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					   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. mjose@fcu.um.es

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

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