| Water resource is a kind of fresh water resource that can restore in water circulation cycle and can directly utilized by ecology and mankind. Mainly it is close and relevant to human social, domestic water and can bring in constant renewal in. It is also the environmental resources that the living beings depend on for existence, including surface water , groundwater and soil water. The amount of water resource in the earth's surface is usually expressed with the flow of rivers and creeks foot-path. The groundwater and amount of soil water resource can be expressed with the supply amount. Three kinds of water bodies maintain close ties and transform each other , and the total amount of water resource after deducting the repeating amount is equivalent to the precipitation in the same area. Average precipitation in China is 6,007,600 million m~3 for many years (deep 628mm of rainfall). Among them surface flow is 2,016,700 million m~3 (deep 211mm of surface flow ) , accounting for 34%; 704,300 million m~3 (or 74mm of depth of water ) to enter oozing the groundwater of the supply , accounting for 12%; The evaporation capacity of the earth's surface is 3,286,600 million m~3 (or 343mm of depth of water ), accounting for 54%.Among the various countries at the earth, water resource store exists obvious space-time nature and disparity in, and widely different. This has determined development and utilization and disposition of the water resource must be in accordance with the principle of suiting measures to local conditions. Our country is a country with little water resource , with serious lack of water . The per capita water amount is only 2300 m~3, only a quarter of per capita water resource in the world at present, taking the 109th place in the world, and is classified as one of the 13 poor water countries of per capita water resource in the world. So, economizing the water, it is our basic direction in the future to set up water-saving society.Soil water means water in unsaturated soil layer from the earth's surface to underground surface of water. However, because it is not the same view about the meaning at home and abroad , so the range of understanding of soil water is limited too. Abroad generally the unsaturated layer is divided into three layers, or soil water layer, middle layer and capillary layer, and the study on soil water is only limited to a part in unsaturated layer. In our country academia, it puts the study on soil water on the whole unsaturated layer. So the study on soil water resources has nothing in common with each other. In fact, soil water not only has important resource value, but also is the most convenient fresh water resource in the world. At first, the supply , memory and transporting and moving not only are favorable to offering livelihood of the mankind, but also are easy to the recovery and maintenance of the ecological environment. Secondly, strong memory and regulating ability of soil reservoir not only can pile up moisture of not sowing time to vigorous one on crop, but also is favorable to the regulation of water cyclical process. Therefore, the resource value of soil water is obvious .Soil water as one important link, water of cyclical process, offer characteristic that crops grow generally acknowledged. But for a long time, because soil water, to such naturalcharacteristics as the excessive dependence of precipitation and easy dissipating , etc., makes people fail to mention with traditional water resource (the water resource in the earth's surface and groundwater resources ) in the same breath. But with the expansion of the water resource category, the intensification to soil water, soil water seems particularly important in terms of resource.First of all, soil water is the link that surface water, groundwater and atmospheric water connect each other, and has the same characteristic as other water resources—Circulation regeneration and regulation.Secondly, soil water is a main moisture source which maintains crop growing, and ecological environment benign cycle. The moisture that crop grows and develops to need gets from the soil by the root system. Other every water of part only turn into soil water, then soil water is utilized to absorb for crop. The quantity and quality of soil water will directly influence the growth of the crop. A key link that the crop circulates benignly as the ecological environment, the crop participates in maintaining the normal operation of the ecological environment indirectly while soil water act on directly.Thirdly, soil water is quite large in quantity. The statistics show that the reserves of soil water are 16,500 billion m3 in the world, and it is 7.8 times of the long-term water demand of all rivers in the world. 