Psychrometric Measurements of Soil Samples Equilibrated on Pressure Membranes

Abstract

AbstractThe osmotic pressure or solute suction (SS) of the extract from a “saturated” soil paste can be measured with a thermoelectric psychrometer which is calibrated by use of standard osmotic solutions. The same psychrometric procedure can be used to measure the total soil‐moisture stress or total suction (TS) of water in soil that has been equilibrated with a pressure membrane at known soil‐moisture tension or matric suction (MS). From membranous and psychrometric measurements, the difference ΔS = TS ‐ (MS + SS) was evaluated for 134 samples of Pachappa soil at three SS levels (0.3, 2.5, and 5 bar) attained by leaching with calcium chloride solutions and three MS levels (5, 10, and 15 bar). Mean ΔS values at 5, 10, and 15 bar MS were, respectively, −0.6, −0.4, and −0.1 bar. Mean ΔS values at 0.3, 2.5, and 5 bar SS were, respectively, −1.0, +0.04, and +0.5 bar. Standard deviation values for MS, SS, and TS, respectively, were 0.07, 0.1, and 0.5 bar.