Biochar single application and reapplication decreased soil greenhouse gas and nitrogen oxide emissions from rice–wheat rotation: A three-year field observation

Abstract

Biochar application to soil has been proposed as a promising tool for sequestering carbon, ensuring food security, mitigating greenhouse gases (GHGs), and lowering nitrous oxide (N2O) and nitric oxide (NO) emissions. Efforts and observations to determine whether biochar can be repeatedly amended to soil to further sequester carbon while meeting those targets from long term and practical perspective are limited. A three-year field experiment was conducted to observe simultaneous methane (CH4), N2O, and NO emissions in a rice–wheat rotation system, where six treatments were established as follows: control plot without biochar (B0), biochar-enriched soil with biochar applied once in 2012 at 20 t ha−1 (B20−) and 40 t ha−1 (B40−), reapplication of half rate biochar in 2015 at 10 t ha−1 (B20+) and 20 t ha−1 (B40+) to the above described biochar-enriched soils, single application of biochar in 2015 to the control soil at 40 t ha−1 (B40). Then a series of incubation experiments explored the mechanism for mitigating trace gases. The results showed that compared with nonamended soils, the soils with the single biochar application and the biochar reapplication had similar effects on CH4, N2O, and NO emissions, significantly decreasing them by 14.5%–27.1%, 31.5%–43.4%, and 22.4%–33.6%, respectively, when compared with non-amended soils. The decrease in CH4 emissions was largely due to the decrease in CH4 production and the increase in CH4 oxidation in the biochar application treatments. Biochar single and reapplication significantly decreased yield-scaled GHGs by an average of 31.5% and yield-scaled N-oxides by an average of 41.0%. Nonetheless, the effectiveness of biochar in decreasing yield-scaled GHGs and yield-scaled N-oxides did not increase with the biochar reapplication at the two different application rates. Both single and reapplied biochar appeared to be promising practices to mitigate GHG and N-oxide emissions from the rice–wheat rotation system. Biochar can be repeatedly applied for further carbon sequestration while not hindering improvements in crop yield or mitigation of other GHGs and N-oxides.