Application of municipal sewage sludge to agricultural land in shallow soils

Abstract

Application of municipal sewage sludge to agricultural land, especially in shallow soils, demands to validate the maximum amount of heavy metal, monitoring its effects on soil and on crops. To achieve this goal, four farms, considered replicates, were chosen in Castro Verde region, to apply four experimental treatments (T1 – conventional fertilization (CF); T2 – subsoiling (S) + (CF); T3 – (S) + (CF) + sludge injection (SI) and T4 – (S) + recommended fertilization (RF) + (SI)), to get mixing effects of sludge injection with fertilization modalities.

They were sown wheat (Triticum aestivum) and oat (Avena sativa) as test crops, and sewage sludge, containing heavy metals level according to law (MAOTDR, 2009), was furnished by Castro Verde sewage treatment plants.

Results did not show any soil pollution by the metals Cd, Cr, Ni, Pb, Cu, Zn and Hg, and the treatments did not affect significantly (p>0.05) the crops. This study validated, at these particular conditions, heavy metals limits established by law to avoid health and environmental risks.