Studies on Artificial Controlling Biosphere in Paddy Field and Its New Cropping System Ⅲ.The Eftect of External Water-sprikling System on Dissolves Oxygen

Experitmental results indicated that water dissolved oxygen(DO)need to be more than 3mg/l to meet the healthy growth of Clossoma brachypomum,Tilapia,Cyprinus carpio and Clarias fuscus.The variance of daily DO of artificial biosphere in paddy field(ABPF)is similar to that of the pond,which was high in daytime and low in night tirne,but DO of ABPF is lower than that of the pond,and the DO in pit of ABPF is lower than that on surface.The DO of ABPF frequently deficient during night time of the late stage of fish culture.The experitmental results also showed that,225m3/hm2 sprikling volum for 45min.from external watersprikling(EWS)system during night time could meet the DO requirements of fishes with the yield of 4377.2kg/hm2 in ABPF.The effect of EWS systern is negatively related to the fish density in ABPF,With the same fish mixted rate,the fish yield of ABPF is double to high-density fish culture which without EWS system.