Effects Of Water And Nitrogen Regulation In Salinized Farmland On Soil Fertility And Water And Salt Nutrients In Freezing And Thawing Period

Hetao Irrigation District is an important grain and oil production base in China,and the problem of soil salinization restricts the development of the region.In this paper,based on the problems of poor soil water,low water and nitrogen utilization rate and secondary salinization control in salinized farmland,different water and nitrogen regulation modes were set up to carry out field experiments,and the effects of water and nitrogen regulation on corn yield and water and nitrogen use efficiency were studied.A comprehensive analysis of the effect of water-nitrogen-yield regression simulation equation on corn yield was established.Comprehensive evaluation of soil fertility in the next year based on RAGA-PPC model.The effects of single factor application of water and nitrogen on the soil and water environment during the freezing and thawing period were analyzed.Principal component analysis was used to evaluate the soil fertility in the next year.The main findings are as follows:(1)The amount of irrigation and nitrogen application had significant effects on maize grain yield and its constituent factors.The interaction between the two had significant effects on dry matter quality and grain yield,and had significant effects on 100-grain weight and grain number.When the amount of irrigation is the same,the application of nitrogen fertilizer will increase the water use efficiency within a certain range.When the nitrogen application level is the same,the water use efficiency is as follows:high water<middle water<low water.Under high nitrogen treatment,nitrogen fertilizer has low agronomic efficiency.The agronomic efficiency of nitrogen fertilizer reached a maximum in low water in medium water.Nitrogen application and irrigation and interaction have significant effects on maize agronomic efficiency of nitrogen.(2)A water-nitrogen-yield binary quadratic regression model was established,and the actual yield and the simulated yield have a high degree of fitness.The two factors of water and nitrogen have a positive effect on the yield within a certain range.With the increase of water and nitrogen,the yield is in line with the diminishing returns.The order of positive effect size is:nitrogen application amount>irigation amount>interaction effect.The maximum yield simulation can reach 12696kg/hm2,the corresponding irrigation amount is 317 mm,and the nitrogen application rate is 261kg/hm2.The optimal water and nitrogen combination value of different target yields is basically consistent with the measured output,which can provide a theoretical basis for local production practice.(3)During the freezing and thawing period,soil nutrients mainly concentrated on the soil surface layer,and the contents of total nitrogen,alkali nitrogen and organic matter increased first and then decreased during the freezing and thawing period,and the maximum appeared in the maximum freezing depth.After autumn pouring,the soil aggregates increase with the increase of nitrogen application rate during the freezing period,and the high nitrogen treatment aggregates decrease during the melting period,and the salt will affect the agglomeration structure.The C/N treatment with different nitrogen application rates increased by 0.9-2.02%as the freeze-thaw period increased.(4)Using the principal component analysis method to comprehensively evaluate the soil fertility before spring sowing with a single factor,the comprehensive score is:N3<N0<N1<N2,W3<N2<N1.The highest nitrogen treatment score was obtained.It is recommended that the nitrogen application rate during the growth period of maize in this area is 225 kg/hm2.The low water treatment score is the highest,but the soil salinity rate does not meet the crop demand.Therefore,it is recommended that the salinized soil corn irrigation system is 225mm for the growth period and 150mm for the autumn irrigation.(5)Based on the RAGA-PPC model,the comprehensive evaluation of soil fertility before spring sowing was carried out by different water and nitrogen.According to the evaluation results,the soil fertility was better in the treatment of nitrogen,medium water and low water and high water and low nitrogen.Combined with corn grain yield analysis,the highest grain yield was high water and high nitrogen and medium water nitrogen treatment,the difference between the two is not significant.In the early stage of water and nitrogen regulation and soil fertility before spring sowing,it is recommended that the water and nitrogen regulation mode in this area is W2N2(nitrogen application rate:225 kg/hm2,irrigation volume:225+150 mm).