Scientific Research and Essays Vol. 6(29), pp. 6068-6074, 30 November, 2011 Available online at http://www.academicjournals.org/SRE DOI: 10.5897/SRE11.509 ISSN 1992-2248 © 2011 Academic Journals Full Length Research Paper Assessment of evaporation and salt accumulation in bare soil: Constant shallow water table depth with saline ground water Jalili, S.*, Moazed, H., Boroomand Nasab, S and Naseri, A. A. Faculty of Water Sciences, Shahid Chamran University, Ahvaz, I. R. Iran. Accepted 9 May, 2011 Salinization of soil is a major problem in arid and semi-arid regions with saline shallow water table. This is influenced by climate, soil type, crop, irrigation water quality and management practice, depth of water table and salinity of the water table. The objective of this study was the assessment of evaporation and salinization of bare soil profile with various water table depths including 300, 500 and 800 mm by saline groundwater (3 g NaCl/L + 3.5 g CaCl2/l). In this research we were monitoring amount of evaporation from bare soil, and observing profiles of soil water and salinity over periods of up to 80 days. The experiments started on April, 10th, 2010. Results showed that, salts mainly accumulated in the soil surface and volume of evaporation from bare soil in lower water table depth (D = 300 mm) is greater than other lysimeters (D = 500 and 800 mm), and salt accumulation in this lysimeter was higher than others. After 80 days, amount of salinity (ECe) in soil surface was 83.84, 65.76 and 24.05 dS/m, for D = 300, 500 and 800 mm, respectively. Key words: Evaporation, salinity, water table. INTRODUCTION Salinization of soil is a major problem in arid and semi- flux can be beneficial to agriculture from the standpoint of arid areas with saline shallow water table. Salinization is meeting crop water requirements, but on the other hand, influenced by climate, soil type, crop, irrigation water salinity in the water can lead to crop damage and soil quality and management practice, depth of water table degradation. Young et al. (2007) reported that upward and salinity of water table. About 30% of arable land in flux was limited by the atmospheric evaporative potential Iran is saline where salinization of soil is primarily caused when the water table was shallow. With deeper water by capillary rise from saline shallow water table tables, soil physical properties limited upward flow. (Jorenush and Sepaskhah, 2003). Shallow water table Gardner (1958) also describes the contribution of the conditions may be found quite extensively in arid and vapor phase to overall evaporation. It was concluded that semi-arid environments. Their existence in irrigated areas subsurface vapor movement would seldom exceed 20% is often associated with problems of irrigation-induced of maximum liquid transport and would usually be much salinisation. However, they may exist also in non-irrigated less. More recent research has reinforced this conclusion environments, as, for example in playa areas and on the by finding that liquid water movement deeper in the soil fringes of rivers and lakes. Water that moves upwards limits total evaporation on daily or greater time scales through capillary rise from a shallow water table can (Saravanapavan and Salvucci, 2000). In this regard, the enter the atmosphere through plant transpiration or direct term "critical water table depth" is often mentioned and evaporation from bare soil. On the one hand, this upward considered as the level above which water rising by capillarity will cause salinization of the arable soil horizons. Kovda (1973) relates this critical depth to the salt content of the groundwater in arid zone and areas *Corresponding author. E-mail: [email protected]. provided with irrigation and drainage as, respectively, Jalili et al. 6069 Table 1. The selected chemical and physical properteis of original soil. Soil properties Amount Ca2+ 10 meq/L Mg2+ 3 meq/L Na+ 24.8 meq/L K+ 1.41 meq/L Cation exchange capacity 31.34 meq/100 g soil pH 7.7 ECe 2.55 Organic material 0.74% Texture Clay loam being 2 to 2.5 when the salt concentration is 10 to 15 g/L, water and salt from a shallow saline water table in field and 1 to 1.5 m for a less mineralized groundwater, 1 to 2 condition evaporation. In the author's opinion, the g/L. For bare soils, the critical depth coincides with the effective control of soil salinity and also of salinity in depth from soil surface to the water table but for cropped Shallow water table conditions requires the following: i) soils, this depth should be taken below an estimated knowledge of the magnitude, extent and distribution of active root zone. soil salinity and, ii) knowledge of the changes and trends The significance of the depth to water table comes from of soil salinity over time. its influence on capillary rise; the