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Massive amount of food waste has been generated annually, posing a threat to ecological sustainability and the social economy due to current disposal methods. Urgent action is needed worldwide to convert the traditional pathway for treating food waste into a sustainable bioeconomy, as this will significantly benefit food chain management. This study explores the use of pyrolysis to produce different types of food waste biochars and investigates their adsorption capabilities for removing Cd2+ and Pb2+ in aqueous solution. The results indicated that co-pyrolysis biochar from fresh food waste and rice husk (FWRB) exhibited superior adsorption performance for Cd2+ (61.84 mg·g−1) and Pb2+ (245.52 mg·g−1), respectively. Pseudo-second-order kinetics (0.74 ≤ R2 ≤ 0.98) and Langmuir isotherms (0.87 ≤ R2 ≤ 0.98) indicated that the immobilized Cd2+ and Pb2+ on biochars were mainly attributed to the chemisorption, including precipitation with minerals (e.g., carbonates, silicates, and phosphate), complexation with functional groups (–OH), cation exchange (–COO−), and coordination with π-electrons. Furthermore, FWRB demonstrated reduced EC and Na content in comparison to food waste digestate biochar (FWDB) and food waste digestate co-pyrolysis with sawdust biochar (FWSB), with levels of Cd and Pb falling below China's current guideline thresholds. These findings suggested that co-pyrolysis of fresh food waste with rice husk could be applicable to the recycling of food waste into biochar products for heavy metal stabilization in contaminated water and soils. [ABSTRACT FROM AUTHOR]

The mechanisms of rape straw biochar that affect the fixation of cadmium (Cd) in paddy soil by influencing redox of iron and sulfur are unclear. Several anaerobic incubation experiments were carried out using Cd-contaminated paddy soils (LY and ZZ). Rape straw biochar at pyrolysis temperatures of 450 °C (LRSB) and 800 °C (HRSB) was selected as the soil remediation agent. The electron exchange capacity and electrical conductivity were higher in HRSB than those in LRSB. The lower pe + pH in HRSB enhanced Fe oxide reduction, with a maximum increase in Fe2+ of 46.0% in ZZ. Compared to treatment without biochar (CK), the poorly crystallized Fe oxide (Feo) in HRSB increased by 16.8% in ZZ. This induced Cd bound to Fe, and Mn oxides fraction (Fe-Mn Cd) increased by 42.5%. The SO42−-S content in LRSB was 4.6 times that of HRSB. LRSB addition increased acid-volatile sulfide by 46.4% and 48.9% in LY and ZZ soils, respectively, compared to CK. This resulted in an increase in sulfide's contribution to Cd fixation, with values rising from 24.2% to 37.8% in LY and 19.1% to 29.8% in ZZ. Overall, LRSB reduced Cd mobility by forming more sulfide, while HRSB increased Fe-Mn Cd by increasing Feo. [ABSTRACT FROM AUTHOR]

Microbial communities of soil aggregate-size fractions were explored with molecular and networking assays for topsoil samples from a clayey rice paddy under long-term fertilization treatments. The treatments included no fertilizer (NF) as control, chemical fertilizer only (CF), chemical fertilizer with swine manure (CFM), and chemical fertilizer with rice straw return (CFS). Following a wet-sieving protocol, water-stable aggregates were separated into size fractions of large macroaggregates (L-MacA, >2,000 μm), macroaggregates (MacA, 2,000–250 μm), microaggregates (MicA, 250–53 μm), fine microaggregates (F-MicA, 53–2 μm), and fine clay (F-Clay, <2 μm). Mass proportion was 32.3–38.2% for F-MicA, 23.0–31.5% for MacA, 19.0–23.1% for MicA, 9.1–12.0% for L-MacA, and 4.9–7.5% for F-Clay, respectively. The proportion of MacA was increased, but F-Clay was reduced by fertilization, whereas the mean weight diameter was increased by 8.0–16.2% from 534.8 μm under NF to 621.5 μm under CFM. Fertilization affected bacterial 16S rRNA and fungal 18S rRNA gene abundance in F-MicA and F-Clay but not in aggregates in size larger than 53 μm. However, bacterial and fungal community α-diversities and community structures were quite more divergent among the fertilization treatments in all size fractions. Organic carbon and gene abundance of bacteria and fungi were enriched in both L-MacA and MacA but depleted in F-Clay, whereas microbial Shannon diversity was rarely changed by fraction size under the four treatments. L-MacA and MacA contained more bacteria of r-strategists and copiotrophs, whereas F-MicA and F-Clay were demonstrated with a higher abundance of K-strategists and oligotrophs. Guilds of parasitic and litter saprotrophic fungi were enriched in F-MicA but depleted in L-MacA. Furthermore, most of bacterial and fungal operational taxonomic units were strongly interacted in L-MacA and MacA rather than in MicA and F-Clay. Thus, MacA acted as micro-hotspots enriched with functional and networked microbial communities, which were enhanced with organic/inorganic fertilization in the rice paddy. [ABSTRACT FROM AUTHOR]

