Abstract: Studies of soil acidification in rice nurserv soil show that the activity of soil urease is decreased,the activitv of phosphatase in alkaline soil is increased and that in neutral soil is decreased after acidifing soils to pH4.5.The volatilization rate of ammoniacal nitrogen in the soils is decreased obviously by acidifing the soil,especially in alkaline soils. The available phosphate in alkaline soils is increased,but that in neutral soil is decreased slightly as the soil is acidified.The amount of positive trace elements in soil are increased differently in acid conditions.Thus acidifing dry nursery soils in early spring can improve available nutrients for rice in the soils.

Key words: dam engineering, ecological risk, summed dominance ratio, species.