Effects Of Nitrogen Fertilizer And Density Regulation On Greenhouse Gas Emission And Resources Utilization Efficiency Of Double-cropping Rice Field

Nitrogen is an essential nutrient element during the growth and development of rice.Appropriate nitrogen application can increase rice yield,However,in recent years,excessive nitrogen fertilization has been serious,resulting in low nitrogen use efficiency in paddy fields,increased greenhouse gas emissions in rice fields,polluted farmland soil and atmospheric environment,and restricted the efficient and sustainable production of rice.Reasonably reducing the application of nitrogen fertilizer and increasing the density to regulate the loss of yield caused by the reduction of nitrogen have become current research hotspots.Aiming at the effects of reasonable density control technology under the background of nitrogen reduction and different nitrogen density control measures on greenhouse gas emissions and resource utilization efficiency of double-cropping rice fields,this study took the conventional nitrogen density model（CK）as a control and set two nitrogen reduction amounts（N₁and N₂）combined with three planting densities（D₁,D₂,D₃）in a two-factor field experiment to analyze the effects of each nitrogen density control combination on greenhouse gas emissions,climate resource utilization efficiency,nitrogen utilization efficiency,yield and soil nutrient status to discuss the resource-saving and environment-friendly nitrogen density regulation measures in rice production.The main research result are as follows:（1）Nitrogen reduction and densification regulation has effectively reduced greenhouse gas emissions from rice fields.The cumulative emissions of CH₄,N₂O,and CO₂from the nitrogen reduction and densification treatments in the double-cropping rice year were significantly lower than the conventional nitrogen density treatment（CK）,and the reduction degrees of the three greenhouse gases reached 6.8%～26.1%and 25.1%respectively.61.9%,11.4%～17.4%.Among the treatments,the N₂D₂treatment has the most obvious annual emission reduction effect.The cumulative emissions of CH4,N₂O,and CO₂are 1207.0kg·hm^-2,0.35 kg·hm^-2,and 26100.5 kg·hm^-2,respectively.Compared with the control,the GWP of the treatments of reducing nitrogen and increasing density was significantly reduced.In the early and late rice seasons,N₁D₂and N₂D₂decreased the most,with a decrease of 17.1%and 22.1%.The results of the two-factor analysis showed that the amount of nitrogen fertilizer had a very significant impact on the emissions of the three main greenhouse gases（P<0.01）,the nitrogen density interaction significantly affected the CH₄emissions,and the N₂O and CO₂emissions were not significant.（2）Increasing density can increase the seed setting rate of early and late rice,and increasing density under reduced nitrogen conditions is beneficial to increase rice yield.The yield of early rice in each treatment was:N₁D₃>N₁D₂>N₂D₃>N₁D₁>N₂D₂>N₂D₁>CK.Compared with the control,each treatment increased by 24.9%,18.3%,11.5%,5.6%,1.4%,0.9%,respectively.Theorderoflatericeyieldis:N₂D₃>N₁D₃>N₁D₂>N₂D₂>N₁D₁>N₂D₁>CK,with the increase in order of 27.8%,16.7%,14.6%,13.6%,12.0%,6.3%.In the anniversary year,N₂D₃has the best yield increase effect,followed by N₁D₃.（3）Nitrogen reduction and densification have significantly improved the annual solar energy utilization rate,heat energy utilization rate and precipitation utilization rate.The annual solar energy utilization rate（RUE,%）of each treatment is distributed between 0.65and 0.81,the heat energy utilization rate(HUE,kg·℃^-1·d^-1·hm^-2)is distributed between 3.16and 3.93,and the precipitation utilization rate(PEU,Kg·hm^-2·mm^-1)distributed in10.38～13.11.Compared with the control,the light energy,heat energy and water use efficiency of each nitrogen density control treatment increased by 4.9%～23.7%,5.2%～24.3%,7.0%～26.3%,respectively.Among them,N₁D₃and N₂D₃have the highest resource utilization rate,followed by N₂D₂.（4）The soil alkali-hydrolyzable nitrogen content of each treatment of reducing nitrogen and increasing density decreased.Compared with CK,the decrease range of early rice season was 8.0%～22.0%,and the late rice was 7.2%～22.0%.Reasonable reduction of nitrogen and densification can increase the nitrogen accumulation of plant ears.The N₁D₃combination had the highest nitrogen accumulation in each treatment,which increased by11.9%～34.7%compared with the control;the N₂D₁treatment had the lowest nitrogen accumulation,which was comparable to CK,the ratio decreased by 13.1%～26.0%,and each nitrogen density control treatment can increase the partial productivity of nitrogen fertilizer,and the increase range is 17.3%～59.7%,and N₂D₃is the highest for early and late rice.（5）The soil nutrient content of each nitrogen density treatment decreases with the deepening of the soil layer,and as the amount of nitrogen decreases,the soil available potassium content decreases,while the density increases the soil organic matter and available potassium content.Nitrogen application rate significantly affects the available potassium and available phosphorus content of the cultivated layer,and the density significantly affects the total phosphorus and available phosphorus content of the cultivated soil.A reasonable combination of nitrogen density can maintain the balance of paddy soil nutrients and ensure the sustainable use of soil resources.（6）Each treatment reduces greenhouse gas emissions to varying degrees and improves resource utilization efficiency.Among them,N₂D₂treatment has the best emission reduction effect,and N₁D₃treatment has the highest nitrogen accumulation,climate resource utilization and yield performance.In general,N₂D₃in each treatment can effectively reduce the system’s warming potential,increase the partial productivity of nitrogen fertilizer and the nitrogen fertilizer harvest index,and maintain a high utilization rate and yield of rice climate resources,with the best overall performance.