Aims: Although elevated atmospheric CO2 and global warming are important climate factors that affect soil carbon sequestration and greenhouse gases emission from agricultural soils, it remains unclear how these factors affect the soil microbial communities that involved in nitrous oxide (N2O) emission. The objectives of this study were to evaluate the interactive effects of elevated CO2 and warming on soil microbial community and its relationship with soil N2O emission. Methods: Soil N2O emission was monitored in a Free-Air CO2 Enrichment facility equipped with warming during wheat growth season. The abundance and community composition of ammonia-oxidizing bacteria (AOB) and archaea (AOA) and denitrifiers (nirK, nirS and nosZ) in the rhizosphere were determined using real-time PCR and Illumina MiSeq sequencing technique. Results: Elevated CO2 increased N2O emission, the abundance of AOB and nirK, the concentration of rhizospheric soil organic carbon (SOC) and total nitrogen (TN); while it decreased the concentration of soil available phosphorus and potassium. Warming decreased soil pH, and the abundance of AOB, nirK and nosZ; and the effect of warming on soil N2O emission, SOC, TN and AOB abundance was significantly interacted with elevated CO2. Under elevated CO2, warming decreased soil N2O emission but increased the concentration of rhizosphere SOC and TN. Pyrosequencing showed that AOB, nirK, and nosZ community compositions were altered by elevated CO2 levels, and redundancy analyses further showed that variations in SOC, TN and pH determined these community compositions. Soil N2O emission was positively corelated with soil pH, the content of SOC and nitrate, and the abundance of AOB and nirK. Conclusions: Our results demonstrated that future climate change of elevated CO2 plus warming will not lead to a significant increase in agricultural soil N2O emission. Ammonia oxidizer (AOB) and denitrifier (nirK) are the key soil microbial community that regulate the response of soil N2O emission to elevated CO2 and warming. [ABSTRACT FROM AUTHOR]

Improving nitrogen (N) use efficiency (NUE) in crop plants is important to reduce the negative impact of excessive N on the environment. Although biochar‐blended fertilizer had been increasingly tested in crop production, the fate of fertilized N in soil and plant had not been elucidated in field conditions. In this study, a novel biochar‐blended urea (BU) was prepared by pelleting maize straw biochar, bentonite, sepiolite, carboxymethylcellulose sodium, and chitosan with urea (commercial urea without biochar [CU]). N fertilization in a winter wheat field was treated with BU and CU at both 265 kg N ha−1 (HL) and 186 kg N ha−1 (LN). Within a treatment plot, a microplot was fertilized with 15N‐labeled urea at a relevant N level. We investigated the influence of fertilizer management on biomass, grain yield, bioaccumulation of nutrient, soil properties, 15N isotopic abundance, and greenhouse gas emissions. Microscopic and spectroscopic analysis showed that micro/nanonetwork of biochar could bind N to form a loss control agglomerated particle, and organo‐mineral coatings on BU may protect N from quick release. Compared with CU, BU significantly increased grain yield by 13% and 38%, and grain N allocation by 19% and 55%, respectively, at HN and LN level. The total recovery of urea 15N in wheat plant (15N based NUE) was 32.8% under CU regardless of N rates but increased to 41.7% (HN rate) and 56.3% (LN rate) under BU. Whereas, the soil proportion (soil residual 15N) was 20.1% and 13.4% under CU but 32.5% and 18.8% under BU, in 0‐20cm topsoil, respectively, at HN and LN rate. Compared with the CU, BU had no effect on CO2 and CH4 emissions but significantly reduced the total N2O emission by 23%–28%. These important findings suggested that BU can be beneficial to uplift plant NUE to reduce reactive N loading but boost crop production. [ABSTRACT FROM AUTHOR]

