Using Time-Domain Reflectometry to Measure Soil Water in Hawaiian Sugarcane
1990
Grantz, D. A. | Perry, M. H. | Meinzer, F. C.
Time-domain reflectometry (TDR) has been suggested as a convenient technique for quantifying soil water in agronomic experiments. Sampling protocols and installation techniques remain to be described and the validity of a “universal” calibration equation remains to be tested in Ferich volcanic soils. Thus, TDR was evaluated in this study for measurement of Volumetric soil-water content in an extensive sugarcane field in Hawaii. Matched pairs of probes, 0.359 m and 0.725 m long, were installed vertically at various distances from the drip irrigation line at six locations in a well-watered field. This sampling protocol resolved the diurnal depletion of soil water due to evapotranspiration and the decline in soil water wilh distance from the drip inrigation line, both occurring largely within the surface 0.36 m of soil. Independent measurements of soil-water content using gravimetric methods confirmed the accuracy of the TDR determinations and validated a universal calibration for Ferich Hawaiian soils. A rapid technique was developed to install probes, which remained functional throughout the 2-yr crop cycle. Use of spaced arrays of TDR probes is safer, more convenient, and more suited to automation of data acquisition, reduction, and analysis, than conventional methods of assessing volumetric water content. Contribution from USDA-ARS, Sugarcane Physiol. Res. Unit and Hawaiian Sugar Planters' Assoc. Published as Paper no. 675 in the journal series of the HSPA.
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