Researchers from Nanjing Agricultural University reviewed 395 individual experiment observations derived from 50 peer-reviewed publications which were synthesized to examine the response of soil carbon dioxide fluxes, soil organic carbon and microbial biomass carbon (MBC) to biochar amendment using meta-analysis procedures. Their work published in journal, Global Change Biology Bioenergy examined the effect of size of biochar amendment on soil carbon dioxide fluxes, SOC and MBC contents and identified the key factors that influence the response of soil carbon dioxide fluxes, soil organic carbon and microbial biomass carbon to biochar amendment.
Biochar as carbon-rich co-product of pyrolysis biomass subject to high-temperature and oxygen-derived conditions for biofuel production has been advocated as potential management strategy to improve soil quality, crop yield increase and soil carbon sequestration enhancement.
In order to have an understanding on the effects of soil carbon dioxide and microbial biomass carbon, there is need to have deeper understanding on how biochar amendment effects whether negative or positive. However, inconsistent results from various researchers was observed which may be due to variation in soil type or study methods.
Experiments examined by researchers have shown no systematic synthesis as potential biochar amendment to improve soil carbon sink capacity and its effect on soil carbon dioxide are still under debate in which direction and magnitude of effects seem to depend on variety of factors such as soil properties, land-use type, experimental methods, vegetation presence and biochar characteristics.
For implementation of the experiment the authors conducted a detailed review of literature published in peer-reviewed journals through the year 2014 and data was extracted from 50 published research papers with 395 individual observations including both control and biochar-amended treatments.
For measurement, original documentation included mean soil carbon dioxide fluxes, standard deviation and number of replicates from both biochar-amended and control treatments as well as direction and magnitude of effects stated earlier.
Means of soil carbon dioxide fluxes, soil organic carbon and microbial biomass carbon contents from biochar treatment and control groups were used to compute effect sizes in the form of natural log-transformed response ratio (RR). Meta-analysis was conducted using response ratios where mean effect size for each category was calculated using a categorical random effects model. In addition to meta-analysis procedure, fitting of data to linear and Gaussian distribution functions were carried out using SigmaPlot version 12.0 software. Sensitivity analysis also followed suit in order to test the robustness of meta-analysis.
Results showed a significantly positive linear relationship as observed between soil carbon dioxide fluxes in biochar amended and control likewise soil organic carbon and microbial biomass carbon contents but carbon dioxide flux wasn’t significant. Key factors mediating carbon dioxide fluxes were seen to be soil texture, pH, vegetation presence, feedstock presence and carbon-nitrogen ratio to biochar amendment. Land-use type and biochar carbon to nitrogen ratio were two critical parameters affecting response of soil organic content while microbial biomass carbon response to biochar amendment was sensitive to almost all parameters.
For land-use change, biochar amendment significantly increased soil organic carbon content 40% across all ecosystem but increased significantly with biochar treatments found in rice paddies. In soil carbon, biochar amendment significantly decreased carbon dioxide fluxes on pot experiments but positive effects was seen in laboratory incubations. There was decrease in microbial biomass carbon by biochar amendment in incubation and pot studies but greatly increased soil organic carbon content when using the three pots.
For soil texture and pH, biochar amendment in coarse soils exerted a significant positive effects on soil carbon dioxide fluxes while significant negative effects were observed in fine-textured soils which had similar result with microbial biomass carbon significantly. Biochar was effective at decreasing soil carbon dioxide fluxes but did not benefit soil organic carbon enhancement in neutral or alkaline soils and significant positive responses of soil carbon dioxide fluxes were observed in moderately acid soils. Soil microbial biomass carbon content was significantly increased by biochar amendment in acid soils relative to in neutral or alkaline soil conditions.
Biochar amendment significantly increased soil carbon dioxide fluxes when synthetic nitrogen fertilizer was applied. Soil organic carbon content by biochar amendment did not significantly differ in soils with or without nitrogen fertilizer application but organic nitrogen fertilizer had the largest increment potential for soil organic carbon. Biochar addition had significantly positive effect on microbial biomass carbon when combined with nitrogen fertilizer or synthetic nitrogen fertilizer.
In meta-analysis, removal of outliers did not change the general results. After removing outliers, the mean effect sizes of biochar treatments was 5% (Cl: -2% to 12%) for carbon dioxide, 40% (Cl: 30% to 58%) for soil organic carbon and 19% (Cl: 12% to 24%) for microbial biomass carbon comparable to 5% (Cl: -3% to 12%), 40% (Cl: 32% to 56%) and 18% (Cl: 12% to 23%) for carbon dioxide, soil organic carbon and microbial biomass carbon when all datasets included respectively.
Limited range of study durations did not allow examination of effect of biochar aging on soil carbon dioxide fluxes, soil organic carbon and microbial biomass carbon in meta-analysis, hence field experiment with longer durations across a wider range of spatial and temporal scales are required.
Shuwei Liu1,2,Yaojun Zhang1,2,Yajie Zong1,2,Zhiqiang Hu1,2,Shuang Wu1,2,Jie Zhou1,2,Yaguo Jin1,2,Jianwen Zou1,2. Response of Soil Carbon Dioxide Fluxes, Soil Organic Carbon and Microbial Biomass Carbon to Biochar Amendment: A Meta-Analysis. Global Change Biology Bioenergy, 2016, Volume 8, pp 392-406.Show Affiliations
- Jiangsu Key Laboratory of Low Carbon Agriculture and GHGs Mitigation, Nanjing Agricultural University, Nanjing, China
- Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, Nanjing Agricultural University, Nanjing, China
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