DETERMINING SOIL HYDROLOGIC PROPERTIES FROM RAIN SIMULATOR OR DOUBLE RING INFILTROMETER EXPERIMENTS - A COMPARISON

Two infiltration experiments were conducted on two plots of 1 m2, 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 simulator for the determination of soil hydrologic properties.,