Journal of Hydrology, 135 (1992) 73-86 Elsevier Science Publishers B.V., Amsterdam 73 [3] Determining soil hydrologic properties from rain simulator or double ring infiltrometer experiments: a comparison J. Toama and J. Albergel Centre ORSTOM de Dakar B.P. 1386. Dakar. Senegal (Received I June 1991; accepted 25 October 1991) ABSTRACT Touma, J. and Albergel, J., 1992. Determining soil hydrologic properties from rain simulator or double ring infiltrometer experiments: a comparison. I, Hydrol., 135: 73-86. Two infiltration experiments were conducted on two plots of I m 2, each equipped with a neutron meter access tube and tensiometers. One infiltration was performed with a constant head of water maintained at the soil surface, the other using a rain simulator. The order of experiments was reversed on the two plots, i.e. on the first plot, simulated rain preceeded infiltration under constant head, while on the second plot, ponded infiltration was performed prior to the simulated rain. For each plot, the water pressure and hydraulic conductivity relationships versus water content were determined from both experiments for the various horizons of the soil profile. It is shown that the range of data obtained from the double ring infiltrometer is much wider than that corresponding to the rain simulator. This is due probably to surface sealing during the latter experiment. Application of the Van Genuchten model (1980) to predict the hydraulic conductivity from the water retention curve shows good agreement for some horizons but is not satisfactory for others. It is concluded that when the soil surface is subject to crusting, the double ring infiltrometer is more suitable than the rain simuiator for the determination of soil hydrologic properties. INTRODUCTION Ring infiltrometers are commonly used for in situ determination of soil hydraulic properties (i.e. the water content-pressure head relationship, or water retention carve h(O), and the relation between water content and hydraulic conductivity, K(0)), measurement of infiltration capacity (Ahuja et al., 1976; Chong et al., 1981; Youngs, 1986) and determination of spatial variability of soil properties (Vieira et al., 1981; Vauclin et al., 1983). On the other hand, rain simulators are widely used to study soil erosion (Bryan and De Ploey, 1983; Miller, 1987; Remley and Bradford, 1989), soil crusting Correspondence to: J. Touma, Centre ORSTOM de Dakar, B.P. 1386, Dakar, Senegal. 0022-1694/92/$05.00 © 1992- Elsevier Science Publishers B.V. All rights reserved