Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 10/21/2001
Publication Date: 10/21/2001
Technical Abstract: Accurate soil profile water content measurements are required for determining crop water use and the hydraulic characteristics of soils. We compared the Sentek EnviroSCAN and Diviner 2000 capacitance devices, the Trime tube-probe, a prototype TDR tube-probe, the Delta-T Profiler capacitance probe and the neutron probe, all of which can be used in access stubes. Experiments were conducted in triplicate soil columns of three soils, packed in 5-cm layers with air-dry soil (0.03 m**3 ** 3 water content). Each 75-cm deep, 55-cm diameter column was continuously weighed to 50 g precision on a platform scale. Conventional time domain reflectometry (TDR) measurements of water content and thermocouple measurements of temperature were made at depths of 2, 5, 15, 25, 35, 45, 55, and 65-cm in each column every 30 min. Comparisons of soil water content reported by the devices vs. soil temperature were made before the columns were wetted. The capacitance sensors were more sensitive to 24-h soil temperature fluctuations than were TDR or neutron scattering; and, factory calibrations gave water contents ranging from 0.03 to 0.06 m**3 ** 3 larger than gravimetrically measured water content of the air-dry soil. Depth resolution of the sensors was tested by lowering them in increments from a position well above the soil surface, taking measurements at each increment until the sensors were well below the soil surface. The 95% response window for the Diviner, Trime, and Delta-T devices was approx. the same as the height of the sensor; but for the neutron probe it was twice the detector tube height.