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To explore the effects of biochar application on CO2 and CH4 emissions as well as the temperature response of CO2 emissions, a 1-year experiment was conducted with three treatments (control; CF, chemical fertilizer only; BCF, biochar combined with chemical fertilizer) in a vegetable field. The results showed that (1) compared with CF, short-term application of biochar significantly enhanced the cumulative CO2 emissions by 27.5% from a soil–plant system by increasing the soil microbial biomass (e.g., MBC) and C substrates (e.g., SOC); (2) lowest emissions of CH4 were observed in the BCF treatment, and an increase in CH4 consumption and reduced competition with NH4+ may be responsible for the significant reduction in CH4 source strength in biochar-amended soil; and (3) activation energy (Ea) was identified as an important factor influencing the temperature sensitivity (Q10) of CO2 emissions. Fertilization (CF and BCF) reduced the average Q10 and Ea values of CO2 emissions by 9.0–26.7% and 23.5–10.1%, respectively, relative to the control. In addition, the average Ea value in the BCF treatment (51.9 kJ mol−1) was significantly higher than those in the control and CF treatments. The increase in Q10 and Ea values following biochar application possibly contributed to the supplementation of limited labile C and nutrients but highly resistant C following biochar application. Soil pH and crop cultivation may play key roles in influencing the change in Ea. Our study concludes that biochar amendment increased CO2 emissions and temperature response of CO2 emission from the soil–plant system while reducing CH4 emissions. [ABSTRACT FROM AUTHOR]

Biochar is an effective method for increasing soil carbon (C) sequestration and nitrogen (N) supply under continuous monocropping. To investigate the impact of biochar placement methods on soil C and N, a one-year field experiment with five treatments was conducted including control, mineral fertilizers only (F), biochar hole placement (BFH; biochar applied to the soil layer at 5–10 cm) + F, biochar band placement (BFB; biochar applied to the soil layer at 15–20 cm) + F, and biochar band and hole placement + F (BFBH). The results showed that, regardless of the placement method, biochar application increased soil total organic C (TOC) and C pool management index by 6.9–39.7% and 4.1–36.1%, respectively, especially for dissolved organic C (DOC; 6.9–51.3%), readily oxidizable C (ROC; 2.4–46.4%), and microbial biomass C (MBC; 10.4–41.7%). Single biochar placement methods significantly influenced DOC, MBC, and ROC contents of both soil layers in the rank order of BFH ≈ BFBH > BFB at 0–15 cm and BFB ≈ BFBH > BFH at 15–30 cm. Soil TN and microbial biomass N (MBN) mainly accumulated at the site of biochar placement. The increased soil TOC:TN and MBC:N ratios under biochar treatments promoted inorganic N immobilization and reduced the loss of ammonium N and nitrate N (NO3−-N) through leaching at the early stage of tobacco growth. Biochar-adsorbed N was remobilized at a later period (vigorous growth stage and maturity), possibly causing the slow decrease in NO3−-N content. Additionally, soil C and N pools were significantly influenced by the main effects of soil layer and growth stage. Overall, biochar application increased soil C and N pools and inorganic N supply through N remobilization. However, the increased labile organic C content and microbial activity may prevent C sequestration in biochar-amended soils. [ABSTRACT FROM AUTHOR]

Carbon-fixing functional strain-loaded biochar may have significant potential in carbon sequestration given the global warming situation. The carbon-fixing functional strain Bacillus cereus SR was loaded onto rice straw biochar pyrolyzed at different temperatures with the anticipation of clarifying the carbon sequestration performance of this strain on biochar and the interaction effects with biochar. During the culture period, the content of dissolved organic carbon (DOC), easily oxidizable organic carbon, and microbial biomass carbon in biochar changed. This finding indicated that B. cereus SR utilized organic carbon for survival and enhanced carbon sequestration on biochar to increase organic carbon, manifested by changes in CO 2 emissions and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) enzyme activity. Linear regression analysis showed that the strain was likely to consume DOC on 300 °C biochar, although the Rubisco enzyme activity was higher. In contrast, the strain had a higher carbon sequestration potential on 500 °C biochar. Correlation analysis showed that Rubisco enzyme activity was controlled by the physical structure of the biochar. Our results highlight the differences in the survival mode and carbon sequestration potential of B. cereus SR on biochar pyrolyzed at different temperatures. • Carbon-fixing strain Bacillus cereus SR survived on biochar by using organic carbon compositions of biochar. • Increase in organic carbon fractions of biochar by RubisCO enzyme of strain. • The strains changed the pore size structure of biochar. • Physical properties of biochar limited the function of carbon-fixing strain. [ABSTRACT FROM AUTHOR]

Ferromanganese oxide biochar composite (FMBC) is an efficient remediation material for cadmium -contaminated soils. However, the effect of FMBC under varied water managements on the remediation of Cd-polluted soil is unclear. In this study, we conducted both incubation and field experiments to investigate the combined effects of corn-stover-derived biochar modified with ferromanganese on the immobilization and uptake of Cd by rice under continuous aerobic (A), aerobic-flooded (AF), and flooded-aerobic (FA) water management regimes. The results showed that loading iron-manganese significantly increased the maximum sorption capacity (Q m) of Cd on FMBC (50.46 mg g−1) due to increased surface area, as compared to the pristine biochar (BC, 31.36 mg g−1). The results revealed that soil Eh and pH were significantly affected by FMBC and it's synergistic application with different water regimes, thus causing significant differences in the concentrations of DTPA-extractable Cd under different treatments. The lowest DTPA-extractable Cd content (0.28–0.46 mg−1) was observed in the treatment with FMBC (2.5 %) combined FA water amendment, which reduced the content of available Cd in soil by 2.63–28.4 %. Moreover, the treatments with FMBC-FA resulted the proportion of residual Cd increased by 22.2 % compared to the control. Variations in the content and fraction of Cd had a significant influence on its accumulation in the rice grains. The FMBC-FA treatments reduced the Cd concentration in roots, shoots and grains by 37.97 %, 33.98 %, and 53.66 %, respectively, when compared with the control. Predominantly because of the reduction in Cd biological toxicity and the improved soil nutrient content, the combined application increased the biomass and yield of rice to some extent. Taken together, the combination of the Fe-Mn modified biochar and flooded-aerobic water management may potentially be applied in Cd-polluted soil to mitigate the impacts of Cd on rice production. [Display omitted] • Iron-manganese biochar (FMBC) remarkably increased the sorption capacity of Cd(II). • FMBC combined flooded-aerobic mode (FA) improved soil nutrients with incubation time. • FA facilitated the release of Fe2+/Mn2+ from FMBC and decreased Cd availability. • FMBC-FA reduced Cd accumulation in rice grains statistically under field condition. • An optimized coupling strategy for minimizing Cd pollution is proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new concept for utilization corn stalk by coupling anaerobic fermentation and pyrolysis. • An anaerobic fermentation step was used to further ferment corn stalk silage. • Fermented liquid feed was prepared by spontaneously fermentation. • Biochar derived from non-fermented residue showed improved physic-chemical property. • Biologically modified biochar is an effective adsorbent for Cd removal from water. The recycling of agricultural waste is a global challenge to the sustainable development of agriculture. By using corn stalks, we studied the feasibility of combining anaerobic fermentation and pyrolysis processes to produce both fermentated liquid feed and biologically modified biocharas cadmium adsorbents. Anaerobic ensiling enhanced the biodegradation of corn stalks by increasing crude protein and reducing fiber contents. After 24-h anaerobic fermentation, corn stalks silage was decomposed into the liquid filtrate and non-fermented residue. Fermented liquid feed (FLF) was prepared by storing feed and liquid filtrate (1:4.0, wt/wt) in a closed tank at 20 °C for 4 days, which showed desired properties (pH < 4.5, lactic acid bacteria greater than 9.0 lg cfu g−1, lactic acid greater than 100 mmol L-1). The non-fermented residue was pyrolyzed at 500 °C to prepare biologically modified biochar (BCB24). In comparison with pristine biochar produced from corn stalks (CB), anaerobic ensiling and anaerobic fermentation significantly increased the surface area, oxygen-containing functional groups, as well as mineral components in BCB24. The maximum sorption capacity of Cd(II) for BCB24 was 2.1 times of CB, suggesting that BCB24 is an effective adsorbent for Cd(II) removal from water. Our results indicated that coupling anaerobic fermentation and pyrolysis technology can significantly improve the efficiency of corn stalks recycling. [ABSTRACT FROM AUTHOR]

Biologically modified biochars derived from digestion residue of corn straw silage at different pyrolysis temperature (300–700 °C) were prepared for removing Cd from water. Compared with the pristine biochar derived from corn straw (CB), transabdominal transformation of corn straw silage (TCB) significantly increased surface area (4.24–56.58 m2 g−1), oxygen-containing functional group (C O C, Mg O, Si O) and mineral components (CaCO 3 , KCl). The sorption isotherms could be well described by Langmuir model, the kinetic data was best fitted by the Pseudo second order model. The maximum sorption capacity (Q m) obtained from Langmuir model for TCB700 (175.44 mg g−1) was 3 times of CB700 (56.82 mg g−1). Precipitation with minerals, ion exchange and complexation with oxygen-containing functional groups were the main mechanisms of Cd(II) sorption on TCB. These results imply that biologically modified biochar derived from digestion residue of corn straw silage at ≥600 °C is an effective sorbent for Cd removal from water. Unlabelled Image • Transabdominal transformation significantly increased surface area of biochar derived from digestion residue of corn straw silage • Pyrolysis temperature affect the sorption capacity of Cd(II) on transabdominal transformation modified biochar (TCB) • TCB made at ≥600 °C has a high sorption capacity for Cd(II) • Cd(II) sorption on the TCB fits a pseudo second order and Langmuir model. • Precipitation, ion exchange, and complexation mechanisms dominated Cd(II) sorption on TCB. [ABSTRACT FROM AUTHOR]