Summary: Biochar amendment has been proposed as a promising means to increase carbon (C) sequestration and simultaneously benefit plant productivity. However, quantifying the assimilation and dynamics of photosynthetic C in plant–soil systems under biochar addition remains elusive.This study established two experimental factors involving biochar addition and nitrogen (N) fertilization to quantitatively assess the effect of biochar on photosynthetic C fate in a rice plant–soil system. The rice plants and soil samples were collected and analyzed after 6‐h pulse labeling with 13CO2 at the tillering, jointing, heading and ripening stages.Biochar did not affect the proportions of photoassimilated carbon‐13 (13C) allocations in plant–soil systems. Nevertheless, biochar enhanced the 13C contents in the shoot, root, and soil pools, especially when combined with N fertilization, and biochar increased the cumulative assimilated 13C contents in the shoot, root, and soil pools by 23%, 14% and 20%, respectively, throughout the whole growth stage. Moreover, biochar addition significantly enhanced the N use efficiency (NUE) by c. 23% at the heading and ripening stages.In summary, biochar increases the content of photoassimilated C in plant–soil systems by improving plant productivity via enhancing NUE, thus resulting in a higher soil C sequestration potential. [ABSTRACT FROM AUTHOR]

Although biochar amendment could increase crop yield globally, it remains unclear how biochar improves grain yield. A two-year field experiment was conducted to investigate the role of plant roots in promoting crop growth under biochar amendment. The field experiment, started in 2015, was conducted in a rainfed region of North China. We hypothesized that biochar increases maize yield by promoting root growth. In the first year (2015), maize grain yield increased by 23.9% and 25.3% under biochar application rate of 20 and 40 t ha−1, respectively. Biochar increased the biomass of maize stalk and root and their potassium uptake significantly. The root morphology of maize also improved significantly following biochar amendment. Yet, the double increase in biochar application rate did not lead to any additional grain yield increase. The grain yield was positively correlated with the maize ear size, the soil organic carbon content, the biomass of maize stalk and root and their K uptake. In the second year (2016), however, biochar had no effect on the root morphology and the grain yield was not affected. Here we show that biochar increases maize yield by increasing maize ear size directly and by promoting root growth and nutrient uptake indirectly. [ABSTRACT FROM AUTHOR]

As one of the most important nutrients for plant growth, phosphorus was often poorly available in soil. While biochar addition induced improvement of soil structure, nutrient and water retention as well as microbial activity had been well known, and the effect of biochar soil amendment (BSA) on soil phosphorus availability and plant P uptake had been not yet quantitatively assessed. In a review study, data were retrieved from 354 peer-reviewed research articles on soil available P content and P uptake under BSA published by February 2019. Then a database was established of 516 data pairs from 86 studies with and without BSA in agricultural soils. Subsequently, the effect size of biochar application was quantified relative to no application and assessed in terms of biochar conditions, soil conditions, as well as experiment conditions. In grand mean, there was a significant and great effect of BSA on soil available P and plant P uptake by 65% and 55%, respectively. The effects were generally significant under manure biochar, biochar pyrolyzed under 300 °C, soil pH <5 and fine-textured soil, and soils that are very low in available P. Being significantly correlated to soil P availability (R2=0.29), plant P uptake was mostly enhanced with vegetable crops of high biomass yield. Overall, biochar amendment at a dosage up to 10 t ha−1 could be a tool to enhance soil availability and plant uptake of phosphorus, particularly in acid, heavy textured P-poor soils. [ABSTRACT FROM AUTHOR]

