Mitigating N2O and CH4 emission via crop husbandry practices under elevated CO2 and warming

Many studies have shown that future climate warming and the elevation of atmospheric carbon dioxide (CO2) will increase methane (CH4) and nitrous oxide (N2O) from terrestrial ecosystem. However, it remains unclear how to offset this increment in agroecosystem. Thus, the objective of this study was to test the possibility of mitigating their emission by optimizing crop husbandry methods. To do so, CH4 and nitrous oxide N2O were monitored under a couple of crop husbandry practices in a rice-winter wheat rotation system in a T-FACE facility. The facility was designed to simulate atmospheric CO2 enrichment and climate warming. The crop husbandry practices tested including cultivar selection, addition of nitrification inhibitor (CP) and biochar-based inorganic fertilizer (BF), and increasing rice transplanting density. In winter wheat growing season, we found that N2O emission rate of Sumai 188 (cultivar name) under elevated CO2 was similar to the rate under ambient CO2. However, N2O emission rate of Yangmai 16 and Zhenmai 9 (cultivar name) under elevated CO2 increased by 86.4 % and 38.9 % respectively compared to ambient CO2. Different from elevated CO2, warming had little effect on N2O emission of Yangmai 16 and Sumai 188 whereas it decreased N2O emission for Zhenmai 9 by 37.9 %. CP addition decreased N2O emission by 15.8 % while BF had no effect on N2O emission. N2O emission under BF was 28.3 % greater than that of CP. However, the addition of CP and BF did not alter the response of N2O emission to elevated CO2 and warming. In rice growing season, higher planting density increased N2O emission by 119.3 % from 0.497 kg N ha-1 to 1.090 kg N ha-1 under ambient CO2, whereas it had no effect under elevated CO2. Nevertheless, increasing rice planting density did not change the response of the aggregate emission of CH4 and N2O (in CO2 equivalent) to elevated CO2 and warming. In conclusion, under future climate warming and elevated atmospheric CO2, we could mitigate N2O emission by selecting crop cultivars with greater nitrogen use efficiency and applying nitrification inhibitors in wheat season; in rice season, however, increasing rice transplanting density will not increase CH4 and N2O emission.