• Energy Research

AbstractImproving 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.

AbstractWhile 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.

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 40t/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 40t/ha treatment compared to the control (0t/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 40t/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 40t/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.

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.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.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.

AbstractWhile 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.

AbstractSoil organic carbon (SOC) sequestration with enhanced stable carbon storage has been widely accepted as a very important ecosystem property. Yet, the link between carbon stability and bio-activity for ecosystem functioning with OC accumulation in field soils has not been characterized. We assessed the changes in microbial activity versus carbon stability along a paddy soil chronosequence shifting from salt marsh in East China. We used mean weight diameter, normalized enzyme activity (NEA) and carbon gain from straw amendment for addressing soil aggregation, microbial biochemical activity and potential C sequestration, respectively. In addition, a response ratio was employed to infer the changes in all analyzed parameters with prolonged rice cultivation. While stable carbon pools varied with total SOC accumulation, soil respiration and both bacterial and fungal diversity were relatively constant in the rice soils. Bacterial abundance and NEA were positively but highly correlated to total SOC accumulation, indicating an enhanced bio-activity with carbon stabilization. This could be linked to an enhancement of particulate organic carbon pool due to physical protection with enhanced soil aggregation in the rice soils under long-term rice cultivation. However, the mechanism underpinning these changes should be explored in future studies in rice soils where dynamic redox conditions exist.

Impacts of climate variability and climate change are on the rise in China posing great threat to agriculture and rural livelihoods. Consequently, China is undertaking research to find solutions of confronting climate change and variability. However, most studies of climate change and variability in China largely fail to address farmers' perceptions of climate variability and adaptation. Yet, without an understanding of farmers' perceptions, strategies are unlikely to be effective. We conducted questionnaire surveys of farmers in two farming regions, Yifeng, Jiangsu and Qinxi, Anhui achieving 280 and 293 responses, respectively. Additionally, we used climatological data to corroborate the farmers' perceptions of climate variability. We found that farmers' were aware of climate variability such that were consistent with climate records. However, perceived impacts of climate variability differed between the two regions and were influenced by farmers' characteristics. In addition, the vast majorities of farmers were yet to make adjustments in their farming practices as a result of numerous challenges. These challenges included socioeconomic and socio-cultural barriers. Results of logit modeling showed that farmers are more likely to adapt to climate variability if contact with extension services, frequency of seeking information, household heads' education, and climate variability perceptions are improved. These results suggest the need for policy makers to understand farmers' perceptions of climate variability and change in order to formulate policies that foster adaptation, and ultimately protect China's agricultural assets.

ABSTRACTBiochar amendments in rice‐wheat systems are sustainable for reducing GHGs (greenhouse gases) and improving soil health but the widespread adoption of biochar faces economic challenges. To address limitation, a novel biochar‐based urea was formulated for environmental and cost advantages. A pot experiment within a rice‐wheat rotation was conducted to evaluate comparative effects of biochar‐based urea (CKBU), biochar + urea (BCU), and biochar‐based urea + biochar (BCBU) over conventional mineral fertilizer (CKU) on soil ammonia (NH3) volatilization, GHG emissions, soil structure, and crop productivity. Furthermore, fertilizer N fate was tracked using the 15N isotope during wheat season. The results indicated that compared to CKU, CKBU, BCU, and BCBU treatments significantly mitigated NH3 volatilization by 22%–31% during the rice season, and a 19% reduction was observed under the BCBU treatment during the wheat season due to the response of N‐cycling microorganisms. Regarding GHG emissions, the CKBU, BCU, and BCBU treatments significantly decreased the global warming potential (GWP) value by 49%–55% during the rice season and by 26%–45% during the wheat season, compared to CKU. Additionally, CKBU enhanced 15N use efficiency by 29% during wheat season, without affecting the rice season. The economic performance indicated that applying BU alone offered a net economic benefit, whereas biochar amendment led to a net economic loss. However, biochar amendment improved SOC and aggregation structure, with a significant increase in macroaggregate distribution over 50% compared to CKU and CKBU. Therefore, BU with small portions of biochar can be as effective in reducing NH3 emissions and mitigating GHG emissions as the use of a large quantity of biochar. Additionally, the BCBU did not show additional synergistic benefits regarding emission reduction or yield enhancement. Therefore, shifting biochar to BU could be a cost‐effective approach to achieving sustainable productivity in rice‐wheat crop rotation systems.