STUDY OF AMMONIUM CONTAMINATION IN LEACHATES FROM AN ULTISOL FOLLOWING APPLICATION OF VARIOUS TYPES OF AMENDMENT A. LÓPEZ 1∗ , R. ESPEJO 2 and M. VIDAL 3 1 Escuela Politécnica Superior, Universidad de Santiago, Campus Universitario, E-27002 Lugo, Spain; 2 E.T.S.I. Agrónomos, Universidad Politécnica, Ciudad Universitaria, E-28040 Madrid, Spain; 3 Escuela Superior y Técnica de Ingeniería Agraria, Universidad de León, Ctra. Circunvalación s/n, E-24071 León, Spain ( ∗ author for correspondence, e-mail: lfabal@lugo.usc.es) (Received 13 December 1999; accepted 22 December 2000) Abstract. The composition of leachates from an Ultisol reconstructed in lysimeters and amended with limestone, sugar foam waste and gypsum rock was studied. The typical rainfall of the area from which the soil was collected was simulated under laboratory conditions over a five-month period. The soil samples treated with gypsum behaved markedly differently from the rest. Thus, the samples amended with gypsum gave leachates with substantially increased ammonium contents that might result in contamination of aquifers. The gypsum-treated samples also exhibited marked differences in pH, EC and the Ca, Mg, Na and K contents from the rest. Keywords: acidity, ammoniacal contamination, leachates, liming, soil, sugar foam waste 1. Introduction A‘rañas’ are continental detrital formations from the Pliocene related to quartzitic sierras in the Iberian Peninsula (Oehme, 1935; Vidal, 1944; Menshing, 1958; Vau- dour, 1977; Espejo, 1987). Their soils, Ultisols (USDA, 1999), are strongly acidic, highly weathered, rich in Al (the dominant cation in the exchange complex) and substantially deficient in nutrients such as P, Ca and K (Espejo, 1993). These char- acteristics by themselves considerably restrict the agricultural potential of these soils in Mediterranean areas, hence their marginal use for cropping. Traditionally, these restrictions have been overcome by incorporating products containing enough calcium or magnesium to raise the pH of the soil and neutralize phytotoxic aluminium, which is present in excess amounts in the exchange com- plex (Pavan et al., 1982; Cameron et al., 1986, Wright, 1989). To this end, ground limestone, dolomite and various agricultural food processing residues containing abundant calcium or magnesium (e.g. drying ‘foams’ produced in the industrial extraction of sugar from beet root) are used. Gypsum is also employed for this purpose as it exerts a self-liming effect that results in the adsorption of sulphate ion; it also raises the Ca/Al ratio and facilitates the formation of non-toxic SO 4 Al + ion- pairs (Reeve and Sumner, 1972; Pavan et al., 1982; Noble et al., 1988). Gypsum Water, Air, and Soil Pollution 133: 133–143, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.