Effect Of Irrigation With Saline Water And Nitrogen Forms On N₂O And CO₂ Emission In Farmland Soil Of The North China Plain

The increasing greenhouse gas emissions has became the main factor caused global climate change,and reducing greenhouse gas emissions is a hot contemporary issue facing humankind.Global climate change has exacerbated regional extremes,such as drought.In arid-semiarid areas,people often use saltwater irrigation to irrigate farmland to alleviate the shortage of freshwater resources,but the salinity brought by irrigation also makes the soil unavoidably affected,resulting in changes in the physical and chemical properties and biological properties of the soil,which in turn affects crop growth and yield,in order to offset the disadvantages brought by saline water irrigation,people explore the application of different forms of nitrogen fertilizer to promote the stable yield and high yield of crops,but the specific technical theory has not yet lacked scientific systematic research.Improper use of nitrogen will not only cause waste of resources and environmental pollution,but also cause secondary salinization of the soil,which is not conducive to today's agricultural production methods with low-carbon green goals.Therefore,the effects of different nitrogens on soil physicochemical properties,soil nitrification-denitrification potential and greenhouse gas emissions under saline water irrigation were studied by setting up indoor culture experiments of three saline water concentration gradients(0 g/L,6 g/L and 12 g/L)and three nitrogen treatments(nitrate nitrogen,ammonium nitrogen and organic nitrogen)under saline water irrigation.The results can provide data support and theoretical basis for the accurate assessment of greenhouse gas emissions from farmland after the implementation of irrigation practice reforms in water-scarce areas and the achievement of low-carbon emission reduction targets.The main results were as follows:(1)There were no statistical differences in the interaction between saline water concentration,nitrogen morphology and field water holdings on soil p H and EC means.Saline water concentration interacts with field holding and soil p H and EC,while saline water concentration interacts with nitrogen speciation only on p H.Under saline water irrigation,with the increase of saline water concentration,the soil p H value and EC value showed an increasing trend,and under different waters,the p H and EC under70%FC were also higher than 50%FC,and the effect of nitrate nitrogen on p H was the most significant(P<0.05),and the addition of nitrogen had no significant effect on changes in EC.(2)The nitrification and denitrification rates of soil are affected by irrigation water,saline water concentration and nitrogen form to varying degrees.Soil nitrification rate will be inhibited with the increase of saline water concentration in the early stage of culture,and will have a promoting effect under high concentration of saline water in the late stage,and will decrease with the increase of water.Under the condition of saline water irrigation,the addition of inorganic nitrogen is conducive to the nitrification of the soil.The denitrification rate of soil showed an overall upward trend with the increase of saline water concentration,and the denitrification rate of 6 g/L saline water concentration under 70%FC reached the maximum.The addition of organic nitrogen under clean water conditions contributes to soil denitrification,while under saltwater irrigation,the addition of nitrate nitrogen is more conducive to denitrification.(3)Both N₂O and CO₂fluctuated during the incubation period,and both had brief emission peaks at the beginning of the culture,the average emissions of N₂O under 70%FC were significantly higher than those under 50%FC,and the emissions of CO₂were also more intense under high moisture.There were interaction effects between different saline water concentrations and nitrogen forms and field water holdings on cumulative N₂O emissions(P<0.05),but no interaction effects on cumulative CO₂emissions(P<0.05).Under saline water irrigation,the cumulative emission of N₂O will decrease with the increase of saline water concentration,while the addition of inorganic nitrogen to the soil is more conducive to inhibiting N₂O emissions,and under fresh water irrigation,organic nitrogen is more likely to inhibit.