Nitrous oxide emission from agricultural soils: Application of animal manure or biochar? A global meta-analysis.

Organic amendments (animal manure and biochar) to agricultural soils may enhance soil organic carbon (SOC) contents, improve soil fertility and crop productivity but also contribute to global warming through nitrous oxide (N ₂ O) emission. However, the effects of organic amendments on N ₂ O emissions from agricultural soils seem variable among numerous research studies and remains uncertain. Here, eighty-five publications (peer-reviewed) were selected to perform a meta-analysis study. The results of this meta-analysis study show that the application of animal manure enhanced N ₂ O emissions by 17.7%, whereas, biochar amendment significantly mitigated N ₂ O emissions by 19.7%. Moreover, coarse textured soils increased [lnRR‾ = 182.6%, 95% confidence interval (CI) = 151.4%, 217.7%] N ₂ O emission after animal manure, in contrast, N ₂ O emission mitigated by 7.0% from coarse textured soils after biochar amendment. In addition, this study found that 121-320 kg N ha ^{- 1} and ⩽ 30 T ha ^-1 application rates of animal manure and biochar mitigated N ₂ O emissions by 72.3% and 22.5%, respectively. Soil pH also played a vital role in regulating the N ₂ O emissions after organic amendments. Furthermore, > 10 soil C: N ratios increased N ₂ O emissions by 121.4% and 27.6% after animal and biochar amendments, respectively. Overall, animal manure C: N ratios significantly enhanced N ₂ O emissions, while, biochar C: N ratio had not shown any effect on N ₂ O emissions. Overall, average N ₂ O emission factors (EFs) for animal manure and biochar amendments were 0.46% and -0.08%, respectively. Thus, the results of this meta-analysis study provide scientific evidence about how organic amendments such as animal manure and biochar regulating the N ₂ O emission from agricultural soils.
(Copyright © 2021 Elsevier Ltd. All rights reserved.)