Vol. 35 – 2009 - Ecologia Mediterranea - Université d'Avignon et des ...

density which are respectively 0.5 and 0% of
its initial level at the end of the experiment
(Amir et al. 1996). Rooting of the date palms
in the Ouargla basin is subjected to a salinity
of phreatic origin, above 1.5 to 6 times the
threshold of disappearance of the pathogen,
which confers to this area a resistance to the
bayoud disease.
The plant root system cannot easily penetrate
the hardened massive calcareous horizon.
Moreover, water is mainly confined in the
zone above the massive horizon, so that the
geometrical model of root growth changes.
Roots, seeking water, tend to grow laterally,
favouring the development of the horizontal
secondary roots (Esteban & Klappa 1983;
Alonso-Zarza et al. 1989).
Practically, in oasis, these gypseous formations
of water table constitute a very important
limiting factor, in particular for the
shrubby cultures (date palms and fruit trees).
Sometimes, they brutally block root depth
increase which come to be crushed on a true
sandy bank (Durand 1959; Pouget 1968).
Gypseous calcareous crusts are compact and
not very porous. Because of mechanical resistance
posed by the crusts, roots of the palm
tree have difficulty penetrating soil. Root
depth decreases in soil and rooting takes a
lateral orientation. The groundwater rise exasperates
the problem, because the root zone is
impoverished in oxygen, which produces
asphyxiation and root rot. According to Callot
et al. (1982), root development of plants is
not only related to soil porosity, but also to
moisture and soil resistance to penetration.
Our study showed that date palm tolerated
high moisture because, according to Went &
Darley (1953), date palm does not have the
capacity to form a fine root mass. In spite of
its tolerance to moisture, description of roots
of the palm trees in Arizona showed that root
depth in contact with the groundwater does
not exceed 2.2 m, and horizontal lengthening
increases to 8.3 m. Vertical development of
the roots is slowed down by the level of the
water table (Simmons 1926). Bad drainage of
salted water from the water table increases the
concentration of salts in soil solution; soil
becomes toxic and incompatible with normal
date palm vegetation (Monciero 1954). Salinity
of groundwater in the root zone exceeds
the standard limit of the salinity threshold,
estimated at 3 dS.m-1 by Ayers and Westcot
(1976). Contact of the roots with very salted
groundwater, causes fall of the outputs, then
ecologia mediterranea – Vol. 35 – 2009
Effects of hydro-edaphic environment on the rooting of date palm (Phoenix dactylifera L.) Deglet Noor
in the Ouargla Basin (south-east algeria)
Figure 7 – Relationship between date palm rooting and shallow water table
in areas without crusts.
drainage becomes paramount under these
conditions (Weeks 1957; Furr 1975). To counter
all these difficulties, it is necessary to
maintain the water level at approximately
1.3 m in sandy soils, possibly up to 1.5 m in
silty soils (Dubost 1991).
Conclusion
In light of the results obtained from different
soil classes, we can conclude that the shallow
groundwater in the Ouargla basin constituted
the main obstacle to the root development of
Deglet Noor date palms in soil depth. Roots
avoided both water saturated zone and mechanical
resistance in crusts, causing them developping
in a horizontal direction. Salinity of
the groundwaters proved to be less important
to rooting of the date palm compared to level
of the groundwater. Long term, clogging of
the soils by water can cause hypoxia problems,
root rot, salinization, dropping crop
yields, and, deterioration and degradation of
palm plantations in certain extreme situations.
Lastly, to avoid all these problems for date
palm crops, it is necessary to maintain the
level of the water table below root zone of
date palms by using a good drainage network
in the Ouargla basin.
Taking into account the prevailing situation,
it is advised that groundwater salinity levels
be reduced by implementing suitable hydroagricultural
improvements. However, it is
necessary for groundwater salinity to remain
above the threshold which allows the date
palm to resist the bayoud disease. In crust
zones, it is recommended to break soil before
plantation of young date palms using subsoi-
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