Effects Of Different Drip Irrigation Methods On Soil Water-salt Transport And Crop Growth In Salinized Cotton Field

In view of the salinization risk of existing drip irrigation under film and low efficiency of flood irrigation in non-growth stage,this study aims to improve the efficiency of water saving and soil salinity reduction in saline-alkali cotton field.Through the study of water and salt regulation mechanism and crop effect of integrated irrigation and drainage in saline-alkali cotton field during growth stage,the effect of different drip irrigation technology and irrigation quota on water and salt transport,soil desalting rate,cotton growth index and yield index were explored,and the optimal control strategy of water and salt was proposed under the integration of irrigation and drainage in growth period.In this study,cotton was selected as the research object,and field experiments were carried out in the east side of Moguhu Lake(85°58’13"E,44°28’49"N)of no.146 Regiment of the Eighth Agricultural Division of Xinjiang Production and Construction Corps from April to September 2020.Two drip irrigation methods(W,Subsurface drip irrigation SW)and three irrigation levels(W1:120 mm+80%ET_c,W2:240 mm+80%ET_c,W3:360 mm+80%ET_c;Among them,120 mm,240 mm and 360 mm are irrigation and salt water quota in growth period,and 80%ET_c is water requirement for cotton growth).There are 7 treatments in total.The effects of different drip irrigation methods and irrigation leaching quota on water and salt transport law,desalting efficiency,cotton growth index,yield and water use efficiency in salt-alkali cotton field were studied.The main conclusions were as follows:(1)The distribution of soil water and salt changed dynamically during the growth period of cotton,with significant spatial and temporal distribution characteristics.The amount of irrigation and drip irrigation had significant influence on the spatial and temporal distribution of soil water and salt in each stage of growth period.As a whole,soil water content increased with the increase of irrigation leaching quota,while soil salt content decreased with the increase of irrigation leaching quota.After treatment with W0 and W1,semi-ellipsoidal wet bodies were formed.After treatment with SW1,an ellipsoidal wet body was formed with the dropper as the center and diffused outwards.When the leaching quota of a single irrigation increased by 80 mm,the infiltration mode of soil water in the soil layer of 20-100 cm was close to uniform infiltration.Compared with the initial distribution of salt,the soil salt in each treatment at the end of growth showed a bidirectional migration characteristic from membrane to membrane and from upper layer to lower layer,and due to the effect of surface evaporation,a heavy salt zone was formed in the bare surface between membranes.(2)After irrigation,the infiltration depth of soil water in the vertical direction gradually increased with the increase of irrigation amount in the growth period.Under the same irrigation amount,the wetting front of subsurface drip irrigation was larger than that of subsurface drip irrigation.In the horizontal direction,the water content of 0-20 cm surface layer of each treatment showed the pattern of"high in the middle and low at both ends",with narrow row>wide row>bare land between films.The difference of soil water content decreased gradually with the increase of irrigation amount,soil depth and water convection and diffusion.(3)Soil salinity in cotton root region under W0 treatment increased gradually with the development of growth period,and increased by 1.76 g/kg in total during the whole growth period.The curve of salt content in cotton root zone fluctuated and decreased with the increase of rinsing irrigation.With the increase of irrigation leaching quota,the salt content in root zone gradually decreased.When the leaching quota of single irrigation was increased to 80 mm(W2),the soil salt layer was less than 100 cm,which effectively reduced the risk of secondary salinization under mulch drip irrigation.The salt content of cotton main root area was mostly less than 5.8 g/kg,which provided better water and salt conditions for cotton growth.When the irrigation leaching quota is the same,subsurface drip irrigation has better leaching effect on middle and deep soil than drip irrigation under film,but the surface soil salt content of subsurface drip irrigation is greater than that of drip irrigation under film.(4)Increasing irrigation leaching quota can promote cotton growth,increase plant height,stem diameter,leaf area index and dry matter accumulation significantly,and further obtain higher yield and irrigation water use efficiency.There were no significant differences in H,LAI,DMA and Y between W3 treatment and W2 treatment,but IWUE decreased significantly,resulting in water resource waste.(5)Comprehensive analysis showed that cotton growth and development,yield,irrigation water use efficiency,desalting rate in root zone,desalting rate in 0-100 cm soil layer and salt content in root zone,single irrigation leaching quota of 80 mm and total irrigation quota of240 mm+80%ET_c during the growth period of mulch drip irrigation were the optimal irrigation regulation combination.It can provide theoretical support for local cotton field to realize water saving,salt control and high yield.