PS 22-14 - Effects of Biochar Application on Soil Nitrous Oxide Emission using Mega-Analysis: Synthesis of Meta-Analyses

Background/Question/Methods

Nitrous oxide (N₂O) is the third important long-lived greenhouse gas (GHG) next to carbon dioxide and methane and cropland soils are considered biogeochemical hotspots of N₂O emission. Many studies have been conducted to test the impacts of agricultural practices such as biochar application on soil N₂O emission. To synthesize the results from individual studies, meta-analysis has been widely used. However, results from different meta-analyses also differ, but are seldomly evaluated. In this study, we conducted mega-analysis by synthesizing and evaluating meta-analyses on the effects of biochar on soil N₂O emission. Meta-analysis papers were search and response ratio was extracted from these papers. Grand mean response ratios were quantify based on those meta-analyses.

Results/Conclusions

We found 18 meta-analysis papers on the impacts of biochar application on soil N2O emission published between 2014 and 2022. Sample size (publications or experiments) varied from 29 to than 1375. While four meta-analyses did not find a significant effect of biochar application on soil N2O emission, all others reported reductions of soil N2O emission, but the magnitude ranged from -8% to -54%. Based on all meta-analyses, the overall reduction of soil N2O emission by biochar application was -38.92% with 95% confidence interval of (-44.8%, -32.4%). The impacts of experimental type, properties of biochar and soil, and agricultural practices on the effects of biochar application were also explored. This mega-analysis provided a more comprehensive and better estimation of soil N2O reduction with biochar application. Future meta-analysis needs to have a large sample size and consider more on the impacts of other covariates related to soil N2O emission.