Abstract: Main eco-effects of the rice-duck-azolla compound system were studied.Results show that the system improved soil fertility by increasing organic matter,available N,P and K by 7.95%,7.05%,6.47% and 4.46%,respectively,over CK.Besides,it controlled weeds by 98.94%,and reduced significantly infestation of former dominant species of weeds in the paddy fields.As a result,fewer weeds survived and Pielou evenness index rose sharply.It was also quite effective in controlling planthoppers,thus obviously suppressing incidence of rice stripe disease that is spread through planthoppers.Though the system also showed significant effect on controlling of rice sheath blight,it couldn′t put an end to incidence of the disease.As azolla absorbed some organic substances and humus from the water,the rice-duck-azolla system was 8.70% lower than the rice-duck system in COD of the submerging water.Thus the water in the former was more transparent.

Key words: rice-duck-azolla system, compound system, ecological effect, soil fertility, weed, disease and insect pest, water quality of rice field