Effects Of Biochemical Inhibitors On Greenhouse Gas Emissions And Nitrogen Use Efficiency In Paddy Fields Under Water-Saving Irrigation

Rice field is an important source of greenhouse gas emission.Meanwhile,resource waste and environmental problems caused by nitrogen fertilizer application need to be solved urgently.Nitrification inhibitors and urease inhibitors have been considered by many scholars to improve the efficiency of nitrogen use and reduce the negative effects caused by nitrogen loss.Water-saving irrigation can not only save water resources and improve resource utilization efficiency,but also is considered as the most effective management measure to reduce emissions of rice fields.Therefore,it is a new idea and method to explore the combined effect of water-saving irrigation and biochemical inhibitors on greenhouse gas emission reduction in paddy fields and the development of sustainable agriculture with high yield and high efficiency.The experiment was carried out in the Modern Agriculture Demonstration Center base of Wuxu city,Hubei Province from 2021 to 2022.The two-factor split zone design was adopted,and the water treatment was conventional irrigation（CF）and alternate wet and dry irrigation（AWD）.Fertilizer treatment consisted of conventional fertilization（U）,conventional fertilization+nitrification inhibitor（NI）,conventional fertilization+urease inhibitor（UI）,conventional fertilization+nitrification inhibitor（NI）+urease inhibitor（UI）.The effects of different water management and biochemical inhibitors on soil physicochemical properties,greenhouse gas emissions,ammonia volatilization,nitrogen use efficiency,rice yield,crop water use efficiency,economic benefit and net eco-economic benefit of paddy field were studied.Key results include:（1）Both water management and biochemical inhibitors can significantly affect the contents of NH₄⁺-N and NO₃^--N in soil.Under conventional fertilization,AWD treatment reduced the NH₄⁺-N content by 16%and increased NO₃^--N content by 48%in the key growth period of rice.The effects of DMPP（nitrification inhibitor）or NBPT（urease inhibitor）on soil NH₄⁺-N content were opposite.Under CF treatment,DMPP alone increased soil NH₄⁺-N content by 36.5%on tillering stage and decreased NO₃^--N content by 34.8%on tillering stage,NBPT alone decreased soil NH₄⁺-N content on tillering stage and full head stage,but had little effect on soil NO₃^--N content.The combined addition of DMPP and NBPT had little effect on soil NH₄⁺-N,but could reduce soil NO₃^--N content by 20.9%on average.Under AWD treatment,the effect of biochemical inhibitors on NH₄⁺-N and NO₃^--N contents in soil was the same as that under CF treatment,but the effect was better under CF treatment.（2）DMPP had a significant effect on the nitrification potential of soil.Under the same water treatment,adding DMPP alone or combined with NBPT significantly decreased the nitrification potential of rice at tillering stage,full head stage and maturity stage by 11.8-32.5%.The addition of NBPT had little effect on soil nitrification potential,but had significant effect on soil urease activity.The addition of NBPT alone significantly decreased the soil urease activity at tiller stage and full head stage of rice under conventional fertilization by 20.2-36.4%.（3）AWD treatment can significantly reduce irrigation water use,improve water resource utilization efficiency by 26%,improve soil Eh,and significantly reduce CH₄emission under CF treatment.Compared with CF treatment,AWD treatment significantly reduced CH₄ cumulative emissions by 43.5-53.6%,but also increased N₂O cumulative emissions by 10.2-43.5%.The effect of DMPP alone on greenhouse gas emission reduction was better than that of NBPT alone or DMPP combined with NBPT.Under CF treatment,the addition of DMPP can significantly reduce the cumulative CH₄ emissions by 18%and the cumulative N₂O emissions by 22.4%.Under AWD treatment,the addition of DMPP or NBPT alone can significantly reduce the cumulative emission of N₂O by 31.6%.Considering the comprehensive effect of CH₄ and N₂O,AWD treatment can significantly reduce GWP and GHGI by 42.5-52.3%and 41.4-58.5%,respectively,compared with CF treatment.Under CF treatment,adding DMPP alone has the best effect on paddy field emission reduction.Significantly reduced GWP and GHGI by 18.1%and 19%under conventional fertilization,respectively.（4）The peak value of ammonia volatile flux appeared 1-3 days after three times of fertilization,especially after the application of base fertilizer.Adding DMPP alone significantly increased the cumulative ammonia volatilities of the whole growth period of the paddy field by 10%-18.4%,adding NBPT alone significantly reduced the cumulative ammonia volatilities of the whole growth period of the paddy field by 11.4-14.2%,and the combined addition of DMPP and NBPT had no effect on the cumulative ammonia volatilities of the whole growth period of the paddy field.（5）The addition of biochemical inhibitors had a significant effect on the nitrogen use efficiency of rice at mature stage.Under the same water condition,adding biochemical inhibitors alone or in combination could significantly increase nitrogen uptake efficiency of rice by 9.6%-24.7%.Water management had little effect on yield,while NBPT had significant effect on yield.Under CF treatment,adding NBPT alone could increase the yield by 8.9%under conventional fertilization.Under AWD treatment,NBPT alone or DMPP combined with NBPT significantly increased the yield under conventional fertilization by 9.6%and 11.4%,respectively.（6）Under CF treatment,EB and NEEB added with NBPT alone were the highest,which increased by 12%and 13.5%under conventional fertilization,respectively.Under AWD treatment,EB and NEEB added with NBPT alone or combined with DMPP and NBPT showed the best effect,both of which increased by about 14%.In conclusion,the single addition of NBPT under alternating wet and dry irrigation can not only save limited fresh water resources while ensuring stable yield,but also reduce global warming potential and ammonia volatilization of paddy fields,and improve nitrogen use efficiency.It is a good green and low-carbon technology,which plays an important role in sustainable agricultural development.