacy of improved soil health for better production over years in biochar field. • Mechanistic link between C increase, aggregation and microbial promotion unraveled. "4 per 1000 Initiative" launched at COP21 has strongly recommended that increasing soil organic carbon (SOC) is a global imperative. However, the strategies to improve agricultural soil functioning and health by an increase in soil C have been poorly addressed. In a rice farm trail, topsoil samples were collected in 2015 respectively in a field amended with biochar (BA) (equivalent to 10 t ha−1) in 2009 and an adjacent field with no biochar (NB). Soil aggregation, biochemical activities and microbial communities of the samples were analyzed with microscopic, micro-biochemical and molecular assays respectively. Compared to NB field, SOC storage increased by 45%, total and available nitrogen pool enhanced by approximately 30% while the bulk density decreased and soil pH unchanged in BA field. A 25% increase in mean weight diameter of water stable aggregates was observed in the BA compared to NB field. Correspondingly, microbial biomass nitrogen and enzyme activities in BA field was enhanced both by approximately 30% compared to NB field. Furthermore, with community structure altered, a moderate (32%) increase in total bacterial abundance and a significant decrease in microbial abundance of amino acid metabolism and fungal pathotrophs were observed in BA field compared to NB field. This could link to the higher (10%) grain yield with lower yield inter-annual variability in BA field compared to NB field, reported previously. All these changes clearly demonstrated a legacy of paddy soil health improvement over years following one time biochar amendment. Overall, addition of biochar to the clayey nutrient rich paddy soil could sustain an increase in SOC, soil aggregation and soil health functioning, with positive changes in microbial community over years. Thus, carbon increase as per required by the "4 per 1000 Initiative" could be a mechanistic driver to enhance soil fertility and improve soil-(plant) health for ensuring food production in world rice agriculture facing land degradation and climate change impacts, which could be assisted by biochar from crop residue in an approach of circular economy. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB), caused by the fungal pathogen Fusarium graminearum , is a destructive and widespread wheat disease. Chemical fungicides are becoming less effective at reducing the disease severity of FHB, and there is a need to find a more effective, low-cost natural product. A by-product of the pyrolysis of wheat straw is a condensate known as wheat straw vinegar, which was hypothesized to be an effective F. graminearum inhibitor in wheat. The organic and mineral compositions of wheat straw vinegar were analyzed. The results of GC–MS indicated that the major organic compounds in wheat straw vinegar are phenolics and acetic acid. The main inorganic elements in the liquid were K, Ca, S and Mg. A bio-test of wheat straw vinegar showed strong antifungal activity on F. graminearum growth and production of deoxynivalenol (DON) with an EC 50 (concentration for 50% of maximal effect) value of 3.1 μl ml−1. Field tests showed that the application of wheat straw vinegar diluted 200-fold significantly decreased the wheat FHB infection rate and DON content by 66% and 69%, respectively. The control efficacy of wheat straw vinegar at a dilution of 200-fold was similar to that of typical chemical fungicide applications. The use of wheat straw vinegar may increase farmers' income by reducing the net fungicide costs. Therefore, wheat straw vinegar has high potential as a natural fungicide for the control of FHB and can reduce the dependence on synthetic fungicides. Unlabelled Image • Wheat straw vinegar inhibited F. graminearum growth and deoxynivalenol production. • Wheat straw vinegar has a high potential as natural fungicide to the control of FHB • Using of wheat straw vinegar increase farmers' income by reducing the fungicide cost. • Recycling wheat straw vinegar may benefit the pyrolysis industry in China. [ABSTRACT FROM AUTHOR]

