A Modulated Soil Moisture Budget

Abstract

Most meteorological soil moisture budgets do not account for soil moisture stress changes in the drying cycle or for changes in ground cover or expanding root system. A simple modulated technique is described which considers these factors. Soil moisture stress determined by this technique has a significantly higher correlation with wheat yield than does moisture stress determined by R common method. factors AE, PE, and dejicit (calculated by common (A) anrl rnodulated (B) methods) and yield of wheat at Lethbridge, Alberta I Correlation coefficient and method Soil moisture ry 123 July rY3 June ry2 May r y l

BASINWIDE WATER‐BALANCE MODELING WITH EMPHASIS ON SPATIAL DISTRIBUTION OF GROUND WATER RECHARGE1

“…Budgeting methods for estimating soil moisture and actual evapotranspiration from vegetated soil, when water supply is at times limited, are comparatively more complicated, because they account for various soil and plant characteristics that modulate or alter the potential rate. In this report a meteorological soil-moisture budget approach called "Versatile Budget" (Baier and Robertson, 1966), which is a multigeneration evolution of the Holmes and Robertson (1959) modulated budget, is employed. It should be noted that other similar and more elaborate hydrologic simulation models are available in the literature, and the reader is referred to Haan, et al (1982), for a compilation of some of these models.…”

A simple method of estimating the soil water balance

“…As the crop develops through the various stages of growth, its roots appear in varying locations of the soil at different times. Hence, depths to which drying takes place, and the amounts of water available for evaporation or evapotranspiration, are different and even if the entire soil profile is at field capacity the available soil moisture for evapotranspiration differs at each stage of crop growth {Holmes and Robertson, 1959). Therefore, (Thornthwaite and Mather, 1954, Transpiration); C = computed 0.8 x AEn, where AE n is estimated using eq.…”

“…However, many of the models are soil-or climate-or crop stage-specific (Baier et al, 1972). The generalized water-balance models of Holmes and Robertson (1959), Shaw (1964), Baier and Robertson (1966) and Fitzpatrick and Nix (1969) were developed for application to specific crop systems (Nix, 1975). In the case of Robertson's (1966} model, Baier et al (1979) noted large deviations between observed and estimated soil moisture under fallow and wheat crop conditions.…”

Management strategies for corn production and drying systems

“…There are numerous such soil moisture budgets in use today, namely, a modulated soil moisture budget as developed by Holmes and Robertson (1959), a versatile soil moisture budget as proposed by Baier and Robertson (1966), and an estimated soil moisture budget under com as presented by Shaw (1963).…”