HR: 0830h
AN: NS51B-02    [Abstracts]
TI: Hydrogeophysical Monitoring of Water Uptake in Root Zones of Small Plants
AU: * al Hagrey, S
EM: sattia@geophysik.uni-kiel.de
AF: University of Kiel, Institute of Geosciences Otto-Hahn-Platz 1, Kiel, 24118 Germany
AU: Werban, U
AF: University of Kiel, Institute of Geosciences Otto-Hahn-Platz 1, Kiel, 24118 Germany
AU: Meissner, R
AF: University of Kiel, Institute of Geosciences Otto-Hahn-Platz 1, Kiel, 24118 Germany
AU: Ismaeil, A
AF: University of Kiel, Institute of Geosciences Otto-Hahn-Platz 1, Kiel, 24118 Germany
AU: Rabbel, W
AF: University of Kiel, Institute of Geosciences Otto-Hahn-Platz 1, Kiel, 24118 Germany
AB: We have monitored the water content in root zones in hydrogeophysical experiments and studied daily and seasonal variations of water uptake. Plants grew in plastic pots filled with fine sand. The surface of the pots was isolated to minimize evaporation, i.e., most water is consumed for transpiration. We installed geoelectric surface and subsurface profiles (electrode interval = 1.5 cm), and used 900/1500 MHz antennas to measure the travel times of radar waves reflected from a metallic plate at the base. Also a central and peripheral TDR and a tensiometer probe were installed. A continuous data acquisition was conducted to monitor the spatiotemporal water content of root zones and its variations.
Our observations clearly reflect a decrease of pore water content with time and its abrupt increase directly after each irrigation cycle. TDR and tensiometer curves are parallel and mirror images of the resistivity curve. Observed soil water content in the day time was consistently lower than in the night time (no plant transpiration). Long-term observations of water uptake by roots show that the plants behavior is a function of the background moisture content. The maximum water uptake of optimum growth occurs at intermediate water content. Seasonal variations could be observed. The water uptake in May is obviously twice that of November. This can be explained by the fact that the available light (required for photosynthesis) was higher in May than in November. Also the effect of day light on the water uptake can be observed. The light sunny days show higher water uptake than the dark rainy days. The peripheral water content values that decrease with time are lower than that of the central root zone and show small night and day changes. This may imply that the central TDR probe measures the water content both within the wet root branches and the bounding soils, whereas the peripheral TDR reading represents the soil pore water only. Electrical models of the root zone show a systematic daily resistivity minimum in the morning that jumps continuously during the day time approaching maximum in the night time. We established empirical petrophysical relationships of water content to both resistivity and radar velocity and studied root effects in the 4-phase medium (sand, air, water, organic roots).
DE: 0400 Biogeosciences
DE: 0925 Magnetic and electrical methods
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
DE: 1894 Instruments and techniques
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly