Authors: Dyer, J.A. And W. Baier
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Published in: CBE Journal » CBE Journal Volume 21 (1979)

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Description: Various empirical relationships have been suggested between the ratio of actual evaporation from a crop (AE) and potential evapotranspiration (PE) and soil moisture content (Baier 1969 Baier et al. 1972). It has also been shown that these relationships are controlled by soil properties, particularly texture (Baier 1968 Salter and Williams 1965). Several previously published soil moisture drying curves were used by Baier and Robertson (1966) in budgeting plant available soil moisture over the growing season. Their curves were controlled by tables of coefficients which were made independent of the plant available soil moisture capacity (ASMC) by expressing available soil moisture (ASM) as a fraction of ASMC. The drying curves have the general form of allowing evaporation to proceed at potential (AE = PE) until some critical value of ASM, where the AE:PE ratio starts to decrease as a function of ASM/ASMC. The decreasing portion of the curves have three typical shapes concave upwards, linear and convex downwards. A separate table of coefficients had to be selected for each drying curve and only a few of these tables are currently available. This paper describes a simple technique for indexing the so-called z-coefficients used in the Versatile Budget (Baier and Robertson 1966 Baier et al. 1972). This index characterizes the falling portion of the curves (AE < PE) as well as the potential case (AE = PE). This approach, which approximates the three curve shapes, was felt to be more useful than several independent functions that exactly fit each existing table of z-coefficients.

Keywords: an index for soil moisture drying patterns
Citation: Dyer, J.A. and W. Baier 1979. AN INDEX FOR SOIL MOISTURE DRYING PATTERNS. Canadian Agricultural Engineering 21(2):117-118.
Volume: 21
Issue: 2
Pages 117 - 118
Date: 1979
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Publication type: Journal
Coverage: Canada
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