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Soil Sampling for Moisture Retention and Bulk Density Measurements¹

ABSTRACT

Four groups of soils were sampled at random and certain physical measurements were made on the samples to evaluate associated variances and sampling schemes. The measurements made were 0.1, 0.5, 1, 5, 10 and 15-bar percentages along with bulk density. Locations were classified as to soil group strictly by soil map without field inspection. One of the objectives was to evaluate the utility of a soils map in estimating physical properties.

Although the soil groups studied are considered relatively uniform, there is considerable variation within each group. It was interesting to find that the variation within an 18-acre tract is of the same order of magnitude as that between 18-acre tracts. The variation among tracts was such that a mean for a soil group is a very rough estimate for a single tract within the soil group. In characterizing a soil group, it was calculated that 2 sites per 18-acre tract were optimum. For characterizing a given 18-acre tract, it would take up to 10 sites per tract to estimate the true mean within 20%, or 35 samples to estimate within 10%.

¹ Technical Paper No. 1343. Oregon Agr. Exp. Sta.

² Graduate student and Associate Soil Scientist, respectively.

Received for publication July 14, 1960. Accepted for publication February 24, 1961.