RATE OF LEAF ELONGATION AS AFFECTED BY THE INTENSITY OF THE TOTAL SOIL MOISTURE STRESS

Abstract

Recent studies (1, 7, 9) have indicated that an interrelationship exists between soil salinity and the soil moisture content in their effect on plant growth. These two factors may be logically evaluated in terms of the decrease in the specific free energy of the soil moisture. Thus, salinity may be expressed in terms of the osmotic pressure of the soil solution, and the soil moisture status with respect to surface force action is expressable in terms of the soil moisture tension in atmospheres. The sum of these two components has been termed the soil moisture (7). It is difficult to evaluate the moisture stress to which a plant is responding when grown on a given mass of saline soil. This moisture stress which is conditioning the entry of water into the roots will be largely affected by five variables:*(a) the variation in salt distribution within the soil mass and its consequent effect on the variation in the osmotic pressure of the soil solution at a given moisture content; (b) variation in osmotic pressure in relation to change in moisture content; (c) variation in moisture tension in relation to moisture content; (d) variation in moisture content within the soil mass at a given time; and, (e) variation in total water content of the soil mass with time, i.e., over an irrigation interval. A method has been developed to integrate these variables as they obtain within a large container of saline soil (8). This method makes it possible to determine the relation of the theoretically uniform stress, S, throughout that part of the soil mass within which moisture movement into the plant is taking place, to the total moisture content, W, of the soil. That is, S-f(W)