[Display omitted] • Wheat straw, rice husk, pig manure, and oyster shell were used for co-pyrolysis. • Co-pyrolysis promoted syngas heat value and biochar characteristics. • Co-pyrolysis biochar was superior to limestone for soil remediation. • Application of COPB could be financially viable due to yield increase of cabbage. Co-pyrolysis is a potentially effective method for both biomass waste management and multi-functional biochar-based product design. It involves the thermochemical decomposition of biomass waste under anoxic conditions, which can reduce the cost of disposal and produce biochar with beneficial properties. Herein, this study aimed to investigate the properties and environmental applications of biochar from single- and mixed- feedstocks of wheat straw, rice husk, pig manure, and oyster shell at 450 ℃, respectively. A pot experiment with Chinese cabbage was carried out to compare the effects of biochars with limestone on soil Cd and Pb immobilization at two harvest periods. The results indicated that co-pyrolysis of various biomasses exhibited synthetic effects on promoting the calorific value of syngas and enhancing the quality of produced biochar. The pot experiment revealed a significant promotion on soil pH, soil organic matter, cation exchange capacity, and soluble Ca, which consequently reduced Cd and Pb availability. In contrast with limestone treatment, soil amendment with single biomass-derived and co-pyrolysis-derived (COPB) biochars had a significant positive impact on soil fertility and microbial biomass. Application of COPB at a 0.5% dosage consistently and most effectively enhanced the shoot biomass, increased leaf Vitamin C content but reduced leaf content of nitrate and heavy metals in both harvests. Using COPB for soil remediation would be financially visible due to the enhancement of crop yield. Therefore, this study proposes a strategy for targeted enhancement of the functions of biochar derived from co-pyrolysis of selected biomass waste for soil remediation and agricultural production. [ABSTRACT FROM AUTHOR]

Dicyandiamide (DCD) could reduce composting nitrogen (N) losses, but the decomposes at high temperatures limited its efficacy, which might be mitigated by co-application with biochar (BC) and wood vinegar (WV). Our study revealed that DCD alone or co-applied with BC and WV did not reduce N 2 O emissions during the composting of chicken manure and wheat straw. However, it significantly decreased NH 3 and CH 4 emissions by 22.6–45.6% and 53.8–85.6%, respectively, equivalent to a 24.1–44.8% reduction in GWP compared to the control. Furthermore, the combined use of DCD with BC and WV enhanced total N content by 5.6–36.6%, increased the compost accumulation temperature by 3.8–6.1%. DCD alone addition increased the compost dissolved organic matter (DOM) content by 12.2%, and when coupled with BC and WV, it enhances the biological index value to promote new DOM generation. DCD combined with BC could increase the final humus content of compost, thereby enhancing its quality, which approach also produced greater economic benefits (266.3 CNY t−1), compared to conventional composting. In conclusion, co-application of DCD with BC and WV in composting not only reduces the emission of NH 3 , N 2 O and CH 4 , but also increases the compost fertility and provides more economic benefits. [Display omitted] • DCD was alone or co-applied with BC and WV into composting. • DCD effectively reduced gaseous N losses during composting. • DCD plus BC reduced composting NH 3 volatilization by 45.6%. • All DCD-amended treatments lowered the GWP of composting by 24.1–44.8%. • DCD plus BC amended composting yields the highest net benefits. [ABSTRACT FROM AUTHOR]

• N from the urea was bound strongly by the functionalised surfaces of the biochar. • Biochar-mineral urea composite reduced the N leaching in soil. • Biochar-mineral urea composite was more effective on the retention of NH 4 +-N. • Biochar-mineral urea composite increased maize root growth and N use efficiency. Over use of N fertilizers, most commonly as urea, had been seriously concerned as a major source of radiative N (Nr) for severe environment impacts through leaching, volatilization, and N 2 O emission from fertilized croplands. It had been well known that biochar could enhance N retention and use efficiency by crops in amended croplands. In this study, a granular biochar-mineral urea composite (Bio-MUC) was obtained by blending urea with green waste biochar supplemented with clay minerals of bentonite and sepiolite. This Bio-MUC material was firstly characterized by microscopic analyses with FTIR, SEM-EDS and STEM, subsequently tested for N leaching in water in column experiment and for N supply for maize in pot culture, compared to conventional urea fertilizer (UF). Microscopic analyses indicated binding of urea N to particle surfaces of biochar and clay minerals in the Bio-MUC composite. In the leaching experiment over 30 days, cumulative N release as NH 4 +-N and of dissolved organic carbon (DOC) was significantly smaller by >70% and by 8% from the Bio-MUC than from UF. In pot culture with maize growing for 50 days, total fresh shoot was enhanced by 14% but fresh root by 25% under Bio-MUC compared to UF. This study suggested that N in the Bio-MUC was shown slow releasing in water but maize growth promoting in soil, relative to conventional urea. Such effect could be related mainly to N retention by binding to biochar/mineral surfaces and partly by carbon bonds of urea to biochar in the Bio-MUC. Therefore, biochar from agro-wastes could be used for blending urea as combined organo/mineral urea to replace mineral urea so as to reduce N use and impacts on global Nr. Of course, how such biochar combined urea would impact N process in soil-plant systems deserve further field studies. [ABSTRACT FROM AUTHOR]

