Abstract: The population dynamics of pests and natural enemies from 3 types of cotton field, in which cotton seeds were sowed on April 27, May 15 and June 15 of 2000, were investigated and compared, respectively. The less number of 2nd generation cotton bollworm(Helicoverpa armigia)and more number of 3rd and 4th generation cotton bollworms were observed in late sowed cotton than in early sowd cotton. The greatest population of seedling aphids(Aphis gossyppi)and summer aphids were found in cotton field in which cotton seeds were sowed on May 15 and June 15, respectively. With the delay of planting date, population number of natural enemies and community diversity index of pests and their natural enemies were decreased. The pest management strategies for 3 types of different sowting date for cotton agroecosystem were also discussed in this paper.

Key words: Chinese fir plantation, Soil active organic matter, Microbial biomass C, Water-soluble organic C, Water-soluble carbohydrate