CONCEPTS OF SOIL MOISTURE AVAILABILITY AND THEIR EFFECT ON SOIL MOISTURE ESTIMATES FROM A METEOROLOGICAL BUDGET

Soil moisture measurements by means of Colman electrical resistance blocks over 10 years were used to test the effect of various relationships between plant-available soil moisture (SM) and the ratio of actual (AE) to potential (PE) evapo-transpiration on soil moisture estimates obtained by the Versatile Budget. Depending on the type of relationship used, correlation coefficients (ranging from 0.76 to 0.85) between 5-day means of SM observations and estimates differed significantly and mean errors varied from 3% to 39% of the observed seasonal means. Under the local experimental conditions, a linear relationship between SM and AE/PE gave estimates most closely related to the observations. The results suggest that when a realistic SM vs. AE/PE relationship is used in the Versatile Budget, a precision of the estimates comparable to the error involved in measuring soil moisture in the field by conventional methods can be achieved. © 1969.