Study On Salt Anti-salinization Mechanism Of High Frequency Drip Irrigation

The process of soil salinity transport includes the distribution process of salt with water infiltration and the evaporation of salt with soil moisture distribution.The overall anti-salinization effect should depend on the depth and velocity of soil moisture to carry salt and the rate of evaporation to carry salt.Therefore,when using high frequency drip to inhibit salt,the irrigation frequency should be determined according to the surface evaporation intensity.Based on the basic principles of soil hydrodynamics and soil solute transport through the physical experiments,the experiments about soil solution dynamic under drip irrigation with different irrigational frequency and evaporation intensity were conducted in soil tanks to investigate the mechanism of high frequency drip irrigation reducing the soil salinization.In these experiments,the drip design flow was 1 L/h and irrigated with identical total water 10 L.4 irrigational frequencies,which was denoted with IF1,IF2,IF3 and IF4 separately,were treated with single drip water respectively in 2 L,3.33 L,5 L and 10 L,as well as drip intervals in 1 day,2 days,3 days and 4 days.The effects of the single drip water and the drip intervals on the soil salt transferring and desalting efficiency were observed in these experiments.4 evaporation intensities,which was denoted with EI1,EI2,EI3 and EI4 separately,were treated with plastic film mulching,natural condition and continuous light treatment.The main results are:(1)high frequency drip irrigation,the soil salinity immediately transferred to deep soil after watering,but it would not move to the top soil immediately under evaporation as the salt migration speed being slow;only when the drip interval was larger(more than 2 days),the soil salt would move in fluctuate along soil depth.(2)The anti-salinization effect of high frequency drip irrigation mainly depends on a single drop water.With the identical total drip water,the greater single drip water should result in deeper leaching of soil salt and favorable efficiency of anti-salinization.(3)In the absence of groundwater recharge,the evaporation of soil solution was limited during the drip intervals.The upper soil of salt is still in the state of desalination,which just brought the depth of salt accumulation decreasing.The anti-salinization effect of high frequency drip irrigation is not absolutely dependent on the evaporation time,but depends on the coupling of water and salt.(4)In the absence of groundwater recharge,the evaporation of soil solution was limited during the evaporation intensity,which mainly affects the desalination rate of 0 ~ 20 cm soil layer.Increasing the intensity of evaporation,it would not move to the top soil immediately as the salt migration speed being slow;only when the drip interval was larger(more than 2 days),the soil salt would move in fluctuate along soil depth.(5)The salt of lower layer in the soil is dynamic.The desalination rate of the upper layer is fast,but the salt is Accumulated gradually of the lower layer.The upper layer soil in the stable evaporation depth is always desalted,while the Salt accumulation area in lower layer has a high salt content,but the moisture content is less than the stable evaporation depth,the soil water conductivity is small,the salt is mainly transported in the form of dispersion.The speed of salt transportation is slow,so salt migration upwards is limited.(6)High frequency drip irrigation is mainly to suppress the salt of the bottom soil.As the upper layer of high moisture content,high frequency drip irrigation in a stable evaporation stage,and the convective transport is the upward migration resistance of salt.However,when the high-frequency drip irrigation,the salinity of upper layer is low by irrigation desalination,the salt can move upwards,the salt that moves to the upper part is not much.The salt content is high salt in the lower layer,as the water content ia small and the conductivity is also small,convective dispersion is the main movement power,at this time the water transport speed is slow,lending to salt transport speed is also slow,so the salt of the bottom is in the fluctuations but the amount of salt is not much by evaporation.Therefore,the synchronism of coupling of water and salt in soil determines the anti-salinization effect of high frequency drip irrigation.