Based on investigation and laboratory test of the field soil quality in the sewage irrigation area and the Yellow River irrigation area in Baiyin city,the influences of sewage irrigation on the field soil quatity were analyzed.The results showed that those harmful substances,such as Cr,Cu,Pb,Zn,Cd,As,Hg,F etc,had exceed the content limit of the national standard and the tendency has been increasing year by year.In addition,the countermeasures for sewage irrigation control and polluted soil improvement have been preliminarily discussed.

To investigate the effects of humic acid on the speciations of heavy metals,such as Cu,Pb,Zn and Cd in sewage farm in Baiyin Prefecture,four kinds of organic matters including humic acid,EDTA,citric acid and acetic acid were added,respectively,in polluted soil with a method of successive extraction performed to determine the species of heavy metals.The results show that humic acid could remarkably decrease the content of soluble heavy metals with about 60%~80%,while increase the fractions of Fe+Al+MnO_x and carbonate,which demonstrated clearly that huimc substance,under certain conditions,could effectively increase the resistance to bioavailability and toxicity of heavy metals in sewage farm.