Effects of biochar and other amendments on the physical properties and greenhouse gas emissions of an artificially degraded soil

Biochar amendment with fertilizers increases peanut N uptake, alleviates soil N2O emissions without affecting NH3 volatilization in field experiments

Biochar application to soil is currently widely advocated for a variety of reasons related to sustainability. However, the synergistic effects of biochar combined with mineral or organic fertilizer on soil N₂O emissions, NH₃ volatilization, and plant N uptake are poorly documented. Field plot experiments planted with peanut were conducted under the application of biochar (derived from rice husk and cottonseed husk, 50 t ha^-1) with organic or mineral fertilizer. It was found that biochar increased soil nutrient availability and decreased surface soil bulk density, demonstrating that biochar could improve the soil quality especially in the 0-20-cm profile. The total N content of the plant changed little with treatments, but the kernel N concentration increased significantly when biochar was applied with organic fertilizer. Peanut yield increased with biochar amendment while no significant difference was observed in plant biomass, suggesting biochar had a positive effect on belowground biomass. Peanut N uptake was also increased following biochar amendment with either organic or mineral fertilizers. While biochar amendment had no significant effect on soil NH₃ volatilization, it did decrease the cumulative N₂O emission by 36.3% on average with organic fertilizer, and by 32.6% with mineral fertilizer, respectively (p < 0.05). The copy numbers of 16S rDNA, nifH, nirK, and nirS were not influenced by the application of biochar; however, the copy number of nosZ was significantly increased under biochar plus mineral fertilizer treatment. The results imply that biochar application can suppress N₂O emissions, as a result of abiotic factors and enhanced peanut N uptake rather than changes of denitrification genes.

Impacts of simulated erosion and soil amendments on greenhouse gas fluxes and maize yield in Miamian soil of central Ohio

Erosion-induced topsoil loss is a threat to sustainable productivity. Topsoil removal from, or added to, the existing surface is an efficient technique to simulate on-site soil erosion and deposition. A 15-year simulated erosion was conducted at Waterman Farm of Ohio State University to assess impacts of topsoil depth on greenhouse gas (GHG) emissions and maize yield. Three topsoil treatments were investigated: 20 cm topsoil removal, 20 cm topsoil addition, and undisturbed control. Results show that the average global warming potential (GWP) (Mg CO₂ Eq ha⁻¹ growing season⁻¹) from the topsoil removal plot (18.07) exhibited roughly the same value as that from the undisturbed control plot (18.11), but declined evidently from the topsoil addition plot (10.58). Maize yield decreased by 51% at the topsoil removal plot, while increased by 47% at the topsoil addition plot, when compared with the undisturbed control (7.45 Mg ha⁻¹). The average GWP of erosion-deposition process was 21% lower than that of the undisturbed control, but that greenhouse gas intensity (GHGI) was 22% higher due to lower yields from the topsoil removal plot. Organic manure application enhanced GWP by 15%, and promoted maize yield by 18%, but brought a small reduction GHGI (3%) against the N-fertilizer application.

The influence of particle size and feedstock of biochar on the accumulation of Cd, Zn, Pb, and As by Brassica chinensis L

Biochar produced from rice straw (RC) and maize stalk (MC) was amended to the heavy metal-contaminated soil to investigate the effects of different biochar feedstock and particle size (fine, moderate, coarse) on the accumulation of Cd, Zn, Pb, and As in Brassica chinensis L. (Chinese cabbage). The concentrations of Cd, Zn, and Pb in shoot were decreased by up to 57, 75, and 63%, respectively, after biochar addition (4%). Only MC decreased As concentration in B. chinensis L. shoots by up to 61%. Biochar treatments significantly decreased NH₄NO₃-extractable concentrations of Cd, Zn, and Pb in soil by 47-62, 33-66, and 38-71%, respectively, yet increased that of As by up to 147%. Amendment of RC was more effective on immobilizing Cd, Zn, and Pb, but mobilizing soil As, than MC. A decrease in biochar particle size greatly contributed to the immobilization of Cd, Zn, and Pb in soil and thereby the reduction of their accumulations in B. chinensis L. shoots, especially RC. Increases in soil pH and extractable P induced by biochar addition contributed to the sequestration of Cd, Zn, and Pb and the mobilization of As. Shoot biomass, root biomass, and root system of B. chinensis L. were enhanced with biochar amendments, especially RC. This study indicates that biochar addition could potentially decrease Cd, Zn, Pb, and As accumulations in B. chinensis L., and simultaneously increase its yield. A decrease in biochar particle size is favorable to improve the immobilization of heavy metals (except As). The reduction in Cd, Zn, Pb, and As levels in B. chinensis L. shoots by biochar amendment could be mainly attributed to a function of heavy metal mobility in soil, plant translocation factor, and root uptake.

