Leaching Curves of Highly Saline-Sodic Soil Amended with Phosphoric Acid and Phosphogypsum Mamoun Gharaibeh + , Nabil Eltaif and Shady Shra’a Department of Natural Resources and the Environment, Faculty of Agriculture, Jordan University of Science and Technology, P.O. Box: 3030, Irbid 22110, Jordan Abstract. Column experiments were conducted to determine desalinization and desodification leaching curves of a highly calcareous saline-sodic soil. Soil columns were amended with phosphoric acid and by- product gypsum (phosphogypsum) and leached with canal water. Phosphogypsum was applied to soils at application rates of 15, 20, 30, and 40 ton ha -1 , while phosphoric acid was dissolved in leaching water at application rates of 450, 600, and 900 kg ha -1 . Desalinization curves showed that both amendments had similar efficiency in reducing soil salinity, whereas desodicfication curves revealed a superiority of phosphoric acid in reducing soil sodicity. In addition, the Hoffman’s approach was adopted to determine the leaching constant (k) of both amendments. Desalinization curves showed that application rates did not appear to have a strong effect on k in both amendments, while desodification curves showed that increasing rates of phosphoric acid appeared to have no affect on k. The leaching constants (k) of phosphogypsum and phosphoric acid averaged 0.26 and 0.24 for desalinization and 0.23 and 0.18 for desodification, respectively. The smaller values of k in phosphoric acid treatments depicted lesser amounts of water required for leaching and reclamation compared to phosphogypsum. Keywords: leaching curves, saline-sodic soil, reclamation, phosphoric acid, gypsum 1. Introduction Globally, it is estimated that 100 million hectares are classified as salt affected soils [1], half of which are saline-sodic soils [2]. These soils are commonly found in arid and semi arid regions and characterized by high levels of sodium that deteriorate soil structure, reduce water intake, and cause fertility problems leading to reduction in crop production [3]. Reclamation of these soils is accomplished by either an addition of chemical amendment(s) commonly mixed with the upper parts of the soil or directly dissolved in water, or by planting crops (phytoremediation) capable of accumulating salts in their parts [4]. Gypsum (CaSO 4 .2H 2 O) is mostly used for the reclamation of saline-sodic and sodic soils and to a lesser extent calcium chloride (CaCl 2 .2H 2 O) or sulfuric acid (H 2 SO 4 ). The first two amendments provide a direct source of calcium ions to replace exchangeable sodium, while sulfuric acid increases the dissolution of calcite in soil [5]. Recently, phosphoric acid (H 3 PO 4 ) was recommended as a reclaiming material for highly saline sodic soils [6]. Reclamation requires high amounts of water to leach salts. The principle of leaching is very simple; the salts must be washed downwards and away from the root zone by means of flooding and presence of good drainage conditions. In practice, the quantity of drained water is used as an index of the actual amount of leaching water. It is important to have reliable estimate of the required amount of leaching water needed to reduce soil salinity/sodicity to a desirable level. The empirical approach is by far the most suitable way that can be adopted to tackle this problem. This approach involves plotting the decrease in soil salinity in relation to the + Corresponding author. Tel.: + (96227201000); fax: + (96227095069). E-mail address: (mamoun@just.edu.jo). 2011 2nd International Conference on Agricultural and Animal Science IPCBEE vol.22 (2011) © (2011) IACSIT Press, Singapore 1