Soil Salinization Induced by Runoff Collection in Small Forested Limans in the Negev Desert
Investigators (most current known information)
Soil salinity is one of the factors limiting agricultural development of semiarid and arid areas. Salinization is especially widespread in fine-grained soils which have a high water absorption capacity and a low to very low infiltration rate. The natural process of soil salinization may be seriously exacerbated by irrigation practices that add substantial amounts of salts into the soil. Salinization risk is great in closed systems with an impeding layer at a shallow depth. Saline soils are characteristic of the northern Negev desert where EC figures of 14-25 mmho/cm had been reported at a depth of 50 cm.
In the 1960's the Jewish National Fund constructed numerous small earth dams across ephemeral small watersheds. Runoff waters collected upstream of the dams were used for the plantation of small groves. As the limans operate as closed systems, over time there can be a build-up of salts brought by runoff waters and severe salinization can result. In order to determine whether the process of salt accumulation did occur over the period considered, trenches were dug in 20 limans representative of the conditions prevailing in the study area. At each trench the soil profile was described and soil samples were taken for the analysis of particle size distribution, bulk density, electrical conductivity and soil moisture. In addition, runoff waters were sampled in order to estimate the rate of salt input.
Despite a relatively high salt input, data obtained do not support the hypothesis that the limans suffer from salinization. In all limans examined, the soil down to a depth of 3 m. was found non-saline. Salinity inside the limans was found lower than in the control trenches, pointing at an efficient process of salt removal. Results obtained are due to a combination of several factors; despite a relatively high clay content a Bt horizon, with a limited infiltration rate, did not form due to the assumed young age of the sediment, as well as due to the fact that all limans had been constructed in relatively leached alluvial reaches and flood plains. Vertical water movement is greatly enhanced by the occurrence, in many limans, of sandy and gravely layers. Finally, runoff volumes collected by the limans are beyond the originally estimated values. On years with high runoff, the water depth can exceed 1000 mm allowing, under the good percolation conditions prevailing in the area, deep water infiltration and salt removal.
Ziha, I. 1995. Soil salinization induced by runoff collection in small forested limans in the Northern Negev desert. M.S. Thesis. Institute of Earth Sciences, The Hebrew University.