Biochar soil amendment has been increasingly recommended for enhancing soil fertility and crop productivity while reducing greenhouse gas emissions in agricultural soils. However, a clear understanding of the cost benefits and longevity of the positive effects over long term would be a prerequisite for large scale biochar production and application in agriculture. In this study, the long-term effects of a single biochar amendment on soil fertility, crop yield and greenhouse gas emissions were assessed in a six-year field experiment of a fertile rice paddy from Southwest China. The field trial was established in 2010 and was managed under a rice-winter wheat rotation system throughout six years until 2016. The experiment employed a nested design with biochar soil amendment at application rates of 0, 20 and 40 t ha−1 without N fertilization, and 150 kg ha−1 with N fertilization, respectively. Soil properties and crop yields were measured and the emissions of CH 4 and N 2 O were monitored during the rice cultivation period in the 1st, 2nd and 5th year since 2010. Soil pH, organic carbon, total N and available potassium content were all increased under biochar amendment and persisted throughout the six years. However, grain yields across the years were generally not affected by biochar amendment except a yield increase in 2015. This grain yield increase (18.3%) was reported in the wheat season of 2015, when biochar had been applied at 40 t ha−1 in plots along with N fertilizer. Biochar amendment reduced N 2 O emissions from the rice paddies only for the first two seasons following the single amendment. In conclusion, a single but high rate of biochar amendment provided limited and temporary benefits for improving grain yields and reduction of greenhouse gases in the fertile paddy soil. • Long-term lasting effects of a single biochar amendment were investigated; • Biochar provided limited and temporary benefits for grain production; • Biochar addition improved soil fertility and this effect could last at least for 6 years. • Soil fertility improvement with biochar addition did not lead to rice yield increase. • Reduction effect of N 2 O emission with biochar only lasted two rice seasons. [ABSTRACT FROM AUTHOR]

While metal immobilization had been increasingly reported with biochar soil amendment (BSA), changes in microbial activity and nitrogen (N) transformation in metal contaminated croplands following biochar addition had been insufficiently addressed. In a field experiment, a Pb/Cd contaminated Inceptisol from North China was amended to topsoil with wheat straw biochar at 0 (CK), 20 (C1) and 40 t ha −1 (C2). The changes within two years following BSA were tested in microbial biomass and respiration, and in abundance of N transforming microbial communities and their activities. Corresponding to the results of decreased soil extractable Cd and Pb, significant reductions in q CO 2 were found in rhizosphere and bulk soil only under C2 in the first year. The potential nitrification activity was significantly increased by 20–71%, along with an increase in ammonium (by 7–21%) and nitrate (by 21%–70%) concentration, with BSA compared to CK. Meanwhile, N 2 O production activity was slightly increased (by up to 20%) but N 2 O reduction activity greatly enhanced (by up to 84%), with a higher ratio of nosZ /( nirS  +  nirK) , under C2 in rhizosphere in both wheat seasons. Whereas, such changes were not remarkable in bulk soil. Moreover, microbial communities were less respondent to biochar in the second year following the addition. Therefore, microbial growth and functioning for N transforming and cycling in metal contaminated soils could be largely improved with BSA at 40 t ha −1 . Of course, studies are still deserved to mimic the long term changes with biochar in N cycling of the metal contaminated dry croplands. [ABSTRACT FROM AUTHOR]

