Impact of sewage sludge and mineral fertilizers application in soils un­der pasture from the Alentejo region

Abstract

We evaluated the changes in the soil indi­cators pH in water, total OM and N, ex­changeable cations, available P, K, Cu, and Zn, heavy metals (Cd, Cr, Cu, Ni, Pb, and Zn), and faecal origin bacteria, between 2004 and 2007, as affected by sewage sludge (SS) application and mineral fertili­sation in two field experiments with pas­tures. The treatments were the combinations of two types of pasture (natural and sown) with three fertilisation treatments (0, SS, in­organic fertilisers) in the experiment of Herdade do Revez (Haplic Luvisols and Haplic Leptosols), and four fertilisation treatments (0, SS, Liming+SS, and Lim­ing+inorganic fertilisers) in Herdade da Criméia (Ferric Luvisols).

The OM and available P contents were the chemical properties that significantly in­creased (P ≤ 5%) in the soil surface layer of both field experiments. The SS application also caused the highest significant increases in soil total N and exchangeable Mg con­tents in Herdade do Revez. Liming in­creased soil pH and exchangeable Mg, in Herdade da Criméia. The SS did not pollute the soils with heavy metals. The bacterial populations of faecal origin increased im­mediately after the SS application, but pro­gressively decreased as time went by, reach­ing values similar to the controls.