Effects of underground water on soil salinity and dates production in Kebili oases area (Tunisia): The case of El Bahaier oasis

Abstract

The risks of increase of the level of the salted underground water and its salinization effect on the soils in oasis
creations are inescapable because of their altitude which is very close to that of the next salted depressions. To
control this phenomenon, some monitoring points called piezometers were installed in these perimeters,
among them the one of El Bahaier located at the north of Kébili city in Tunisia and being the subject of the
follow-up of the current study. Two measurement operations of the level of the underground table and its
salinity were carried out in the functional piezometers of this oasis in March and April 2011; in parallel, two
series of soils samples were taken around these same piezometers on a depth of 1 meter. The determination of
the salinity of these soils samples showed that the most waterlogged zones are those which are salinized
explaining as well as the increase of the underground water level is a principal cause of the soils salinization in
these zones known by their high potential evapotranspiration and very weak rainfall. This observation is
confirmed by the correlation tests between various couples of parameters, where the correlation coefficient r
was generally high and significant. Moreover, the effect of the waterlogging and the soils salinity on the output
of the principal culture practiced in this perimeter, the date palm (Phœnixdactilifera), was highly significant. The
improvement, the clearing out and the cleaning of the drains are necessary to push the level of in-depth subsoil
water more and to relieve the trees of its negative effect on their production. However, an optimal level of this
water table located at 2 meters of depth would be more beneficial on the yield.