The Design Of The Reference Arable Land Evaluation Units And The Application In Wolong District

As a method to classify the arable land, study on "the reference unh.s" method started in China not long ago. Until now, double series of reference units whose qualities are the best or the worst respectively have not been applied to evaluate arable land at county level. This dissertation designs double series of reference units and classifies the arable land of Wolong District. The elementary idea of the reference units method can be described as follows: firstly, by the setting of double series of reference units, we can control the highest and lowest land quality class of each village or town; secondly, the class of the arable land will be get through the contrast between the arable land with the reference unit which has been selected in the same area, the difference in quality is the key factor to classify the land.The results show, 87.6% of the lands from I to III distribute on alluvial and lacustrine plains, where the associated soils are mainly grey fulvo-aquic and calcareous concretions black ones. And 61.4% of them from IV to VI distribute on slightly rolling parts with mainly yellow-cinnamon soil developed from the diluvial and slope deposits. The rest of lands of Vfl and VI are concentrated at the foothills associated with skeletal yellow-cinnamon soil developed from the residual and slope deposits. These imply that the spatial distributions of the different grades of the arable land, classified by the reference land unit method, reflect reasonably the spatial changes of geomorphological units and soil types. The linear estimation model between comparable productions and the corresponding quality ratings of 210 sample units shows that the coefficient of determination R2 is 0.876, which means that 87.6% of the change of Y is explained by the change of X. It is concluded that the arable land quality ratings calculated by the method can reflect the biologic productivities of land. In conclusion, by the setting and application of double series of reference land units, we can get reasonable classification results; moreover, the reference land units method has some study and application values which can provide as a reference method or model for other counties in China.