Element composition of tomatoes grown on four soils mixed with sewage sludge

Abstract

Dried digested sewage sludge from the Manukau Purification Plant, Auckland, was mixed at 5 different rates with 4 local soils and used to grow tomatoes in a glasshouse pot trial. Analysis of the sludge showed that it had less heavy metals than most sludges from industrial towns overseas. Addition of sludge to soil increased the concentration in the plant of Mo, P, Zn, S, Ni, Cu, Na, Ca, B, Mn, and Cd but decreased Al, V, Ti, Ba, Si, Sr, Fe, Cl, and Cr. Analyses of root, leaf, and fruit showed that the fruit had the lowest concentration of most elements. Application of sludge to soils slightly increased concentrations of Ni, Cu, Mo, Mn, and Zn in the fruit but gave no change in Cr, Pb, and Cd. Relationships of plant yield and plant composition to soil material were lost by applying sludge to the 4 soils.