Dagu Basin Soil And Water Resources Assessment And Agricultural Water-saving Irrigation Mode,

Qingdao is one of the cities lacking water resources seriously in Northern China coastal areas,the contradiction between supply and demand of water resources is rather sharp.On the other hand,because of serious waste of water for farming and low efficient of irrigation water use,the potential of field water-saving is very great.This paper established Pedotransfer functions of soil hydraulic parameters by large numbers of field samplings and laboratory analysis in the Dagu river basin,calculated four evaluating indexes of soil water resources at basin scale based on GIS and Hydrus-1D,analyzed the laws of field soil water movement and root water uptake by establishing mathematical model of soil water movement of typical farmland which had been planted to winter wheat-summer maize under the condition of different hydrographic years and different irrigation modes,finally,proposed the corresponding water-saving irrigation modes according to different hydrographic years.First,the traditional statistics and geostatistics methods were used to analyze the statistical characteristics and spatial variabilities of soil physical and chemical properties in the Dagu river basin,then Pedotransfer functions of soil hydraulic parameters were established by four methods which contained point regression,linear regression, nonlinear regression and artificial neural network based on a large amount of soil physical and chemical properties and soil water retention curves.The results showed that the best prediction for sandy loam and loam soil by point regression method and clay loam soil by artificial neural network method,respectively.Four evaluating indexes of soil water resources at basin scale had been proposed. The actual storage amount,maximal storage amount and unavailable quantity of soil water were calculated by long-term site-specific observatory study of soil water content based on GIS in the Dagu river basin,which were 1.135 billion cubic meters,1.430 billion cubic meters and 0.745 billion cubic meters,respectively.Soil water resources was also evaluated,which was 2.433 billion cubic meters,based on Hydrus-1D model in the basin for the year 2008-2009.In contrast to the conventional irrigation mode,the results of numerical simulation for soil water movement of typical farmland which had been planted to winter wheat-summer maize under the condition of different hydrographic years and different irrigation modes showed that soil water deep drainage decreased significantly by water-saving irrigation mode which met water requirement for crop while improving the efficiency of irrigation water.The amount of water-saving were 240mm in wet year, 140mm in medium precipitation year,and 90mm in draught year,it had positive realistic significance for alleviating water resources tension in Qingdao.