Sewage sludge and refuse composts as peat alternatives for conditioning impoverished soils: Effects on the growth response and mineral status of Petunia grandiflora

A glasshouse pot experiment is described comparing the growth reponse, nutritional , status and heavy metal content of Petunia grandiflora in an impoverished acid sandy soil amended with peat or composted sewage sludges and refuse. The composts consistently out-performed peat as soil améliorants because of greater nutrient availability. However, results indicated that rates of application of composts to soil should be adjusted according to the conductivity of the applied material and the salt tolerance characteristics of the plant species to be grown to avoid detrimental effects on plant growth. There were no phytotoxic effects on plant growth due to contamination of the composts with heavy metals irrespective of the level of incorporation into soil, indicating that proposed lower metal limits for composts compared with sewage sludge would be unnecessarily restrictive to compost use. Composted sewage sludges and refuse are shown to have considerable potential for use in the amenity and landscape industry for improving impoverished soils.