CH_4 and N_2O emissions from double-rice field under different intensified cultivation patterns in Hunan Province

Methane (CH4) and nitrous oxide (N2O) from rice field in the double rice ecosystem in Hunan province were studied using static-chamber/gas chromatography. Five cultivation patterns or treatments were established including NN (no N as control), FP (farmers′ practice), YE (10%～15% higher in yield and 15%～20% higher in N use efficiency), HY (30%～40% higher in yield), and HE (20%～30% higher in yield and 30%～50% higher in N use efficiency). The results showed that cumulative seasonal CH4 emissions ranged between (206.5±37.5) kg · hm-2 (FP, early rice) and (490.5±65.7) kg · hm-2 (HE, late rice) while cumulative seasonal N2O emissions ranged between (0.08±0.05) kg · hm-2 (NN, early rice) and (0.326±0.15) kg · hm-2 (HY, late rice). During the rice growing season, CH4 and N2O emissions were significantly affected by different cultivation patterns (p0.05). CH4 emissions under HE pattern increased significantly by 62%～87% during the late rice growing season. Except for NN, N2O emissions from the four fertilized patterns did not differ significantly among each other. The fallow period was a vital source of CH4 and N2O emissions which accounted for 9.7%～19.7% and 42%～62%, respectively, of the total annual emissions. Global warming potential (GWP) of CH4 emissions dominated the total GWPs under the double-rice ecosystem for all patterns, accounting for more than 95% of the total GWPs. The application of nitrogen fertilizer reduced greenhouse gas intensity (GHGI) significantly by increasing the rice yield. The YE and HY patterns produced lower GHGIs than other patterns, with only (0.97±0.16) kg(CO2-eq) · kg-1 of yield for the HY. Therefore, as compared to the FP, the YE and HY patterns should be promoted due to the increased rice yields and nutrient use efficiency and the reduced GHGI; while the HE pattern produced relatively higher GWP and GHGI thus deserving further research for greenhouse gas mitigations.