GROWTH OF TRIFOLIUM-SUBTERRANEUM IN SCHISTIC SOILS TREATED WITH SEWAGE-SLUDGE HAVING HIGH CU CONTENT

Use of subterranean clover pastures is one of the better ways to increase soil fertility and to reduce soil erosion. To eliminate difficulties in establishment of subterranean clover pastures, it is necessary to increase initial soil fertility, mainly in shallow soils degraded by erosion. Samples of two soils derived from schist (Eutric Leptosol and Chromic Luvisol) were treated with five rates of a sewage sludge with high Cu content (872 mg kg(-1)), equivalent to 0, 5, 10, 20, and 60 Mg ha(-1), and PK fertilization, in a pot experiment. Dry matter yields of subterranean clover (Trifolium subterraneum L.) differed significantly (p < 0.01) between soils and sludge treatments. Yields with sludge treatment were less than those with PK fertilization. Foliar analysis indicated that yield differences could be explained not only by Zn added to the soil by sewage sludge in Leptosol, but mainly by differences in the properties of the two soil samples. Soil Cu levels were unrelated to clover yield, even when Cu content in postexperiment soil samples was similar to the limits values of heavy metals concentration in soils established by the CEE Directive concerning environmental protection for the agricultural use of sewage sludge.