| Based on the research papers studied by foreign and domestic researchers,aiming at the characteristics of the border irrigation and the film-hole irrigation of field crops in northern China,and the characteristics of sediment in muddy water(sand content rate and sediment particles gradation)in the Yellow River Basin,with the support of project of National Scientific Fund of China.This paper takes the method of combining the theoretical analysis and laboratory test to carry out the study of the formation characteristics and influencing factors of the dense layer(deposition layer and stranded layer)of the border irrigation and the film-hole irrigation with muddy water,reveals the characteristics of muddy water infiltration reduction and clarifies the mechanism of muddy water infiltration reduction.The main research results are as follows:(1)The infiltration characteristics of one-dimensional vertical infiltration and the characteristics of dense layers formation with muddy water were studied.The influence of factors such as sediment particle gradation,sand content rate,soil bulk density and soil initial moisture content on the formation and development of dense layers under the border irrigation were revealed.The models of the cumulative infiltration,the wetting front distance and thickness of the deposition layer of one-dimensional vertical infiltration with muddy water with the different influencing factors were established.For the soil particle composition of the dense layer,it was found that the soil particle composition at the infiltration depth of 0?1 cm was quite different from that of the original soil,and the fine particles in the soil particles was more than that of the original soil,but the difference was not obvious at 2?3 cm.Therefore,from the soil surface to the infiltration depth of 2 cm,it could be used as a one-dimensional vertical infiltration stranded layer of muddy water.With the increases of sand content rate and physical clay particles content,the sediment retention phenomenon became more obvious,so that the relative content of fine particles in the deposition layer was less,and the relative content of fine particles in the stranded layer was higher,especially the infiltration depth was 0?1 cm.However,with the increases of soil initial water content and soil bulk density,the opposite law was presented.The thickness of the deposition layer increased as the increase of the infiltration time,which conformed to the power function positive correlation.The thickness of the deposition layer at the initial stage of infiltration(0-20 min)was small,and the increase in the middle stage of infiltration(20-130 min)was rapid,while the rate of increase of its thickness gradually decreased,and the thickness of the deposition layer increased steadily in the late infiltration stage(130-210 min).(2)The influences of multiple factors on infiltration characteristics of one-dimensional vertical infiltration and formation characteristics of dense layers with muddy water were studied,and the main factors affecting one-dimensional vertical infiltration with muddy water were put forward.Moreover,the empirical models between the accumulative infiltration per unit area,the distance of wetting front movement,and the thickness of the deposition layer and the influence factors had been built respectively.The sand content rate,sediment particle gradation and soil bulk density had extremely significantly effects on accumulative infiltration per unit area;The initial soil moisture content had a significant effect on the accumulative infiltration per unit area,and it had a negative correlation with the four factors.Sand content rate was the main factor affecting the accumulative infiltration per unit area,followed by sediment particle gradation,soil bulk density and initial soil moisture content.The distance of wetting front movement was more sensitive to the influence of soil bulk density,followed by the sediment particle gradation and sand content rate,and the least sensitive to the influence of initial soil moisture content.The distance of wetting front movement was positively correlated with initial soil moisture content,and negatively correlated with sand content rate,sediment particle gradation and soil bulk density.The influence of various factors on the thickness of deposition layer were sand content,sediment particle gradation,soil bulk density,and initial soil moisture content in descending order.The thickness of deposition layer was positively correlated with sand content rate,physical clay content and soil bulk density,and negatively correlated with initial soil moisture content.