An incubation experiment was conducted to study the dynamic response of soil microbial biomass C

N

P in an atrazine-added paddy soil

at a rate of 10 mg/g soil. Results showed that soil microbial biomass C

N

P significantly decreased after addition of atrazine. As composed with control

microbial biomass C

N and P decreased averagely 13.5%

10.1%

20.0%. However

microbial biomass C

N and P significantly increased after application of organic matters and fertilizers. The effect of organic amendments and fertilizers on microbial biomass C

N followed the order of pig manure > Chinese clover> rice straw> NP combined treatment> sole N treatment> sole P treatment. But the effect of organic materials and fertilizers on microbial biomass P was pig manure >NP combined treatment>Chinese clover>sole N treatment> sole P treatment>rice straw.