Wednesday, November 7, 2007 - 11:10 AM
282-6
Steady State Conditions of Water Content and Salinity in Regularly Irrigated Soil.
Uri Shani, Effi Tripler, and Yechezkel Mualem. Department of Soil and Water Science, The Hebrew University of Jerusalem, P.O. box 12, Rehovot, 76100, Israel
A comprehensive knowledge of plant response to environmental conditions such as water quality, water quantity, soil type and climate is essential for sustainability of both agriculture and the environment. Interactions between root- zone hydraulic characteristics, crop physiological responses, and irrigation management are complex and difficult to quantify. Mathematical solutions, commonly numerical, of water and solute flow combined with mechanistically based plant uptake functions and varied climatic conditions, are usually complicated and based on large set of inputs which adds uncertainty. A considerable simplicity is obtained where steady state conditions are assumed. The objective of this presentation is to evaluate the error and limitations of the steady state assumption for water and salinity in irrigated soils. While cyclical, daily, fluctuation in water uptake is obvious, the application of the representative elementary time (RET) concept (Bear et al., 1968) defines an apparent-steady state (ASS). The ability of plant roots to compensate for a local decrease in water content by greater water uptake from zones of higher water content decreases fluctuations in water uptake and errors associated using the ASS approach. Solutions of water content and soil solution EC as a function of time for daily transpiration and water application of growing crops on Arava soil illustrate the ASS. Both variables are found to oscillate in a daily manner within bands of approximately constant width. Experimental and model results suggest that the assumption of ASS is reasonable in cases of frequent, regular irrigation regimes.