Abstract: The microorganisms and nutrients in the rhizosphere soil of leaf yellowing and normal pear trees in Jingtai County， Gansu Province were studied to find out the factors related with leaf yellowing. The results showed that bacteria and actinomyce in soil of the leaf yellowing pear trees were significantly lower than those in the soil of normal trees. The bacteria and actinomyce in the shallow layer （0-20 cm） of soil in leaf yellowing orchard were 4662% and 5249% less than those of normal orchard; while in the deeper layer （20-40 cm） of soil of leaf yellowing pear orchard， bacteria and actinomyce were 7822% and 5013% less than those from normal orchard. There was no significant difference between the two kinds of pear trees in the amount of fungus. In 20-40 cm deep soil from the leaf yellowing pear orchard， the content of organic matter， total N， total Fe and total Mg were significantly lower than those from normal pear tree soil and those in 0-20 cm deep soil from the leaf yellowing orchard. Therefore， decrease of bacteria， actinomyce and organic matter， total N， total Fe and total Mg in 20-40 cm deep soil were the main factors related to leaf yellowing. Thus， applying decomposed manure to soil of 20-40 cm deep in leaf yellowing pear orchards should be suggested.

Key words: leaf yellowing pear trees, quantity of soil microorganisms, soil nutrient, correlation analysis