| Available water capacity (AWC) of soil is important for studying soil humidity, irrigation management, ecological agricultural planning, evaluation of crop growth potential and simulation of change of globe land cover under affection of economical factors and climate changes. The survey of soil AWC is expensive due to cost consuming and time-consuming. Moreover, it is probably unfeasible because of extension of study area and spatial changes of soil. It is better way to estimate the soil AWC through a few measured data. The geographic spatial models of AWC of soil, based on geographic information system (GIS), are essential for quantitative evaluation of AWC of soil in an area. AWC of soils is necessary parameters for evaluation of capacity of soil bearing drought, for irrigation and for evaluation of productive rate of plant.There are two goals of the study. The first one is to fabricate the estimating model of typical sort soils and region soils and simulate the soil AWC in china. The second is to compose spatial model of AWC of main soils and evaluate it in China.Based on physical and chemical characteristics of soils, the estimating models of soil AWC for the Black soils, Cinnamon soils and soils of the main sorts in China were researched by multiple regression and curve simulation in the study. The results showed that the estimating model of one sort of soil, droved by multiple regressions, was not adapted to others. Moreover, physical or chemical parameters of soils, which were vital to one sort of soil, were not significant to other sorts. The estimating models of the available water capacity (AWC) of main soils in China, which are based on texture and organic matter and droved by multiple regression or curve simulation, can be probably used to estimate the soil AWC of one large-scale area. When used for one certain sort of soil, it maybe inaccurate relatively. Statistical models cannot be explained with explicit theory, and it may be used to estimate soil water constant with lower precision. But they were simple and feasible for estimation of soil AWC in a large-scale area.The AWC of main sorts in China was estimated with the studied model and elementary soil physical and chemistry data. As showed in results, the data of soil AWC in China mainly rang from 16% to 22% and the values, higher than 25% or lower 10%, are few.Based on elementary soil physical and chemistry data and digital soil map, the spatial modes of AWC of soil in China were composed with GIS. The spatial models of AWC of soils presented the difference of soil AWC in China. As a whole, the difference of soil AWC was significant and the value of soil AWC in southeast is higher than that in northwest. In certain area, the value could be different according to the soil sorts. The value of AWC of soils ranges commonly from 11% to 23% and mainly from 17% to 21%.The spatial model of soil AWC in China, based on texture and organic matter, was analyzed. It was presented that the level of soil AWC was mostly between 17.2% and 21.2%, secondly between 12.0% and 15.0%. As a whole, the soil AWC of humid soil area of eastern China is mainly between 17.2% and 21.2%; The soil AWC of arid soil area ofnorthwest of China and that of high and frigid soil area of southwest of China mostly range from 12% to 21.2%, and secondly rang from 12% to 15% in the two areas..The innovation of this study is to estimate the Available water capacity (AWC) of main soil types based on physical and chemical characteristics of soils and to model it with geographic information system (GIS) in China. It is valuable for practice and methods of studies on AWC of soil in some area in China.This is primary study of estimating models and spatial models of AWC of soil in China. There are more to do, such as methods of studies on estimating models, selection of parameters, construction of geographic spatial models and precision of models for research of AWC of soil in China in future.
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