55% of Precipitation was turned into soil water in 1956-1979 year in China, generally in half arid, half moist plain district, it is higher than this number value.Fourthly, medium of soil water resource------soil has certain receiving corrupt ability andpurifying function. Through circulation, soil water resources have important function on the changes of surface water resources and groundwater resources quality.Fifthly, it is not a kind of simple water circulation medium on the unsaturated soil layer, but has " soil reservoir " of the enormous capacity, water resource among them ~ soil water resource has common characteristic with water resource in the earth's surface and groundwater resources-regeneration for circulation and regulation for the reserves and objective reality with enormous reserves. This is enough to prove that the appraisal of soil water resource is very essential.Though soil water do not concentrate on being distributed or assembling like surface water , groundwater , It can't be drawn , transported and made the application of different uses artificially directly. But people can pass indirect development and utilize it. Water of any kind could be absorbed and utilized by the plant after turning into soil and water, Thus making soil water turn into important component of the natural source of the human means of production and the means of livelihood. So, store , supply, consumption , renewal and balance for soil water, To agriculture , animal husbandry , forestry , natural ecological environment and water resource balance have extremely important meanings.This text is divided into five chapters altogether, narrated it as follows:Chapter one. Study the survey. In terms of the intension and characteristic of soil water resource mainly, the current situation both at home and abroad and the necessity studied, main content studied are drafted. In addition, store strongly and regulating ability of soil reservoir canpile up the moisture of not sowing time to vigorous growth in the crop, and it is favorable to the regulation of water cyclical process in order to explore our country to resist the flood, to prevent and cure arid ability and utilization efficiency of the moisture under the condition of great space-time change.Chapter two. Study on the theory and method of the soil moisture movement. At first, study on the potential energy of soil water, existence form of soil water energy state and change characteristic of space-time of soil water. Secondly, According to Da Xi law and quality conservation principle, rainfall entering the amount of supply oozed or dive under water evaporation capacity is calculated with the law of flux of the soil moisture. The special cases of the flux laws are mainly zero flux law, Oriented flux law and flux of surface law. Flux law of soil water is a way in which soil water supply, elimination and balance are studied. It has important using value in studying soil water. Thirdly, soil-plant-atmosphere continuum water and heat transmission and transpiration of the crop and evaporation among one are studied. Finally use of the use of soil water resource is studied. Dynamic simulation absorbing water through the root system shows that changing the measure of the soil environment of the root system such as irrigating, applying fertilizer, cultivation will influence the density of the root system and distribution, finally influence the absorption of the moisture of root system. So, with the rise and development of water-saving agriculture, the research on the root system seems particularly important. It is necessary to know the growth law of the crop root system in an all-round way, distributed law and absorbed water mode.Chapter three Study on evaluation of soil water resource. According to the method of appraisal on soil water resource, the commenting of soil water resource quantity, validity appraisal and appraisal on the thickness of storing, the system of appraisal on soil water has been established. The balanced law of moisture movement of soil water and law of flux of water circulation are adopted.The appraisal of soil water resource quantity is divided into the supply one and eliminated one. Farmland moisture circulation and water yield balance are the foundation of appraising soil water resource. In the course of moisture circulation, Soil water often gets the supply and is consumed constantly too. So, appraisal of soil water resource uses its circulation amount, like appraisal of the surface water and groundwater resources, or participates in annual soil water circulation amount of land moisture circulation, on average for many years, annual amount of circulation equals to annual supply or annual consumption.Chapter four Study on cases. Firstly, according to tested materials on the simulation laboratory of artificial control in Shijiazhuang, the special cases of the flux laws are used to calculate the amount of supply oozed. Secondly, Taking Chaohe River as an example, with balanced principle of the amount of water utilized, the reserves of soil water resource in the Chaohe river valley are Calculated, which takes up 64.3% of quantity of water resource of those years. It fully shows that soil water resource is enormous and important. Finally, soil-plant-atmosphere continuum water and heat transmitted model with the growth of crop isestablished. Phreatic evaporation process is simulated with different stage of bearing in order to explore change law of phreatic evaporation process under different groundwater level. It exploits deep intension on the theory combining with practice, and has important meaning to the development of water-saving agriculture in the future.Chapter five Conclusion. Research results to the full text have summarized. Main innovation of this text is briefly summedg up, and puts forward the problem remained.
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