Study On Technical Parameters Of Subsurface Drainage In Saline Cotton Field With Drip Irrigation Under Mulch

Soil salinization is a global problem that leads to soil degradation and affects the sustainable development of irrigated agriculture.Because of its advantages of high efficiency and water saving,drip irrigation under mulch has been widely used in Xinjiang for more than 20 years.However,soil salt accumulation will occur in the year of drip irrigation under mulch,in the long run,the secondary salinization of drip irrigation under mulch in farmland will be more serious.Subsurface drainage is a highly effective technology to solve the problem of waterlogging and salinization,It has dual functions of regulating groundwater level and reducing soil water and salt content.However,it is still unable to clearly describe the law of soil water and salt movement under the condition of subsurface drainage,which limits the potential of subsurface drainage technology in cotton field production under drip irrigation to a certain extent.Therefore,it is urgent to study the response mechanism of soil water and salt distribution to different parameters of subsurface drainage,and determine the soil desalination mechanism of subsurface drainage on drip irrigation cotton field under mulch and its effect on crop growth and yield.In the experiment,two factors,namely,spacing and depth of subsurface pipe were selected,and three spacing levels of 10m(W10),20m(W20)and 30m(W30),and two depth levels of 0.8m(D0.8)and 1.1m(D1.1)were set to carry out the experiment of subsurface drainage improvement in cotton field under saline film in southern Xinjiang.By measuring soil moisture and salt,crop physiological growth(seedling rate,plant height,leaf area,dry matter mass,root activity,chlorophyll content),yield(plant number,boll number per plant,boll mass per plant,actual seed cotton yield)and other indicators,the suitable subsurface drainage technical parameters based on soil moisture and salt distribution,desalination rate,groundwater depth,cotton physiological growth and yield were determined.The main conclusions are as follows:(1)Compared with CK,subsurface drainage significantly reduced soil moisture and salt content,and both decreased with the decreased of subsurface pipe spacing and depth;Under the condition of subsurface drainage,the soil of drip irrigation under mulch is desalinated within a year and between years,which can appropriately reduce the winter and spring irrigation quota or avoid winter and spring irrigation in southern Xinjiang,so as to achieve the purpose of water saving.(2)The effect of subsurface drainage on the desalination efficiency of drip irrigation under mulch was significant,and the desalination efficiency would be higher for the soil with higher salt content.Under the condition of the same irrigation quota,the smaller of subsurface pipes spacing and the depth,the better of desalination effect;under the condition of the same soil leaching effect,the spacing of subsurface pipes increases,and the increment of irrigation quota increases in multiple.The subsurface drainage can effectively reduce the depth of groundwater level,and can reduce the impact of natural groundwater level on the depth of underground in subsurface drainage condition.(3)Compared with CK,subsurface drainage significantly improved the physiological growth and yield index of cotton,and the physiological growth and yield index of cotton increased significantly with the decrease of subsurface pipe spacing.Taking soil moisture,salt and cotton physiological growth index as independent variables,path analysis was conducted on actual seed cotton yield,the results showed that soil moisture,salt,cotton emergence rate,dry matter quality and chlorophyll content had significant contribution to the actual seed cotton yield,The effect of cotton emergence rate on cotton yield was the most significant,The most significant contribution to the high yield of cotton is through the way of reducing soil salt content and increasing the emergence rate of cotton.(4)Taking soil water and salt distribution,desalination rate,groundwater depth and cotton physiological growth and yield as evaluation indexes,the suitable technical parameters of subsurface drainage were determined as spacing of 10 m and depth of 0.8 m.