Water and Salt Distribution in a Field Irrigated with Marginal Water under High Water Table Conditions

tion of salt in the soil, salt leaching from the root zone should be conducted. In regions where the rainfall is Development of an impermeable layer at some depth beneath the low, a leaching fraction (the fraction of applied water soil surface and the presence of a high groundwater level are common that appears as drainage water) is added to the irrigation phenomena in the Yizre’el Valley, Israel. The main objective of this study was to determine the salt and water distributions and salt leachwater to hold the salt concentration in the soil below a ing in a field irrigated by sprinklers, under nonisotropic and high specific value (Rhoades et al., 1973). In contrast, in groundwater level conditions. A field experiment was conducted in regions, where the rainfall is relatively high, the wet a cornfield (Zea mays L.) on a Vertisol (Typic Chromoxerets) with season rainfall can ensure leaching of the salt. subsurface drains. The electrical conductivity (EC) of the irrigation The water percolating below the root zone moves water was 2.5 dS m21. The variations in water table level, in EC of downward to the groundwater and may cause the water soil solution and soil saturation paste, and in gravimetric water content table to rise. As the water table approaches the soil along the field were determined at different times. Likewise, corn surface, poor soil aeration and/or high salinity in the yield from various sites across the field was determined at the end root zone may reduce crop yields. Consequently, instalof the growing season (August). The water table level increased lation of a subsurface drainage system, to keep the water sharply in the winter to 49.5 m, and then decreased continuously in table from rising and to allow salt leaching, is commonly the summer despite the irrigation. The EC increased in the downhill direction, more sharply in the deeper soil layers. In the upper part considered to be essential for long-term productivity of the field, the average EC in saturation paste in the 0to 1.2-m soil (Bradford and Letey, 1992). layer was 1.1 dS m21 in March (end of the rainfall season) and 2.1 Under steady-state and isotropic conditions, the salt dS m21 in August. Conversely, in the lower part of the field, the ECs distribution in a field is independent of landscape posiin March and August were 4.4 and 3.7 dS m21, respectively. A linear tion and time. Many studies (e.g., Beven and Germann, reduction of the corn yield with increasing EC was observed. The 1981; Meyer et al., 1990; Bradford and Letey, 1992; relatively low level of the groundwater at the upper part of the field Thorburn et al., 1995) have described the water and salt allowed vertical salt leaching by the rainfall. Conversely, the rise of movements and distributions under these conditions. the saline (EC ≈20 dS m21) groundwater in the lower part of the field In many cases, particularly in valleys, such as the in the winter with lateral salt movement increased the soil EC. Decline Imperial Valley in California (Grismer and Tod, 1991) of the water table in the latter part in the summer allowed vertical and the Yizre’el Valley in Israel (Shalit et al., 1998), leaching of salt by the irrigation water. the top soil is a Vertisol. In this soil, development of a compacted, low-permeability layer at some depth beA and semiarid regions are characterized by long, neath the soil surface, which, in turn, causes a high water dry summers and short rainy winters. Therefore, table, is a common phenomenon (Yaalon and Kalmar, agricultural production in these regions relies mainly 1978; Gafni and Salinger, 1992; Ben-Hur et al., 1998). on irrigation. The soil solution in irrigated fields is freUnder these conditions and under irrigation with marquently more saline than the irrigation waters because ginal water, the salt content in the field can change with of evapotranspiration that leaves the salts from the irritime: accumulation of salt in the soil during the dry gation water in the soil and the dissolution of some soil season and salt leaching in the rainy season. Moreover, minerals (Rhoades et al., 1973). Consequently, irrigathe salt distribution in the field may depend on the local tion may increase the salinity and the sodicity of the topography because of lateral flows of groundwater and soil profile to a point at which plant growth is reduced variations along the field in its depth beneath the soil (Maas and Hoffman, 1977) and the soil structure is damsurface. Water and salt distributions in a field receiving aged (Ben-Hur et al., 1998). sprinkler irrigation under nonisotropic and non-steadyConventional sources of good quality water in arid state conditions have elicited less documentation. and semiarid regions are scarce, which has led to inA Vertisol is defined as a deep (.50-cm depth) soil creased use of marginal water (saline waters and treated containing at least 30% clay in all horizons and in which sewage effluent) for irrigation (Bresler et al., 1982; Feithe dominant clay (.50%) is smectite (FAO, 1990). gin et al., 1991). This enhances the salinization of the Such a soil swells when wet and develops cracks when irrigated lands in these regions. To avoid the accumuladry (Yaalon and Kalmar, 1978). The Yizre’el Valley can be used as a case study for high water table level and nonisotropic conditions. This M. Ben-Hur, F.H. Li, R. Keren, and G. Shalit, Agricultural Research valley is the largest in Israel, located in Lower Galilee Organization, The Volcani Center, POB 6, Bet Dagan 50250, Israel; in northern Israel, and is known for its fertile soil. The I. Ravina, Agricultural Engineering, Technion, Israel Institute of area of this valley is 250 km2, of which 200 km2 are Technology, Haifa 32000, Israel. Contribution from the Agricultural Research Organization, the Volcani Center, POB 6, Bet Dagan 50250, under cultivation and 140 km2 under irrigation, mostly Israel, no. 639/99, 1999 series. Received 9 Mar. 1999. *Corresponding author ([email protected]). Abbreviations: CV, coefficient of variance; EC, electrical conductivity; ESP, exchangeable Na percentage; SAR, Na adsorption ratio. Published in Soil Sci. Soc. Am. J. 65:191–198 (2001).