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

In the last decade, an increasing number of studies have reported that soil nitrous oxide (N2 O) emissions can be reduced by adding biochar. However, the effect of biochar amendment on soil N2 O 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 N2 O emissions during FTC, and estimate the relationships between N2 O emissions and soil inorganic nitrogen contents/microbial biomass content/enzyme activities. The results showed that biochar amendment suppressed soil N2 O emissions by 19.9-69.9% as compared to soils without biochar amendment during FTC. However, N2 O emissions were only significantly correlated to soil nitrate nitrogen (NO3 - -N) contents, which decreased after biochar amendment, indicating that the decreased soil nitrification by adding biochar played an important role in mitigating N2 O emissions during FTC. Further studies are needed to estimate the effectiveness of biochar amendment on reducing freeze-thaw induced N2 O emissions from different soils under field conditions.