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The conversion of bio-wastes to useful products such as biochar provide a suitable option not only to minimize the mass of wastes, but also to use the biochar as soil amendment. In the present study, food waste biochar (FWB) and agricultural waste derived biochar (AB), either alone or in combination (FWB + AB), were tested for their effects on soil microbiological characteristics (soil enzymes, soil basal as well as substrate-induced respiration), plant growth and photosynthetic parameters. Four treatments were tested: control, FWB, AB and FWB + AB. The results indicated that the application of AB significantly enhanced the plant above ground and below ground fresh and dry biomass as compared to other amendments and control (+41 to +205% compared to control). The application of FWB enhanced the quantum yield of photosystem II (QY-max, +4% compared to control) and normalized difference vegetation index (NDVI, +13% compared to control). Moreover, the FWB application improved the soil dehydrogenase (DHA) activity (+24% compared to control). Furthermore, the soil basal respiration was found to be increased under AB application (+46% compared to control) and the substrate-induced respirations were relatively decreased, depicting negative effects of applied biochars on substrate-induced respirations. Thus, we concluded that the differential responses of observed crop and soil attributes might be related to the biochar specific effects on soil properties. [ABSTRACT FROM AUTHOR]

A field experiment was carried out to study the responses of soil respiration, soil C and N, composition of main microbial groups, enzyme activity, and microbial C source utilization to two organic amendments (i.e., straw and manure) added alone or combined with biochar for 9 months in an infertile soil. In comparison with the non-amended control, soil CO2 emission rates were significantly increased following straw and manure addition, but they were decreased by 19% and 36% on average when co-applied with biochar. Organic amendments significantly increased the size of labile C pool by 21%, total phospholipid-fatty acid (PLFA) concentrations by 32%, activities of α-glucosidase by 51%, β-glucosidase by 115%, β-D-cellobiosidase by 105%, β-xylosidase by 43%, phenol oxidase by 59%, and peroxidase by 91% on average relative to the non-amended control, whereas biochar co-application with organic amendments had no effect on soil PLFA concentrations but significantly decreased the enzyme activities by 38% and the sizes of labile C and N pools by 16% on average. The results of the substrate-induced respiration confirmed a lower capacity of biochar-treated soils to use the C sources of carbohydrates and carboxylic acids. Structural equation modeling indicated that the response of soil CO2 emission rates to organic amendment and biochar was directly linked to their effects on microbial activities. Therefore, our study demonstrated that biochar co-applied with straw or manure mitigated soil C loss by decreasing soil microbial activities. [ABSTRACT FROM AUTHOR]

Biochar has been proven to participate in the biotic reduction of hexavalent chromium (Cr(VI)) in environment since its involvement may accelerate the extracellular electron transfer (EET). However, roles of the redox-active moieties and the conjugated carbon structure of biochar in this EET process remain unclear. In this study, 350 °C and 700 °C were selected to produce biochar with more O-containing moieties (BC350) or more developed conjugated structures (BC700), and their performances in the microbial reduction of soil Cr(VI) were investigated. Our results showed that BC350 presented a 241% increase of Cr(VI) microbial reduction after 7-day incubation, much higher than that of BC700 (39%), suggesting that O-containing moieties might play more important roles in accelerating the EET process. Biochar, especially BC350 could serve as an electron donor for microbial anaerobic respiration, but its contribution (73.2%) as an electron shuttle for EET was dominant to the enhanced Cr(VI) reduction. The positive correlation between electron exchange capacities (EECs) of pristine and modified biochars and the corresponding maximum reduction rates of Cr(VI) evidenced the crucial role of redox-active moieties in electron shuttling. Moreover, EPR analysis suggested the nonnegligible contribution of semiquinone radicals in biochars to the accelerated EET process. This study demonstrates the crucial role of redox-active moieties, i.e. , O-containing moieties in mediating the EET process during the microbial reduction of Cr(VI) in soil. Findings obtained will advance the current understanding of biochar as an electron shuttle participating in the biogeochemical processes of Cr(VI). [Display omitted] • Biochar could enhance the microbial reduction of Cr(VI) in soil extract. • Biochar as an electron shuttle for EET induced the enhanced Cr(VI) reduction. • The maximum reduction rate was positively correlated with EEC of biochar. • Semiquinone-type radicals of biochar contributed to the acceleration of EET. • Redox-active moieties on biochar determined the electron-shuttling ability. [ABSTRACT FROM AUTHOR]