Emissions intensity and carbon stocks of a tropical Ultisol after amendment with Tithonia green manure, urea and biochar

Biochar has been shown to reduce soil emissions of CO₂, CH₄ and N₂O in short-term incubation and greenhouse experiments. Such controlled experiments failed to represent variable field conditions, and rarely included crop growth feedback. The objective of this study was to assess the effect of biochar, in comparison to green manure and mineral nitrogen, on greenhouse gas Emissions Intensity (EI = emissions in CO₂ equivalents per ton of grain yield) in a low-fertility tropical Ultisol. Using a field trial in western Kenya, biochar (0 and 2.5 t ha^-1; made from Eucalyptus wood) was integrated with urea (0 and 120 kg N ha^-1) and green manure (Tithonia diversifolia; 0, 2.5 and 5 t ha^-1) in a factorial design for four consecutive seasons from October 2012 to August 2014. Compared to the control, biochar increased soil CO₂ emissions (9-33%), reduced soil CH₄ uptake (7-59%) and reduced soil N₂O emissions (1-42%) in each season, with no seasonal differences. N₂O emissions increased following amendment with T. diversifolia (6%) and urea (13%) compared to the control. Generally, N₂O emissions decreased where only biochar was applied. The greatest decrease in N₂O (42%) occurred where all three amendments were applied compared to when they were added separately. EI in response to any of the amendments was lower than the control, ranging from 9 to 65% (33.0 ± 3.2 = mean ± SE). The amendments increased SOC stocks by 0.1-1.2 t ha^-1 year^-1 (mean ± SE of 0.8 ± 0.09 t ha^-1 year^-1). The results suggest decreased net EI with biochar in low fertility soils mainly through greater net primary productivity (89% of the decrease).

Effects of biochar and wood pellets amendments added to landfill cover soil on microbial methane oxidation: A laboratory column study

Alternate landfill covers designed to enhance microbial methane (CH₄) oxidation and reduce the negative impacts of landfill gas emissions on global climate have recently been proposed and investigated. In this study, the use of biochar as a soil amendment is examined in order to assess the feasibility and effectiveness for enhanced CH₄ removal in landfill covers when incorporated under high compaction conditions and relatively low soil moisture. Four different cover configurations were tested in large soil columns for ∼510 days and potential CH₄ oxidation rates were determined following long-term incubation in small batch assays. Cover designs tested include: a thin biochar layer at 15-18 cm; 2% mixed soil-biochar layer at 20-40 cm; 2% mixed soil-uncharred wood pellets at 20-40 cm; and soil obtained from intermediate cover at an active landfill site. The placement of a thin biochar layer in the cover significantly impacted moisture distribution and infiltration, which in turn affected CH₄ oxidation potential with depth. An increase in CH₄ removal rates was observed among all columns over the 500 day incubation period, with steady-state CH₄ removal efficiencies ranging from ∼60 to 90% in the final stages of incubation (inlet load ∼80 g CH₄ m^-2 d^-1). The thin biochar layer had the lowest average removal efficiency as a result of reduced moisture availability below the biochar layer. The addition of 2% biochar to soil yielded similar CH₄ oxidation rates in terminal assays as the 2% uncharred wood pellet amendment. CH₄ oxidation rates in terminal assays were positively correlated with soil moisture, which was affected by the materials' water holding capacity. The high water holding capacity of biochar led to higher oxidation rates within the thin biochar layer, supporting the initial hypothesis that biochar may confer more favorable physical conditions for methanotrophy. Ultimate performance was apparently affected by soil type and CH₄ exposure history, with the highest oxidation rates observed in the unamended field soil with higher initial methanotrophic activity.

Efficiency of sewage sludge biochar in improving urban soil properties and promoting grass growth

It is meaningful to quickly improve poor urban soil fertility in order to establish the green land vegetation. In this study, a series rates (0%, 1%, 5%, 10%, 20% and 50%, in mass ratio) of biochar derived from municipal sewage sludge was applied into an urban soil and then turf grass was grown in pots. The results showed that biochar amendment induced significant increases in soil total nitrogen, organic carbon, black carbon, and available phosphorus and potassium by more than 1.5, 1.9, 4.5, 5.6 and 0.4 times, respectively. Turf grass dry matter increased proportionally with increasing amount of added biochar (by an average of 74%), due to the improvement in plant mineral nutrition. Biochar amendment largely increased the total amounts of soil heavy metals. However, 43-97% of the heavy metals in the amended soil were concentrated in the residual fraction with low bioavailability. So the accumulation of heavy metals in turf grass aboveground biomass was highly reduced by the addition of biochar. These results indicated that sewage sludge biochar could be recommended in the poor urban raw soil as a soil conditioner at a rate of 50%. However, the environmental risk of heavy metal accumulation in soil amended with sewage sludge biochar should be carefully considered.

Mitigating cadmium accumulation in greenhouse lettuce production using biochar

Greenhouse experiments were conducted to investigate the influence of rice straw biochar (RSB) on soil cadmium (Cd) availability and accumulation in lettuce. The RSB was applied either in bands or broadcast in the test site of four greenhouses with soil Cd concentrations ranging from 1.70-3.14 μg g-1. Biochar doses applied in bands were half of those broadcast. The Cd levels in the shoots of lettuce were observed to be reduced by up to 57% with increasing RSB application rate (0, 6, 12, 18 t ha-1). Following RSB application, shoot Cd concentrations of lettuce were reduced to below the Chinese threshold value set for food, and hazard quotients for Cd associated with vegetable consumption were reduced from 0.70-1.11 to 0.42-0.65. A decrease in soil bulk density (11%) and increases in water holding capacity (16%), available phosphorus (30%), available potassium (197%), and lettuce yield (15%) were observed after RSB application. Multiple linear regression analysis suggested that the soil extractable Cd level (but not biomass dilution) and soil bulk density, as influenced by RSB addition, were the dominant contributors to the shoot Cd levels in lettuce and lettuce yield, respectively. These results highlight the potential for RSB to mitigate the phytoaccumulation of Cd and thereby to reduce human exposure from vegetable consumption. Application of biochar in band, rather than broadcasting over the entire area, represents an opportunity to halve the biochar cost while retaining a good remediation effect.

