Multisensor capacitance probes (MCAP) are an alternative to gravimetric or nuclear soil water content (θv, m3 m−3) measurements. Their θv measurements are more convenient than gravimetric, and don't carry the nuclear regulatory burdens. Previous studies noted potential salinity and temperature effects on MCAP θv determinations. Our objectives were to calibrate and verify MCAP θv measurement accuracy in two soil materials, two water salinities (1.3 and 11.3 dS m−1), and with diurnal temperature fluctuations. The surface and calcic horizons of an Olton soil (fine, mixed, superactive, thermic Aridic Paleustoll) were packed into triplicate, 0.5‐m‐tall, 100‐L columns and wetted. We compared θv determined by volumetric measurements, time domain reflectometry (TDR), and MCAPs. The TDR θv were within ±0.01 m3 m−3 of volumetric determinations for air‐dry and saturated soil. The factory supplied universal MCAP calibration provided accurate θv estimates for air dry (±0.01 m3 m−3) surface and calcic soil materials but not after wetting (≈−0.05 m3 m−3). Also, imprecise MCAP sensor positioning during water frequency parameter determination was problematic and biased initial θv measurements. After calibration against TDR, the MCAP θv varied ±0.01 m3 m−3 from measured θv for air‐dry and saturated conditions for both soil materials, which were then pooled to obtain one calibration. Column resaturation with saline water affected permittivity and elevated MCAP θv ≈0.25 m3 m−3 above the available pore space. Cyclical soil temperature fluctuations of 15°C induced similar fluctuations in indicated θv throughout the column (0.04 m3 m−3 for MCAP and 0.02 m3 m−3 for TDR), which was attributed to variations in permittivity.

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climate-dependent threshold time, then an irrigation event of a fixed depth is scheduled (Fig. 1). Evett et al.The application of the temperature-time threshold (TTT) method (1996, 2000) demonstrated in drip-irrigated plots that of irrigation scheduling to self-propelled irrigations systems requires a method of estimating the diurnal canopy temperature dynamics automatic irrigation using the TTT method was more using only a one-time-of-day measurement. Other research efforts responsive to plant stress and showed the potential to such as the crop water stress index (CWSI) and field canopy temperaoutyield manual irrigation scheduling based on a 100% ture mapping using moving irrigation systems could also be served replenishment of crop water use as determined by neuby the use of this method. This was accomplished using a stationary tron probe soil water content measurements. It is desirreference measurement to capture the canopy temperature dynamics.able to apply the TTT method to moving irrigation sys-Two different methods were developed for estimating a temperature tems such as center pivots or linear-move systems. curve for a remote location from a one-time-of-day measurement at However, infrared thermometers (IRTs) mounted on that location. The first method (scaled method) uses the ratio between moving irrigation systems provide only one-time-of-day the reference temperature and the remote location temperature, refermeasurements. This necessitates a method of estimating enced to the predawn temperature, to scale the reference curve to yield the predicted curve. In the second method (Gaussian difference the diurnal canopy temperature dynamics using only a method), a three-parameter Gaussian equation was empirically fitted one-time-of-day canopy temperature measurement. to the temperature differences between the reference and the mea-Other canopy temperature-based crop stress indicasured remote canopy temperature curves. To test these two methods, tors such as the Crop Water Stress Index (CWSI; Jackcanopy temperature data, sensed using stationary infrared thermomeson, 1982) are sensitive to the time of day that the meaters, from three different crops {corn (Zea mays L.), cotton (Gossypsurements are taken (U.S. Water Conserv. Lab., 2004). ium hirsutum L.), and soybean [Glycine max (L.) Merr.]} were ana-There is also an increased interest in quantifying spalyzed. For a few hours after dawn and before sunset, the scaled method tially varying crop response to soil-, water-, disease-, or was generally more accurate while during the middle of the day, the