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Simplified Model of Integrated Water and Solute Uptake by Salts- and Selenium-Accumulating Plants

Jacob Blaustein Inst. for Desert Research, Ben Gurion Univ. of the Negev, Sede Boqer Campus, Israel

*Corresponding author (benasher{at}bgumail.bgu.ac.il).

ABSTRACT

The rate of soil salinization and the accumulation of toxic ions in soils are affected by evapotranspiration and the uptake of ions by plant roots. These are two counteracting processes and the interrelationship between them can be quantified by a mathematical model. The objectives of this study were to: (i) formulate an analytical model describing soil salinization and accumulation of toxic ions and (ii) suggest a criterion for irrigation water quality (C*₀) and demonstrate its behavior under varying transpiration rates. The processes by which the soil becomes saline were simulated with an analytical solution to the convection-diffusion equation. The model was based on ion and water uptake by plant roots. The calculations indicated that crops classified as salinity tolerant remove more salt from the soil than salinity-sensitive crops. The rates of ion removal are 5, 15, and 40 x 10^–3 dS m^–1 d^–1 for salinity-sensitive, semisensitive, and tolerant crops, respectively. Therefore the ratio between the uptake rates of ions and water per unit soil volume is presented here as a criterion for the upper limit of allowable salinity in irrigation water. This ratio is inversely related to transpiration rate (evaporation neglected). Theoretically, the maximum allowable salinity of salt-tolerant crops, C*₀, decreases from 20 to 4 dS m^–1 when the transpiration rate increases from 2 to 10 x 10^–3 m d^–1. For the same transpiration rate increase, C*₀ of sensitive crops decreases from 3 to 0.5 dS m^–1; thus, a lower quality of water can be permitted for irrigation in a moderate or cool climate than in an arid climate. The model applies also for Se-accumulating crops. Theoretically, at a transpiration rate of 5 x 10^–3 m d^–1, Se can be removed from a soil solution containing a high concentration (C*₀ = 1 mg kg^–1) when the uptake rate of the growing crop is 25.8 x 10^–3 mg kg^–1 d^–1.

Received for publication August 28, 1992.

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