The Influence Of Irrigation Amounts On Transport Characteristics Of Soil Water-salt-nitrogen In Spring Maize Fields Under Ridge Mulched With Plastic Film-furrow Irrigation In Hetao Irrigation District

With less precipitation and strong evaporation in Hetao Irrigation District（HID）,the reduction of Yellow River Diversion quota limits the development of local agriculture.Ridge mulched with plastic film-furrow irrigation（RMFI）is an irrigation method with better water-saving and salt control effects in arid irrigation area of Northwest China.However,how the different irrigation amount affects the soil water and salt movement and the growth characteristics of spring maize under RMFI system in HID has not been systematically discussed,and the mechanism of water-saving,fertilizer conservation and yield increase is not clear.The field experiment was carried out in Shuguang experimental station in HID from April to October in 2019 and 2020.Five typical irrigation rates（T1:200 mm,T2:275mm,T3:350 mm,T4:425 mm,T5:500 mm）were set to study the characteristics of soil water,salt and nitrogen migration under RMFI and its effect on spring maize yield.The results presented that:1.Different irrigation amounts affect the distribution and movement of soil water,salt and nitrogen in farmlandWith the increase of irrigation amount,salt accumulation decreased first and then increased in a"V"shape.The results showed that soil water storage of T1 and T2 was significantly lower than others,and the salt storage was significantly high.The water storage of T3 in the root zone soil layer was significantly increased,and the salt accumulation was significantly low.The water storage of T4 and T5 in the root zone soil layer was close,and the salt accumulation was gradually increased.Combined with two-years irrigation experiment,the nitrate nitrogen storage in the root zone soil layer increased first and then decreased with the increase of irrigation water.The soil fertility retention ability of T2 and T3 was strong.NO₃^--N was mainly accumulated in 0-20 cm of the surface layer,while NH₄⁺-N was leached in the surface layer and distributed evenly in the deep layer of the soil,and there was no significant difference among the treatments.2.Different irrigation amounts affect crop physiological growthWith the increase of irrigation amount,the average leaf area index and chlorophyll content first increased and then decreased,and the plant height and photosynthetic rate gradually increased,but the difference between the treatments became insignificant with the increase of irrigation amounts.The dry matter weight at maturity increased first and then stabilized with the increase of irrigation amounts,and there was no significant difference from T3 to T5.3.Different irrigation volume affects the characteristics of water and salt leachingUsing the Hydrus-2D model to simulate the water and salt transport in the three rainfall years of dry years,normal years and wet years,it is found that the amount of water leakage increases linearly with the increase of irrigation amount,and the amount of salt leaching increases first with irrigation amount and then stabilized.The leached salt amount of the 425mm irrigation water treatment was at the peak,which could significantly reduce the soil salt content.4.Different irrigation amounts affect crop yield and water and nitrogen use efficiencyThe results showed that with the increase of irrigation water,grain yield,grain nitrogen concentration and crop nitrogen uptake increased first and then decreased,water and nitrogen leaching loss and crop water consumption increased significantly,nitrogen use efficiency decreased gradually,while water use efficiency and nitrogen transfer rate increased first and then decreased.In conclusion,the results of two-year irrigation experiment and model simulation showed that the water and nitrogen use efficiency of 200 mm and 275 mm treatments was higher,but the irrigation amount was small,and the water and salt stress was high,which not only consumed the initial soil water,but also led to significantly lower nitrogen uptake,yield and grain quality than other treatments.The results showed that 350 mm treatment had less water loss,stronger salt leaching ability,more nitrogen retention,stronger ability of nitrogen transfer to grain,higher grain yield and better quality.Although the water consumption and nitrogen uptake of 425 and 500 mm treatments were significantly higher than those of 350mm treatments,they resulted in a large amount of leaching of soil water and nitrate nitrogen,which was not conducive to the maintenance of soil water and fertilizer environment,and caused gradual increase of salt accumulation,resulting in a gradual decrease in grain yield,water use efficiency and nitrogen use efficiency.Therefore,in order to meet the requirements of the mandatory reduction of water diversion from the Yellow River and the prevention and control of farmland environmental pollution,the 350 mm irrigation amount under RMFI is an important mode to meet the requirements of water saving,salt suppression,yield and quality improvement of spring maize field in HID.