Desalination and Desodification Curves of Highly Saline-Sodic Soil Amended with Phosphoric Acid and By-Product Gypsum

International Journal of Environmental Science and Development, Vol. 3, No. 1, February 2012

Desalination and Desodification Curves of Highly Saline-Sodic Soil Amended with Phosphoric Acid and by-Product Gypsum

Mamoun A. Gharaibeh, Nabil I. Eltaif, and Shady H. Shra’a, Member, IACSIT

extent calcium chloride (CaCl2.2H2O), and sulfuric acid Abstract—Desalinization and desodification curves of a (H2SO4). The first two amendments provide a direct source of highly calcareous saline-sodic soil were determined calcium ions (Ca2+) to replace exchangeable sodium, whereas experimentally using soil columns. Phosphoric acid and sulfuric acid increases the dissolution of calcite in soil [5]. by-product gypsum (phosphogypsum) to soil columns and leached with moderately saline-sodic canal water. Recently, phosphoric acid (H3PO4) was recommended as a Phosphogypsum was applied to soils at application rates of 15, reclaiming material for highly saline sodic soils [6]. 20, 30, and 40 ton/ha, while, phosphoric acid was applied at Reclamation process usually requires huge amounts of application rates of 450, 600, and 900 kg/ha. Desalinization water to leach salts from soil profile. The principle of curves showed that both amendments had similar efficiency in leaching is very simple; the salts must be washed reducing soil salinity, whereas desodicfication curves revealed a downwards and away from the root zone by means of superiority of phosphoric acid in reducing soil sodicity. Salt flooding and presence of good drainage conditions. In leaching efficiency (k) was determined using the Hoffman’s practice, the quantity of drained water is used as an index of equation. The leaching constants (k) of phosphogypsum and phosphoric acid averaged 0.26 and 0.24 for desalinization and the actual amount of leaching water. It is imperative to 0.23 and 0.18 for desodification, respectively. Desalination of know that leaching is not required until soil salinity exceeds soils required more water than desodification. Moreover, the salt tolerance threshold of the crop. Leaching can be application rate did not have a strong effect on k for both done either every irrigation event or less frequently as amnendmnets. Phosphoric acid required lesser amount of water seasonally or at even longer periods. for leaching and reclamation compared to phosphogypsum, The amount of leaching water depends on initial soil therefore it could be recommended as a reclaiming material. salinity level, applied water technique, and soil type. Water suitable for irrigation is normally suitable for reclamation. Index Terms—Leaching curves, saline-sodic soil, reclamation, Therefore, it is important to have reliable estimates of the phosphoric acid, gypsum. 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

I. INTRODUCTION that can be adopted to tackle this problem. This approach Globally, arable lands cover around 7 billion hectares involves plotting the decrease in soil salinity in relation to (bha), 1.5 bha are cultivated. Of the cultivated lands, 23% are the required amount of leaching water. The relationship saline and 37% are sodic [1], [2]. Moreover, Food and between the fraction of the initial salt concentration (Co) Agriculture Organization (FAO, 1989) reported that 20% of remaining in the soil profile (C/Co) and the amount of water the total irrigated lands (0.227 bha) are salt affected soils. leached through the profile (DW) per depth of soil (DS) to These soils exist in more than 100 countries of the arid and be leached (DW/DS) can be described ()()= semi arid regions and characterized by high sodium levels by kDSDWCoC . k is a constant that differs with soil that cause deterioration of soil structure, reduction in water type. Therefore, the leaching relationship is considered a intake leading to reduction in crop production [3]. useful tool for deciding which amendment is the most Reclamation of salt affected soils is accomplished by either suitable and economically justified for soil reclamation, an addition of chemical amendment commonly mixed with taking into account local soil and agricultural conditions. the upper parts of the soil or directly dissolved in water, or In Jordan, it is estimated that more than 30% of recently by planting crops capable of accumulating salts agricultural land in the Jordan valley is salt affected soils [7]. (phytoremediation) in their parts [4]. Salinity and sodicity problems are expected to be enlarged in future as a result of using poor quality irrigation water [8]. Gypsum (CaSO4.2H2O) is commonly used for the reclamation of saline-sodic and sodic soils and to a lesser Moreover, little work has been done to evaluate the efficiency of moderate saline-sodic water in soil reclamation. It is reported that such water contains adequate calcium and

Manuscript received January 3, 2012. This work was supported in part magnesium ions that can potentially prevent destruction of by Jordan University of Science & Technology, Deanship of Research. soil structure and improve water penetration [9]. Desalination and Desodification Curves of Highly Saline-Sodic Soil The objectives of this study were: (1) to establish Amended with Phosphoric Acid and by-Product Gypsum. M. A. Gharaibeh, N. I. Eltaif and S. H. Shra’a are with Jordan University desalinization and desodicfication curves of a highly of Science & Technology, Department of Natural Resources & Environment, calcareous saline sodic soil amended with by-product Faculty of Agriculture, Irbid 2210, Jordan (e-mail: mamoun@ just.edu.jo; gypsum and phosphoric acid under continuous ponding using nieltaif@ just.edu.jo; XXXX@ just.edu.jo). moderatly saline-sodic canal water, (2) to compare the

39 International Journal of Environmental Science and Development, Vol. 3, No. 1, February 2012 efficiency and optimum application rate of gypsum and needed for successful reclamation. Leaching curves are only phosphoric acid needed for soil reclamation, (3) and to applicable for specific soil and salt conditions and used to determine the amount of water required to accomplish describe the relation between soil salinity (desalinization) or reclamation process. sodicity (desodification) and the depth of leached water. Since it is not feasible to carry out time-consuming and expensive leaching experiments in the field; column II. MATERIALS AND METHODS experiments were used for this purpose. A highly saline sodic soil was sampled from cultivated Leaching curves (desalinization curves) are constructed by fields in the southern parts of the Jordan valley. Soil cores [19 plotting relative changes in soil ( − − ) cm i.d., 40 cm long equipped with sampling cutter] were salinity oeq ECECECEC eq on the ordinate and used to extract undisturbed soil samples. Selected soil DW/DS on the abscissa (Fig. 1). EC is soil salinity after an physiochemical properties are shown in table I. application of specified depth of leaching water, (ECo) is the initial salinity of soil, DW is the depth of leaching water, DS TABLE I: SELECTED PHYSIOCHEMICAL PROPERTIES OF USED SOIL is the depth of soil, and ECeq is the salinity of soil at the end of Soil Property Value reclamation process (equilibrium). ECeq is equal to the ECe (dS/m) 50 salinity of the upper 5 cm of reclaimed soil. When ECeq is pH 7.8 3 subtracted both from initial soil salinity (EC ) and salinity of Bulk Density (Mg/m ) 1.35 o CEC (cmole(+)/kg) 49 soil after application of specified leaching depth (EC); the ESP (%) 35.7 relationship becomes independent of salinity of irrigation CaCO3 (%) 27 water and evaporation conditions. Texture Sandy Clay Loam Similarly, desodification curves were constructed by

plotting relative changes in soil sodicity represented by To obtain undisturbed samples; a metallic core was ( − − ESPESPESPESP ) on the ordinate and DW/DS pressed into the soil to a certain depth, then a trench was eq o eq excavated around the core, the core was then pressed down to on the abscissa (Fig. 2). ESP is soil sodicity (exchangeable about 50 cm depth. Soil cores (columns) were carefully sodium percent, ESP) after an application of specified trimmed away, avoiding as much as possible any sample leaching depth, (ESPo) is the initial sodicity of soil, and ESPeq disturbance, sealed from the bottom and placed in a stand. is the required or desired sodicity after reclamation (ESP = The total soil depth was 30 cm (DS). Phosphogypsum (a 10). by-product from the phosphate industry, 80% pure) was Desalinization curves (Fig. 1) show that both amendments spread on the top and mixed with the upper five centimeters had similar efficiency in reducing soil salinity and required of soil column. On the other hand, Phosphoric acid (50% similar amounts of leaching water. The control was slightly pure) was directly dissolved and applied with leaching water. less efficient in reducing soil salinity when comparing with Gypsum was applied at application rates of 0, 15, 20, 30, 40 the two amendments. Application of 1.0 DW/DS of canal t/ha, whereas phosphoric acid was applied at application rates water (control) reduced soil salinity to 25%, whereas, the of 450, 600, and 900 kg/ha. Calculation of gypsum lowest application of phosphoric acid (450 kg/ha) or requirement (GR) was based on the amount of gypsum phosphogypsum (15 ton/ha) reduced soil salinity to 20% (application rate) needed d to reduce soil sodicity after 1.0 PV (equivalent to 0.5 DW/DS) was leached out from (exchangeable sodium percent - ESP) to 10% [6]. Water from soil columns. Moreover, only after applying an equivalent of King Abdullah Canal (KAC) was used to leach soil cores (EC 2.5 DW/DS (150 cm water) soil salinity was reduced to less = 2.2 dS/m, pH = 8.4, SAR = 4.8). Five pore volumes of than 4 dS/m. The steepness of the curves (slope) shows that leaching water were allowed to pass through each column. salt leaching was not rapid to reduce soil salinity (EC) to Each pore volume represents the amount of water required to acceptable levels (4 dS/m). This could be attributed to saturate all soil pores and this was equivalent to 19.6 cm of different migration velocities of various ions during leaching leaching water. Water was kept at constant hydraulic head of (hydrodynamic dispersion and molecular diffusion), and it is 5 cm, then leachate (effluent) was collected in successive 300 expected that the concentration of different ions will not mL aliquots and the quantity of leached water (DW) was decrease proportionally. recorded throughout reclamation process. Leaching was Desodification curves (Fig 2) show that ESP decreased terminated when salinity of leachate approached that of considerably with leaching. Soils amended with gypsum leaching water. Soil samples were taken out from cores; air required higher amounts of water to reduce soil sodicity dried and analyzed for electrical conductivity in saturated compared to those amended with phosphoric acid. Both paste extract (ECe) and exchangeable sodium percentage amendments showed greater desodification compared to the (ESP). Treatments were carried out in triplicates, and soil control (simple leaching with canal water). Application of chemical and physical analysis was determined according to 1.5-2 DW/DS of canal water (control) reduced soil sodicity the standard methods of soil analysis [10], [11]. to 25%.However, application of either 450 kg/ha of phosphoric acid or 40 ton/ha of phosphogypsum reduced soil sodicity to 25% after an equivalent 0.5 DW/DS of water was III. RESULTS AND DISCUSSION leached out from soil columns (15 cm depth). Moreover, Leaching curves are useful tools to determine the application of water greater than an equivalent of 0.5 DW/DS efficiency of amendments and the required depth of water to phosphoric acid treatments only caused an extra 10%

