Résumé:
In the plain of Lower-Cheliff, a northwest Algerian region with a semi-arid climate and
high rates of evapotranspiration, the recourse to irrigation for most of the crops is
indispensible. For the last twenty years, the water shortage allocated to agriculture has
constrained the farmers to privilege the use of the groundwater resource which is of poor
quality. This recourse has been accentuated these years witnessing a deterioration of the
irrigation supply network.
The mapping of groundwater salinity in the plain of Lower-Cheliff has shown the
advanced state of this resource vulnerability to salinity where more than 60% of the
underground water resource has EC > 3dS/m. The use of indicator Kriging method has
improved the mapping of groundwater salinity in the region with a better evaluation of the
obtained surfaces by optimizing the estimates of the extreme values often male estimated by
the ordinary Kriging.
The assessment of the water groundwater quality of the Lower-Cheliff plain, compared
to the hydro geochemical process which controls its ionic load and its aptitude of being used
for agricultural needs showed that the most diluted water is likely to precipitate salts
containing divalent elements (Ca and Mg) in the form of calcite, gypsum and dolomite. That
will give more mobility to the sodium which is likely to be fixed on the exchange complex,
causing thus, an impoverishment of the irrigated soil. The concept of generalized residual
alkalinity, simplified, has confirmed these results. The water with residual alkalinity calcite,
positive sepiolite, and gypsum are those provoking the degradation of the irrigated soil. The
experimental scheme carried out through this study showed that the concentration of a water
of RSC1>0 causes an increase in the SAR, at the same time in soils with balanced or clayey
texture, whereas they do not show a risk of sodisation according to the traditional methods of
classification such as that of Richards (1954).
The concept of residual alkalinity constitutes an indicator of the groundwater quality
used for irrigation, whereas the SAR cannot be considered in certain particular cases, i.e.
when the sign of AR is positive.
Finally, the various experimental and theoretical results showed high risks related to the
use of groundwater for soils irrigation in the plain of Lower-Cheliff. In addition, the
agronomic aptitude of these soils is threatened, which can be a determining factor in the
subsistence and the viability of agriculture in the area.
