Abstract:
Oasis agrosystems play an important role in the development of arid lands. Water is the
limiting factor for the improvement of these areas. However, if development under irrigation
contributes to the increase of agricultural production, its extension is accompanied by serious threats to
the preservation of the environment, especially the quality of the soil, which is already weakened by
extreme climatic conditions. In this topic, the spatial variability of the properties of irrigated soils is a
means of knowing the state of the latter. This study aims to determine the spatial variability of organic
carbon, salinity, PHWATER, pHKCL, total and active limestone in the soil using a geostatistical approach.
The present study was carried out in the region of Zelfana (Ghardaïa) located in the Algerian central
Sahara. We opted for a random sampling method, where we carried out 15 profiles. The edaphic study
was done on three depths (0-30 cm, 30-60 cm, 60-120 cm). The main results obtained show that the
irrigation water coming from the Albian aquifer has a medium to poor quality (C3 S1). The
granulometric results show that the study area is characterised by a predominantly sandy to sandy-clay
texture. The analytical results show that the soils studied are generally very poor in organic carbon
(CO < 1%) in all three levels. The soil is low to very saline, with EC values at 25°C ranging from 0.64
to 3.87 dS/m with an ascending saline profile. The soil is slightly to highly calcareous, with total
limestone values ranging from 2.08 to 30.94% 15.62%. The soil is alkaline with a pH ranging from
8.25 to 8.31.The results of the spatial distribution of the studied parameters show a high to very high
variation of organic carbon, moderate to very high for limestone, and high to moderate for salinity. On
the other hand, the spatial variability of pHWATER and pHKCL is low. The nugget effect is very low for
all parameters studied. The results of the cross-validation led to the selection of the most reliable
variogram models, namely the circular, spherical, gaussian and exponential, which were used to
produce the spatial variability maps by ordinary kriging.
