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 (N2O) emission. However, the effects of organic amendments on N2O 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 N2O emissions by 17.7%, whereas, biochar amendment significantly mitigated N2O emissions by 19.7%. Moreover, coarse textured soils increased [lnRR‾ = 182.6%, 95% confidence interval (CI) = 151.4%, 217.7%] N2O emission after animal manure, in contrast, N2O 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 N2O emissions by 72.3% and 22.5%, respectively. Soil pH also played a vital role in regulating the N2O emissions after organic amendments. Furthermore, > 10 soil C: N ratios increased N2O emissions by 121.4% and 27.6% after animal and biochar amendments, respectively. Overall, animal manure C: N ratios significantly enhanced N2O emissions, while, biochar C: N ratio had not shown any effect on N2O emissions. Overall, average N2O 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 N2O emission from agricultural soils.

Biochar in the Agroecosystem-Climate-Change-Sustainability Nexus.

Interest in the use of biochar in agriculture has increased exponentially during the past decade. Biochar, when applied to soils is reported to enhance soil carbon sequestration and provide other soil productivity benefits such as reduction of bulk density, enhancement of water-holding capacity and nutrient retention, stabilization of soil organic matter, improvement of microbial activities, and heavy-metal sequestration. Furthermore, biochar application could enhance phosphorus availability in highly weathered tropical soils. Converting the locally available feedstocks and farm wastes to biochar could be important under smallholder farming systems as well, and biochar use may have applications in tree nursery production and specialty-crop management. Thus, biochar can contribute substantially to sustainable agriculture. While these benefits and opportunities look attractive, several problems, and bottlenecks remain to be addressed before widespread production and use of biochar becomes popular. The current state of knowledge is based largely on limited small-scale studies under laboratory and greenhouse conditions. Properties of biochar vary with both the feedstock from which it is produced and the method of production. The availability of feedstock as well as the economic merits, energy needs, and environmental risks-if any-of its large-scale production and use remain to be investigated. Nevertheless, available indications suggest that biochar could play a significant role in facing the challenges posed by climate change and threats to agroecosystem sustainability.