Effect Of Fertilizations On Rice Yield,quality And Emissions Of CH₄ And N₂O In Paddy Field Under Shading Conditions

Decrease in solar radiation is one of the main issues of climate change.Few reports are available regarding the effects of decreased solar radiation and fertilization on methane（CH₄）and nitrous oxide（N₂O）emissions under paddy field conditions.This study provides an experimental basis for enduring rice sustainable production and response to climate change,field experiment was conducted to investigate the effects of the NPK compound fertilizer and silicate fertilization on rice yield and the emission intensity of CH₄ and N₂O under shading conditions.The orthogonal experimental design was adopted with 3 factors and 3 levels.The shading was set at three levels,i.e.no shading（S₀,0%of shading rate）,from flowering period to maturity period shading（S₁,64%of shading rate）,and from tillering period to maturity period shading（S₂,64%of shading rate）;The NPK compound fertilizer was set at three levels,i.e.100 kg?ha^-1（F₁）,200 kg?ha^-1（F₂）,300 kg?ha^-1（F₃）;The silicate fertilizer were set at three levels,i.e.no silicate fertilizer（R₀）,slag fertilizer 200 kg?ha^-1（R₁）,and slag fertilizer 400 kg?ha^-1（R₂）.The tested soil was hydromarphic paddy soil,the tested rice variety was Nanjing 5055,the tested NPK fertilizer was high concentration NPK compound fertilizer（15-15-15）,silicate fertilizer was slag fertilizer.The main findings are listed as follows:（1）Biomass and yield of riceThe effects of shading treatment on biomass and yield were basically the same in the two-year field experiments.Shading reduced the biomass in rice.The yield components including1000-grain weight,effective panicle number,panicle number and setting rate were significantly reduced.Shading reduced the biomass in rice,which eventually led to a yield reduction by43.32%to 48.52%.The compound fertilizer and silicate fertilizer had no significant effect on biomass and yield of rice,but for yield components.Applying slag fertilizer increased rice biomass;Applying slag fertilizer significantly reduced 1000-gtain weight in 2019 and increased1000-gtain weight in 2020.（2）Rice qualityThe effects of shading treatment on rice quality were basically the same in the two-year field experiments.Shading significantly reduced the brown rice rate,milled rice rate and head rice rate.All the processing qualities were in order of S₀>S₁,S₁<S₂.Shading had no significant effect on the ratio of grain length to width and amylose content.Shading significantly increased protein content,with S₀<S₂<S₁.The NPK compound fertilization and Slag fertilization had no significant effects on the processing quality,grain length-width ratio and amylose content of rice in 2019 and 2020.The amylose content was in the sequence of F₂>F₁>F₃,protein content F₁<F₂<F₃ under the supply of the compound fertilizer.Slag fertilizer increased the head rice rate and reduced the protein content.Rational use of the compound fertilizations and slag fertilizer could improve the quality of rice.（3）CH₄ and N₂O emissions from rice soilShading extremely reduced cumulative amount of CH₄emissions and significantly increased cumulative amount of N₂O emissions.The NPK compound fertilization significantly increased the CH₄ emission 2019 and 2020,with F₁<F₂<F₃ in 2019,and F₁<F₃<F₂ in 2020.The NPK compound fertilization significantly increased N₂O emissions in 2019 and 2020,F_1<F₂<F₃.Slag fertilization had significant effect on the cumulative of CH₄ emission in 2019,R₂>R₀>R₁.Slag fertilizer decreased the CH₄emissions and increased N₂O emissions in 2020.Shading had significant effect on the sustained-flux global warming potential（SGWP）in 2019 and 2020,the NPK compound fertilizer and silicate fertilizer had significant effect on SGWP in 2019.but not significant in 2020.The effects of each treatment on the greenhouse gas emission intensity（GHGI）were not significant.Shading decreased the SGWP,but the NPK compound fertilization increased the SGWP and the greenhouse gas emission intensity（GHGI）.Slag fertilizer supply reduced the SGWP and the GHGI.CH₄ emissions in rice fields played a dominant role in the SGWP of the rice field.Under decreased solar radiation,the optimal combination of this study was suggested as 100kg/ha（F₁）and 400kg/ha（R₂）to ensure rice yield production.