A NEW VERSATILE SOIL MOISTURE BUDGET

A new technique for the estimation of daily soil moisture on a zone-by-zone basis from standard meteorological data is herewith presented. The method, which is more versatile than existing meteorological budgets and therefore called "versatile budget" (VB), makes use of some basic concepts employed in the modulated budget, such as taking potential evapotranspiration (PE) as a possible maximum of actual evapotranspiration (AE) and subdividing the total available soil moisture into several zones of different capacities. The VB facilitates moisture withdrawal simultaneously from different depths of the soil profile permeated by roots in relation to the rate of PE and the available soil moisture in each zone. Adjustments for runoff, drainage, different types of soil-drying curves and the effect of different atmospheric demand rates on the AE/PE ratio are also incorporated.Comparisons between daily soil moisture readings from Colman blocks with estimates from the modulated budget and from the VB showed the feasibility of estimating daily soil moisture from standard meteorological data. The estimates of the VB were superior to those from the modulated budget on a zone-by-zone basis. The application of soil moisture statistics obtained from meteorological budgets is discussed.