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Influence of Soil Moisture, Aerodynamic and Plant-Water Conditions on the Transpiration Rate of Rice and Cotton
Dissertation Abstract:
Rice and cotton plants were grown outdoor in medium-sized plastic containers filled with either silty clay loam or sandy sandy loam soil. When two months old, the plants were transferred to a wind tunnel and subjected to two aerodynamic conditions.
Measurement of potential, actual and relative water content showed that when soil water was unlimited, potential transpiration was mainly controlled by evaporative demand. However, when soil water stress set in, the effect of evaporative demand declined. The simple effect of soil water stress was to reduce transpiration, which was opposite that of evaporative demand.
The soil matric at which transpiration showed a sharp decline, referred to as ‘critical’ matric potential, depended on evaporative demand, plant type and soil texture. Under low evaporative demand, the critical matric potentials for rice were -10.8 bars in sandy loam and -10.0 bars in silty clay loam soil, whereas for cotton in sandy loam it was -1.0 bar and in silty clay loam, -1.5 bars.
Under high evaporative demand, the critical matric potentials for rice were -1.1 bars in sandy loam and -5.0 bars in silty clay loam. For cotton, it was -0.33 bar in sandy loam and -1.2 bars in silty clay loam.
Except for rice in silty clay loam, the effect of soil water stress on transpiration was much greater than that of the evaporative demand at a lower range of water stress, especially in sandy loam soil.
The interaction of evaporative demand with soil water stress was noted in all treatments; that is, the effect of evaporative demand on transpiration and relative water content depended on the degree of soil water stress and, to some extent, on plant type. When relieved of water stress, the plants grow in sandy loam recovered faster than those in silty clay loam soil.