Effects of maize stover and its derived biochar on greenhouse gases emissions and C-budget of brown earth in Northeast China

Concerns regarding rising population levels and the impacts of atmospheric greenhouse gas (GHG) emissions on world climate have encouraged effective alternative methods to increase agricultural production while mitigating climate change. Soil GHG emissions from maize (Zea mays L.) fields treated with stover and a stover-derived biochar amendment during two consecutive maize growing seasons were studied in a brown earth soil type in Liaoning, China. We considered three treatments: CK (basal application of mineral NPK fertilizer; 120 kg N ha^-1, 60 kg P₂O₅ ha^-1, and 60 kg K₂O ha^-1, respectively), ST (maize stover application; 7.5 t ha^-1), and BC (7.5 t ha^-1 of maize stover was charred, with a yield of 35% of the original biomass; 2.63 t ha^-1). Both ST and BC treatments received the same fertilization as CK. Soil GHG emissions were monitored using the static chamber-gas chromatography method. The mean CO₂ emissions of the two-year experiment indicated that ST and BC were significantly higher than CK by 131.0 and by 21.3%, respectively, and there was a striking difference between ST and BC treatments. The N₂O-N emissions decreased in the following order, BC < ST < CK, and cumulative reduced CH₄ emissions in BC and ST were 1.58 and 2.21 times higher than observations in CK, respectively. The total global warming potential (GWP) in 2013 and 2014 decreased in the following order: BC < ST < CK. For the yield average data of two-year experiment, compared to CK and BC treatments, ST treatment showed 7.9 and 4.5% reduction, respectively. The C gains in BC treatment were significantly higher than that observed in ST treatment by 7.3%. Compared with the stover incorporating, biochar application significantly decreased the total CO₂ emissions and GHG intensity (GHGI), and it enhanced C-sequestration.

Stoichiometric ratio of dissolved organic carbon to nitrate regulates nitrous oxide emission from the biochar-amended soils

Biochar has the potential to mitigate nitrous oxide (N₂O) emissions from soils. However, the mechanisms responsible for N₂O emission in biochar-amended soils are yet to be elucidated. In this study, an incubation experiment was carried out to investigate the effects of seven biochars (eucalyptus, softwood mixture, mallee, jarrah, peanut shell, green waste and radiata pine) on the stoichiometric shifts of dissolved organic carbon (DOC), nitrate (NO₃^--N) and N₂O emission in two contrasting soils (Ferrosol with 5.3% total C, 0.46% total N; Tenosol with 0.4% total C, 0.01% total N). All biochar treatments were found to significantly reduce N₂O emission in Tenosol by 61-72%. However, in Ferrosol, biochars' impacts on N₂O emission were variable, with only peanut shell, green waste and radiata pine bicohars significantly reducing N₂O emission by 17-23%. A decrease in NO₃^- availability in most biochar-amended treatments also was observed in both soils compared with the control. The N₂O fluxes in Ferrosol were mainly regulated by the shifts in the availability and stoichiometry of DOC and NO₃^- induced by the biochar amendments. The DOC derived from biochars increased DOC:NO₃^- ratio in Ferrosol at the beginning of the experiment, but these effects disappeared 7days after incubation. Overall, the N₂O fluxes were C-limited due to the presence of high concentrations of NO₃^- in Ferrosol. However, in Tenosol, the relationship between stoichiometry of DOC:NO₃^- and N₂O fluxes was much weaker than Ferrosol and N₂O fluxes mainly limited by the concentration of NO₃^-. This study demonstrated that the mechanisms responsible for biochar effects on soil N₂O fluxes are considered to be soil and biochar specific.

Biochar applied with appropriate rates can reduce N leaching, keep N retention and not increase NH3 volatilization in a coastal saline soil

The impacts of biochar addition on nitrogen (N) leaching, (ammonia) NH₃ volatilization from coastal saline soils are not well understood. In this soil column study, the effects of wheat straw biochar application at rates of 0.5%, 1%, 2% and 4% by weight to a coastal saline soil on N leaching, NH₃ volatilization, soil pH and N retention were investigated. Results showed that 0.5% and 1% biochar amendments reduce the NH₄⁺-N, NO₃^--N and total N concentrations of leachate and thereby significantly decrease their cumulative lost loads by 11.6-24.0%, 13.2-29.7%, and 14.6-26.0%, respectively, in compared with the control. The biochar-induced soil N leaching mitigation efficiency was weakened when the biochar application rates increased to 2% and 4%. However, the impact of biochar addition on cumulative NH₃ volatilizations were negative and significantly 25.6-53.6% higher NH₃ volatilizations in soils with 2% and 4% biochar amended than control were detected, which was mainly attributed to the averaged 0.53-0.88units higher soil pH as results of biochar addition. On average, the total N concentrations of soil were kept same with 1.01-1.06gkg^-1 under control and biochar treatments. Therefore, biochar application to the coastal saline soils with appropriate rates (i.e., 0.5% and 1% in current study) can reduce N leaching, keep soil N retention, and not increase NH₃ volatilization, which was beneficial for sustainable use of saline soils.

