The current study is an attempt to define the relationship between
originated mineral constituents and essential nutrients that could be derived
into the formed soils under cyclic-formation sequences at El Fayoum
depression. To achieve this target, four soil sites were selected to represent
some soils developed on the main parent materials, i.e., the Nile alluvium,
recent lacustrine, desert formations of siliceous (aeolian) and carbonatic in
nature (Eocene limestone). The obtained results showed wide variations in
the characteristics of the studied soil sites, i.e., topographic-sequence (-40 to
+25 m), soil texture grades (sandy to clay), CaCO3 content (1.12 to 38.54%),
ground-water table depth (65 to >150 cm), soil salinity (ECe=1.65-23.96
dS/m) and sodicity levels (ESP=3.42-32.68), consequently they differ in
their soil taxonomic units and the suitability classes for agricultural
purposes. Wetness, soil texture, CaCO3, gypsum and salinity/alkalinity are
the most effective limitations for soil productivity, with an intensity degree
ranged between slight and very severe (rating >90 and <40). Also, the
suitability classes of the studied soils ranged between moderately (S2s1s4n)
and not suitable (N1ws1s4) for the current condition as well as highly (S1s1)
and marginal suitable )S3s1s4).
The polarizing microscopic examination for light and heavy minerals
of sand fraction as well as the x-ray diffractions of both silt and clay
fractions were also suggested to identify the different nutrient-bearing
mineral assemblages. Moreover, soil constituent-bound nutrient forms, i.e.,
exchangeable, organic matter, carbonate, manganese oxides, amorphous &
crystalline iron oxides and the residual content were identified due to their
crucial importance for soil fertility status. Most of P amounts in soil were
bound with organic matter fraction, with maximum values reached about 26
and 20% of total bound P-forms for both the fluvial sediments and
carbonatic desert formation, respectively. The greatest value of K bound
with organic matter fraction was about 15% of total bound K-forms for the
recent lacustrine sediments. Ca and Mg were more combined with carbonate
fraction, especially in the carbonatic desert formation, with greatest values
of more than 39 and 68% of the total bound forms, respectively.
Relatively high S-amounts of about 30-31% of the total bound Sforms were bound with organic matter fraction of the Nile alluvial and
lacustrine sediments. A pronounced amount of bound micronutrients was
more obvious in the Nile alluvial sediments, where Fe was more combined
with amorphous and crystalline iron oxide fractions (i. e., about 24 and
40 %, respectively); Mn was more bound with MnO2 and both iron oxides
fractions with maximum values of 23.54 and 30.75 %, respectively; Zn
was mostly combined with the amorphous and crystalline iron oxides
fractions with about 22 and 37%, respectively; whereas, Cu was also
more related to amorphous and crystalline iron oxides fractions (i.e.,
about 20 and 22 %, respectively) in the recent lacustrine sediments.
The distribution pattern of total macronutrients could be arranged in a
descending order of aeolian < carbonatic desert formation < recent
lacustrine < Nile allluvial sediments for P and K; aeolian < fluvial < recent
lacustrine or carbonatic desert formation for Ca, Mg and S. Total amounts
of Fe, Mn, Zn and Cu greatly differed among the studied soil sites; the
highest and lowest values were existed in the fluvial and siliceous desert
formations, respectively. The relatively highest values of these
micronutrients were mainly due to the occurred high contents of organic
matter, amorphous or crystalline iron oxides and clay fractions. The
available contents of the studied nutrients followed an almost similar trend
to that of the total ones, except for phosphorus and micronutrients in the
desert formations. This is mainly due to the low contents of organic
matter, nutrient bearing minerals and retention or adsorption process in
the siliceous desert formation and/or precipitation with CaCO3 in the
carbonatic one.
The statistical analysis, using the program of SPSS (1997), and
obtained data of simple coefficient showed significantly correlations
between each of the studied nutrients and some specific bearing-minerals in
the different soil mechanical fractions with a contribution percentage. Thus,
the final goal of this work was achieved by proposing a simple relationship < br />between the identified mineral nutrient sources and their contribution
percentages for nutrients supply in soil sediments under study.