Soil microbial necromass plays a critical role in soil organic C (SOC) sequestration, while the long-term response of microbial necromass to climate change remains largely unclear. Here, we used amino sugars as biomarkers and examined their variation after 8 years of continuous manipulation of elevated CO2 (eCO2), warming, and their combined interaction in a paddy soil. Our results showed that eCO2 increased the concentrations of all amino sugar compounds by 6.5–28.9% while warming had no effect on the accumulation of glucosamine and galactosamine but increased muramic acid concentration by 22.1–29.1%. Elevated CO2 increased the contribution of microbial necromass C to SOC storage, mainly by increasing fungal-derived C, whereas warming increased the bacterial-derived C proportion in SOC. Furthermore, the combined effect of eCO2 and warming yielded the highest total microbial necromass and SOC accumulation, although the ratio of fungal to bacterial necromass C in SOC remained unchanged. Structural equation models showed that root biomass had an indirect positive effect on total amino sugar concentration, mainly through increased microbial biomass, whereas N-acetylglucosaminidase activity had a direct negative effect on total amino sugar accumulation. These differential responses of microbial necromass to climate change may further alter the sequestration of SOC. This study is only based on one sampling time, and future research should involve more sampling times so as to have the temporal dynamics of the studied properties. Our findings emphasize the contribution of the microbial-derived C to soil C stock under long-term elevated CO2 and warming in a rice-wheat rotation system, which reveals an important mechanism of microbial-mediated C sequestration under climate change. [ABSTRACT FROM AUTHOR]

While biochar use in agriculture is widely advocated, how the effect of biochar on plant growth varies with biochar forms and crop genotypes is poorly addressed. The role of dissolvable organic matter (DOM) in plant growth has been increasingly addressed for crop production with biochar. In this study, a hydroponic culture of rice seedling growth of two cultivars was treated with bulk mass (DOM-containing), water extract (DOM only), and extracted residue (DOM-free) of maize residue biochar, at a volumetric dosage of 0.01, 0.05, and 0.1%, respectively. On seedling root growth of the two cultivars, bulk biochar exerted a generally negative effect, while the biochar extract had a consistently positive effect across the application dosages. Differently, the extracted biochar showed a contrasting effect between genotypes. In another hydroponic culture with Wuyunjing 7 treated with biochar extract at sequential dosages, seedling growth was promoted by 95% at 0.01% dosage but by 26% at 0.1% dosage, explained with the great promotion of secondary roots rather than of primary roots. Such effects were likely explained by low molecular weight organic acids and nanoparticles contained in the biochar DOM. This study highlights the importance of biochar DOM and crop genotype when evaluating the effect of biochar on plants. The use of low dosage of biochar DOM could help farmers to adopt biochar technology as a solution for agricultural sustainability. [ABSTRACT FROM AUTHOR]

Cadmium pollution in the environment is ubiquitous and can be a serious health issue. Crop straw-based biochar is a promising adsorbent, yet few studies have systematically examined the effects of both feedstock and pyrolysis temperature on biochar efficacy for cadmium (Cd) sorption. Sorption-desorption experiments were conducted to explore the mechanisms of Cd sorption for biochars derived from wheat straw (WSB), rape straw (RASB), soybean straw (SSB), and peanut straw (PSB) feedstocks, which were produced by pyrolysis at 450 °C and 650 °C. For biochars pyrolyzed at 450 °C, the sorption capacities varied as PSB>SSB>RASB≈WSB, while the order changed as RASB≈WSB>PSB>SSB for 650 °C biochars. With the increase in pyrolysis temperature, for wheat straw biochar and rape straw biochars, Cd sorption capacities increased by 72% and 63%, while there were 61% and 63% decreases for peanut straw biochar and soybean straw biochar, respectively. Compared to the non-legume straw biochars (WSB and RASB), legume straw biochars (SSB and PSB) have higher sorption capacities for Cd. Peanut straw biochar (PSB) produced at 450 °C was found to be the most promising adsorbent for cadmium. Examination of the sorbed biochars using a range of analytical techniques indicated that 450 °C PSB immobilized cadmium by precipitation with non-electrostatic adsorption. The precipitation of Cd on 450 °C PSB was mainly induced by cation exchange between Cd with mineral cations, which caused Cd complexation with carboxyl functional groups. [ABSTRACT FROM AUTHOR]

