PERMANENT WILTING PERCENTAGES OF SOILS OBTAINED FROM FIELD AND LABORATORY TRIALS

Abstract

Permanent wilting percentages of soils obtained in the field sometimes differ from those detd. in the laboratory. In most cases these differences are due to rather abrupt changes in texture in the sub-soil. Soils that are uniform to the depth sampled show close agreement between the permanent wilting percentages obtained in the field and those in the laboratory. The permanent wilting percentages obtained from sunflower plants in small containers are not affected if the tops and roots are kept within the range of temps. ordinarily found in the field. Sunflower plants reduced to 1 or 2 leaves wilted at the same soil-moisture content as entire plants. The permanent wilting % is shown to be a small range of soil-moisture contents within which permanent wilting takes place. This range is about 1% for fine-textured soils or 0.5% for coarse-textured ones. The constancy of the permanent wilting % and its recurrence within close limits each season in regions of rainless summers make it a useful basis for calculating the amt. of water that can be stored in a soil.