Physical and chemical properties of long-term salinized soils

In some areas, particularly in the Mediterranean regions, saline water is a source of water for crop irrigation. Consequently during the time, the use of this water may cause significant modifications of the soil physic-chemical properties and plant toxicity. The purpose of this investigation was to assess the variation of soil stability index and of ECe, ESP, pH, exchangeable potassium, bulk density, soil hydraulic conductivity and water retention curve (h(θ)), for a clay sandy soil, which was irrigated over 12 years with saline water. The soil stability index was evaluated by 2 methods: after wetting the sample (Water Stability Index = WSI) and without the pre-wetting step (Water Stability Dry Index = WSDI). The measures have been taken at three depths along the soil profile: 0-0.30, 0.30-0.60 and 0.60-0.90 m. The saline water was obtained by adding commercial sea salt to the irrigation water with the result of a final concentrations of 0.25 (2.5 g l-1), 0.5 (5 g l-1) and 1% (10 g l-1). A non-salinized control was also included. The increasing salinity of the irrigation water increased at all the depths ECe, ESP and pH, while exchangeable potassium decreased. Assessment of soil aggregates stability without samples pre-wetting (WSDI) allowed us to better discriminate among the different samples examined. Aggregate stability for each of the soil layers decreased at increasing salinity of the irrigation water. Long term salinization affected the aggregate stability of the deepest layers. The soil hydraulic conductivity decreased also, while bulk density increased. The shape of the soil water retention curve was also affected by salinity. In the salinized plots less water is relaxed within -150 ÷ -12 cm ψ range. The available water was reduced at increasing salinity. Irrigation with saline water on clay-sandy soils increases ECe, pH and ESP, all of which negatively affect the soil aggregate stability. Damage to the soil structure remarkably reduces the available water and soil hydraulic conductivity. The magnitude of these deleterious effects may increase through the years and in proportion to salt concentration in the irrigation water.