Application of iron (Fe)- and silica (Si)-enhanced biochar compound fertilisers (BCF) stimulates rice yield by increasing plant uptake of mineral nutrients. With alterations of the nutrient status in roots, element homeostasis (e.g., Fe) in the biochar-treated rice root was related to the formation of biominerals on the plaque layer and in the cortex of roots. However, the in situ characteristics of formed biominerals at the micron and sub-micron scale remain unknown. In this study, rice seedlings (Oryza sativa L.) were grown in paddy soil treated with BCF and conventional fertilizer, respectively, for 30 days. The biochar-induced changes in nutrient accumulation in roots, and the elemental composition, distribution and speciation of the biomineral composites formed in the biochar-treated roots at the micron and sub-micron scale, were investigated by a range of techniques. Results of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) showed that biochar treatment significantly increased concentrations of nutrients (e.g., Fe, Si, and P) inside the root. Raman mapping and vibrating sample magnetometry identified biochar particles and magnetic Fe nanoparticles associated with the roots. With Fe plaque formation, higher concentrations of FeOx− and FeOxH− anions on the root surface than the interior were detected by time-of-flight secondary ionization mass spectrometry (ToF-SIMS). Analysis of data from scanning electron microscopy energy-dispersive spectroscopy (SEM-EDS), and from scanning transmission electron microscopy (STEM) coupled with EDS or energy electron loss spectroscopy (EELS), determined that Fe(III) oxide nanoparticles were accumulated in the crystalline fraction of the plaque and were co-localized with Si and P on the root surface. Iron-rich nanoparticles (Fe–Si nanocomposites with mixed oxidation states of Fe and ferritin) in the root cortex were identified by using aberration-corrected STEM and in situ EELS analysis, confirming the biomineralization and storage of Fe in the rice root. The findings from this study highlight that the deposition of Fe-rich nanocomposites occurs with contrasting chemical speciation in the Fe plaque and cortex of the rice root. This provides an improved understanding of the element homeostasis in rice with biochar-mineral fertilization. [ABSTRACT FROM AUTHOR]

While high soil carbon stability had been well known for biochar‐amended soils, how conversion of crop residues into biochar and subsequent biochar amendment (BA) would favor microbial carbon use and carbon sequestration had not been clearly understood. In this study, topsoil samples were collected from an upland soil and a paddy soil, both previously amended with straw and straw‐derived biochar. These samples were incubated with 13C‐labeled maize residue (LMR) for 140 days to compare carbon mineralization, metabolic quotient (qCO2), and microbial carbon use efficiency (CUE) under laboratory incubation. 13C‐phospholipid fatty acid (13C‐PLFA) was used to trace the use of substrate carbon by soil microorganisms. Comparing to straw amendment (SA), BA significantly decreased the native soil organic carbon (SOC) mineralization rates by 19.7%–20.1% and 9.2%–12.0% in the upland and paddy soils, respectively. Meanwhile, total carbon mineralization from the newly added LMR was significantly decreased by 12.9% and 11.1% in the biochar‐amended soils, compared with the straw‐amended soils from the upland and paddy sites, respectively. Furthermore, compared to non‐amended soils, the qCO2 value was unchanged in straw‐amended soils, but was notably decreased by 15.2%–18.6% and 8.9%–12.5% in biochar‐amended upland and paddy soils, respectively. Microbial CUE was significantly greater in biochar‐amended soils than in straw‐amended soils due to the increasing dominance of fungi in carbon utilization. Compared to SA, BA increased CUE by 23.0% in the upland soil and 21.2% in the paddy soil. This study suggests that BA could outperform SA in the long term to enhance the biological carbon sequestration potential of both upland and paddy soils. This could be due mainly to biochar input as a special substrate to promote microbial community evolution and increase the fungal utilization of carbon substrates, especially for the soil with lower SOC levels. [ABSTRACT FROM AUTHOR]