Reduced carbon sequestration potential of biochar in acidic soil

Biochar application in soil has been proposed as a promising method for carbon sequestration. While factors affecting its carbon sequestration potential have been widely investigated, the number of studies on the effect of soil pH is limited. To investigate the carbon sequestration potential of biochar across a series of soil pH levels, the total carbon emission, CO₂ release from inorganic carbon, and phospholipid fatty acids (PLFAs) of six soils with various pH levels were compared after the addition of straw biochar produced at different pyrolysis temperatures. The results show that the acidic soils released more CO₂ (1.5-3.5 times higher than the control) after the application of biochar compared with neutral and alkaline soils. The degradation of both native soil organic carbon (SOC) and biochar were accelerated. More inorganic CO₂ release in acidic soil contributed to the increased degradation of biochar. Higher proportion of gram-positive bacteria in acidic soil (25%-36%) was responsible for the enhanced biochar degradation and simultaneously co-metabolism of SOC. In addition, lower substrate limitation for bacteria, indicated by higher C-O stretching after the biochar application in the acidic soil, also caused more CO₂ release. In addition to the soil pH, other factors such as clay contents and experimental duration also affected the phsico-chemical and biotic processes of SOC dynamics. Gram-negative/gram-positive bacteria ratio was found to be negatively related to priming effects, and suggested to serve as an indicator for priming effect. In general, the carbon sequestration potential of rice-straw biochar in soil reduced along with the decrease of soil pH especially in a short-term. Given wide spread of acidic soils in China, carbon sequestration potential of biochar may be overestimated without taking into account the impact of soil pH.

Combination of biochar amendment and phytoremediation for hydrocarbon removal in petroleum-contaminated soil

Remediation of soils contaminated with petroleum is a challenging task. Four different bioremediation strategies, including natural attenuation, biochar amendment, phytoremediation with ryegrass, and a combination of biochar and ryegrass, were investigated with greenhouse pot experiments over a 90-day period. The results showed that planting ryegrass in soil can significantly improve the removal rate of total petroleum hydrocarbons (TPHs) and the number of microorganisms. Within TPHs, the removal rate of total n-alkanes (45.83 %) was higher than that of polycyclic aromatic hydrocarbons (30.34 %). The amendment of biochar did not result in significant improvement of TPH removal. In contrast, it showed a clear negative impact on the growth of ryegrass and the removal of TPHs by ryegrass. The removal rate of TPHs was significantly lower after the amendment of biochar. The results indicated that planting ryegrass is an effective remediation strategy, while the amendment of biochar may not be suitable for the phytoremediation of soil contaminated with petroleum hydrocarbons.

Soil biochar amendment as a climate change mitigation tool: Key parameters and mechanisms involved

Biochar, a solid porous material obtained from the carbonization of biomass under low or no oxygen conditions, has been proposed as a climate change mitigation tool because it is expected to sequester carbon (C) for centuries and to reduce greenhouse gas (GHG) emissions from soils. This review aimed to identify key biochar properties and production parameters that have an effect on these specific applications of the biochar. Moreover, mechanisms involved in interactions between biochar and soils were highlighted. Following a compilation and comparison of the characteristics of 76 biochars from 40 research studies, biochars with a lower N content, and consequently a higher C/N ratio (>30), were found to be more suitable for mitigation of N2O emissions from soils. Moreover, biochars produced at a higher pyrolysis temperature, and with O/C ratio <0.2, H/Corg ratio <0.4 and volatile matter below 80% may have high C sequestration potential. Based on these observations, biochar production and application to the field can be used as a tool to mitigate climate change. However, it is important to determine the pyrolysis conditions and feedstock needed to produce a biochar with the desired properties for a specific application. More research studies are needed to identify the exact mechanisms involved following biochar amendment to soil.

Short-Term Responses of Soil Respiration and C-Cycle Enzyme Activities to Additions of Biochar and Urea in a Calcareous Soil

Biochar (BC) addition to soil is a proposed strategy to enhance soil fertility and crop productivity. However, there is limited knowledge regarding responses of soil respiration and C-cycle enzyme activities to BC and nitrogen (N) additions in a calcareous soil. A 56-day incubation experiment was conducted to investigate the combined effects of BC addition rates (0, 0.5, 1.0, 2.5 and 5.0% by mass) and urea (U) application on soil nutrients, soil respiration and C-cycle enzyme activities in a calcareous soil in the North China Plain. Our results showed soil pH values in both U-only and U plus BC treatments significantly decreased within the first 14 days and then stabilized, and CO₂emission rate in all U plus BC soils decreased exponentially, while there was no significant difference in the contents of soil total organic carbon (TOC), dissolved organic carbon (DOC), total nitrogen (TN), and C/N ratio in each treatment over time. At each incubation time, soil pH, electrical conductivity (EC), TOC, TN, C/N ratio, DOC and cumulative CO₂ emission significantly increased with increasing BC addition rate, while soil potential activities of the four hydrolytic enzymes increased first and then decreased with increasing BC addition rate, with the largest values in the U + 1.0%BC treatment. However, phenol oxidase activity in all U plus BC soils showed a decreasing trend with the increase of BC addition rate. Our results suggest that U plus BC application at a rate of 1% promotes increases in hydrolytic enzymes, does not highly increase C/N and C mineralization, and can improve in soil fertility.