40 International Journal of Environmental Science and Development, Vol. 3, No. 1, February 2012 reduction in sodicity. The efficiency of desodification is Leaching of soluble salts from the top 40 to 60 cm of soil is influenced by the solubility of amendment and the usually adequate for most crops [12] and can be done by homogeneity of leaching solution [6]. Phosphoric acid is ponding water continuously or intermittently. Continuous more soluble, produces acidic-homogeneous solution which ponding (carried out under near saturated soil-water helps to increase calcite dissolution, and thus supplying conditions) usually requires more water than intermittent source of calcium ions during reclamation process. In ponding (carried out under unsaturated conditions). The contrast, gypsum is less soluble, and produces high efficiency of leaching increases as the contents of the soil electrolyte solution mostly at the early stages of reclamation water decrease during leaching. The range of soil pore size and thus requires greater amounts of water; therefore it is less distribution also affects salt leaching. Salt leaching efficiency efficient in reclamation than phosphoric acid. (Fig. 1) is especially low in deeply plowed, clay rich fields, and this is

Gypsum due to percolation of leaching water between large clods that are to wet to slake [12]. Drying and disking the soil reduces

) 1.0 this problem, yet pore sizes may vary enough to produce eq 0.7 Control 0.5 during ponded leaching. Such dispersion decreases under -EC o 15 ton/ha 0.3 unsaturated flow, resulting in efficient leaching of salts. Even 0.2 20 ton/ha

) / (EC) / after adopting intermittent ponding (lesser water

eq 30 ton/ha 0.1 requirements); leaching can take more time than continuous 40 ton/ha 0.05 ponding. This is because leaching water is applied at the rate (EC-EC 0.03 below the saturated hydraulic conductivity. It increases the leaching time and water evaporation. Moreover, drainage 01234 conditions affect the distribution of soil water and salts. In DW / DS well-drained uniform soils, infiltrated water penetrates Phosphoric acid deeper into soil profile than poorly drained soils. Consequently, salts will be leached deeper [13]. Hoffman [14]

) 1.0 eq 0.7 described the leaching constant by the following equation: 0.5 Control -EC

o = ()× () k 0.3 450 kg/ha DSDWECoECk , where is an empirical 0.2 600 kg/ha coefficient that differs with soil type. In general, k values ) / (EC ) /

eq 0.1 900 kg/ha range from 0.1 for sandy soils to 0.3, for clay soils. The 0.05 Hoffman equation can be used to calculate the depth (EC-EC 0.03 (quantity) of water needed to leach salts from a desired depth 01234 of soil for specified initial salinity and desired salinity. This DW / DS equation is valid only when (DW/DS) exceeds k. In other words, the leaching efficiency decreases sharply when DW to Fig. 1. Desalination curves under phosphogypsum and phosphoric acid DS ratios exceeds 0.5 for sandy loam and 0.7 for clay loam to application. clay soils. Larger k values indicate more water is required for Gypsum leaching.

