Studies were conducted to determine the use of an organic residue (sewage sludge compost) for
four years (1996-1999), to study effects of sewage compost on crop yield and chemical properties
of soil under field condition. Productivity studies showed that the greatest growth is obtained
in mixed II treatment (12000 kg/ha sewage sludge compost plus 350 kg/ha urea) with 20 %
more than mineral fertilization, followed by mixed I (8000 kg/ha sewage sludge compost plus 350
kg/ha urea) with 10 % more than mineral fertilization. No toxic effects arising from the heavy
metals in the plant were observed. Moreover, the concentration of heavy metals in the soil are
below Spanish and European legal limits.