Spatial heterogeneity of soil biochar content affects soil quality and wheat growth and yield

Biochar (BC) is a carbonaceous material obtained by pyrolysis of organic waste materials and has been proposed as a soil management strategy to mitigate global warming and to improve crop productivity. Once BC has been applied to the soil, its imperfect and incomplete mixing with soil during the first few years and the standard agronomic practices (i.e. tillage, sowing) may generate spatial heterogeneity of the BC content in the soil, which may have implications for soil properties and their effects on plant growth. We investigated how, after two agronomic seasons, the spatial heterogeneity of olive-tree prunings BC applied to a vertisol affected soil characteristics and wheat growth and yield. During the second agronomic season and just before wheat germination, we determined the BC content in the soil by an in-situ visual categorization based on the soil darkening, which was strongly correlated to the BC content of the soil and the soil brightness. We found a high spatial heterogeneity in the BC plots, which affected soil characteristics and wheat growth and yield. Patches with high BC content showed reduced soil compaction and increased soil moisture, pH, electrical conductivity, and nutrient availability (P, Ca, K, Mn, Fe, and Zn); consequently, wheat had greater tillering and higher relative growth rate and grain yield. However, if the spatial heterogeneity of the soil BC content had not been taken into account in the data analysis, most of the effects of BC on wheat growth would not have been detected. Our study reveals the importance of taking into account the spatial heterogeneity of the BC content.

Nutrient release and ammonium sorption by poultry litter and wood biochars in stormwater treatment

The feasibility of using biochar as a filter medium in stormwater treatment facilities was evaluated with a focus on ammonium retention. Successive batch extractions and batch ammonium sorption experiments were conducted in both deionized (DI) water and artificial stormwater using poultry litter (PL) and hardwood (HW) biochars pyrolyzed at 400°C and 500°C. No measureable nitrogen leached from HW biochars except 0.07 μmol/g of org-N from 400°C HW biochar. PL biochar pyrolyzed at 400°C leached 120-127 μmol/g of nitrogen but only 7.1-8.6 μmol/g of nitrogen when pyrolyzed at 500°C. Ammonium sorption was significant for all biochars. At a typical ammonium concentration of 2mg/L in stormwater, the maximum sorption was 150 mg/kg for PL biochar pryolyzed at 400°C. In stormwater, ion competition (e.g. Ca(2+)) suppressed ammonium sorption compared to DI water. Surprisingly, ammonium sorption was negatively correlated to the BET surface area of the tested biochars, but increased linearly with cation exchange capacity. Cation exchange capacity was the primary mechanism controlling ammonium sorption and was enhanced by pyrolysis at 400°C, while BET surface area was enhanced by pyrolysis at 500°C. The optimal properties (BET surface area, CEC, etc.) of biochar as a sorbent are not fixed but depend on the target pollutant. Stormwater infiltration column experiments in sand with 10% biochar removed over 90% of ammonium with influent ammonium concentration of 2mg/L, compared to only 1.7% removal in a sand-only column, indicating that kinetic limitations on sorption were minor for the storm conditions studied. Hardwood and poultry litter biochar pyrolyzed at 500°C and presumably higher temperature may be viable filter media for stormwater treatment facilities, as they showed limited release of organic and inorganic nutrients and acceptable ammonium sorption.

Transport and retention of bacteria and viruses in biochar-amended sand

The transport and retention of Escherichia coli and bacteriophages (PRD1, MS2 and ФX174), as surrogates for human pathogenic bacteria and viruses, respectively, were studied in the sand that was amended with several types of biochar produced from various feedstocks. Batch and column studies were conducted to distinguish between the role of attachment and straining in microbe retention during transport. Batch experiments conducted at various solution chemistries showed negligible attachment of viruses and bacteria to biochar before or after chemical activation. At any given solution ionic strength, the attachment of viruses to sand was significantly higher than that of biochar, whereas bacteria showed no attachment to either sand or biochar. Consistent with batch results, biochar addition (10% w/w) to sand reduced virus retention in the column experiments, suggesting a potential negative impact of biochar application to soil on virus removal. In contrast, the retention of bacteria was enhanced in biochar-amended sand columns. However, elimination of the fine fraction (<60μm) of biochar particles in biochar-amended sand columns significantly reduced bacteria retention. Results from batch and column experiments suggest that land application of biochar may only play a role in microbe retention via straining, by alteration of pore size distribution, and not via attachment. Consequently, the particle size distribution of biochar and sediments is a more important factor than type of biochar in determining whether land application of biochar enhances or diminishes microbial retention.

Typical agricultural diffuse herbicide sorption with agricultural waste-derived biochars amended soil of high organic matter content

Biochar application has been identified as the effective soil amendment and the materials to control the diffuse herbicide pollution. The atrazine was selected as the typical diffuse herbicide pollutant as the dominant proportion in applications. The biochar treated from four types of crops biomass were added to soil with high organic matter content. The basic sorption characteristics of biocahrs from corn cob (CC), corn stalk (CS), soybean straw (SS), rice straw (RS) and corn stalk paralyzed with 5% of ammonium dihydrogen phosphate (ACS) were analyzed, along with the comparison of the sorption difference of the raw soil and soil amended with biochars at four levels of ratio (0.5%, 1.0%, 3.0% and 5.0%). It was found that the linear distribution isotherm of raw soil was much effective due to the high organic matter background concentration. The addition of five types of biochars under two kinds of initial atrazine concentration (1 mg/L and 20 mg/L) demonstrated the sorption variances. Results showed the soil amended with RS and CS biochar had the biggest removal rate in four regular biochars and the removal rate of the ACS was the biggest. The sorption coefficient and the normalized sorption coefficient from Freundlich modeling presented the isothermal sorption characteristics of atrazine with soil of high organic matter content. The normalized sorption coefficient increased with the equilibrium concentration decreased in the biochar amended soil, which indicated the sorption performance will be better due to the low atrazine concentration in practice. Results showed that biochar amendment is the effective way to prevent leakage of diffuse herbicide loss.

