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Changes in chemical properties of an acid soil after application of dairy sludge M.E. López-Mosquera 1*, C. Moirón 1, S. Seoane 2 1* Dpto. de Producción Vegetal, Dpto. de Edafología y Química Agrícola, Escuela Politécnica Superior, Universidad Santiago de Compostela, E-27002 Lugo, España. 2 [email protected] SUMMARY The dairy industry generates an effluent, containing cleaning products and milk residues, which is usually treated and forms a semi-liquid sludge as a by-product. One of the best methods of disposal of this waste product, given that it has a low content of heavy metals and is rich in N and P, is to recycle it by fertilizing agricultural land. Many studies have dealt with the effects of urban waste on soils and crops, but only very few report the influence of the addition of dairy-sludge on the productive capacity of soils. We investigated the short-term changes (6 and 25 weeks after applications) produced by different doses of dairy-sludge (0, 80, 160 and 240 m3 ha–1) on the chemical properties of a cultivated Humic Cambisol. Application of the highest dairy sludge rate caused the most significant changes in the soil properties studied six weeks after being spread (increase in exchangeable Na, saline effect, strong decreases in exchangeable Al and Ca and extractable P), but these effects were no longer apparent twenty five weeks after sludge application. Our results indicate that the most suitable rate of dairy sludge to use, in terms of sward sustainability was 80 m3 ha–1, since it did not cause significant negative changes in soil properties and led to an increase in production of 65 % with respect to the control plots. Key words: grassland, fertilization, short-term effects INTRODUCTION The generation of waste products as a consequence of the treatment of urban or industrial sewage leads to serious problems involving its storage and, more importantly, its disposal. Although the composition of these wastes is variable, they are usually rich in organic * Autor para correspondencia Recibido: 16-1-01 Aceptado para su publicación: 21-9-01 Invest. Agr.: Prod. Prot. Veg. Vol. 17 (1), 2002
