EFFECT OF SALINITY ON THE HEAVY METALS MOBILITY IN CALCARIC FLUVISOLS. Martinez-Sanchez MªJ., Pérez-Sirvent C., Vidal J., Marin P. Department of Agricultural Chemistry, Geology and Pedology, Faculty of Chemistry. University of Murcia, E-30071. Spain. email@example.com INTRODUCTION.- In this paper a study on the space-temporal variability of chemical species in a calcaric Fluvisols zone, is carried out. The zone studied (about 60 Km2) is mainly devoted to the cultivation of citrics. The soils located at the Vega del Segura (Region de Murcia, SE. Spain) have been cultivated during many centuries, the crop yields being so high that this zone has been named as Europe Garden. The traditional cultivation systems including culture rotations, made that, in spite the fact that the soils have been extensively cultivated for so long periods of time, no degradation processes or fertility losses have been noted for many years. MATERIALS AND METHODS.- To carry out this study 17 samples were obtained and for comparison purposes these were the same that were previously studied three years ago. The general characteristics of the arable soil layer were determined by the methods used to draw up a soil map of the area in the LUCDEME project (ALIAS et al, 1989; SOIL SURVEY STAFF, 1994) . The total metal content (Zn, Pb, Cr and Cd) was determined by electrothermal atomization atomic absorption spectrometry (ETAAS) or flame atomic absorption spectrometry (FAAS) (BAUTISTA et al, 1984) . To this end, the samples were slurried in a dilute hydrofluoric acid solution and the suspensions were directly introduced into the flame or the electrothermal atomizer. The selective extractants used for the soil samples were: sodium dithionite + sodium citrate (MEHRA and JACKSON, 1960), DTPA (LINDSAY and NORVELL,1978), HNO3 M 0.1 and Na HCO3 N 0.1 (OLSEN and SOMMERS, 1982). The mineralogical composition of the samples was determined by XRD analysis using radiation Cu-K, and a semiquantitative analysis was made of the treated and untreated samples. RESULTS AND DISCUSSION.- Table 1.- Analytical data of soil samples % Ca CO3 equiv. % O.M 1993 % O.M 1996 % Sand %Silt %Clay Minimun 31,2 1,5 1,1 8,0 54,7 26,3 Maximun 45,3 2,9 2,7 18,8 59,4 41,8 Average 39,8 1,8 1,6 9,0 56,3 34,8 Our data indicate that errors in the cultivation procedures are the responsible of the chemical degradation of the soils. The use of high salinity waters has produced a high salinization velocity and even a high alkalinization which is specially severe in some sampling points (FAO, 1984; FAO, 1988). In addition, there is a loss in the soil fertility, since the levels of assimilable elements (Fe, Mn, Zn and Cu) has decreased considerably, the assimilation of heavy metals such as Pb and Cd being increased. The heavy metals mobilization is especially severe for the more degradated soils. Table 2. Mean values obtained from soil samples Total HNO3 DTPA HCO3- M-J mg*Kg-1 % ext % ext % ext % ext 1993 Zn 130 33 2.6 2 25 Pb 55 9 20 <0.1 8.5 Cr 54 6 <0.1 <0.1 5 Cd 0.5 80 10 <1 50 1996 Zn 135 35 3 2 28 Pb 60 9 2.5 <0.1 9 Cr 54 8 <0.1 <0.1 7 Cd 0.7 80 12 <1 60 REFERENCES ALIAS, L.J., SÁNCHEZ NAVARRO A. , LINARES MORENO, P. MÁRTINEZ , J., MARIN SANLEANDRO, P. , ORTIZ SILLA, R. And ALCARAZ ARIZA, F. 1991. Proyecto LUCDEME. Mapa de suelos escal 1:100.000. Caravaca. ICONA- Universidad de Murcia. BOWER, C. A. and WILCOX, L.V. 1965. En C.A.., Black, De. Methods of Soil Analysis, part 2, 933-940. Amer. Soc. Agronomy, Inc. Madison, Wis. BAUTISTA, M.A., C. PÉREZ-SIRVENT, I. LÓPEZ-GARCÍA, and M. HERNÁNDEZ- CÓRDOBA. Fresenius J Anal Chem, 350: 359-364, (1994). LINDSAY, W.L. and NORVELL, W. A. 1969. Agron. Abstr., 84. MEHRA O.P. and M.L. JACKSON, Clays and Clay minerals, Monograph nº5, Earth Science. Series: 317-327, (1960). OLSEN S.R. and L.E. SOMMERS, In Methods of soil analysis. Part 2. 2end (Edited by A.L. Page) Ed. American Society of Agronomy, Madison, WI, (1982). SOIL SURVEY STAFF. 1994. Keys to soil taxonomy. SMSS tecnical monograph nº 6. Blacksburg, Virginia. FAO. 1984. Metodología provisional para la evaluación y representación cartográfica de la desertización. FAO. Roma. 74 pp. FAO. 1988. FAO-Unesco Soil Map of the World, Revised Legend. World Soil Resources Report 60, FAO. Roma. 119 pp.