An Evaluation of Permanent‐Wilting Percentage, 15‐Atmosphere Moisture Percentage, and Hygroscopic Coefficient of Three Soils in Eastern Nebraska

Abstract

AbstractPermanent‐wilting percentage, 15‐atm. moisture percentage, and hygroscopic coefficient frequently have been used as indirect measures of the lower limit of readily available moisture for soils in situ. These three methods were evaluated by comparison with a field method for determining the lower limit of moisture readily available to sunflowers growing in Dickinson sandy loam, Wabash silt loam, and Sharpsburg silty clay loam. Since the locations of the soils occurred in a subhumid region, the soil sites were covered with plastic film about the base of the plant stems to rainproof the soils. Soil moisture percentages from 6 horizons of each of the 3 soils were obtained at frequent intervals during the 11‐week growth period preceding plant maturity.Differences between the lower limit of readily available moisture in the field and the permanent‐wilting percentage were relatively small at all depths in the Dickinson sandy loam and Wabash silt loam, and in the surface foot of Sharpsburg silty clay loam. Permanent‐wilting percentages of Sharpsburg silty clay loam at depths of 12 to 18, 18 to 24, 24 to 30, and 30 to 36 inches were markedly less than the values of the lower limit of readily available moisture in the field. The 15‐atm. moisture percentage of puddled Sharpsburg subsoil was more reliable in predicting the lower limit of readily available moisture in the field than was the permanent‐wilting percentage. Alway's hygroscopic coefficient was the least accurate of the three indirect methods studied for estimating the lower limit of readily available moisture in the field.