R. Khosla et N. Persaud, PERFORMANCE OF A NONNUCLEAR RESONANT-FREQUENCY CAPACITANCE PROBE .1. CALIBRATION AND FIELD TESTING, Communications in soil science and plant analysis, 28(15-16), 1997, pp. 1333-1345
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.