STUDY ON "RICE-AZOLLA-FISH" CROPPING ECOSYSTEM AND EFFICIENCY OF AZOLLA NITROGEN IN THE VALLEY PADDY FIELD OF NORTHERN FUJIAN

The cropping technology of rice- azolla- fish ecosystem were applled intovalley paddy field. It was showed by the plot experiment that the grass fish and T.nilotica is 3568 and 3702kg/hm2 respectively, when the azolla was used as fish fodderin the valley paddy field. The yields of monocropping rice and the ratooning rice in theplot of rice -azolla-fish was 5710~6006kg/hm2 and 3478~ 3772kg/hm2, respectively,and they were higher as 689. 0 ~1132. 5kg /hm2 and 458. 4~ 658. 9kg /hm2 than thetreatment of applying chemical nitrogen fertilizer. It was showed that the totalefficiency of N-azolla is 52. 8%~57. 9% in the rice- azolla -fishecosystem and that only33. 5% in the treatment of applying chemical nitrogen ferti1izer by 15N- tracingexperiment. The rice-azolla-fish ecosystem had been applied for two years, the organicmatter in the soll from valley paddy field increased O. l5% and the index of diseasedecreased 42. 0% ~ 50. 7% in this cropping ecosystem. It was a good method forimproving eco-environment and reached to increasing both yield and income when thetechnblogy of cropplng ecosystem was applled successifully.