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 unsaturated characteristics of the hydraulic conductivity, sorptivity, and mean pore radius was performed using tension-disk infiltrometers in two different soils of the Mediterranean region: a sandy soil (Xerochrept) and a heterogeneous, stony, and sandy soil (Alfisol). Both soils were cropped with maize (Zea mays L.) and underwent conventional tillage and different irrigation practices, namely furrow irrigation and gun irrigation. The mobile water content was also deduced from soil samples extracted underneath the disk following a period of infiltration with the tension infiltrometer filled with a Cl- tracer. Results are presented here of measurements made after plowing and again at the end of the growing season, During the growing season, the sandy soil under furrow irrigation showed a significant decrease in its hydraulic properties. This followed an increase in the bulk density and was a result of sealing of the small interconnected pores at the soil surface. Strong nonlinearity in the hydraulic conductivity was found for the stony soil, yet there was no significant change in this nonlinearity during the 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 results in an increase of the mobile water content during the growing season. It is shown that a good understanding of the porous network can be obtained from tension infiltrometers and can explain changes in both the hydraulic conductivity and the sorptivity. These changes were also partially corroborated by the mobile water content measurements obtained from tracer observations under the disk.