Restoration of carbon and microbial activity in salt-induced soil by application of peanut shell biochar during short-term incubation study

For the present study, soil samples of four artificially-induced salinity gradients (S0: control, S1: 2.0, S2: 4.0, S3: 6.0 ECiw) was incubated with fine-textured peanut shell biochar at various ratios (B0: control, B1: 2.5%, B2: 5.0%, B3: 10% w/w) for 30 days. At 1, 3, 7, 15, 30 days of incubation, samples were analyzed for soil carbon and selected enzyme activities. Results showed that biochar could increase soil organic carbon on application of highest rate of biochar addition (B3), hence potentially restored the saline soils by less C mineralization, and more sequestration of soil C. However, soil enzyme activities were biochar rate(s), day(s) of incubation and enzyme dependent. The lowest rate of biochar addition (B1) showed highest dehydrogenase (20.5 μg TPF g(-1) soil h(-1)), acid phosphatase (29.1 μg PNP g(-1) soil h(-1)) and alkaline phosphatase (16.1 μg PNP g(-1) soil h(-1)) whereas the higher rate (B2) increased the urease (5.51 μg urea-N g(-1) soil h(-1)) and fluorescein diacetate hydrolyzing activities (3.95 μg fluorescein g(-1) OD soil h(-1)) in soil. All the positive changes persisted at higher levels of salinity (S2, S3) suggesting biochar-amended soil may be potential for better nutrient cycling. Soil enzymes were found to be correlated with soil carbon and with each other while principal component analysis (PCA) extracted the most sensitive parameters as the acid and alkaline phosphatases and urease activities in the present experimental condition. This is the first time report of examining soil microbial environment using peanut shell biochar under a degraded (saline) soil.

Interactive effects of straw-derived biochar and N fertilization on soil C storage and rice productivity in rice paddies of Northeast China

Impacts of biochar on greenhouse gas emissions and C sequestration in agricultural soils have been considered as the key to mitigate climate change. There is limited knowledge regarding the effects of rice straw-derived biochar and interaction with N fertilization on soil C sequestration and rice productivity in fertile paddy fields. A 2-year (2013 and 2014) consecutive field trial was performed using straw treatment (5.05 t ha(-1)) and biochar amendment (0, 1.78, 14.8 and 29.6 t ha(-1)) with or without urea application in a rice paddy in Northeast China. A super high yielding rice variety (Oryza sativa L. subsp. Japonica cv. 'Shennong 265') was cultivated with permanent flooding. Results showed that biochar amendments significantly decreased CH4 emissions relative to straw treatment irrespective of N fertilization, especially in N-fertilized soils with 1.78 t ha(-1) biochar. There were no differences in CO2 emissions with respect to biochar amendments, except for 14.8 t ha(-1) biochar with N fertilization. Straw treatment had the highest global warming potential over a 100-year time frame, which was nearly 1.5 times that of 14.8 t ha(-1) biochar amendment without N fertilization. Biochar addition increased total soil C by up to 5.75 mg g(-1) and 11.69 mg g(-1) (with 14.8 and 29.6 t ha(-1) biochar, respectively), whereas straw incorporation increased this value by only 3.92 mg g(-1). The aboveground biomass of rice in biochar-amended soils increased to varying degrees compared with that in straw-treated soils. However, biochar application had no effects on rice yield, regardless of N fertilization. This study indicated that transforming straw to biochar was more stabilized and more suitable to mitigate greenhouse gas emissions and increase C storage in agriculture soils in Northeast China.

Soil respiration characteristics in different land uses and response of soil organic carbon to biochar addition in high-latitude agricultural area

The farmland tillage practices changed the soil chemical properties, which also impacted the soil respiration (R s ) process and the soil carbon conservation. Originally, the farmland in northeast China had high soil carbon content, which was decreased in the recent decades due to the tillage practices. To better understand the R s dynamics in different land use types and its relationship with soil carbon loss, soil samples at two layers (0-15 and 15-30 cm) were analyzed for organic carbon (OC), total nitrogen (TN), total phosphorus (TP), total carbon (TC), available nitrogen (AN), available phosphorus (AP), soil particle size distribution, as well as the R s rate. The R s rate of the paddy land was 0.22 (at 0-15 cm) and 3.01 (at 15-30 cm) times of the upland. The average concentrations of OC and clay content in cultivated areas were much lower than in non-cultivated areas. The partial least squares analysis suggested that the TC and TN were significantly related to the R s process in cultivated soils. The upland soil was further used to test soil CO2 emission response at different biochar addition levels during 70-days incubation. The measurement in the limited incubation period demonstrated that the addition of biochar improved the soil C content because it had high concentration of pyrogenic C, which was resistant to mineralization. The analysis showed that biochar addition can promote soil OC by mitigating carbon dioxide (CO2) emission. The biochar addition achieved the best performance for the soil carbon conservation in high-latitude agricultural area due to the originally high carbon content.

