Biochar decreases the efficacy of the nitrification inhibitor nitrapyrin in mitigating nitrous oxide emissions at different soil moisture levels.

Unprecedented increases in agricultural nitrous oxide (N2O) emissions in recent years have caused substantial environmental pollution that leads to ozone depletion and global warming. Application of biochar and/or nitrification inhibitors (NIs) has the potential to reduce N2O emissions; however, it is not clear how biochar application may affect the efficacy of NI in reducing nitrification rates, soil enzyme activities, and N2O emissions under different soil moisture regimes. We conducted a 60-day laboratory incubation experiment to study the effects of manure biochar and nitrapyrin (as a NI) on N2O emissions from a urea fertilized soil with either 60 (low) or 80% (high) water-filled pore space (WFPS). Nitrification rates were significantly affected by biochar × NI × WFPS and biochar × WFPS interactions. Biochar initially increased and then decreased the rates, resulting in 45.2 and 26.6% (P < 0.001 for both) overall reductions in low and high WFPS, respectively while NI reduced the rates only in the first 10 days at 60% WFPS. Biochar decreased (P < 0.001) and NI increased (P = 0.007) ß-1,4-N-acetyl glucosaminidase activities while urease activities were increased (P < 0.001) by biochar across WFPS. Biochar had significant interaction with NI in cumulative N2O emissions with the efficacy of NI being reduced when co-applied with biochar. Cumulative N2O emissions were greater at high than at low WFPS; the emissions were decreased by biochar at 60% WFPS and NI at both 60 and 80% WFPS. We conclude that biochar reduces efficacy of nitrapyrin in mitigating N2O emissions and their effects on net nitrification rates, enzyme activities and N2O emissions are dependent on soil moisture level.

Biochar decreases and nitrification inhibitor increases phosphorus limitation for microbial growth in a wheat-canola rotation.

Agricultural management practices affect microbial populations and ecoenzymatic activities; however, the effect of these practices on ecological stoichiometry relating the elemental ratio of resources to microbial biomass is poorly understood. In a 2-year field study, we assessed the effects of biochar and nitrapyrin (a commonly used nitrification inhibitor (NI)) on the ecological stoichiometry and microbial nutrient limitation in a wheat (Triticum aestivum L.)-canola (Brassica juncea L.) rotation. This study used a 3 × 2 factorial design that included two treatments: (i) biochar with three levels: no biochar addition (BC0), and biochar added at 10 (BC10) and 20 t ha-1 (BC20), and (ii) NI with two levels: without (NI0) and with NI (NI1). Soil microbial biomass carbon (C), nitrogen (N) and phosphorus (P) were increased by biochar application, regardless of the application rate, but were not affected by NI application. Biochar increased and NI decreased ß-1,4-glucosidase, ß-1,4-N-acetyl glucosaminidase and acid phosphatase (P < 0.05) with subsequent changes in ecoenzymatic stoichiometry. Ecoenzymatic stoichiometry analysis showed microbial P limitation relative to N in the studied area irrespective of the treatment, with contrasting effects of biochar (decreasing) and NI (increasing) on the vector angle of ecoenzymatic stoichiometry (P = 0.037 and 0.043, respectively). Biochar applied at 20 t ha-1 decreased the threshold elemental ratio of C:P at which microbial growth switches between nutrient and C limitations, suggesting a shift towards C relative to nutrient (P) limitation. This study concludes that biochar produced from manure compost can be useful in increasing microbial growth by alleviating P limitations in a wheat-canola rotation.

Activation methods increase biochar's potential for heavy-metal adsorption and environmental remediation: A global meta-analysis.