shallower the depth, the The current study was designed to assess the effect of higher the contribution of groundwater to salinization. water table depth and its salinity on salinization of soil Generally, the decreasing trend of the maximum capillary from evaporation (uncropped soil as follow soil) of saline rise in various uniform soils under a given evaporative solutions. This research conducted in field condition in a demand follows the descending order as sandy loam, semi-arid region- Ahvaz, Iran, with simulating by loam, clay loam, clay medium and coarse sand. Hadas lysimeters. and Hillel (1968) and Ashraf (2000) measured the rate of evaporation as a function of the water table depth and the evaporability. The air circulation over the top of the soil MATERIALS AND METHODS columns was varied to obtain different evaporability The investigation comprised three separate experiments with 42 condition. The experiment was conducted in constant lysimeters. Lysimeters contained (from the base of the soil temperature and no radiation. In addition, evaporation columns) thickness of 5 cm gravel and 5 cm of sand to allow was measured for different water table depth under unrestricted exchange with the supply of groundwater, then conditions of increasing evaporability. His experiments contained soil to top of lysimeters. Air-dry topsoil of the soil from research field of Chamran University of Ahvaz was sieved through a shown that for the loess-derived soil, an inverse relation 2 mm mesh. The soil was packed as uniformly as possible in 10-cm exists between the evaporation and evaporability. He layers to bulk density of 1.35 g/cm3. Selected properties of the soils discarded the salt effect as an explanation and promoted are given in Table 1. The field was excavated in order to place the the idea that the gradual drying of the soil surface zone in lysimeters at a certain depth so that their top was on level with the effect created a two-layer condition. Water movement ground surface. The excavated soil was then placed back into the across the dry surface layer would then be in the vapor lysimeters and the surrounding space. The experiments with saline (3 g NaCl/L + 3.5 g CaCl2/L) and three water table depths (300, 500 phase only. Prathapar and Qureshi (1999) and Ali et al. and 800 mm) (Rose et al., 2005). This study was conducted under (2000) investigated and discussed in detail the effects of field conditions. The soil columns were cylindrical PVC tubes of 120 soil type, ground water quality and ground water depth on mm inside diameter. The base of each column was closed by a salinisation of soils, as well as the other researchers plastic disc. To saturate the soil, tape water was introduced from showed that the high soil salinity and alkalinity restricts the bottom to avoid trapping air. Water was then allowed to drain while keeping the soil surface covered and allowed to stand for one crop growth by reducing the osmotic potential, day in order to deplete the detention storages by gravitational force. decreasing nutrient availability and soil physical quality The soil columns were weighed and then placed in excavated parameters (Gokalp et al., 2010). Also, Many researchers places and left for evaporation in field condition. The Marriot tank investigated experimentally the movement of water and systems were installed to conduct constant water table depth in salts above saline water tables in constant evaporability experimental period. The lysimeters were weighed and sectioned condition (Hassan and Ghaibeh, 1977; Chen, 1992; (10 cm layers) after 5, 15, 30, 45, 60 days and at the end of experiment to determine gravimetric water content. Electrical Shimojima et al., 1996; Ali et al., 2000; Rose et al., 2005; conductivity (ECe) was determined in the end of research period. Gowing et al., 2005). Further experimental and The experiments started on April, 10th, 2010. The rate of capillary theoretical work is needed on the upward movement of rise was taken as the volume of water supplied by the Mariotte 6070 Sci. Res. Essays Figure 1. Pan evaporation data. Figure 2. Average evaporation. tank. This volume was monitored periodically. Potential evaporation evaporation was measured using pan evaporation. The was monitored with a Class-A evaporation pan that located at 10 m amount of EP was equal about 8 mm/day on the first day from the lysimeters. and was 14 mm/day in the end of experiment. Moreover, Figure 2 shows the average evaporation from the soil RESULTS surface versus pan evaporation data. After 10 days, in treatment D300 (D = 300 mm), the average evaporation In a non-steady-state, the rate of evaporation equals the from soil surface decreases from 7 mm/day to 5 mm/day sum of the rates of water loss from the Mariotte tank and and its value was about 4 mm/day after 20 days.