Abstract: Major eco-climatic factors affecting rice yield in Hanzhong basin were analysed. The fuzzy set theory was applied to make comprehensive fuzzy estimation of these factors, which were giouped onto three eco-climatic types. Each of these types had its own evolutionary pattern and affected rice production differently. In order to get high yields, agricultural counter-measures should be taken in accordance with different climatic types.

Key words: Citric acid, Oxalic acid, Pb, Cd, Soil chemical behavior