Abstract: The solar radiation weakening is one of the main characteristics of climate change. It is still unclear concerning the impact of the solar radiation weakening on the emissionsof greenhouse gas (CH4 and N2O) and carbon emission intensity in rice-wheat soils. A field simulation experiment was conducted to investigate the emissions of greenhouse gases in rice-winter wheat rotation ecosystem and the changes in carbon emission intensity with field managements under shading conditions. The two-factorial experiment was adopted with 3 levels of shading intensities, i.e. control (CK, no shading), light shading (S1, 61.26% of shading rate) and heavy shading (S2, 83.65% of shading rate). The shading treatment was performed by covering the crop canopy with black sunshade net and periodically adjust the net hight to maintain the distance at 30 cm between the net and crop canopy. Field managements (water management/planting date) were set 2 levels, i.e. traditional flooding irrigation/conventional planting date (F/P; rice F, water depth 5cm; winter wheat P, planting time November 6, 2017) and moistening irrigation/late planting (M/L; rice M, anhydrous layer; winter wheat L, planting time November 13, 2017). The closed chamber method was used to measure the emission fluxes of CH4 and N2O from 8:00 am to 11:00 am at one-week interval. The tested soil was a hydromorphic paddy soil. The tested cultivars of rice and winter wheat were Nanjing 5055 and Sumai 188, respectively. The field experiment was performed at the Station of Agricultural Meteorology, Nanjing University of Information Science and Technology, Nanjing, Jiangsu prov., China. The results showed that, shading (S1, S2) significantly reduced the cumulative CH4 emission in rice-winter wheat rotation ecosystem under traditional flooding irrigation/conventional planting by 68.08% and 42.22%, and slightly increased the CH4 emission under moistening irrigation/late planting. Moistening irrigation /late planting significantly reduced the cumulative CH4 emissions by 15.6% to 86.61%. The shading significantly increased the cumulative N2O emissions from rice-winter wheat rotation ecosystem by 63.59% to 111.40% (P<0.05), and the cumulative N2O emissions were slightly reduced under traditional flooding irrigation/conventional planting. In terms of global warming potential, compared with no shading, shading significantly reduced the contribution of CH4 and N2O to the global warming potential in rice-winter wheat rotation ecosystem under traditional flooding irrigation/conventional planting date by 36.32% to 62.51%, but slightly increased under moistening irrigation/late planting. The global warming potential of CH4 and N2O under the moistening irrigation/late planting was reduced by 12.1% to 83.22%, compared with the traditional flooding/conventional planting. This study indicates that shading significantly increased the carbon emission intensity of CH4 and N2O in rice-winter wheat rotated soil, while moistening irrigation/late planting without shading significantly reduced the carbon emission intensity of CH4 and N2O, which ensured the yield and improved the ecological benefits.

Key words: Methane, Nitrous oxide, Carbon intensity, Shading, Rice-winter wheat rotation