THE PLANT AVAILABILITY AND DTPA EXTRACTABILITY OF TRACE-METALS IN SLUDGE-AMENDED SOILS

The DTPA extractability of trace metals and their bioaccumulation by r yegrass (Lolium perenne L.), grown on two soils treated with sewage sl udge, were investigated in a greenhouse pot experiment over a period o f 1 year following sludge application. The experiments were carried ou t at ambient temperatures of 15-degrees-C and 25-degrees-C. The sludge application resulted in elevated concentrations of Cd, Cu, Ni, Pb, an d Zn in ryegrass. The plants grown at 25-degrees-C accumulated signifi cantly higher levels of all the metals than those grown at 15-degrees- C. A trend towards increasing plant metal accumulation over successive harvests was observed for all the metals except Cu. This appeared to be caused by the progressive decline in pH and organic matter status. The DTPA extraction data generally supported the results of plant meta l concentrations for a given harvest or temperature; however, it was n ot consistent in predicting the changing metal uptake behaviour by the ryegrass over the residual period.