Rapid Method for Determining Soil Moisture
1951
Uhland, R. E.
Discussion and SummaryThe volume weights of some soils change but little during the year. The moisture content of these soils in per cent by volume is equal to the weight of the wet sample in grams minus the weight of the oven-dry sample in grams, divided by the volume of the sample in cubic centimeters times 100. If the 3- by 3-inch cylinders are used, the soil core volume is 347 cubic centimeters. By multiplying the depth of soil in inches that is represented by each set of cores by the per cent of moisture, the number of inches of moisture contained in that portion of the soil profile is obtained. The following equations are used for determining the amount of water in the field soil and in the soil when saturated: By using this procedure, the amount of moisture that is present in the soil may be quickly calculated without waiting one day or more, as is necessary when the soil must be placed in the drying oven. Once the wilting point in per cent by volume of a given soil has been determined, the difference between this value and the amount of moisture present in the soil when sampled represents the moisture available for evapotranspiration. The author suggests that technicians try this method along with their conventional system on some of the soils on which they make a number of moisture determinations each year. In making the test, it is important that each soil horizon suspected of having a different volume weight and/or moisture content be sampled separately. The depth of soil that each set of replicates for each location on the plot or field represents should be measured and recorded. Additional time can be saved and calculations simplified by preparing a table or chart which lists the number of inches of water that will be contained in the soil for each increment of weight.
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