Dual water flow pattern in the unsaturated zone under a gypsum‐amended soil

Sediment samples were obtained from boreholes down to c. 20 m in a gypsum‐treated, saline‐water irrigated soil and from nearby uncultivated fields at two locations (Nir Oz and Nahal Oz). Measurements of tritium concentrations in the soil solution enabled the determination of water flow rates in the unsaturated zone. Two types of flow, fast and slow, were identified in the profiles. The slow component, the ‘piston‐flow type’ in the sandy loess section in Nir Oz and in the clayey loess section of Nahal Oz, had a vertical velocity of 0.16 and 0.23 m a⁻¹, respectively. The faster component typically transported the solution through fractures and other preferred paths. The percentage of the slow component in the sandy and in the clayey loess was 40% and 60% respectively. A previous prediction of delayed transport of salts was verified and is related to the interaction between chemical composition of irrigation water and the agro technical practices of gypsum application.