A survey of some Siwa oasis area soils was carried out in 2001-2002. Measurements of topsoil properties were made at 36 grid system (350x350m.) sites.
The results have been statistically and geostatistically analyzed to assess the degree
and nature of spatial variability and spatial dependence in the soil properties.
Classical statistical analysis showed that the coefficients of variation (C.V.) were 2.09,
2.07,1.54,1.50,1.47,1.43,1.40,1.18,1.13,1.06,0.90, 0.78, 0.76 and 0.73 for K+, S04-, cr, Na", EC, HCO'3, gravel, Mg++, ca", V.F.S., SAR, CaC03,
fine sand and very coarse sand, respectively. Principal component analysis (PCA)
was carried out to reduce data redundancy and interpretation. The first sex PC's were
selected as each of them explained more than 4.55% of the total variance. These six
PC's explained 80.26% of the total variance. This is confirmed by the coefficient of
variation (C.V.). Geostatistical analysis showed that the semi-variogram model was
Spherical for depth and CaC03%, Gaussian for EC and SAR, and Exponential for O.
M. and tatol sand. The only variables that showed the EC, SAR, depth and total sand
has the highest nugget variances of 2460,324, 167 and 122.1 which indicate their
strong spatial dependence and high inherited variability. The maximum interpolation
distances for CaC03, depth EC, SAR, O.M and total sand, are 540.1, 531.0, 275.3,
124.4, 619 and 616 m., respectively. Highly variable soil properties were used to
produce kriging maps, using Punctual kriging method. The information taken from the
semi-variogram model for each property was used in drawing the isarithmic maps for
these properties, indicating their spatial distribution.