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

Abstract

Development of an impermeable layer at some depth beneath the soil surface and the presence of a high groundwater level are common phenomena in the Yizre'el Valley, Israel. The main objective of this study was to determine the salt and water distributions and salt leaching in a field irrigated by sprinklers, under nonisotropic and high groundwater level conditions. A field experiment was conducted in a cornfield (Zea mays L.) on a Vertisol (Typic Chromoxerets) with subsurface drains. The electrical conductivity (EC) of the irrigation water was 2.5 dS m−1 The variations in water table level, in EC of soil solution and soil saturation paste, and in gravimetric water content along the field were determined at different times. Likewise, corn yield from various sites across the field was determined at the end of the growing season (August). The water table level increased sharply in the winter to 49.5 m, and then decreased continuously in the summer despite the irrigation. The EC increased in the downhill direction, more sharply in the deeper soil layers. In the upper part of the field, the average EC in saturation paste in the 0- to 1.2-m soil layer was 1.1 dS m−1 in March (end of the rainfall season) and 2.1 dS m−1 in August. Conversely, in the lower part of the field, the ECs in March and August were 4.4 and 3.7 dS m−1, respectively. A linear reduction of the corn yield with increasing EC was observed. The relatively low level of the groundwater at the upper part of the field allowed vertical salt leaching by the rainfall. Conversely, the rise of the saline (EC ≈20 dS m−1) groundwater in the lower part of the field in the winter with lateral salt movement increased the soil EC. Decline of the water table in the latter part in the summer allowed vertical leaching of salt by the irrigation water.