Cd is normally associated with sulfide and Fe oxides in flooded paddy soil. The mechanisms of biochar enhanced Cd immobilization by promoting Fe transformation and sulfide formation are unclear. Rape straw biochar (RSB) pyrolyzed at 450 °C (LB) and 800 °C (HB) was added to Cd-contaminated paddy soil at 1% (LB1, HB1) and 2% (LB2, HB2) doses. The results showed that Fe/Mn oxide–Cd (Fe/Mn–Cd) and free Fe oxide (Fe d) concentrations decreased in the first 12 days and then rose, while Fe2+ in pore water (W–Fe2+) tended to rise first and then fall. The electron transfer rate of soil in the HB2 treatment was 4.9-fold higher than that in the treatment without biochar (CK). Fe oxide reduction was enhanced by RSB, with a maximum increase in W–Fe2+ by 62.1% in HB2 on Day 12. The negative correlation between W–Fe2+ and Fe d showed that Fe2+ promoted the reformatted of seconded Fe minerals after Day 12, and the Fe d in the HB2 treatments increased by 31.5% in this period. RSB addition also promoted the reformation of poorly crystallized Fe oxide (Fe o) by increasing soil pH, which increased by 17.2% and 15.1% on average in the LB2 and HB2 treatments, respectively, compared to CK. Compared to Day 7, the increased rate of Fe/Mn–Cd on Day 30 in RSB was approximately twice that of CK. Compared to the molybdate group, the maximum decrease in CaCl 2 –Cd was 29.1% in LB2 on Day 12. LB2 increased SO 4 2− and acid-volatile sulfide concentrations by 6.9- and 4.1-fold, respectively, compared to CK. These results suggested that RSB, particularly HB, promoted more Cd adsorption in Fe minerals by increasing Fe hydroxylation and recrystallization processes. LB increased the contribution of sulfide to Cd immobility. [Display omitted] • HB with higher electron exchange capacity markedly promoted Fe oxides reduction. • Higher Fe2+ in HB treatment promoted Cd adsorption during Fe recrystallization. • Biochar facilitated formation of poorly-crystallized Fe by increasing soil pH. • LB increased the contribution of S to Cd immobilization by forming more sulfide. [ABSTRACT FROM AUTHOR]

While biochar use for soil amendment has been widely tested in world agriculture, little is known on crop production, greenhouse gases (GHG) emissions and economic performance of biochar used as compound fertilizer (BCF) combined with chemical nutrients. Using a field experiment in a low fertility Inceptisol from North China Plain, changes under different combinations with BCF in maize ( Zea mays L.) growth, in grain yield and in GHGs emission were examined, as well as economical net farm income impact was analyzed. The treatments included: No fertilizer (Blank), inorganic compound fertilizer in 100% N dose (ICF-N) as control, combination of BCF and ICF in 100% N dose (BCFj-N, 40% of N derived from BCF) and in 80% N dose (BCFj-Nr, 50% of N derived from BCF) as well as BCF in 100% N dose (BCF-N, all N derived from BFC). Soil properties, agronomic traits and grain yield were measured at harvest while soil GHG emissions monitored across the whole growing season as well as cost-benefit analysis performed using the sale prices of all fertilizer inputs and grain outputs, for a single maize production cycle. Results showed that BCF significantly increased grain yield by 10.7% and carbon efficiency by 46.2%% of maize production, compared to the ICF. Meanwhile, BCF with full N provided exerted a 43.1% increase in nitrogen agronomic use efficiency, a 12% increase in net income and in cost efficiency, over the ICF. However, the fertilization partly combined with BCF did not exert positive effects. These benefits of BCF fertilization could be attributed partly to soil improvement especially of moisture regime and phosphorus supply for maize growth, apart from its potential to slow nutrient release for prolonged supply to plant nutrition. Our findings suggest that biochar compound fertilizers can substitute chemical fertilizers for maize production in North China and allow farmers to receive higher net income via increased yields. [ABSTRACT FROM AUTHOR]