Effects of two different organic amendments addition to soil on sorption-desorption, leaching, bioavailability of penconazole and the growth of wheat (Triticum aestivum L.)

This study investigated the effects of sugarcane bagasse compost (SBC) and chicken manure compost (CMC) on the sorption-desorption, leaching and bioavailability of the fungicide penconazole in soil in a laboratory setting. The autoclave-treated SBC or CMC was applied at 2.5% and 5.0% (w/w). Results of batch equilibrium experiments exhibited that the sorption capacity of soils for penconazole was significantly promoted by the addition of SBC or CMC, whereas desorption of penconazole was drastically reduced; the influence was enhanced as the amount of organic amendments increased. Results of column leaching experiment indicated that the addition of SBC or CMC significantly limited the vertical movement of penconazole through the soil columns, considerably decreasing the content of penconazole in the soil leachate. Furthermore, results of bioavailability experiments demonstrated that the addition of organic amendments (SBC or CMC) remarkably influenced the uptake and translocation of penconazole, decreased penconazole accumulation in the plant tissues and increased the plant elongation and biomass. These data revealed important changes in pesticide behavior under SBC or CMC application, which should be useful for developing strategies to protect groundwater and crops from contamination from the residual pesticides in soil.

Predicting the impact of biochar additions on soil hydraulic properties

Different physical and chemical properties of biochar, which is made out of a variety of biomass materials, can impact water movement through amended soil. The objective of this research was to develop a decision support tool predicting the impact of biochar additions on soil saturated hydraulic conductivity (Ksat). Four different kinds of biochar were added to four different textured soils (coarse sand, fine sand, loam, and clay texture) to assess these effects at the rates of 0%, 1%, 2%, and 5% (w/w). The Ksat of the biochar amended soils were significantly influenced by the rate and type of biochar, as well as the original particle size of soil. The Ksat decreased when biochar was added to coarse and fine sands. Biochar with larger particles sizes (60%; >1 mm) decreased Ksat to a larger degree than the smaller particle size biochar (60%; <1 mm) in the two sandy textured soils. Increasing tortuosity in the biochar amended sandy soil could explain this behavior. On the other hand, for the clay loam 1% and 2% biochar additions universally increased the Ksat with higher biochar amounts providing no further alterations. The developed model utilizes soil texture pedotransfer functions for predicting agricultural soil Ksat as a function of soil texture. The model accurately predicted the direction of the Ksat influence, even though the exact magnitude still requires further refinement. This represents the first step to a unified theory behind the impact of biochar additions on soil saturated conductivity.

Relationships between Chemical Characteristics and Phytotoxicity of Biochar from Poultry Litter Pyrolysis

Three biochars were prepared by intermediate pyrolysis from poultry litter at different temperatures (400, 500, and 600 °C with decreasing residence times) and compared with biochars from corn stalk prepared under the same pyrolysis conditions. The phytotoxicity of these biochars was estimated by means of seed germination tests on cress (Lepidium sativum L.) conducted in water suspensions (at 2, 5, and 40 g/L) and on biochars wetted according to their water-holding capacity. Whereas the seeds germinated after 72 h in water suspensions with corn stalk biochar were similar to the control (water only), significant inhibition was observed with poultry litter biochars. In comparison to corn stalk, poultry litter generated biochars with higher contents of ash, ammonium, nitrogen, and volatile fatty acids (VFAs) and a similar concentration of polycyclic aromatic hydrocarbons (PAHs). Results from analytical pyrolysis (Py-GC-MS) indicated that nitrogen-containing organic compounds (NCCs) and aliphatic components were distinctive constituents of the thermally labile fraction of poultry litter biochar. The inhibition of germination due to poultry litter biochar produced at 400 °C (PL400) was suppressed after solvent extraction or treatment with active sludge. A novel method based on solid-phase microextraction (SPME) enabled the identification of mobile organic compounds in PL400 capable of being released in air and water, including VFAs and NCCs. The higher phytotoxicity of poultry litter than corn biochars was tentatively attributed to hydrophilic biodegradable substances derived from lipids or proteins removable by water leaching or microbial treatments.

The origin and reversible nature of poultry litter biochar hydrophobicity

Transient changes in wettability complicate the prediction of biochar's hydrologic effects. Biochar wetting properties were characterized from poultry litter biochar (PLBC) produced from slow pyrolysis at temperatures between 300 and 600°C with water drop penetration time (persistence of hydrophobicity) and contact angle (CA; severity of hydrophobicity) measurements. Hydrophobicity was associated with semivolatile organic compounds coating PLBC surfaces, which resulted in 24.4 carbon layers and CAs of 101.1 ± 2.9° at a pyrolysis temperature of 300°C but only 0.4 layers of surface coverage and CAs of 20.6 ± 1.3° when pyrolyzed at 600°C. Mixing PLBC with water removed organic coatings, and storage in water for 72 h decreased CA as much as 81° for the most hydrophobic PLBCs. When mixed with quartz sand of the same particle size, CAs of PLBC-sand mixtures increased from 6.6 ± 1.4° at 0% PLBC mass fraction to 48.3 ± 2.0° at 15% mass fraction. Hydrophobic and hydrophilic PLBCs increased CA by nearly identical amounts at 2 and 5% mass fractions, which was explained by the influence of PLBC particle topology on macroscopic surface roughness of PLBC-sand mixtures. For environmentally relevant situations, PLBC-sand mixtures at mass fractions ≤15% remained water wetting. However, all PLBC additions increased CA, which may alter infiltration rates and induce preferential water flow.

