FURROW IRRIGATION ADVANCE AND INFILTRATION EQUATIONS FOR A MEDITERRANEAN SOIL

For Mediterranean soils, infiltration has a particular behaviour owing to a layered profile with two very different horizons: a sandy permeable layer overlying a clayey hard layer. The equations of Kostiakov, Kostiakov-Lewis and Philip can be used to describe the infiltration process into irrigated soils. Their potentiaI for fitting infiltration for Mediterranean soils is analysed. The volume-balance technique presented by EIliott and Walker using data from the irrigation advance phase is applied to find the parameters of the infiltration equations pertinent to each irrigation event. On Mediterranean soil, the rate of irrigation advance decreases quite slowly and stays nearly constant. This characteristic is the reason for negative values to arise for the exponent of time in the Kostiakov-Lewis equation, if determined by the volume-balance technique, as was observed for experimental furrows in the present work. Negative values were also obtained for the constant in the second term of the Philip equation, as advance was relatively linear. No negative values were found for any of the Kostiakov terms. Of the three equations, this is the sole one whose parameters are generally obtainable by the volume-balance technique in Mediterranean soils. For the 20 irrigation events analysed, the Kostiakov equation described infiltration best of the three equations, with an average absolute error of 65% and standard deviation of 4.8%. (C) 1995 Silsoe Research Institute