) The leaching constant was calculated and averaged per eq 1.0 each amendment rate and depth of leached water. Values of k 0.7

-ESP Control

o 0.5 ranged from 24 to 29% and from 22 to 24% (26% control) for 0.3 15 ton/ha gypsum and phosphoric acid rates, respectively. However, k 0.2 20 ton/ha

) / (ESP) / ranged from 2 to 85% and from 2 to 78% (27% control) per 30 ton/ha eq 0.1 40 ton/ha depths of leached water for gypsum and phosphoric acid, 0.05 respectively. Average k for all rates and depths of leached 0.03

(ESP-ESP water was 26 and 23%; application of an equivalent depth of

01234 water equal to depth of soil, reduced initial salinity levels by DW / DS 80% and by 83% for gypsum and phosphoric acid, respectively (80% for control). Typically, 70% or more of Phosphoric acid initial salt content will be removed by leaching with a depth )

eq 1.0 of water equivalent to a depth of soil to be reclaimed when 0.7 water is ponded continuously on the soil surface. -ESP 0.5 o Control Desalinization of soil shows that gypsum and phosphoric 0.3 450 kg/ha 0.2 acid rates appeared not to have a strong effect on k (Table 2). 600 kg/ha ) / (ESP) / eq 0.1 900 kg/ha The lowest application of both amendments was as effective as the highest rate. It is recommended to apply more water to 0.05 0.03 reduce soil salinity; the amount of applied water could be (ESP-ESP reduced by intermittent method, however this requires further 01234 field work. DW / DS The Hoffman approach could also be adopted for soil = ()× () Fig. 2. Desodification curves under phosphogypsum and phosphoric acid desodification as follows: ESPoESPk DSDW . application.

