Increasing concentrations of in surface water and groundwater can cause ecological and public health effects and has come under increased scrutiny by both environmental scientists and regulatory agencies. For many regions though, including the Sahel of Tunisia, little is known about the sorption capacity of soils. In this project we measured sorption by a profile of an iso-humic soil from Chott Meriem, Tunisia. Soil samples were collected from four soil depths (0–25, 25–60, 60–90, and 90–120？cm) on 1 June 2011, and their sorption capacity was determined using batch experiments under laboratory conditions. The effects of contact time, the initial concentration, and the soil-solution ratio on sorption were investigated. In general, the results suggested that was weakly retained by the Chott Meriem soil profile. The quantity of sorption increased with depth, contact time, initial concentration, and soil-solution ratios. To evaluate the sorption capacities of the soil samples at concentrations ranging between 25 and 150？mg？L？1 experimental data were fitted to both Freundlich and Langmuir isotherm sorption models. The results indicated that Freundlich model was better for describing sorption in this soil profile. 1. Introduction Nitrogen (N) is a critical nutrient needed by all plants for growth [1]. Input of inorganic N as a fertilizer is considered essential in modern agriculture in order to satisfy the dietary needs of a growing world population. Nitrate ( ) is the one of the principal N forms taken up by plants. As such, inorganic N is widely used in agriculture and numerous studies have suggested that leaching of following high input rates of chemical fertilizer and due to mineralization of organic N already present in the soils can cause degradation of surface and groundwater quality. Excess contaminated water supplies have been linked to outbreaks of infectious disease [2]. Also, can be converted to nitrite in the digestive tracts of infants and ruminant animals, which then combines with blood hemoglobin, reducing its ability to carry oxygen, occasionally leading to death. The ability of soil to adsorb anions can reduce leaching to the deeper horizons and maximize the available for plant nutrition and can thus play a fundamental role in enhancing soil nutrition in regions, such as Mediterranean areas, where availability is often a limiting factor [3]. Previous studies have reported the sorption of by soils [4, 5]. However, mobility in soils is mainly controlled by a number of soil properties including iron and aluminum oxide concentrations [6],
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