Study On Soil Water And Salt Regulation And Cotton Growth Charcteristics Under Film-mulched Drip Irrigation With Brackish Water

Combining brackish water irrigation and film-mulched drip irrigation could be helpful in moderating fresh water resource deficit and soil salinization in arid area.The field experiments were conducted in 2012-2016 focusing on the cotton filed with film-mulched drip irrigation.The effects of multi-year film-mulched drip irrigation and different soil water and salt regulations(controlling methods in bare strips and irrigation treatments)on soil water and salt and cotton growth dynamics were investigated based on water and salinity balances and crop model.The main results are summarized as follows:(1)The characteristics of soil water and salinity distribution and cotton growth were consistent in the experimental years.As for soil water and salinity distribution,both largest values for soil water and salinity in root zone were found in bare strips and the smallest in narrow strips.The soil-water content in root zone increased at first and then declined over time,and there no significant differences in soil salinity.At harvest,the salt accumulation amount in main root zone account for above 57.3%in total salt accumulation amount,and the salt mainly distributed in the bare strips.The soil salinity in root zone increased linearly over the years for film-mulched drip irrigation application.The growth rate was 0.707dS/m using the electrical conductivity of saturated paste extract(ECe)to represent salinity.As for cotton growth,The ranking of the ET at growing stage for cotton was in an order of boll stage>flowering stage>squaring stage>seedling stage>boll-opening stage.Dynamics of height and LAI for cotton over time can be described by Logistic and adjusted Logistic models,respectively.The maximum root depth increased over time and mainly distributed in the narrow strips which had accounted for 57.2-70.3%in total root length.The effective root length distribution could be expressed by Vrugt model.The response of cotton yield to soil salinity in root zone was established based on Maas model.(2)The effects of different controlling methods in bare strips(straw mulching,applying PAM,soil compaction,and sand mulching)on soil water and salinity distribution and cotton yield and productivity were quantified.These methods could stabilize soil temperature.Compared to control treatment,controlling methods in bare strips reduced soil evaporation and salt accumulation in root zone by 34.6-96.2%and 20.2-92.8%,respectively.The controlling methods enhanced the water use efficiency(WUE)by 1.1-12.2%.The maximum yield and WUE were found in sand mulching treatment,which was more effective than the other treatments.(3)The relationships between brackish water irrigation amount and ET,drainage and salt leaching amount,LAI,and yield and productivity for cotton were determined.ET,drainage and salt leaching amount and maximum LAI raised with the increase in brackish water irrigation amount.When the relative irrigation amount(Irel)was lower than 100%,yield increased with increasing of irrigation amount.While irrigation water use efficiency decreased and there no significant difference in WUE.Comparing soil water and salt and plant indictors among all treatments,higher yield,WUE,and IWUE could be found the irrigation amount with 80%<Irel<90%.(4)The cotton growth model with film-mulched drip irrigation was established.The model can well simulate dynamics of soil water in root zone and cotton growth with the coefficient of determination(r2)higher than 0.74 and the index of agreement(d)higher than 0.92.The model underestimated soil salinity in root zone when Irel>80%.Additionally,the model slightly underestimated cotton yield.The appropriate brackish water irrigation amounts(358-457mm for silty loam and 406-462mm for sandy loam)and water production function(1-Ya/Ym =1.062(1-ETa/ETm),n=180,r2=0.952)were determined,according to different scenario simulations.The multi-year soil water and salt and cotton growth dynamics in growing season for cotton were revealed by conducting field experiments.Moreover,the response of cotton yield to soil salinity were determined.The suitable soil water and salt regulation modes were selected.The response of drainage and salt leaching amount and cotton growth to brackish water irrigation amount were quantified.Additionally,the cotton growth model was established.It could provide a reference for efficienct utilization of brackish water and optimization for soil water and salt regulation mode and irrigation scheme determination.