Effects Of Intermittent Combined Irrigation On The Characteristics Of Soil Water And Salt Movement In Moderately Saline-Alkali Soil

One dimensional perpendicular infiltration experiments were carried out in an attempt to reveal characteristics of soil and water movement in the fields under intermittent combined irrigation(ICI).The experiments were designed to have two treatments in terms of irrigation water qualities,i.e.3 g·L^-1and 5 g·L^-1,have five treatments in terms of combination ratios of the irrigation water,i.e.simple fresh water(F),simple brackish water(B),2:1(brackish and fresh water),1:1(brackish and fresh water)and 1:2(brackish and fresh water),have two treatments in terms of combination sequences of the irrigation,i.e.the infiltration sequence of fresh water irrigation first and brackish water irrigation later(F-B)and the infiltration sequence of brackish water irrigation first and fresh water irrigation later(B-F),have four treatments in terms of interval in intermittent irrigation,i.e.0 min,30 min,60 min and 120 min.In this study,the applicability of the Green-Ampt model,Philip model and Kostiakov model for the treatments of ICI in moderately salt-affected soil was discussed.The theoretical relationship among parameters of the Philip model and the Green-Ampt model was analyzed and illustrated using the experimental data of One-dimension vertical infiltration experiments.The influence of various factors on the desalting effect and the perpendicular distribution rule of soil salinity under ICI was analyzed.Main results showed that:(1)Cumulative infiltration and wetting front movement were relatively high during the initial stage of infiltration,and dropped drastically with the experiment going on.The cumulative infiltration and wetting front depth of the treatments of 5 g·L^-1intermittent combined irrigation were less than that of 3 g·L^-1.The cumulative infiltration and wetting front depth of Treatments F-B were less than Treatments B-F,but differed slightly from Treatment F.Determination of cumulative infiltration and wetting front depth at the same time shows that the treatments of ICI exhibited an order of ICI 2:1(Brackish water:Fresh water)>ICI 1:1>ICI 1:2,indicating that cumulative infiltration and wetting front depth were positively related proportional to ratio of brackish water.The cumulative infiltration and wetting front depth increased as the interval in intermittent irrigation increased.Cumulative infiltration was in good linear relationship with wetting front movement(R²>0.9960).(2)Infiltration rate was higher during the initial stage of infiltration,while infiltration rate decreased rapidly versus infiltration time,and then reached a stable value.The mineralization of brackish water has a minimal impact on infiltration rate.Treatments F-B reached a steady infiltration rate first.At the same time,compared with Treatments B,the treatments of ICI had the effect of infiltration reduction.Compared with Treatments F,the treatments of ICI had the effect of infiltration increment.The infiltration rate decreased as the interval in intermittent irrigation increased.The results of simulation model indicated that the Kostiakov model appears to be a best choice to describe the characteristics of soil infiltration,compared with the Green-Ampt model and the Philip model.However,the Kostiakov model showed lower predictive power in the second cycle of ICI.The fitting effect of the theoretical equation of the Philip model deduced from the Green-Ampt Model was better than the theoretical equation of the Green-Ampt Model deduced from the Philip model.(3)The soil water content of the treatments of 3 g·L^-1 intermittent combined irrigation were higher than that of 5 g·L^-1.Treatments F-B were beneficial to improve the water hodding capacity of the upper and middle soil layers,but treatments B-F were beneficial to improve the water hodding capacity of the lower and middle soil layers.The effect of combination ratios on the soil water content of each layer was less.In the upper soil layer(5-10cm)and the lower soil layer(40-50cm),soil water content increased as the interval in intermittent irrigation increased,but in the upper and middle soil layers(10-40cm),the soil water content of the interval in intermittent irrigation(30min and 60min)was highest.Treatments ICI were all higher than Treatment F in irrigation uniformity,but differed slightly from Treatment B.(4)Soil salinity content increased as the interval in mineralization degree of infiltration water increased.The soil salinity content of the treatments of ICI was all less than Treatments B.Treatments B-F were beneficial to reduce the soil salinity content of the upper soil layers,but treatments F-B were beneficial to reduce the soil salinity content of the lower and middle soil layers.In the 5-45 cm crop root zone,soil desalinization rate was significantly higher in Treatments ICI than in Treatment B,and varied sharply between the treatments.The higher the proportion of fresh water,the higher the soil desalinization rate,the more favorable the salt-water environment for the crop to grow in.Significance tests of the effects of Treatments ICI on soil desalinization rate show that all the treatments reached significant levels,regardless of combination ratio and length of interval,indicating that the parameters of ICI have important on soil salt movement.