Mechanism Research On Water Repellency Of Sewage Irrigated Soil

Water recourses are one of the most important strategic resources in human being's life. But the shortage of water resources is the serious crisis in 21 century. Since the population is becoming much larger and economy develops much faster than before, the shortage of water resources has become even more serious. And the contradiction of water resources and water requirements in agriculture become more aggravated. The shortage of water resources is one factor that restricts the development of agriculture. So the economic water saving for human beings is no time to delay. The treated waste water for agriculture irrigation was used to solve the problem. It is an effective action taken successfully in America, Australia, Israel and Russian. However, another new problem of water repellency occurs after using waste water for irrigation is implemented.Soil water repellency is defined as the situation that the soil is not wet spontaneously when water is applied. That kind of soil is named as water repellent soil. The main impacts of soil water repellency are easy to development of finger flow in structural or textural preferential flow paths. Finger flow can lead to significant variations of the soil water content in the soil profile, reduce the infiltration capacity, resulting in poor seed germination, plant growth and yield, accelerating the agrochemicals and salts leaching. Soil repellency has some disadvantages of the sustainable development for agriculture and its environment. Therefore after analyzing the result of all researches and the affecting factors of soil water repellency, this thesis got some results after doing mechanism researches such as soil moisture, organic matter, different types of irrigation water and different drying temperature and time etc. on water repellency of sewage irrigated soil. The results of this thesis are as follows:(1)The relationship between Water Drop Penetration Time (WDPT) and soil moisture accords Lorentzian model.The present research work studied the relationships between the soil water repellency and soil moisture by measuring WDPT using 10 different water repellent soils collected from Israel. Three mathematic models, namely Gaussian, Lorentzian and lognormal distributions, which were used for fitting the models by regression analysis, and the Lorentzian distribution was found to be the best model for the practical use. (2)The relationship between WDPT and the quality of domestic sewage is positive linear correlation for clay and loam, but there is no significant relationship for sandy soils.The present study investigated the effects of twelve different types of water with different contaminated levels on soil water repellency by measuring WDPT using of the twelve types of water on two clay soils and one loam and two sandy soils collected from Israel. The main affected parameters of the water quality were released by using principal component analysis. The results showed a positive linear relationship between soil water repellency and the integrated water quality value (F) for clay soils The multiple regression analysis exhibited that organic matter expressed as COD is the main factor affecting the soil water repellency. But there is no significant difference among the twelve types of water for sandy soil.(3)The relationship between WDPT and soil organic matter is positive linear correlation for clay, and a single peak curve correlation for sandy soil and loam.This thesis got the contour of WPDT for three kinds of soils namely clay, loam and sandy soil, by measured WDPT in the field and soil moisture and organic matter in the lab. Meanwhile the relationship between WDPT and soil organic matter was got by measuring WDPT after drying soil samples in 25°C and 65°C for clay and sandy soil in the lab. The relationship between WDPT and organic matter shows difference between soils. It is a positive linear correlation for clay, and a single peak curve correlation for sandy soil and loam.(4)The relationship between the reappearance of water repellency for soil which water repellency was eliminated by the physical method and the quality of irrigation water and irrigation is positive.This paper mainly discussed whether soil water repellency will reappear or not shortly after the soil is irrigated with sewage, which the water-repellency soil is eliminated by the physical method. Drip irrigation is adapted for the water-repellency soil with tap water and other three domestic wastewaters. The significance of WDPT was checked after irrigated in 4 and 8 months. The result shows that soil water repellency will appear again after drip irrigation at a certain intervals. Meanwhile, it has a significant positive correlation between irrigation time and water quality.(5)The optimal temperature is 45℃~65℃and the time is 24 hours for measuring potential water repellency.This thesis concerns how to get potential water repellency after drying in four temperatures and six times in the oven for two clay and two sandy soils. The result shows that the optimal temperature is 45℃~65℃and the time is 24 hours for measuring potential water repellency after analyzing the different WDPT among the treatment for each soils.After doing the research, the soil water repellency which caused by sewage irrigation and its character and regulation will be further understood. It will offer the scientific theory for avoiding and ameliorating and reducing soil water repellency caused by sewage irrigation.The innovative points of this paper are proposing that the Lorentzian distribution was the best one to describe the relationship between WDPT and soil moisture. Chemical oxygen demand (COD) is the main factor which affects the soil water repellency when using different kinds of contaminated water to measure the WDPT.Water repellency is too complex. So this thesis only studies mechanism on water repellency of sewage irrigated soil. The further researches include how to use the theory to practice, the effects on the soil water repellency by the soil organic matter, other irrigation with different water, different temperature and time for the same soil with different initial soil moisture drying in the oven, and the relationship between soil moisture and WDPT of other type soil.