Response of N ₂O emissions to biochar amendment in a cultivated sandy loam soil during freeze-thaw cycles

Abstract

In the last decade, an increasing number of studies have reported that soil nitrous oxide (N ₂O) emissions can be reduced by adding biochar. However, the effect of biochar amendment on soil N ₂O emissions during freeze-thaw cycle (FTC) is still unknown. In this laboratory study, biochar (0%, 2% and 4%, w/w) was added into a cultivated sandy loam soil and then treated with 15 times of FTC (each FTC consisted of freeze at −5/−10 °C for 24 h and thaw at 5/10 °C for 24 h), to test whether biochar can mitigate soil N ₂O emissions during FTC, and estimate the relationships between N ₂O emissions and soil inorganic nitrogen contents/microbial biomass content/enzyme activities. The results showed that biochar amendment suppressed soil N ₂O emissions by 19.9–69.9% as compared to soils without biochar amendment during FTC. However, N ₂O emissions were only significantly correlated to soil nitrate nitrogen (NO ₃ ⁻-N) contents, which decreased after biochar amendment, indicating that the decreased soil nitrification by adding biochar played an important role in mitigating N ₂O emissions during FTC. Further studies are needed to estimate the effectiveness of biochar amendment on reducing freeze-thaw induced N ₂O emissions from different soils under field conditions.