Risk assessment of pig manure Cu-contamination of black soil in Northeast China

Copper(Cu) is massively used as feed additives in intensive farms,and the discharge and utilization of livestock wastes may cause certain environmental problems.In this paper,a cultivated black soil in Northeast China was sampled,and added with pig manures that contained different concentration of Cu to simulate the vegetable soil under different years of pig manure fertilization.With this soil,a pot experiment was conducted to study the effects of soil Cu accumulation via the application of the pig manures on the aboveground biomass and its Cu concentration of pakchoi(Brassica chinensis L.),soil microbial biomass carbon,and soil enzymes(dehydrogenase,urease,and acid phosphatase) activities.The results showed that pig manure application increased the aboveground biomass of pakchoi significantly,but had no significant effects on the aboveground biomass Cu concentration.Under the application of pig manure,soil dehydrogenase and urease activities increased in a definite period of time,but their activities as well as soil acid phosphatase activity were depressed gradually with the increase of soil Cu concentration.When the soil total Cu concentration reached 301.3 mg·kg-1,the aboveground biomass of pakchoi,soil microbial biomass carbon,and the activities of dehydrogenase,urease,and acid phosphatase were greatly reducd.The aboveground biomass Cu concentration of pakchoi had significant positive correlations with the concentration of soil total and water soluble Cu(P0.01),while the aboveground biomass was negatively correlated with soil total Cu concentration(P0.05).It was suggested that the threshold value of Cu in black soil under vegetable cultivation should be less than 301.3 mg·kg-1.