• Low-pyrolysis-temperature biochar (CB300) increased total nitrogen in N-poor soil. • CB300 increased nif H gene abundance, nitrogenase activity and Azotobacter abundance. • Changes of electrical conductivity led to the difference in diazotrophic community. • The consumption of DOC improved nitrogenase activity, nif H abundance and Azotobacter. • Soil available molybdenum was positively associated with soil nitrogenase activity. Free-living nitrogen fixation (FNF) is an important input of nitrogen to minimise the use of inorganic nitrogen fertiliser in agricultural ecosystems, but knowledge regarding response of FNF to biochar amendment is still limited. A microcosm study was performed to investigate changes in soil nitrogen content and FNF efficiency for calcareous purple soil applied with biochars prepared at 300 °C (CB300) and 600 °C (CB600). After 56 d of incubation, both CB300 and CB600 applied at any rates significantly (P < 0.01) increased soil total nitrogen (TN) concentrations relative to the controls. However, the soil TN is higher in the CB300 treatment group than in the CB600 group, especially for biochar applied at a 2% rate. Moreover, the concentrations of different N forms (NH 4 +, NO 3 −, microbial biomass nitrogen, and dissolved organic nitrogen) increased with biochar addition during the incubation, among which the peak value of NO 3 − was lagging behind NH 4 +. The acetylene reduction activity (ARA) as well as nif H abundance significantly increased in soil applied with 2% of biochars and peaked at day 56. Notably, the maximum values of ARA and nif H abundance were ~50% greater in soil applied with CB300 than CB600. Further analysis on the soil diazotrophic community composition showed that Azotobacter , Bradyrhizobium , and Skermanella were the most dominant genera. The proportion of Azotobacter, reported as free-living diazotroph, reached the maximum in soil amended with 2% of CB300 at day 56. The redundancy analysis indicated that electrical conductivity was the main factor leading to the difference in diazotrophic community among treatments. Besides, the rapid consumption of dissolved organic carbon (DOC) in CB300 treatment group facilitated soil diazotrophic proliferation, and finally led to the increase of ARA. Increased pH and abundant sulfur in soil applied with biochar promoted the concentrations of available molybdenum, which was positively related with the abundance of Azotobacter. Overall, our study provided clear evidence that application of low-pyrolysis-temperature biochars in calcareous soils greatly contributes to FNF and increased soil N accumulation. [ABSTRACT FROM AUTHOR]

• Subsurface flow was the major runoff pathway in the study sloping land. • Surface flow dominated P transport, subsurface flow dominated TN and NO 3 − transport. • Biochar and fertilizations increased subsurface flow runoff flux. • Biochar treatment showed higher P runoffs in subsurface flow than NPK fertilizations. Nitrogen (N) and phosphorus (P) loss in runoffs has been a serious problem in China due to the amount of chemical fertilizer currently applied to farmland. Biochar has been used as a soil amendment for increasing nutrient retention, water holding capacity, and crop yield. However, little is known about the influence of biochar on the runoff erosion from both surface flow and subsurface flow, especially in sloping regions. Experimental runoff plots were, therefore, set up on Entisols in a sloping farmland, involving four treatments: control (CT), conventional NPK fertilization (CF, based on local practices), optimum NPK fertilization (OF, based on the recommendation from local agriculture committee), and biochar combined with 85% of optimum NPK fertilizer (BF). The effects of the four treatments on the runoff fluxes, sediment yields and the runoff coefficients, as well as the N (ammonium (NH 4 +), nitrate (NO 3 −) and total N (TN)) and P (phosphate (PO 4 3-), total P (TP), dissolved TP (DTP), particulate P (PP)) losses via both surface runoff (i.e., surface flow, 0–20 cm, ploughed layer) and subsurface runoff (i.e., subsurface flow, 20–60 cm, non-ploughed layer) were all monitored and evaluated from April 2018 to September 2019. Results show that, in this sloping farmland, subsurface flow was the main process of runoff and dominated N transport, but surface flow dominated P transport. The three fertilization treatments reduced the runoff erosion by surface flow, while increasing it from subsurface flow (p < 0.05). Compared with two NPK fertilizations, BF treatment significantly increased the total sediment yield, subsurface runoff flux and subsurface runoff coefficient. Among all three fertilization treatments, the differences of grain yields are found not significant (except for the 4th crop). In surface flow, biochar addition increased the loss flux of NH 4 + and P fractions, but reduced the loss flux of NO 3 − with the comparison of the CF and OF treatments. In subsurface flow, biochar addition didn't significantly changed the runoff of N fractions, but increased P runoffs, especially for TP and PP runoffs (p < 0.05). Overall, the risk of N and P loss, and runoff erosion through subsurface flow in biochar incorporated Entisols sloping farmland needs be highlighted. [ABSTRACT FROM AUTHOR]