Meta-Analysis of N₂O Emissions as Affected by Biochar Amendment in Northern China

Global warming is one of the eco-environmental problems of most concern to scientists. N₂O, an atmospheric greenhouse gas, has been widely studied because of its high warming potential. As an excellent soil conditioner, biochar has a very broad research value and application path in the farmland. This work examined the impact of biochar application on N₂O emissions reduction potential of farmland soils in northern China by meta analysis and path analysis. The results were as follows: the N₂O emissions reduction potential changes corresponded with different biochar preparation materials, preparation temperature, C/N ratio and pH. Biochar is more suitable for application in soil with a bulk density < 1.3 g cm⁻³, sandy loam texture, neutral pH, organic matter content 20–30 g kg⁻¹, soil C/N ratio 10–20, and total nitrogen < 2 g kg⁻¹. At the same time, the maximum reduction of N₂O emissions can be achieved in a scenario where the biochar is applied at 20 t ha⁻¹- 40 t ha⁻¹ and the application of nitrogen fertilizer is 100–200 kg N ha⁻¹. Under the above ideal conditions, this study selected the data of soil mineralized nitrogen (X₁), soil organic matter content (X₂), soil water content (X₃), average temperature (X₄), total nitrogen (X₅), and N₂O emissions (Y) for correlation analysis and path analysis, and finally obtained the multiple stepwise regression equation between N₂O emissions and various impact factors as follows: Y = -45.9102 + 0.6874X₁ + 0.4634X₂ + 0.3249X₃ + 0.2698X₄ + 0.2218X₅ (R² = 0.826, p < 0.01, n = 87). The direct relationships between N₂O and soil mineralized nitrogen and soil organic matter content were very significant (P < 0.01). The second is soil water content, average temperature and total nitrogen. Indirect relationships between N₂O and average temperature, total nitrogen and mineralized nitrogen were significant (P < 0.05).