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DIVISION S-1—SOIL PHYSICS

A Macroscopic Water Extraction Model for Nonuniform Transient Salinity and Water Stress

^a Dep. of Soil Science, Univ. of Tarbiat Modarres, Tehran 14155-4838, Iran
^b Sub-Dep. of Water Resources, Wageningen Agricultural Univ., Nieuwe Kanaal 11, 6709 PA Wageningen, The Netherlands

* Corresponding author (Mhomaee{at}hotmail.com)

Quantitative description of root-water uptake under combined salinity and water stress is needed to optimize crop yields and water management in arid and semiarid regions. This study was conducted to develop a simple macroscopic root-water uptake model for nonuniform transient soil water content and salinity conditions in the root zone. This new model and previous models were tested against detailed experimental data obtained with Alfalfa (Medicago sativa L.) grown in the greenhouse in packed sandy loam (Typic Haplaquent) columns. Soil water content, pressure head, and osmotic head distributions in the root zone were varied by means of the amounts, application intervals, and salinities of the irrigation water. Experimental data under separate and combined stresses were used to test the various models using mean values of soil solution osmotic and pressure heads. The simple additive reduction function provided the worst agreement with the experimental data, while for most cases the multiplicative reduction functions could not adequately account for both water and salinity stress conditions. The newly proposed linear reduction function is neither additive nor multiplicative, but was assumed that both the intersect and slope of the reduction function increased with salinity. This model provided excellent agreement with the experimental data, particularly at higher soil solution salinities. The new reduction function could be used with any other nonlinear salinity reduction function.

Abbreviations: EC, salinity value • R, reference treatment

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