PERFORMANCE OF A NONNUCLEAR RESONANT-FREQUENCY CAPACITANCE PROBE .1. CALIBRATION AND FIELD TESTING

Accurate and rapid methods for in situ measurement of soil water conte nt of field soils are required for assessment of plant growth conditio ns, crop water balance, and irrigation scheduling. Advances in electro nics have made possible the recent development of a commercially avail able non-nuclear resonant frequency capacitance probe (Troxler Sentry 200-AP) for measuring water content of various materials. However, the performance of this probe to measure soil water content of the field soils in situ has not been widely reported. This study was undertaken to identify the need for field calibration and to understand the calib ration process and evaluate the performance of the capacitance probe. A field calibration curve for a Uchee loamy sand was made for the Sent ry 200-AP probe. In situ volumetric soil water content obtained using this calibration curve differed markedly from those obtained using the factory calibration provided with the probe. The capacitance probe wa s found to be more sensitive at the lower range (<40%) of soil volumet ric water content. However it appears to be reliable and to give repro ducible results.