Abstract
The soil water available to crops is defined by specific values of water potential limits. Underlying the estimation of hydro-physical limits, identified as permanent wilting point (PWP) and field capacity (FC), is the selection of a suitable method based on a multi-criteria analysis that is not always clear and defined. In this kind of analysis, the time required for measurements must be taken into consideration as well as other external measurement factors, e.g., the reliability and suitability of the study area, measurement uncertainty, cost, effort and labour invested. In this paper, the efficiency of different methods for determining hydro-physical limits is evaluated by using indices that allow for the calculation of efficiency in terms of effort and cost. The analysis evaluates both direct determination methods (pressure plate - PP and water activity meter - WAM) and indirect estimation methods (pedotransfer functions - PTFs). The PTFs must be validated for the area of interest before use, but the time and cost associated with this validation are not included in the cost of analysis. Compared to the other methods, the combined use of PP and WAM to determine hydro-physical limits differs significantly in time and cost required and quality of information. For direct methods, increasing sample size significantly reduces cost and time. This paper assesses the effectiveness of combining a general analysis based on efficiency indices and more specific analyses based on the different influencing factors, which were considered separately so as not to mask potential benefits or drawbacks that are not evidenced in efficiency estimation.
Highlights
In the context of water resource management, various methods have been used to obtain or determine soil hydraulic properties, hydrolimits (Štekauerová et al, 2002) or hydro-physical limits (Oliveira et al, 2004; Gontijo et al, 2008) from properties that can be measured and quantified
For pressure plates (PP), the time needed to determine permanent wilting point (PWP) was computed considering an equilibration time of 3 days, which is in agreement with the recommendations made by Klute (1986), who suggested using an equilibration time of 2 to 3 days
water activity meters (WAM) determinations needed the shortest time, 108 h, which accounts for half the hours needed for PWP determination by PP (216 h)
Summary
In the context of water resource management, various methods have been used to obtain or determine soil hydraulic properties, hydrolimits (Štekauerová et al, 2002) or hydro-physical limits (Oliveira et al, 2004; Gontijo et al, 2008) from properties that can be measured and quantified. Such methods facilitate and shorten the measurement process. Such methods are termed indirect estimation methods (pedotransfer functions - PTF) (Mualem, 1976; Vereecken, 1988; Wösten et al, 1995; Minasny et al, 1999; Tomasella et al, 2003)
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