Sources of spatial variability of soil salinity: the case of Beni Amir irrigated command areas in the Tadla Plain, Morocco

The origins and spatial variability of salinity within irrigated plots are a constraint to good long-term field management. Regional depletion of groundwater resources, as well as soil salinization, have been reported in the Tadla plain, a key production area in Morocco. In the northwestern part, water supply is provided only by the local water table, whose evolution in level and salinity over the last 24 years has been analyzed. A mapping of 17 plots was carried out by electromagnetic induction (ECa) after calibration of the measurements with salinity (R-2 = 0.94). These plots are cultivated with different crops (wheat, olive, sugar beet, alfalfa, carrots) with little or no crop rotation, or left fallow. The results highlight two main factors of salinization. On the one hand, the type of crop leads to salinization that increases according to water needs, which are rarely satisfied, thus favoring the accumulation of salts in the upper part of the soil profile. This first factor explained 80 to 85% of the variance in ECa measurements. On the other hand, the gravity irrigation method associated with numerous leaks is responsible for an unequal distribution of water within the plots, associated with 15-20% of the variance. These results confirm the current unsustainable management of this hydro cultural system and highlight the need for better access to quality water and improved irrigation technology. A development proposal is briefly presented.