Effects of high application rates of a dried sludge to a market garden soil - investigations in mini-plots

Abstract

Oilseed plants, vegetables and forest trees were grown in succession on a market garden soil in mini-plots (concrete containers, 1 m x 1 m x 1 m, sunk in the ground). The soil was treated with 0, 8, 24 and 72 t ha-1 dried sludge with high concentrations of Cd, Cu and Ni. None of the plants developed metal toxicity symptoms. A high, single application of dried and heat-treated sludge is more likely to cause problems with N than with heavy metals. Rates of up to 24 t ha-1 sludge can be used for growing industrial crops such as oilseed plants or forest trees, but should not be used for growing leafy vegetables because of the high Cd content of the sludge. The sludge applications considerably increased the NaHCO3-extractable P in the soil and caused no problems due to soluble salt and chlorides.