Comparison Analysis on Digital Soil Texture Mapping in an area of Zhangye,Heihe River Basin

Abstract

Soil texture is a key input parameter for the land surface process models,hydrological models and atmospheric models.Many digital soil mapping methods based on the soil-landscape model concept have been widely studied and applied.The general methods include the decision tree algorithm,the support vector machine approach and the fuzzy logic theory.In this paper,a study was conducted to compare the above three different soil mapping methods in an area of Zhangye of Heihe River Basin by integrated 200 ground measured soil samples and 13 types of environmental factors.Meanwhile,different soil texture maps based on the three methods were predicted in the study area respectively.Results show that:the support vector machine model gets relatively low accuracies both for test soil samples and training samples,which are 90% and 55% respectively.The decision tree model gets the highest accuracy of 98% for training datasets among the three methods,but its accuracy for testing data decreases into 57%.The fuzzy logic model gets the highest accuracy of 64% for testing data and a compromise accuracy of 74% for training data.As for the structure characteristics of the texture soil maps,the study finds that the support vector machine model predicts a much simplified soil texture map as it may weak the prediction ability of thematic and continuous environmental factors.The decision tree model often gets unstable predictions of unexpected combinations of environmental factors,resulting in a relatively fragile structure of the soil texture map.The fuzzy logic model predicts the most reasonable soil texture map among them,because it can not only keep the soil texture structure much holistic,but also can illustrate an appropriate relationship between different soil types and different environmental factors.It is suggested that combining the decision tree algorithm with the fuzzy logic theory might be an appropriate method to map the soil texture distribution of Heihe River Basin.