PERFORMANCE OF A NONNUCLEAR RESONANT-FREQUENCY CAPACITANCE PROBE .2. MEASUREMENT OF DRYLAND CROP WATER-USE

Resonant frequency capacitance techniques have been recently developed as a safe and reliable method for measuring water content of various materials. A previous study with a commercial capacitance probe (Troxl er Sentry 200-AP) showed it to be a safe, reliable, and a rapid method of in situ measurement of soil water content in the field provided it is calibrated for individual soils. Further testing of this resonant frequency capacitance probe was done to evaluate the performance of th e probe by comparing results of field measured crop water use to those reported in similar studies using other methods of determining in sit u soil water content in the field. These tests were done in two field experiments which were conducted during the summer of 1994 using corn and sorghum as the indicator crops. The experimental field was the sam e used to calibrate the capacitance probe in the previous study. Treat ments consisted of three plant populations of corn and four plant popu lations in two cultivars of grain sorghum. The crop water use for corn and sorghum averaged over all treatments were 452 and 424 mm, respect ively. The measured crop water use values for corn and sorghum were co mparable to the crop water use values reported in several similar prev ious studies using different in situ soil water measuring instruments.