Evaluation of slow pyrolyzed wood and rice husks biochar for adsorption of ammonium nitrogen from piggery manure anaerobic digestate slurry

Due to its high adsorption capacity, the use of biochar to capture excess nutrients from wastewater has become a central focus in environmental remediation studies. In this study, its potential use in adsorption and removal of ammonium in piggery manure anaerobic digestate slurry was investigated. The adsorbed amount of NH4(+)-N (mg·g(-1)) and removal percentage as a function of adsorbent mass in solution, adsorbent particle size, NH4(+)-N concentration in the effluent, contact time, pH and temperature were quantified in batch equilibrium and kinetics experiments. The maximum NH4(+)-N adsorption from slurry at 1400 mgN·L(-1) was 44.64 ± 0.602 mg·g(-1) and 39.8 ± 0.54 mg·g(-1) for wood and rice husk biochar, respectively. For both biochars, adsorption increased with increase in contact time, temperature, pH and NH4(+)-N concentration but it decreased with increase in biochar particle size. Furthermore, the sorption process was endothermic and followed Langmuir (R(2)=0.995 and 0.998) and Pseudo-second order kinetic models (R(2)=0.998 and 0.999). Based on the removal amounts, we concluded that rice husk and wood biochar have potential to adsorb NH4(+)-N from piggery manure anaerobic digestate slurry, and thus can be used as nutrient filters prior to discharge into water streams.

Production of bio-based phenolic resin and activated carbon from bio-oil and biochar derived from fast pyrolysis of palm kernel shells

A fraction of palm kernel shells (PKS) was pyrolyzed in a fluidized bed reactor. The experiments were performed in a temperature range of 479-555 °C to produce bio-oil, biochar, and gas. All the bio-oils were analyzed quantitatively and qualitatively by GC-FID and GC-MS. The maximum content of phenolic compounds in the bio-oil was 24.8 wt.% at ∼500 °C. The maximum phenol content in the bio-oil, as determined by the external standard method, was 8.1 wt.%. A bio-oil derived from the pyrolysis of PKS was used in the synthesis of phenolic resin, showing that the bio-oil could substitute for fossil phenol up to 25 wt.%. The biochar was activated using CO2 at a final activation temperature of 900 °C with different activation time (1-3 h) to produce activated carbon. Activated carbons produced were microporous, and the maximum surface area of the activated carbons produced was 807 m(2)/g.

Impacts of biochar on physical properties and erosion potential of a mudstone slopeland soil

Food demand and soil sustainability have become urgent issues recently because of the global climate changes. This study aims to evaluate the application of a biochar produced by rice hull, on changes of physiochemical characteristics and erosion potential of a degraded slopeland soil. Rice hull biochar pyrolized at 400°C was incorporated into the soil at rates of 2.5%, 5%, and 10% (w/w) and was incubated for 168 d in this study. The results indicated that biochar application reduced the Bd by 12% to 25% and the PR by 57% to 92% after incubation, compared with the control. Besides, porosity and aggregate size increased by 16% to 22% and by 0.59 to 0.94 mm, respectively. The results presented that available water contents significantly increased in the amended soils by 18% to 89% because of the obvious increase of micropores. The water conductivity of the biochar-amended soils was only found in 10% biochar treatment, which might result from significant increase of macropores and reduction of soil strength (Bd and PR). During a simulated rainfall event, soil loss contents significantly decreased by 35% to 90% in the biochar-amended soils. In conclusion, biochar application could availably raise soil quality and physical properties for tilth increasing in the degraded mudstone soil.

Relating physical and chemical properties of four different biochars and their application rate to biomass production of Lolium perenne on a Calcic Cambisol during a pot experiment of 79 days

Three pyrolysis biochars (B1: wood, B2: paper-sludge, B3: sewage-sludge) and one kiln-biochar (B4: grapevine wood) were characterized by determining different chemical and physical properties which were related to the germination rates and to the plant biomass production during a pot experiment of 79 days in which a Calcic Cambisol from SW Spain was amended with 10, 20 and 40 t ha(-1) of the four biochars. Biochar 1, B2 and B4 revealed comparable elemental composition, pH, water holding capacity and ash content. The H/C and O/C atomic ratios suggested high aromaticity of all biochars, which was confirmed by (13)C solid-state NMR spectroscopy. The FT-IR spectra confirmed the aromaticity of all the biochars as well as several specific differences in their composition. The FESEM-EDS distinguished compositional and structural differences of the studied biochars such as macropores on the surface of B1, collapsed structures in B2, high amount of mineral deposits (rich in Al, Si, Ca and Fe) and organic phases in B3 and vessel structures for B4. Biochar amendment improved germination rates and soil fertility (excepting for B4), and had no negative pH impact on the already alkaline soil. Application of B3, the richest in minerals and nitrogen, resulted in the highest soil fertility. In this case, increase of the dose went along with an enhancement of plant production. Considering costs due to production and transport of biochar, for all used chars with the exception of B3, the application of 10 t ha(-1) turned out as the most efficient for the crop and soil used in the present incubation experiment.