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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]

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]

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]

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]

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]

Introduction: Spermatozoa motility is the critical parameter to affect the treatment outcomes during assisted reproductive technologies (ART), but its reproductive capability remains a little informed in condition of severe male factor infertility. This retrospective cohort study aimed to evaluate the effects of reduced sperm motility on the embryological and clinical outcomes in intra-cytoplasmic sperm injection (ICSI) treatment of severe oligozoospermia. Patients and Methods: 966 cycles (812 couples) of severe oligozoospermia diagnosed by spermatozoa count ≤ 5 × 106/mL and motile spermatozoa ≤ 2 × 106/mL were divided into four groups in according to the number of motile spermatozoa in one ejaculate on the day of oocyte retrieval (Group B—E). The control (Group A) was 188 cycles of moderate oligozoospermia with spermatozoa count > 5 × 106/mL and motile spermatozoa > 2 × 106/mL. All female partners were younger than 35 years of age. Logistic regression analyzed embryological outcomes (the rates of fertilization, cleavage and good-quality embryo) and clinical outcomes (the rates of pregnancy, implantation, early miscarriage and live birth). Quality of embryo transfer (ET) was divided into three classes as continuous factor to test the effects of embryo quality on clinical outcomes. Results: The reduction in the number of motile sperm in four groups of severe oligozoospermia gave rise to comparable inability of the fertilization (p < 0.001) and a decreased rate of good-quality embryo at Day 3 (p < 0.001) by compared to the control. The cleavage rate of the derived zygotes was similar to the control. ET classes significantly affected the clinical outcomes (p < 0.001). Class I ET gave rise to similar rates of clinical outcomes between five groups, but Class II and Class III ET retarded the rates of pregnancy, implantation and live birth and this particularly occurred in Group C, D and E. The rate of early miscarriage was not comparably different between groups. Overall rates in all groups were 41.26% clinical pregnancy, 25.74% implantation and 36.32% live birth, which gave live birth to 252 girls and 252 boys. Conclusions: The reduction of motile spermatozoa in severe oligozoospermia decreased the rates of fertilization and good-quality embryo. Obtaining and transfer of good-quality embryos was the good prognostic to achieve prospective clinical outcomes regardless of the severity of oligozoospermia. [ABSTRACT FROM AUTHOR]

Biochar addition to soil has been widely accepted as an option to enhance soil carbon sequestration by introducing recalcitrant organic matter. However, it remains unclear whether biochar will negate the net carbon accumulation by increasing carbon loss through CO 2 efflux from soil (soil respiration). The objectives of this study were to address: 1) whether biochar addition increases soil respiration; and whether biochar application rate and biochar type (feedstock and pyrolyzing system) affect soil respiration. Two series of field experiments were carried out at 8 sites representing the main crop production areas in China. In experiment 1, a single type of wheat straw biochar was amended at rates of 0, 20 and 40 t ha − 1 in four rice paddies and three dry croplands. In experiment 2, four types of biochar (varying in feedstock and pyrolyzing system) were amended at rates of 0 and 20 t ha − 1 in a rice paddy under rice-wheat rotation. Results showed that biochar addition had no effect on CO 2 efflux from soils consistently across sites, although it increased topsoil organic carbon stock by 38% on average. Meanwhile, CO 2 efflux from soils amended with 40 t of biochar did not significantly higher than soils amended with 20 t of biochar. While the biochars used in Experiment 2 had different carbon pools and physico-chemical properties, they had no effect on soil CO 2 efflux. The soil CO 2 efflux following biochar addition could be hardly explained by the changes in soil physic-chemical properties and in soil microbial biomass. Thus, we argue that biochar will not negate the net carbon accumulation by increasing carbon loss through CO 2 efflux in agricultural soils. [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]

BACKGROUND Salinity is a major stress threatening crop production in dry lands. A 2-year field experiment was conducted to assess the potential of a biochar product to alleviate salt-stress to a maize crop in a saline soil. The soil was amended with a compost at 12 t ha−1 of wheat straw biochar and poultry manure compost (BPC), and a diluted pyroligneous solution (PS) at 0.15 t ha−1 (BPC-PS). Changes in soil salinity and plant performance, leaf bioactivity were examined in the first (BPC-PS1) and second (BPC-PS2) year following a single amendment. RESULTS While soil salinity significantly decreased, there were large increases in leaf area index, plant performance, and maize grain yield, with a considerable decrease in leaf electrolyte leakage when grown in amendments. Maize leaf sap nitrogen, phosphorus and potassium increased while sodium and chloride decreased, leaf bioactivity related to osmotic stress was significantly improved following the treatments. These effects were generally greater in the second than in the first year. CONCLUSION A combined amendment of crop straw biochar with manure compost plus pyroligneous solution could help combat salinity stress to maize and improve productivity in saline croplands in arid/semi-arid regions threatened increasingly by global climate change. © 2014 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

