HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Valiantzas, J. D. Articles by Sassalou, A. Search for Related Content PubMed Articles by Valiantzas, J. D. Articles by Sassalou, A. GeoRef GeoRef Citation Agricola Articles by Valiantzas, J. D. Articles by Sassalou, A. Related Collections Soil Physics Hydraulic Conductivity

SOIL PHYSICS

Explicit Formulae for Soil Water Diffusivity Using the One-Step Outflow Technique

Agricultural Univ. of Athens, Lab. of Agricultural Hydraulics, 75 Iera Odos Str., 11855 Athens, Greece

^* Corresponding author (v.londra{at}aua.gr).

One of the most widely used methods in determining soil water diffusivity, D, as a function of the volumetric water content, , is the one-step outflow method. Unfortunately, the calculation of D() according to direct methods usually requires the estimation of the first and second derivative of the outflow volume, V, dV/dt and d²V/dt² of the original measured cumulative outflow data V(t). These derivatives are usually approximated by applying a finite difference technique to two or three consecutive outflow measurements. Therefore, the accuracy of the results depends essentially on the accuracy of local outflow measurements. Inaccuracies are more intensive in the last portion of the outflow curve, where small errors of measurement may yield large inaccuracies in the first and second derivatives of the outflow curve. Furthermore, the entire calculation procedure for estimating dV/dt and d²V/dt² is rather laborious and complicated. We developed a direct method based on a simple curve-fitting procedure applied to the experimental outflow data for a simple power and an extended power form function, which leads to direct calculation of the soil water diffusivity function from explicit formulae. The only parameters involved in these formulae are the empirical parameters obtained by the curve-fitting procedure. The proposed method was verified from one-step outflow experiments performed in nine porous materials (one sand, two soils, and six substrate mixtures). Comparison with previous methods indicated a good performance of the proposed explicit algebraic formulae.