SOIL DENSITY AS A FACTOR IN DETERMINING THE PERMANENT WILTING PERCENTAGE

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Abstract
Soil-moisture contents at the end of the growing season, at depths of 3 ft. or below, in a grape vineyard on Bale gravelly loam, and in an area of native vegetation on a primary chaparral soil, were found to be higher than the permanent wilting percentages obtained by growing sunflowers on disturbed samples of these soils. Apparent specific gravities of these soils in the field were about 1.8. Three soils, belonging to the Bale, Yolo and Madera series, were compacted in containers to a density of about 1.8. With 2 of the soils, where the density was 1.8 or above, sunflower roots either failed to penetrate or made only slight growth; in the 3d case with the density at about 1.75, the roots entered. In the trials with the first 2 soils, the soil-moisture contents were essentially equal at the beginning and at the end of the expt.; in the 3d case, the soil-moisture content was reduced. Grapevine, sunflower and native vegetation roots were unable to penetrate some soils having a density of 1.8 or above. Attention is called to the discrepancies in detns. of moisture equivalents and permanent wilting percentages in the field and in laboratory trials with some compact soils, and to the difficulties in placing instruments in such soils.

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