While biochar soil amendment has been widely proposed as a soil organic carbon (SOC) sequestration strategy to mitigate detrimental climate changes in global agriculture, the SOC sequestration was still not clearly understood for the different effects of fresh and aged biochar on SOC mineralization. In the present study of a two‐factorial experiment, topsoil samples from a rice paddy were laboratory‐incubated with and without fresh or aged biochar pyrolyzed of wheat residue and with and without crop residue‐derived dissolved organic matter (CRM) for monitoring soil organic matter decomposition under controlled conditions. The six treatments included soil with no biochar, with fresh biochar and with aged biochar treated with CRM, respectively. For fresh biochar treatment, the topsoil of a same rice paddy was amended with wheat biochar directly from a pyrolysis wheat straw, the soil with aged biochar was collected from the same soil 6 years following a single amendment of same biochar. Total CO2 emission from the soil was monitored over a 64 day time span of laboratory incubation, while microbial biomass carbon and phospholipid fatty acid (PLFA) were determined at the end of incubation period. Without CRM, total organic carbon mineralization was significantly decreased by 38.8% with aged biochar but increased by 28.9% with fresh biochar, compared to no biochar. With CRM, however, the significantly highest net carbon mineralization occurred in the soil without biochar compared to the biochar‐amended soil. Compared to aged biochar, fresh biochar addition significantly increased the total PLFA concentration by 20.3%–33.8% and altered the microbial community structure by increasing 17:1ω8c (Gram‐negative bacteria) and i17:0 (Gram‐positive bacteria) mole percentages and by decreasing the ratio of fungi/bacteria. Furthermore, biochar amendment significantly lowered the metabolic quotient of SOC decomposition, thereby becoming greater with aged biochar than with fresh biochar. The finding here suggests that biochar amendment could improve carbon utilization efficiency by soil microbial community and SOC sequestration potential in paddy soil can be enhanced by the presence of biochar in soil over the long run. [ABSTRACT FROM AUTHOR]

Safe recycling of the growing amounts of municipal sewage sludge containing toxic metals had been critically challenged with the fast urbanization. In this study, we investigated soil amendment of municipal wastewater treatment (MSS) converted biochar for its recycling in agricultural soils. In a field experiment, unpyrolyzed (USS) and pyrolyzed municipal sewage sludge (PSS) was amended at 20 t ha−1 on dry base to a rice paddy before rice plantation, with a control without amendment. Grain yield and emission of non-CO2 potent greenhouse gases were examined as well as topsoil metal mobility and plant uptake determined throughout a rice-wheat rotation year. Compared to USS treatment, addition of PSS caused a significantly increased grain yield of rice by 35% but no change in grain yield of wheat following the rice season. No distinct difference was observed in grain concentration of major nutrients of N, P, and K between USS and PSS treatments. Compared to USS treatment, PSS treatment reduced CH4 emissions by 91.6% from soil and by 78.5% from ecosystem during rice-growing season. Whereas, PSS treatment led to a reduction of ecosystem N2O emissions by 70.8% relative to USS treatment during wheat-growing season. While both USS and PSS treatments slightly but insignificantly increased soil total content of heavy metals, PSS treatment reduced CaCl2-extractable Cd pool by 33~40% over USS treatment. Grain contents of Cd and Pb and Cd/Zn were markedly reduced under PSS over USS, without exceeding the Chinese state guideline limit. Carbon emission intensity was considerably (by over 20%) reduced for soil and ecosystem but unchanged for wheat soil, under PSS over USS. Thus, soil amendment of pyrolyzed sewage sludge could be a measure for climate smart soil and for safe grain production in rice agriculture. It deserves further study if repeated amendment could exert sustainable impacts on soil health and food security in the paddy. [ABSTRACT FROM AUTHOR]

Biochar soil amendment had been increasingly advocated for improving crop productivity and reducing carbon footprint in agriculture worldwide. However, the long-term benefits of biochar application with farming systems had not been thoroughly understood. This study quantified and assessed emergy, energy, and economic benefits of rice and wheat production throughout 6 rotation years following a single biochar amendment in a rice paddy from Southeastern China. Using the data from farm inventory, the quantified emergy indices included grain outputs, unit emergy value, and relative percentage of free renewable resources, environmental loading ratio, emergy yield ratio, and emergy sustainability index (ESI). The results indicated contrasting differences in these emergy values between biochar-amended and unamended production systems over the 6 years. The overall emergy efficiency of rice and wheat productions in biochar-amended system were higher by 11-28 and 15-47%, respectively, than that of unamended one of which the production being highly resource intensive. Moreover, ESI on average was 0.46 for rice and 0.63 for wheat in amended system, compared to 0.35 for rice and 0.39 for wheat in unamended one. Furthermore, over the 6 years following a single application, the ESI values showed considerable variation in the unamended system but consistently increasing in the amended system. Again, the biochar-amended system exerted significantly higher energy and economic return than the unamended one. Nonetheless, there was a tradeoff between rice and wheat in grain yield and net economic gain. Overall, biochar amendment could be a viable measure to improve the resilience of grain production while to reduce resource intensity and environment impacts in paddy soil from China. [ABSTRACT FROM AUTHOR]

