Point of Limited Availability of Water in Soil and Its Determination

The point of limited availability of water (PLAW) characterizes the lower boundary of the area with the most productive moisture for plants. The analysis of the experimental methods used to determine PLAW is indicative of their high labor intensity and low efficiency. The objective of this study is to develop a high-performance and accurate method to determine PLAW. In the work 18 samples from various soils were used. It is proposed to determine PLAW by the following method: soil samples are placed in a Schott funnel, moistened with excess water, and then water is pumped out using a water jet pump. As water is removed from the sample, the interval between drops falling from the funnel increases. A jump in the intervals between drops is considered as an indicator of experiment completion. According to the experimental results, the soil moisture content obtained by vacuuming correlates with the values calculated for the lowest soil moisture capacity (according to Dolgov) by 87%. The PLAW values obtained by the secant method (according to Voronin) for some soil samples do not fall out of the dependence obtained. This method makes it possible to demonstrate that soil drying leads to a decrease in the measured PLAW value. An explanation of these results from the standpoint of the presence of organomineral gels in soils is proposed.