[Effects of Irrigation and Biochar Application on the Respiratory Temperature Sensitivity of Paddy Soil].

The ecosystem respiration and temperature sensitivity (Q10) of paddy soil play very important roles in the emission of greenhouse gases from paddy ecosystems. Under intermittent irrigation and flooding irrigation conditions, a static opaque chamber and gas chromatography method were applied to study the regulation and influence of ecosystem respiration and Q10 using five treatments:no fertilizer (CK), conventional fertilization (NPK), 10t·hm-2 biochar with chemical fertilizer (LBC), 20t·hm-2 biochar with chemical fertilizer (MBC), and 40t·hm-2 biochar with chemical fertilizer (HBC). The results showed that:① The temperature sensitivity coefficients (Q10) of ecosystem respiration under flooding irrigation were 4.45 (CK), 7.40 (NPK), 6.44 (LBC), 4.58 (MBC), and 3.87 (HBC), respectively. Flooding irrigation significantly reduced the Q10 value of the paddy field ecosystem compared to intermittent irrigation (P<0.01). CK, NPK, LBC, MBC, and HBC decreased by 48.6%, 55.2%, 67.9%, 70.3%, and 70.8% under flooding irrigation, respectively. ② Whether intermittent irrigation or flooding irrigation was adopted, the application of fertilizer with biochar increased the respiration of the paddy field ecosystem than conventional fertilization treatment, but the effect of different biochar levels on respiration was not significant. ③ The application of chemical fertilizer with medium or low amounts of biochar increased the temperature sensitivity of respiration compared with no fertilization in the paddy field ecosystems (P<0.05), but both MBC and HBC treatments reduced the Q10 value of paddy field ecosystem compared with NPK. Furthermore, the temperature sensitivity of respiration in the paddy field ecosystem decreased with an increase in the level of biochar application. Therefore, under the two irrigation methods, HBC treatment was more effective than LBC and MBC treatments to inhibit the effect of increasing soil temperature on the respiration of the ecosystem.

[Effects of Biochar Application Rates on Greenhouse Gas Emissions in the Purple Paddy Soil].

In order to explore the effects of different amounts of biochar applied in purple paddy soil on greenhouse gas (GHG) emissions, potted experiments using a static opaque chamber and gas chromatography method were used to study the regulations and influences of biochar on soil greenhouse gas emission using five treatments:no fertilizer (CK), conventional fertilization (NPK), 10 t ·hm-2 biochar+NPK (LBC), 20 t ·hm-2 biochar+NPK (MBC), and 40 t ·hm-2 biochar+NPK (HBC). ① Soil CH4 emission flux reduced significantly with all biochar application treatments; the emission flux followed the order, from large to small, of NPK > CK > LBC > MBC > HBC. The CH4 emission flux of each treatment showed a single peak curve, and the peak value was mainly concentrated in the late growth stage of the paddy cropland. During the entire observation period, the emission flux of CH4 was between -0.05 mg ·(m2 ·h)-1 and 47.34 mg ·(m2 ·h)-1. The CO2 emission flux of each treatment was complicated and ranged from 32.95 mg ·(m2 ·h)-1 to 1350.88 mg ·(m2 ·h)-1. The CO2 emission flux of the LBC and MBC treatments showed bimodal curves, and the CO2 emission flux of other treatments showed single peak curves. In addition, all biochar treatments delayed the peak time of the CO2 emission flux. The N2O emission flux of each treatment ranged from -309.39 to 895.48 µg ·(m2 ·h)-1, and the N2O emission flux of the LBC treatment showed a bimodal curve, while other treatments showed single peak curves. ② Compared with the CK treatment, biochar treatment can significantly reduce the cumulative emissions of CH4 and promote the cumulative emissions of CO2 and N2O. The average amount of CH4 cumulative emissions followed the order CK > LBC > MBC > HBC, while the average amount of CO2 cumulative emissions followed LBC > MBC > HBC > CK, and the average amount of N2O cumulative emissions followed HBC > MBC≈LBC > CK. Compared with conventional fertilization treatment, different application rates of biochar addition significantly reduced CH4 and CO2 emissions. As more biochar was added, CH4 and CO2 cumulative emissions were lower. Although the regulation of N2O cumulative emissions on biochar addition was not obvious, the application of nitrogen fertilizer could promote the emission flux of N2O to some extent. ③ Over the time scale of 100 years, the integrated global warming potentials (GWP) of CH4 and N2O emission under different biochar treatment were decreased significantly, indicating that biochar combined with chemical fertilizer is an effective GHG emission reduction measure.