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Evaluation of TDR Use to Monitor Water Content in Stem of Lemon Trees and Soil and Their Response to Water Stress

^a Soil and Water Institute, Agricultural Research Organization, Ministry of Agriculture, State of Israel, POB 6 Bet Dagan, Israel, 50250
^b Gilat Research Center, Mobile Post Negev, 85280, Agricultural Research Organization, Ministry of Agriculture, State of Israel
^c Environmental Group, HortResearch, Private bag 11-030 Palmerston North, New Zealand

View larger version (21K): [in a new window]   Fig. 1. A comparison between two methods for evaluating temperature effect on the coaxial cable dielectric length (la probe): 1) Measuring only the probe's end-point reflection and subsequently correcting for temperature-induced shifts of the probe's length (abscissa) compared to 2) the measurement that subtracts the directly-measured probe beginning from measured end-point reflection (ordinate). The 1:1 line is shown.

View larger version (23K): [in a new window]   Fig. 2. Directly measured la probe installed in the wood block as a function of Tair (A) and TWB (B). The corresponding values of stem are within the TDR resolution for a wide range of both air and wood block temperature.

View larger version (21K): [in a new window]   Fig. 3. Changes in the apparent dielectric length of a 4.9 m coaxial cable (la cable) as a function of air temperature determined from five experimental data sets and the equation of best fit to those data sets (See text).

View larger version (52K): [in a new window]   Fig. 4. Seasonal pattern of moisture content in the tree stem (stem) and the root-zone soil (soil) L L-1 for the full (A, E), 50% (B, F), split (C, G), and dry (D, H) irrigation treatments, respectively. (The notations H and V indicate horizontal or vertical installation of TDR probes. DOY refers to the Day of Year. Exceptionally in G, depths of probes are 0.3–0.5 and 0.5–0.7 m, on both sides of the tree.)

View larger version (19K): [in a new window]   Fig. 5. Changes in the average moisture content of the tree stem (stem) and the root-zone soil (soil), normalized to the corresponding values measured on the first day of the experiment.

View larger version (25K): [in a new window]   Fig. 6. Leaf water potential (LWP) as function of time (DOY) as measured at dawn (broken lines) and noon (solid lines) for the four irrigation treatments. Also shown are prestress (DOY < 181) and post-stress (DOY > 250) levels.

View larger version (39K): [in a new window]   Fig. 7. Changes in the electrical conductivity of the soil pore solution (w) as a function of time (DOY), for the 4 irrigation treatments (See text) and at four different depths in the root-zone soil.

View larger version (20K): [in a new window]   Fig. 8. The seasonal changes in the amount of water stored in the root-zone soil for the four treatments, assuming its volume to be 1.8 m3.

View larger version (29K): [in a new window]   Fig. 9. Averaged (n = 6) values of the daily difference in stem moisture status (stem– stem, dawn) by irrigation treatment and as a function of time.