Removal of heavy metals (HMs) by adsorption on biochar's surface has shown promising results in the remediation of contaminated soil and water. The adsorption capacity of biochar can be altered by pre- or post-pyrolysis activation; however, the effect of activation methods on biochar's adsorption capacity varies widely. Here, we conducted a meta-analysis to identify the most effective methods for activation to enhance HM removal by biochar using 321 paired observations from 50 published articles. Activation of biochar significantly improves the adsorption capacity and removal efficiency of HMs by 136 and 80 %, respectively. This study also attempts to find suitable feedstocks, pyrolysis conditions, and physicochemical properties of biochar for maximizing the effect of activation of biochar for HMs adsorption. Activation of agricultural wastes and under pyrolysis temperatures of 350-550 °C produces biochars that are the most effective for HM adsorption. Activation of biochars with a moderate particle size (0.25-0.80 mm), low N/C (<0.01) and H/C ratios (<0.03), and high surface area (> 100 m2 g-1) and pore volume (> 0.1 cm3 g-1) are the most desirable characteristics for enhancing HM adsorption. We conclude that pre-pyrolysis activation with metal salts/oxides was the most effective method of enhancing biochar's potential for adsorption and removal of a wide range of HMs. The results obtained from this study can be helpful in choosing appropriate methods of activations and the suitable choice of feedstocks and pyrolysis conditions. This will maximize HM adsorption on biochar surfaces, ultimately benefiting the remediation of contaminated environments.

Manure pellet, woodchip and their biochars differently affect wheat yield and carbon dioxide emission from bulk and rhizosphere soils.

Application of biochars produced by pyrolyzing organic residues to cropland has been proposed to be an effective approach to better use of organic residues, decrease soil greenhouse gas emission and increase soil fertility. However, the effect of biochar application on processes occurring in the bulk soil vs that in the rhizosphere is poorly understood. This study investigated the effects of manure pellet and woodchip biochars, as compared to that of unpyrolyzed (raw) manure pellet and woodchip, on plant grain yield, and soil respiration in the bulk and rhizosphere soils in a greenhouse experiment using the rhizobox technique. The raw manure pellet and woodchip and their biochars were applied to the soil at the rate of 57 t ha-1 and spring wheat (Triticum aestivum L. var. GP168) was grown in the rhizosphere compartment of the rhizobox. Soil amendment with raw manure pellet and its biochar significantly increased plant grain yield by 36.3 and 16.1%, as compared to the control (without amendment), while raw woodchip and its biochar applications significantly decreased plant grain yield. Manure pellet and woodchip biochars significantly reduced soil respiration from the rhizosphere by 24.6 and 29.7%, respectively, relative to the control, but not that from the bulk soil (P > 0.05). Relativized cumulative CO2 emission was significantly reduced by both manure pellet and woodchip biochars from rhizosphere and bulk soils. Dissolved organic carbon and nitrogen were increased (P < 0.01) in all soil amendment treatments in both bulk and rhizosphere soils, but microbial biomass carbon and nitrogen in the rhizosphere soil were reduced by manure pellet biochar application. We conclude that biochars produced from organic residues have differential impacts on processes in bulk and rhizosphere soils, and thus measurements based on bulk soil alone may result in erroneous conclusions about the effect of biochars on soil CO2 emission.

Pine sawdust biochar reduces GHG emission by decreasing microbial and enzyme activities in forest and grassland soils in a laboratory experiment.

This study investigated the effects of biochar soil amendment on greenhouse gas (GHG) emissions in soils. Pine (Pinus koraiensis Siebold & Zucc.) sawdust biochar was produced at 300 and 550°C with and without steam activation (coded as BC300-S, BC550-S, BC300 and BC550, respectively). They were applied to forest and grassland soils at 1.5% (w/w) rate in a 100-day laboratory incubation experiment. Application of BC550 significantly reduced cumulative CO2 emission from the forest soil by 16.4% relative to the control (without biochar application), but not from the grassland soil. Biochar application did not have significant effects on CH4 uptake from either soil. Application of BC550 and BC550-S reduced the cumulative N2O emission by 27.5 and 31.5%, respectively, in the forest soil and 14.8 and 11.7%, respectively, in the grassland soil, as compared to the control. The effects of BC300 and BC300-S on cumulative CO2 and N2O emission was not significant in both soils, except for the significant reduction in cumulative N2O emission from the forest soil by BC300-S. The effect of BC550 and BC550-S on N2O emission persisted until the end of the 100-day incubation indicating possible long-term effects of these biochars. We conclude that BC550 and BC550-S had the highest potential to reduce CO2 and N2O emission in the 100-day laboratory incubation experiment. These biochars should be tested in long-term field trials to confirm their potential for mitigating CO2 and N2O fluxes in real ecosystems with a relevant time frame.