41 International Journal of Environmental Science and Development, Vol. 3, No. 1, February 2012

The leaching constant was calculated and averaged per each IV. SUMMARY AND CONCLUSIONS amendment rate and depth of leached water. Values of k Leaching curves are useful tool to determine the efficiency ranged from 20 to 26%, and 18% (33% control) per gypsum of amendments and the optimum depth of leaching water and phosphoric acid rates, respectively. However, k ranged needed for successful reclamation. Desalinization and from 8 to 64% and from 7 to 62% per depths of leached water desodification leaching curves showed that a highly of gypsum and phosphoric acid, respectively (27% control). calcareous saline-sodic soil could be reclaimed efficiently Average k for all rates and depths of leached water was 23 with less water using phosphoric acid compared with gypsum. and 20% and an application of a depth of leaching water Application of 450 kg/ha of phosphoric acid and an equivalent to depth of soil, reduced initial sodicity levels by equivalent of 0.5 DW/DS of leaching water; substantially 79% and by 84% for gypsum and phosphoric acid, reduced soil sodicity to acceptable level, whereas soil salinity respectively (80% control). It is obvious that k appeared not could be reduced substantially with an addition of extra 0.5 to be related to phosphoric acid rates (Table II). In other DW/DS of leaching water. Phosphoric acid could be used as words, the lowest rate of phosphoric acid was as efficient as reclaiming material however further field experimentation is the highest one and was substantially enough to reduce soil required before any certain recommendation is drawn. sodicity to a safe level (10% or less). REFERENCES TABLE II: LEACHING CONSTANTS (K) FOR SOIL DESALINIZATION AND Handbook of Plant and Crop DESODIFICATION [1] I. Szabolcs, “Soils and salinization,” in Stress, M. Pessarakli, Ed. New York: Marcell Dekker. 1994, pp. 3–11. Desalinization [k = (EC/ECo)*(DW/DS)] [2] K. K. Tanji, “Nature and extent of agricultural salinity,” in Agricultural Gypsum rates (ton/ha) Salinity Assessment and Management, ASCE manuals and reports on 0 15 20 30 40 engineering practices # 71, K. K. Tanji, Ed. New York: ASCE. 1990, k 0.27 0.24 0.24 0.27 0.29 pp. 1–17. Phosphoric acid rates (kg/ha) [3] D. L. Suarez, “Sodic soil reclamation: Modeling and field study,” Aust. k 0 450 600 900 J. Soil Res., vol. 39, pp. 1225–1246, 2001. 0.27 0.22 0.24 0.24 [4] M. Qadir, and J. D. Oster, “Vegetative bioremediation of calcareous sodic soils: History, mechanisms, and evaluation,” Irrig. Sci., vol. 21, pp. 91–101, 2002. Desodification [k = (ESP/ESPo)*(DW/DS)] [5] J. E. Mace, C. Amrhein, and J. D. Oster, “Comparison of gypsum and Gypsum rates (ton/ha) sulfuric acid for sodic soil reclamation,” Arid Soil Res. Rehab., vol. 13, 0 15 20 30 40 pp. 171-188, 1999. k 0.33 0.26 0.24 0.23 0.20 [6] M. A. Gharaibeh, N. I. Eltaif, and S. H. Shra’ah, “Reclamation of a Phosphoric acid rates (kg/ha) calcareous saline-sodic soil using phosphoric acid and by-product k 0 450 600 900 gypsum,” Soil Use Manage., vol. 26, no. 2, pp. 141- 148, 2010. 0.33 0.18 0.18 0.18 [7] A. M. Mashali, Salinization as a Major Process of Soil Degradation in the Near East, Land and Water Development Div., The amount of water required for leaching salts from soil FAO-AGL/RNEA--LWU/89/9, FAO: Rome (Italy), 1989. pp. 1-9. [8] M. A. Gharaibeh, N. I. Eltaif, O. F. Shunnar, “Leaching and profile can be minimized by intermittent application of reclamation of calcareous saline-sodic soil by moderately saline and leaching water. The effect of soil type is minimal and the moderate-SAR water using gypsum and calcium chloride,” J. Plant required time for reclamation in intermittent leaching Nutr. Soil Sci., vol. 175, no. 5, pp. 713-719, 2009. [9] J. E. Mace, and C. Amrhein, “Leaching and reclamation of a soil (application) is much longer than in ponding method. For irrigated with moderate SAR waters,” Soil Sci. Soc. Amer. J., vol. 65, intermittent ponding, the leaching constant k is equal to 0.1 pp. 199-204, 2001. whereas, k for continuous ponding is a function of soil type. [10] A. Klute, Method of soil analysis, Physical and mineralogical methods, The depth of water needed to reduce the salt content for a part I, 2nd ed., Agronomy monograph 9, ASA, Madison: WI, 1986. [11] A. L. Page, R.H. Miller, and D. R. Keeney, Methods of soil analysis, given application rate can be calculated from desalination Chemical and microbiological properties, part II, 2nd ed., Agronomy graphs. For example, given initial soil salinity ECo of 50 monograph 9, ASA and SSSA, Madison: WI. 1982. dS/m, then the amount of water required to decrease soil [12] R. Keren, and S. Miyamoto, “Reclamation of Saline, Sodic, and Boron Affected Soils,” in Agricultural Salinity Assessment and Management, salinity of 40 cm soil depth to an EC of 4 dS/m with simple ASCE manuals and reports on engineering practices # 71, K. K. Tanji, leaching (control) is equal to 78 cm depth of leaching water. Ed. New York: ASCE. 1990, pp. 410–431. Assuming the intermittent leaching method was adopted [12]; [13] R. W. Terkeltoub, and K. L. Babcock, “Calculation of the leaching required to reduce the salinity of a particular soil depth beneath a the calculated amount of water would be 30 cm. Therefore, specific value,” Soil Sci. Soc. Am. Proc., vol. 35, pp. 411-413, 1971. the amount of water required for leaching is reduced to more [14] G. J. Hoffman, “Guidelines for reclamation of salt-affected soils,” Appl. than one third of that needed when using ponding method. Agr. Sci., vol. 1, no. 2, pp. 66-72, 1986.

Moreover, if a salt tolerant crop (e.g. barely) was cultivated, then desodification curves can be used to calculate Mamoun A. Gharaibeh, Jordan, 1969. Ph.D. degree in Soil Water and the required amount quantity of leaching water to reduce soil Environmental Science, soil reclamation and hydrology, University of sodicity to an acceptable level (10%). For example, given Arizona, Tucson, Arizona, USA, 2000. He is currently an associate professor in the Department of Natural initial soil sodicity ESPo of 36, and an application rate of 450 Resources & Environment (DNRE), Faculty of Agriculture, Jordan kg/ha of phosphoric acid, then the amount of water required University of Science & Technology (JUST). Served as Chairman of DNRE to decrease soil sodicity of 40 cm soil depth to an ESP of 10 is (2008-2011), and Vice Dean of Research at JUST (2006-2007). Publish many scientific articles in the following fields: Reclamation and equal to 20 cm depth of leaching water. The assumption of Phytoremediation of Salt Affected Soils, Wastewater Reuse in Agriculture, applying an intermittent leaching can not be adopted; since Remediation of Heavy Metal polluted Soils, and Conservation of the calculated amount of water would be 10 cm and this Water-Wind Eroded Soils. Dr. M. Gharaibeh is a member of Jordan Agricultural Engineers Association and a member in some Regional amount does not promote any water flow/leaching through wastewater committees. soil profile.