Poplar plantations have been established around the world to provide timber or fuelwood and to control erosion in degraded areas. The objective of this study was to investigate the effects of converting croplands to long-term hybrid poplar ( Populus × euramericana cv. I-72) plantations for 10, 15 and 20 years on soil bacterial and fungal communities and on their relationships with soil organic carbon (SOC) mineralization. Overall, the results indicated that the long-term hybrid poplar plantations increased soil pH, SOC, total N and moisture contents and decreased dissolved organic carbon (DOC), NH 4 + and NO 3 − contents compared to that on the cropland. There were lower cumulative amounts of CO 2 respired and SOC mineralization rates in the hybrid poplar plantation soils compared to that of the cropland. The hybrid poplar plantation with 20 years caused a greater fungal internal transcribed spacer (ITS) gene copy number and a lower bacterial 16S rRNA gene copy number and dehydrogenase and β-glucosidase activities compared to that in the cropland soils. As indicated by Illumina MiSeq sequencing, the establishment of hybrid poplar plantations harbored distinct soil bacterial and fungal communities, which were strongly correlated with specific soil properties. We further found that the SOC mineralization rate was positively correlated to the bacterial abundance and the relative abundances of Actinobacteria and Bacteroidetes, whereas negatively correlated to the fungal abundance. This study suggested that the long-term hybrid poplar plantation reduced SOC mineralization, causing changes in habitats that favor fungal community growth and shifts in bacterial community composition to more facultative and/or obligate anaerobes and less microbes that are capable of decomposing recalcitrant carbon, which may help enhance SOC accumulation in soil and mitigate climate change. [ABSTRACT FROM AUTHOR]

While numerous studies both in laboratory and field have showed short term impacts of biochar on soil microbial community, there have been comparatively few reports addressing its long term impacts particular in field condition. This study investigated the changes of microbial community activity and composition in a rice paddy four years after a single incorporation of biochar at 20 and 40 t/ha. The results indicated that biochar amendment after four years increased soil pH, soil organic C (SOC), total N and C/N ratio and decreased bulk density, particularly for the 40 t/ha treatment compared to the control (0 t/ha). Though no significant difference was observed in soil basal respiration, biochar amendment increased soil microbial biomass C and resulted in a significantly lower metabolic quotient. Besides, dehydrogenase and β-glucosidase activities were significantly decreased under biochar amendment relative to the control. The results of Illumina Miseq sequencing showed that biochar increased α-diversity of bacteria but decreased that of fungi and changed both bacterial and fungal community structures significantly. Biochar did not change the relative abundances of majority of bacteria at phylum level with the exception of a significant reduction of Actinobacteria, but significantly changed most of bacterial groups at genus level, particularly at 40 t/ha. In contrast, biochar significantly decreased the relative abundances of Ascomycota and Basidiomycota by 11% and 66% and increased the relative abundances of Zygomycota by 147% at 40 t/ha compared to the non-amended soil. Redundancy analysis (RDA) indicated that biochar induced changes in soil chemical properties, such as pH, SOC and C/N, were important factors driving community composition shifts. This study suggested that biochar amendment may increase microbial C use efficiency and reduce some microorganisms that are capable of decomposing more recalcitrant soil C, which may help stabilization of soil organic matter in paddy soil in long term. [ABSTRACT FROM AUTHOR]

