hydraulic conductivity

water table

capillary rise

Infiltration functions

moistening of the root zone

steady sorptivity

Soil Hydrology

The purpose of this study is to predict the contribution of the water table in moistening the root zone using theoretical and empirical equations containing the parameters of evapotranspiration, crop factor, and capillary rise in relation to the hydrophysical properties of soil. Five alluvial (clay) soil profiles located at middle Nile Delta were investigated for the application of the assumed equations. Four areas of soils were cultivated with wheat and clover in the winter and maize in the summer, and citrus trees in 2014/2015 growing season. Soil samples from the investigated areas were subjected to chemical and physical analyses. Water table depths were determined using field piezometers in the same places where the soil samples were collected. The other hydro-physical parameters were estimated. It was found that the water table contributed 20-40% of the irrigation water applied to the root zone in winter and 20% or less during the summer in the studied soils areas. An equation was derived to estimate the sorptivity (S) under dry conditions and at steady state infiltration. It was observed that S is decreased from unsaturated state to steady-state infiltration by 23.1 to 45.7% in cultivated soils and to 55.2% in uncultivated soil. Infiltration functions were estimated. It was suggested that the sorptivity at the steady infiltration rate (steady sorptivity, Sw) may be used to predict the hydraulic conductivity and the basic infiltration rate I_b. The calculated values of I_b by Sw corresponded to those obtained by infiltration experiment. This confirmed the significance of steady Sw as a new functional infiltration parameter. Also, data showed that the values of K(θ) calculated by the proposed equations were in the common ranges for such soils. The equations used (models) related K(θ) to soil pore radius (r) which were in turn based on soil hydraulic data including water retention h(θ), field basic infiltration rate, water sorptivity (S) and the distribution density function f(r) of soil pore size. The steady S_w parameter was used in the prediction of the hydraulic conductivity K(θ) and the basic (steady) infiltration rate I_b. It was concluded that in winter the water table contributed 20-40% of irrigation water applied to the root zone and less than 20% during the summer in the studied soils areas. These values should be considered in calculating the crop water requirements.