SEASONAL-VARIATION OF HYDRAULIC-PROPERTIES OF SOILS MEASURED USING A TENSION DISK INFILTROMETER

For sound land management, it is important to understand the temporal changes that soil hydraulic properties undergo. Estimation of the unsa turated characteristics of the hydraulic conductivity, sorptivity, and mean pore radius was performed using tension-disk infiltrometers in t wo different soils of the Mediterranean region: a sandy soil (Xerochre pt) and a heterogeneous, stony, and sandy soil (Alfisol). Both soils w ere cropped with maize (Zea mays L.) and underwent conventional tillag e and different irrigation practices, namely furrow irrigation and gun irrigation. The mobile water content was also deduced from soil sampl es extracted underneath the disk following a period of infiltration wi th the tension infiltrometer filled with a Cl- tracer. Results are pre sented here of measurements made after plowing and again at the end of the growing season, During the growing season, the sandy soil under f urrow irrigation showed a significant decrease in its hydraulic proper ties. This followed an increase in the bulk density and was a result o f sealing of the small interconnected pores at the soil surface. Stron g nonlinearity in the hydraulic conductivity was found for the stony s oil, yet there was no significant change in this nonlinearity during t he growing season. However, from the tracer results, it is stated that for this soil, the structure of the fine fraction changes from a well -interconnected microporous network to a poorly connected one. This re sults in an increase of the mobile water content during the growing se ason. It is shown that a good understanding of the porous network can be obtained from tension infiltrometers and can explain changes in bot h the hydraulic conductivity and the sorptivity. These changes were al so partially corroborated by the mobile water content measurements obt ained from tracer observations under the disk.