Analyzing the fractionation of cadmium (Cd) and lead (Pb) could provide key information to identify how wheat straw biochar (WBC) affects the bioavailability of Cd and Pb in contaminated soils. The fractionations of Cd and Pb were extracted from amended paddy soil according to the approach by European Community Bureau of Reference (BCR). Total Cd and Pb concentrations in contaminated paddy soil were decreased by 7.5–23.3% and 3.7–19.8% with WBC application during five years, respectively. The Cd was distributed primarily in the exchangeable (∼50%) and carbonate (>30%) fractions, and Pb was the mainly carbonate-bound fraction (∼70%). The exchangeable fractions concentration of Cd and Pb were significantly decreased by 8.0–44.6% and 14.2–50.3% during five years. The residual fractions were increased by 4.0–32.4% (Cd) and 14.9–39.6% (Pb). The percentage of exchangeable Cd fractions decreased by 1.2–6.9%, but the incensements of 1.7–7.2% and 1.3–2.2% were observed in carbonate and residual fractions for Cd. Similarly, the percentage of exchangeable Pb fractions decreased by 0.3–1.6%, though the carbonate and residual fraction were increased by 1.2–2.9% and 1.4–12.2%. The changes of Cd and Pb fractions were mainly due to the abundant functional groups and complex structures in WBC, which could improve soil microstructure and increase soil pH and soil organic matter. [ABSTRACT FROM AUTHOR]

Soil degradation is an increasing threat to the sustainability of agriculture worldwide. Use of biochar from bio-wastes has been proposed as an option for improving soil fertility, degraded land restoration, and mitigating the greenhouse gas emissions associated with agriculture. Over the past 10 years, there have been hundreds of research studies on biochar from which it may be possible to determine appropriate methods for use of biochar to improve sustainable agriculture. To address potential gaps in our understanding of the role of biochar in agriculture, in this paper are reviewed the studies of 798 publications of field-, greenhouse- and laboratory-based biochar amendment soil experiments conducted as of August, 2015. Here we report the findings from a quantitative assessment. The majority of published studies have been performed in developed countries in soils that are less impaired than those found in many developing countries. The majority of the works involves laboratory and greenhouse pot experiments rather than field studies. Most published studies on biochar have used small kiln or lab prepared biochars rather than commercial scale biochars. And, most studies utilize wood and municipal waste feedstocks rather than crop residues though the later are often available in agriculture. Overall, the lack of well-designed long-term field studies using biochar produced in commercial processes, may be limiting our current understanding of biochar’s potential to enhance crop production and mitigate climate change. We further recommend greater alliance between researchers and biochar production facilities to foster the uptake of this important technology at a global scale. [ABSTRACT FROM AUTHOR]

Fast accumulation of soil organic matter (SOM) following forest restoration shifted from cropland has been widely reported, but how the pools and molecular composition change across soil aggregate fractions remains unclear. In this study, undisturbed topsoil (0–10 cm) samples were collected across a decadal chronosequence of forest stands (RL10, RL20 and RL40) restored for 10, 20 and 40 years following maize cropland (CL) abandonment in a karst terrain of Guizhou, Southwest China. SOM changes were explored using the size and density fractionation of water-stable aggregates, 13C isotopic signalling and biomarker analyses as well as 13C solid-state NMR assays. Compared to that of CL, SOM content was increased by 24%, 79% and 181%, mass proportion of macroaggregates increased by 136%, 179% and 250%, and particulate organic matter (POM) increased by 13%, 108% and 382%, respectively at RL10, RL20 and RL40. With biomarker analyses, the relative abundances of plant-derived organics (lignin, cutin, suberin, wax and phytosterols), mostly protected in aggregates, increased, while those of microbe-derived OC, predominantly mineral bound, decreased in response to prolonged forest restoration. Calculated as per the Shannon diversity index (H'), changes in SOM pool complexity and molecular diversity were parallel to the SOM accumulation trend. The pool size ratio of POM to MAOM (mineral-associated organic matter) and the molecular abundance ratio of PL (plant-derived lipids) to ML (microbe-derived lipids) appeared to be indicative of SOM accumulation following forest restoration. With prolonged forest restoration, the topsoil OM shifted from microbial MAOM dominance to plant-derived POM dominance. Furthermore, the great topsoil OM enhancement in restored forest stands was shaped by pool complexity and molecular diversity changes with the complex interactions among plant-microbial-mineral assemblages in the karst topsoil. Both the pool complexity and molecular diversity of SOM should be considered in addressing carbon sequestration with forest restoration concerning the functioning of soil ecosystems and services under global change pressures. [Display omitted] • SOM pool and composition analysed in a karst soil chronosequence of forest restoration from cropland. • SOM storage and soil aggregation greatly enhanced following 40 years forest restoration. • SOM shifted from microbial MAOM dominated to plant-derived POM dominated with prolonged restoration. • Pool ratio of POM to MAOM and abundance ratio of plant- to microbe- derived lipids depict SOM accumulation with restoration. • Changes in SOM pool complexity and molecular diversity were parallel to SOM accumulation trend. [ABSTRACT FROM AUTHOR]

