Evaluation and Research of Crop Water Requirements (ET) in the Water-saving Irrigation Area of Beijing Fangshan

As one of the cities that are most serious short of water ,Peking hasits limitation on the developent of agriculture ,which mainly due to the insufficiency of irrigation.Water-saving irrigation is the key to the asrigulture development .In this thesis ,which is part of the "water-saving irrigation"project supported by the world bank to solve the irrigation insufficiency in Peking ,precipitation,evaporation ,the soil moisture state,soil basic physical and chemical properties etc factors are observed during the experiments carried out in Fang Shan district,on which several ways are presented ot compute the crop water requirements,then the main influence factors are analyzed and evaluated ,some effective water-saving measures ate figured out to give technical support of generalizing water-saving irringation ,and quantifiable information are provided to solve the resources insufficiency problem and sustainable water resource development. The factors that affect the crop water requirements are invertigated comprehensively,including meteorological conditions ,soil moisture state and crop biological property,based on which ,methods to compute the crop water requirements are paesented from different points of view. Firstly ,based on soil water conditions,water balance methods including the method of soil water balance and Zero Flux Plane(ZEP) areused ot simulate the soil water balance medel of the district researched ,and analyze the distribution of soil matric potentials and soil water content of different deep,then the model’s quantities are made discrete and Fortran programs are designed and implemented to calculate the crop water requirements. Secondly ,given soil water is unlimited,the crop water requirements that have sufficient irrigation are researched .From the meteorology and crop biological property,reference crop water requirements-crop coefficient method such as Penman-Monteith(as recommended by FAO) areused to calculate the crop water requirements in research district, and the coefficient of crop (such as pearl ) at different srowth period are reckoned ,on which crop water requirements are calculated.Lastly ,the author compared and studied the above results,With the objective status of research district,based on the previous research on the water recycle of field ,the principle and crop wanter requirements and water-saving agriculture ,water balance models are chosen to draw several reference proposals on the irrigation mode ,wate