The present study focuses on the agronomic efficacy evaluation of volcanic rock mining waste and the sewage sludge from a dairy industry as a fertilizer for an acid soil, and to evaluate its nutrients and toxic potentially elements. The waste samples were collected from a volcanic rock mining and a dairy industry located in the southern region of Brazil. X-ray diffraction technique was employed to identify the mineralogical phases present in the rock dust. Rock and sludge major elements composition were analyzed after fusion along with LiBO2 followed by X-Ray Fluorescence. Toxic potentially elements content was measured according to United States Environmental Protection Agency 3050b method. The sludge and rock were applied to small-scale field experiment in which black oats was then sown. Four treatments were compared: (T1) 3,240 kg ha-1 of sewage sludge, (T2) 1,620 kg ha-1 of sewage sludge with 6,000 kg ha-1 of rock, (T3) 12,000 kg ha-1 of rock and control, which did not receive any type of input. Changes in soil properties and the nutritional status of the black oats were monitored after ninety days. The addition of the sludge combined with rock dust led to substantial increases in black oats leaves nutrient concentrations (mainly Ca, K, P and Zn) and in soil available K and P. In addition, the potentially toxic elements levels of both wastes are low and therefore the risks of environmental contamination are considerably reduced. Keywords: dairy industry sewage sludge; volcanic rock mining waste; natural soil fertilization.