• Ragweed and horseweed were directly pyrolyzed to biochars without modification. • The properties and sorption capacity of biochars varied with pyrolysis temperature. • RB450 showed unprecedented adsorption capacity for both Cd and Pb. • RB450 was characterized by better adsorption capacity than most reported biochars. • Precipitation and cation exchange were important mechanisms for Cd and Pb sorption. Global expansion of invasive plant species has caused serious ecological and economic problems. Two such invasive species, ragweed and horseweed, were pyrolyzed at temperatures of 350, 450 and 550 ℃ for biochar production (RB350, RB450, RB550 and HB350, HB450, HB550). The biochars produced were used for Cd(Ⅱ) and Pb(Ⅱ) removal in aqueous solutions. The results indicated that the properties of the biochars varied with pyrolysis temperature, which further affected their adsorption performance. The maximum adsorption capacity of RB450 for Cd(Ⅱ) (139 mg·g−1) and Pb(Ⅱ) (358.7 mg·g−1) was much higher than that shown in previous studies. The immobilized Cd(Ⅱ) and Pb(Ⅱ) fraction on RB450, RB550, HB450 and HB550 was mainly attributable to the acid soluble and non-available fractions. These findings suggested that pyrolysis of invasive plants at 450 ℃ could not only be an option to control invasive plants but also could be of benefit in using biochar as excellent adsorbent. [ABSTRACT FROM AUTHOR]

Biochar-based compound fertilizers (BCF) and amendments have proven to enhance crop yields and modify soil properties (pH, nutrients, organic matter, structure etc.) and are now in commercial production in China. While there is a good understanding of the changes in soil properties following biochar addition, the interactions within the rhizosphere remain largely unstudied, with benefits to yield observed beyond the changes in soil properties alone. We investigated the rhizosphere interactions following the addition of an activated wheat straw BCF at an application rates of 0.25% (g·g−1 soil), which could potentially explain the increase of plant biomass (by 67%), herbage N (by 40%) and P (by 46%) uptake in the rice plants grown in the BCF-treated soil, compared to the rice plants grown in the soil with conventional fertilizer alone. Examination of the roots revealed that micron and submicron-sized biochar were embedded in the plaque layer. BCF increased soil Eh by 85 mV and increased the potential difference between the rhizosphere soil and the root membrane by 65 mV. This increased potential difference lowered the free energy required for root nutrient accumulation, potentially explaining greater plant nutrient content and biomass. We also demonstrate an increased abundance of plant-growth promoting bacteria and fungi in the rhizosphere. We suggest that the redox properties of the biochar cause major changes in electron status of rhizosphere soils that drive the observed agronomic benefits. Unlabelled Image • Biochar-based fertilizer (BCF) is known to enhance crop yields and soil properties. • Wheat straw BCF was applied to the soil to investigate rhizosphere interactions. • There was an increase in rice yield, and N (40%), P (46%), Mg, K and Na uptakes. • Micron and submicron-sized biochar were embedded in the plaque layer. • Biochar increased soil Eh, which resulted in greater plant nutrient content. [ABSTRACT FROM AUTHOR]