EFFECTS OF THREE CONSECUTIVE APPLICATIONS OF MSW COMPOST ON SANDY SOIL UNDER INTENSIVE FERTILIZATION CONDITIONS

Municipal Solid Waste Compost (sieved < 10 mm; MSWC) from Recycling Plant of Villarrasa (Huelva), was applied to 3 consecutive seasons of horticultural crops (Tomato, zucchini and green pepper) under greenhouse and intensive fertilization conditions. A Control treatment (no organic amendment), and a commercial compost (CC treatment) widely used by farmers in the area (Los Palacios, Sevilla) were applied as comparison. Effects on soil properties at the end of the 3 seasons were studied. Furthermore, residual effects of compost amendments at the end of the 4th season (Tomato), with no treatment applica-tions were also study. Positive effects were observed in fertilizing parameters after MSW compost appli-cations, compared to both Control and CC treatments. In this way, at the end of the 3rd season, MSWC increased Organic Matter, available-K, available-Ca and available-Mg in the soil, and avoided pH decrea-se observed in other treatments. Nevertheless, negative effects due to MSWC applications were also obser-ved. MSWC increased NO3-N content in the soil at the end of the 3rd season, what could become a pro-blem, specially in sandy soils, because of the danger of groundwater contamination. After one season without treatment applications, high fertilization used to get high crop yield, masked all these positive and negative effects, and no significant differences were observed between plots of different treatments. Soil metal contents were also affected by treatments applied. After the 3rd application, MSWC increased total (HCl-HNO3 digestion) and DTPA-extractable Cu, Zn, Ni and Pb in 0-25 cm layer, and even Zn and Pb in 25-50 cm layer. Soil metal accumulation was a more lasting effect than other parameters studied, and after the season without treatment applications, metal accumulation were still observed