Biochar is rapidly gaining worldwide interest as an agro-technology for increasing soil health and carbon storage. This study investigated the physicochemical characteristics and impact on soil microbes of biochar amendments from three feedstock sources: date palm leaves (D), mesquite plants (M) and sludge compost (S.C.); pyrolyzed at 450 ℃, 600 ℃ and 750 ℃. Scanning electron microscopy images showed an apparent pore size increase with increasing pyrolysis temperature. The increase in pyrolysis temperature decreased O-H and C-O bonds and increased the proportion of C-C bonds, as obtained from the Fourier transform infrared spectroscopy studies. Thermostability was highest at a pyrolysis temperature of 750 ℃, with distinct thermal decomposition profiles for each of the three feedstock materials used, as indicated by the dynamic thermal gravimetric analysis. The SC biochars showed the highest mineral content (45–66%) with significantly higher water-soluble and total concentrations of mineral elements. The SC samples also showed the presence of possible soil contaminants such as Pb and As, and its use as a soil amendment is not recommended, even though the SC at 450 ℃ was the only nonalkaline biochar in this study. The M feedstock produced biochar with the highest surface area (600 m2 g−1) and carbon content based on loss on ignition (94.98%); nevertheless, the M biochar reduced soil microbial enumeration and respiration. This reduction increased with increasing pyrolysis temperature. Therefore, the M biochar feedstocks are not recommended for improving soil health and may be tested in the future as a microbial inhibitor for soil-borne plant pathogens. Considering the physicochemical properties and the biochar impact on soil, D at 600 ℃ was the best biochar selected for further studies as a soil amendment. The large differences in biochar physicochemical properties and their effect on soil microbes observed in this study suggest that the feedstock type and pyrolysis temperatures must be considered during biochar amendment production for improving soil health in arid-land agroecosystems. • The effect biochar on soil microbes was remarkably affected by feedstock and production temperatures. • The increase in pyrolysis temperature decreased O-H and C-O and increased the of C-C bonds. • Thermostability was highest at the highest pyrolysis temperatures. • The biochars from sludge showed low organic content and presence heavy metal contaminants. • Biochar from mesqute plants reduced soil microbial enumeration and respiration. [ABSTRACT FROM AUTHOR]

Climate change presents an agricultural challenge in the Southeastern USA with implications for maintaining environmental quality. The objective of this study was to assess climate change impacts and adaptation practices (biochar and irrigation) simulated with the Environmental Policy Integrated Climate (EPIC) model on nitrate-N (NO 3 -N) losses, microbial respiration (MR) and soil organic carbon (SOC) in the Southeastern USA. The EPIC model was used to assess the impacts of climate change and adaptations on NO 3 -N losses in leachate and runoff from the soil profile (0–100 cm), loss of soil C via MR (0–100 cm), and impacts on SOC stocks (0–10 cm) for representative farms growing C 3 and C 4 crops within ten Southeastern USA states. The adaptations explored were annual biochar applications and irrigation. Historical baseline (1979–2009) and future (2041–2070) climate scenarios were used for simulations with CO 2 concentrations of 360 ppm and 500 ppm, respectively. Four regional climate models (RCMs), nested within global climate models (GCMs) for their boundary conditions, simulated changes in air temperatures, precipitation, and solar radiation. Climate change increased simulated NO 3 -N losses in leaching and runoff by 40–80%, compared to historical baseline scenarios that was attributed to overall increased annual precipitation under three of the four RCM_GCM models. For the C 4 crops, NO 3 -N leaching and runoff losses were 16–47% and 31–45% lower than for the C 3 crops, respectively. Biochar applications reduced NO 3 -N leaching in the West region during 2066–2070 under the RCM3_CGCM3 model. The differences in MR between the C 4 and C 3 crops ranged from 3 to 75%. SOC increased under C 4 crops and when biochar was applied. We concluded that inclusion of C 4 crops in crop rotations and the applications of biochar under wetter climate scenarios may be a promising adaptation strategy to reduce NO 3 -N losses and increase SOC content in the soils of the Southeastern USA. This study represents one of the first attempts to assess the effectiveness of climate change adaptations such as the agricultural use of biochar and irrigation. The findings from this study strongly contribute to our understanding of potential climate change impacts on a region's agriculture and resulting environmental footprint. This information may be used by the scientific community along with decision and policy makers working on conceptual and practical technologies to mitigate the impacts of climate change on agriculture and the environment. [Display omitted] • Climate change presents a challenge for agriculture in the Southeastern USA with implications to environmental quality • The objective of this study was to assess effects of climate change and adaptations on nitrate loss, microbial respiration and soil organic carbon • Future nitrate loss increased by 40–80% and was lower with biochar and under C 4 than C 3 crops; carbon was higher under C 4 crops and with biochar • Inclusion of C 4 crops in rotations and biochar use under wetter climate scenarios will allow to reduce nitrate loss and increase soil organic carbon • These findings may be used by decision/policy makers working on technologies to mitigate climate change impacts on agriculture and environment [ABSTRACT FROM AUTHOR]