Effect Of Irrigation Water Quality On Soil Physical Properties

Much effort has been put into the study of soil water holding capacity, water movement and water availability, but there exists many problems to be studied in this field. There are various factors affecting physical properties of soil water. However, past researches focused on soil properties, such as soil surface area, soil structure, porosity etc., ignored the fact that soil water is washy solution with kinds of solutes. Few of investigators have studied the effect of water quality on soil water physical properties and water movement. In order to rich the theory of soil physics, the author studied the effect which caused by organic compound on water holding capacity, water movement parameters and soil swell in the aspects of its variety and content on soil.Water scarcity is a big problem for agriculture in China. River water is more or less polluted is the status quo. It's difficult to control irrigation water quality in the near future because of direct sewerage and the disposal lag of sewerage. Polluted water is used to irrigate will keep up for a period of time. However, there're few papers about the effect on soil quality which caused by organic compound in irrigation water. So investigating the instantaneous effect on soil physical properties caused by organic compound in solution is meaningful both on theory and in practice.With a view to pollution status quo of Wei River, we focused on studying the effect of hydrophilic organic matter (ethanol), hydrophobic organic matter (phenol) and multi-organic matters (water from Wei River) on soil physical properties. Soil water characteristic curve, soil water diffusivity, soil saturated hydraulic conductivity and soil swell were measured by indoor simulation test to learn the effect trend of organic compound on soil physical properties. Meanwhile the effect of ethanol and phenol on water density and surface tension was analyzed to explain the influence mechanisms. Conclusions are as follows:1. The variety and content of organic compounds had great effect on soil water retention. The effect mechanism was that organic compound not only changed soil water surface tension but also changed soil properties. Ethanol content influenced soil characteristic curve at different levels while pF was from 0 to 4.1, and the influence degree was different as ethanol content increased. When the ethanol content was greater than or equal to 0.1%, the effect was significant, and soil water-holding capacity decreased as ethanol content increased. Phenol influenced soil characteristic curve only in low soil suction range (pF<1.5), and soil water holding capacity increased as phenol content increased. Effect of organic solutes on water surface tension was one of the important factors affecting soil water-holding capacity. Phenol solution and ethanol solution which concentration was less than or equal to 1 000 mg·L^-1 had the same effect trend on soil water holding capacity and water surface tension, and the capacity increased as their content increased. While Ethanol content was more than 10 000 mg·L^-1, the change of water surface tension was no longer enough to explain how ethanol solution affected soil water retention and the change of soil structure caused by ethanol dissolving part of soil organic matter became the main reason. Multi-pollution improved soil water holding capacity and had a visible effect on soil water characteristic curve.2. The effect level of organic compound on different soil texture was: clay layer of Lou soil>topsoil of Lou soil > sandy soil. The difference showed effect on soil structure and porosity caused by water quality. The effect on topsoil of Lou soil and the effect on clay layer of Lou soil were obviously different. Certain amount ethanol in solution could improve soil water holding capacity in topsoil because topsoil was rich of organic matters which appetency was strong to ethanol. While ethanol had opposite effect on soil in clay layer, and the opposite effect was greater when pF was less than 2. The effect was causd by plenty of inorganic oxid in clay layer and appetency of inorganic oxid thin to ethanol. Effect of phenol solution on soil water holding capacity was investigated to prove the conclusion. Phenol had effect on soil characteristic curve of topsoil only in low soil suction range (pF<1.5), and had greater effect on clay layer while pF was from 0 to 4.1. The results showed that the effect of organic compound on soil water holding capacity had a close relation with the constituents of soils, and the solvency and the appetency of organic solutes were the key factors affecting soil water holding capacity.3. The variety and content of organic compound had obvious effect on soil water diffusivity. Firstly, ethanol and phenol content significantly influenced the total time and the average velocity of water movement. Average velocity of ethanol solutions and phenol solutions were higher than control except on the condition of 100 000 mg·L^-1ethanol solution. Effect trend of ethanol content presented protuberance, while phenol was the opposite and has less effect than ethanol. Secondly, soil water diffusivity of various solutions was obviously different while water content was in the same value. When volumetric moisture content was less than or equal to 0.42 cm3·cm-3, the effect trend of ethanol content presented protuberance. While the effect trend of phenol content was inconstant. Thirdly, ethanol and phenol content markedly influenced the parameters of experiential equation of soil water diffusivity (D(θ)=ae^bθ). The correlation of parameters and LOG(C) were quadratic. To ethanol, correlation of parameter b and LOG(C) was significant. To phenol, correlation of parameter a and LOG(C) was markedly significant, and correlation of parameter b and LOG(C) was significant. Besides, trifle of ethanol and phenol in solution improved soil saturated hydraulic conductivity.4. Relationships between factors of soil water diffusivity were analyzed, and we got some conclusions. The soil water diffusivity with capillary supported water which ranged from 0.30 cm³Â·cm^-3 to 0.42 cm³Â·cm^-3 had great effect on average velocity of water movement. The relationship between t and water content at 2 cm was highly linear correlated, t=-31624θ+17069(r=0.8282), and water content at 2 cm was equal to soil saturated water content in theory, so we can estimate soil water movement velocity by soil saturated water content.5. Soil swelling process was related to the property of soil and the quality of water which used to saturate soil. Research results showed that soil swelling process had two swelling stages. The variety and content of organic compound not only affected the rate of swelling, but also affected the capacity of swelling. First stage swelling capacity of 10 mg·L^-1 ethanol solution was less than control, and 10 000 mg·L^-1 ethanol solution was more than control. First stage swelling capacity of phenol solution was more than control, and the capacity increased as phenol content increased.