While microbial nitrogen transformations in soils had been known to be affected by heavy metal pollution, changes in abundance and community structure of the mediating microbial populations had been not yet well characterized in polluted rice soils. Here, by using the prevailing molecular fingerprinting and enzyme activity assays and comparisons to adjacent non-polluted soils, we examined changes in the abundance and activity of ammonia oxidizing and denitrifying communities of rice paddies in two sites with different metal accumulation situation under long-term pollution from metal mining and smelter activities. Potential nitrifying activity was significantly reduced in polluted paddies in both sites while potential denitrifying activity reduced only in the soils with high Cu accumulation up to 1300 mg kg−1. Copy numbers of amoA (AOA and AOB genes) were lower in both polluted paddies, following the trend with the enzyme assays, whereas that of nirK was not significantly affected. Analysis of the DGGE profiles revealed a shift in the community structure of AOA, and to a lesser extent, differences in the community structure of AOB and denitrifier between soils from the two sites with different pollution intensity and metal composition. All of the retrieved AOB sequences belonged to the genus Nitrosospira, among which species Cluster 4 appeared more sensitive to metal pollution. In contrast, nirK genes were widely distributed among different bacterial genera that were represented differentially between the polluted and unpolluted paddies. This could suggest either a possible non-specific target of the primers conventionally used in soil study or complex interactions between soil properties and metal contents on the observed community and activity changes, and thus on the N transformation in the polluted rice soils. [ABSTRACT FROM AUTHOR]

Background: Biochar from pyrolysis of biomass amended in soils to improve nitrogen use efficiency for enhancing crop productivity and mitigate climate change in agriculture has been well documented. However, application for soil amendment of biochar at high rates could be challenged with cost-effectiveness for small-scale household farms. Results: This study, by field testing four organic/inorganic compound fertilizers of biochars pyrolysed via different biowastes compared with conventional chemical fertilizer in a rice paddy, evidenced that biochar compound fertilizer application at a much lower rate of N input ensured rice productivity by improving N use efficiency and reduced GHG emission in rice production. Conclusion: Use of biowaste-converted biochars for organic/inorganic compound fertilizer can be an option to achieve high productivity and low carbon intensity along with saving N nitrogen fertilizer use in Chinese rice 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]

Soil carbon stocks and sequestration have been given a lot of attention recently in the study of terrestrial ecosystems and global climate change. This review focuses on the progress made on the estimation of the soil carbon stocks of China, and the characterization of carbon dynamics of croplands with regard to climate change, and addresses issues on the mineralization of soil organic carbon in relation to greenhouse gas emissions. By integrating existing research data, China's total soil organic carbon (SOC) stock is estimated to be 90 Pg and its inorganic carbon (SIC) stock as 60 Pg, with SOC sequestration rates in the range of 20-25 Tg/a for the last two decades. An estimation of the biophysical potential of SOC sequestration has been generally agreed as being 2 Pg over the long term, of which only 1/3 could be attainable using contemporary agricultural technologies in all of China's croplands. Thus, it is critical to enhance SOC sequestration and mitigate climate change to improve agricultural and land use management in China. There have been many instances where SOC accumulation may not induce an increased amount of decomposition under a warming scenario but instead favor improved cropland productivity and ecosystem functioning. Furthermore, unchanged or even decreased net global warming potential (GWP) from croplands with enhanced SOC has been reported by a number of case studies using life cycle analysis. Future studies on soil carbon stocks and the sequestration potential of China are expected to focus on: (1) Carbon stocks and the sequestration capacity of the earths' surface systems at scales ranging from the plot to the watershed and (2) multiple interface processes and the synergies between carbon sequestration and ecosystem productivity and ecosystem functioning at scales from the molecular level to agro-ecosystems. Soil carbon science in China faces new challenges and opportunities to undertake integrated research applicable to many areas. [ABSTRACT FROM AUTHOR]

Abstract: Impacts of nutrient management on C mineralization and greenhouse gas (GHGs) emission from soils have been of much concern in global change. Using laboratory incubation, the production of CH4 and CO2 were studied from both bulk samples and the particle size fractions (PSF) of topsoil from a paddy under a long-term different fertilization trial (including non (NF), chemical without (CF) and with manure (CFM) fertilization, respectively) in the Tai Lake Region, China. Four PSFs (2000–200, 200–20, 20–2, <2μm) were separated from undisturbed samples collected after rice harvest by a low-energy ultrasonic dispersion procedure. Both the bulk samples and PSFs were incubated under submerged condition for 72 days. The concentration of CH4 and CO2 evolved during incubation were determined by gas chromatography. C mineralization rates ranged from 0.13 to 0.52mgCg−1 Cday−1, with different fertilizations and size of the PSFs, and were not correlated with C/N ratio. While CO2 production predominated over CH4 from C mineralization from both bulk samples and the size fractions, CH4 production played a predominant role in the total global warming potential (GWP) under all treatments. C mineralization of bulk soil was significantly higher under CF than under CFM and NF. CH4 production, however, was 3 times as under CFM and 27 times as under NF, indicating a tremendous effect of chemical fertilization alone on the total GWP. CO2 production from the PSFs differed from CH4 under a single treatment, which was notably from the coarse PSFs larger than 200μm. Higher C mineralization and CH4 production with a higher metabolic quotient under CF implicated a vulnerability of soil functioning of GHGs mitigation in the paddy receiving chemical fertilizers only. Thus, rational organic amendments should be undertaken for mitigating the climate change. [Copyright &y& Elsevier]