ALTERNATIVE METHOD FOR QUANTIFICATION OF THE LEAST LIMITING WATER RANGE IN THE LABORATORY

The least limiting water range (LLWR) is defined by the amplitude of the water content (theta) in the soil in which limitations to plant growth associated with water availability, aeration and soil resistance to penetration (SR) are minimal. In general, LLWR determination requires expensive equipment, and obtaining water retention and SR data is laborious. The use of pressure membranes and Richards' pressure plates requires a long time to determine the water retention curve (WRC) due to the need for achieving hydrostatic equilibrium, which depends on the dimensions of the sample, the soil type and the pressure applied. Currently, equipment is available for quickly and more cheaply determining water potential (psi), such as automatic tensiometers and psychrometric equipment. The aim of this study was to evaluate a method for quantifying the LLWR from the drying of undisturbed samples in an electric laboratory oven with air circulation and temperature of 40 degrees C (drying times of 20, 40, 60, 80, 100, 120, 180, 240, 300, 360 and 420 min), with subsequent measurements of Psi using a tensiometer or psychrometer, and SR measurements using an electronic penetrometer with automated data acquisition. The WRC and the soil resistance to penetration curve were adequately described using the proposed method which allowed q and SR data to be obtained in 10 days and allowed accurate fitting of the data to describe the LLWR and to obtain the critical bulk density of the soil.