Topsoil samples were collected from plots in a dry cropland in the North China Plain 3 years after a single incorporation of biochar at 20 and 40 t ha and analyzed for abundances and composition of microbial community and for respiration under controlled laboratory conditions at 15, 20, and 25 °C. The addition of biochar generally reduced soil respirations at the three temperatures and the temperature sensitivity (Q) at 15-20 °C. Biochar amendment significantly increased bacterial 16S rRNA gene abundances and fungal ITS gene diversity and induced clear changes in their community compositions due to improvements in soil chemical properties such as soil organic C (SOC) and available N contents and pH. Illumina Miseq sequencing showed that the relative abundances of Actinobacteria, Gammaproteobacteria, Firmicutes, and Alternaria within Ascomycota, capable of decomposing SOC, were significantly decreased under biochar at 40 t ha. The Q values at 15-20 °C were significantly correlated with fungal diversity and dehydrogenase activity. Our results suggest that after 3 years a single biochar amendment could induce a shift in microbial community composition and functioning towards a slower organic C turnover and stability to warming, which may potentially reduce soil C loss in dryland under climate warming in the future. [ABSTRACT FROM AUTHOR]

A field experiment was conducted in a Cd-contaminated rice paddy field to evaluate the effect of inorganic and organic metal stabilizers on Cd mobility and rice uptake. A dose of inorganic stabilizer of calcium hydroxide (CH), silicon slag (SS), and wheat straw biochar (BC) was amended respectively to topsoil before rice transplanting. Rice production was managed with the same water regime and fertilization practices consistently between treatments including a control without amendment. Samples of topsoil and rice plant were collected at rice harvest to analyze the Cd mobility and uptake by rice. Without affecting rice grain yield, the stabilizers significantly decreased CaCl-extractable Cd in a range of 44 to 75 % compared to the control, corresponding to soil pH changes under the different treatments. Accordingly, Cd concentrations both in rice tissue and in rice grain were very significantly decreased under these treatments. The decrease in rice Cd uptake was correlated to the decrease in extractable Cd, which was again correlated to soil pH change under the different treatments, indicating a prevalent role of liming effect by the amendments. While applied at a large amount in a single year, organic stabilizer of BC decreased Cd extractability by up to 43 % and Cd rice uptake by up to 61 %, being the most effective on Cd immobilization. However, the long-term effect on soil health and potential tradeoff effects with different stabilizers deserve further field monitoring studies. [ABSTRACT FROM AUTHOR]

Soil amendment of biochar (BSA) had been shown effective for mitigating greenhouse gas (GHG) emission and alleviating metal stress to plants and microbes in soil. It has not yet been addressed if biochar exerts synergy effects on crop production, GHG emission, and microbial activity in metal-polluted soils. In a field experiment, biochar was amended at sequential rates at 0, 10, 20, and 40 t ha, respectively, in a cadmium- and lead-contaminated rice paddy from the Tai lake Plain, China, before rice cropping in 2010. Fluxes of soil carbon dioxide (CO), methane (CH), and nitrous oxide (NO) were monitored using a static chamber method during the whole rice growing season (WRGS) of 2011. BSA significantly reduced soil CaCl extractable pool of Cd, and DTPA extractable pool of Cd and Pb. As compared to control, soil CO emission under BSA was observed to have no change at 10 t ha but decreased by 16-24 % at 20 and 40 t ha. In a similar trend, BSA at 20 and 40 t ha increased rice yield by 25-26 % and thus enhanced ecosystem CO sequestration by 47-55 % over the control. Seasonal total NO emission was reduced by 7.1, 30.7, and 48.6 % under BSA at 10, 20, and 40 t ha, respectively. Overall, a net reduction in greenhouse gas balance (NGHGB) by 53.9-62.8 % and in greenhouse gas intensity (GHGI) by 14.3-28.6 % was observed following BSA at 20 and 40 t ha. The present study suggested a great potential of biochar to enhancing grain yield while reducing carbon emission in metal-polluted rice paddies. [ABSTRACT FROM AUTHOR]