(3)The infiltration characteristics of film hole irrigation and the formation characteristics of dense layers with muddy water were studied,and the changing laws of the infiltration capacity,the distance of wetting front movement,the soil moisture content of the wetting body,the composition of soil particles in the dense layer,and the thickness of deposition layer of the film-hole irrigation with muddy water were revealed.The study showed that the distribution of soil moisture content in the radius of the wetting body wasan elliptic curve.The cumulative infiltration model including the distance of the horizontal and vertical wetting fronts was established,and considered the distribution range of crop roots and the requirements of crop roots on soil moisture content,a model of irrigation volume suitable for crops was established,and verified that the model had high accuracy.The content of fine particles in the stranded layer was more than that of the original soil.With the increases of infiltration soil layer depth,the difference between the soil particle composition of the stranded layer and the original soil gradually decreased,and the differences wwere small at the infiltration depth of 5-6 cm,so the infiltration depth from the soil surface to 6 cm could be used as the stranded layer of the film-hole irrigation with muddy water.The retention of fine sediment particles presented a gradual distribution law in the stranded layer,Which was that as the depth of the stranded layer increased,the retention volume of fine sediment particles decreased.The logarithmic function could be used to fit the relationship between the accumulation retention volume and the depth of the retention layer of the film-hole irrigation the muddy water.The thickness of deposition layer increased as the infiltration time increase,the initial stage of infiltration was about 10 minutes shorter than the one-dimensional vertical infiltration with muddy water.The relative content of fine particles in deposition layer was less than that of muddy water sediment.Compared with the one-dimensional vertical infiltration with muddy water,the deposition layer soil texture of the film-hole irrigation with muddy water was coarser.(4)The effects of urea,potassium sulfate and water-soluble compound fertilizer on the infiltration characteristics of the film-hole irrigation with muddy water and the formation characteristics of dense layers were studied,and further revealed the effects of fertilizer types and fertilizer solution concentration on the viscosity of muddy water.The relationships between the fertilizer solution concentration of the three types of fertilizers and the cumulative infiltration per unit film-hole area,the wetting front distance and the thickness of stranded layer were established respectively.The study showed that the application of urea could increase the infiltration of muddy water,while the application of potassium sulfate and water-soluble compound fertilizer could prevent the infiltration with muddy water,and the application of potassium sulfate had a stronger barrier effect.The application of urea reduced the thickness of the deposition layer,increased the depth of the stranded layer,and slowed down the speed of the dense layer formation,while the application of potassium sulfate and water-soluble compound fertilizer showed the opposite law.With the increase of urea concentration,the fine sediment particles were more likely to enter the soil along with infiltration water,which made the relative content of fine particles in the deposition layer decreased,and the relative content of fine particles in the corresponding stranded layer increased.However,with the increased of the concentration of potassium sulfate and water-soluble compound fertilizer,the soil particle composition of the dense layer showed the opposite law to that of urea.(5)The effects of muddy water on soil pores,soil structure and soil water-holding capacity under film-hole irrigation were studied,and the influence of muddy water on the soil particle gradation,thickness of deposition layer and soil physical properties of stranded layer were revealed.The study showed that the soil total porosity,the soil saturated hydraulic conductivity and the soil diffusivity in the stranded layer were lower than that in the original soil,while the soil saturated soil water content,soil bulk density and soil water holding capacity in the stranded layer were higher than that in the original soil.With the increase of physical clay content in muddy water,the soil capillary pore content in the stranded layer increased,while the aeration pore and ineffective pore decreased gradually.The higher the sand content rate in muddy water was,the larger increase of the soil capillary pore content in the stranded layer was,while the larger decreases of the aerated pores content and ineffective pores content were.As the content of physical clay particles in muddy water increased,the proportions of hygroscopic water,pellicular water and gravity water in the stranded layer decreased slightly,while the proportion of capillary water increased significantly.The higher the sand content rate in the muddy water was,the larger increases in the proportion of soil capillary water in the stranded layer was,and the larger decreases in the proportion of the corresponding hygroscopic water,pellicular water and gravity water.The proportions of difficult-to-available water and easy-to-available water in the stranded layer were significantly increased,while the proportions of ineffective and excess water were reduced.With the increases of sand content rate and the physical clay content in muddy water,the more obvious increases in the proportions of the hard-to-available water and the easy-to-available water in soil.As the soil depth of stranded layer increased,the difference between the soil moisture type of the stranded layer and the original soil gradually decreased until that of the stranded layer was consistent with the original soil. |
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