Quantifying the carbon footprint (CF) for crop production can help identify key options to mitigate greenhouse gas (GHG) emissions in agriculture. In the present study, both household and aggregated farm scales were surveyed to obtain the data of rice production and farming management practices in a typical rice cultivation area of Northern Jiangxi, China. The CFs of the different rice systems including early rice, late rice, and single rice under household and aggregated farm scale were calculated. In general, early rice had the lower CF in terms of land use and grain production being 4.54 ± 0.44 t CO-eq./ha and 0.62 ± 0.1 t CO-eq./t grain than single rice (6.84 ± 0.79 t CO-eq./ha and 0.80 ± 0.13 t CO-eq./t grain) and late rice (8.72 ± 0.54 t CO-eq./ha and 1.1 ± 0.17 t CO-eq./t grain). The emissions from nitrogen fertilizer use accounted for 33 % of the total CF on average and the direct CH emissions for 57 %. The results indicated that the CF of double rice cropping under aggregated farm being 0.86 ± 0.11 t CO-eq./t grain was lower by 25 % than that being 1.14 ± 0.25 t CO-eq./t grain under household farm, mainly due to high nitrogen use efficiency and low methane emissions. Therefore, developing the aggregated farm scale with efficient use of agro-chemicals and farming operation for greater profitability could offer a strategy for reducing GHG emissions in China's agriculture. [ABSTRACT FROM AUTHOR]

Rice growth and its resistance to pests had been often constrained by soil-silicon (Si) availability. The purpose of this study was to assess the potential of biochar soil amendment (BSA) to improve Si availability in paddy soils. A cross-site field trail with BSA was conducted in six locations with different climatic and crop-production conditions across S China. Plant-available Si content before field-trials establishment and after rice harvest, as well as Si content in rice shoot were determined. Varying with site conditions, plant-available Si content of soil was observed to increase significantly with BSA in most sites. Significant increase in rice shoot Si was detected in four out of the six sites, which was well correlated to the concurrent increase in soil pH under BSA treatment. This study demonstrates an important role of BSA to improve Si availability and uptake by rice mainly through increasing soil pH of the acid and slightly acid rice soils. [ABSTRACT FROM AUTHOR]

Background and aims: For the last decade, there has been an increasing global interest in using biochar to mitigate climate change by storing carbon in soil. However, there is a lack of detailed knowledge on the impact of biochar on the crop productivity in different agricultural systems. The objective of this study was to quantify the effect of biochar soil amendment (BSA) on crop productivity and to analyze the dependence of responses on experimental conditions. Methods: A weighted meta-analysis was conducted based on data from 103 studies published up to April, 2013. The effect of BSA on crop productivity was quantified by characterizing experimental conditions. Results: In the published experiments, with biochar amendment rates generally <30 t ha −1, BSA increased crop productivity by 11.0 % on average, while the responses varied with experimental conditions. Greater responses were found in pot experiments than in field, in acid than in neutral soils, in sandy textured than in loam and silt soils. Crop response in field experiments was greater for dry land crops (10.6 % on average) than for paddy rice (5.6 % on average). This result, associated with the higher response in acid and sandy textured soils, suggests both a liming and an aggregating/moistening effect of BSA. Conclusions: The analysis suggests a promising role for BSA in improving crop productivity especially for dry land crops, and in acid, poor-structured soils though there was wide variation with soil, crop and biochar properties. Long-term field studies are needed to elucidate the persistence of BSA’s effect and the mechanisms for improving crop production in a wide range of agricultural conditions. At current prices and C-trading schemes, however, BSA would not be cost-effective unless persistent soil improvement and crop response can be demonstrated. [ABSTRACT FROM AUTHOR]

Soil respiration, resulting in decomposition of soil organic carbon (SOC), emits CO2 to the atmosphere and increases under climate warming. However, the impact of heavy metal pollution on soil respiration in croplands is not well understood. Here we show significantly increased soil respiration and efflux of both CO2 and CH4 with a concomitant reduction in SOC storage from a metal polluted rice soil in China. This change is linked to a decline in soil aggregation, in microbial abundance and in fungal dominance. The carbon release is presumably driven by changes in carbon cycling occurring in the stressed soil microbial community with heavy metal pollution in the soil. The pollution-induced increase in soil respiration and loss of SOC storage will likely counteract efforts to increase SOC sequestration in rice paddies for climate change mitigation. [ABSTRACT FROM AUTHOR]