Performance of a new capacitance soil moisture probe in a sandy soil

Rapid population growth and increasing urban demand reduce the availability of water for agriculture in Florida. The water-holding capacity of sandy soils in the Central Florida Ridge area is very poor (<0.10 m3 m–3). Improved soil water monitoring probes can help growers manage irrigation more efficiently and conserve water. This study evaluated a new soil water probe (ECH2O EC-5 sensor, Decagon Devices, Pullman, WA) in terms of probe-to-probe signal variability, response to fertilizer-induced salinity, and changes in soil temperature, soil volume sampled, sensitivity to pockets of air or dry soil, and performance in the field. Results were compared with an earlier version of a Decagon probe, the EC-20. Results indicated that the new probe has several advantages. The EC-5 was not sensitive to salinity or temperature fluctuations. Probe output change was almost zero when the salinity of the soil was increased by adding fertilizer to a soluble solids concentration of 14 g kg–1. When temperature was changed gradually from 3 to 38°C, probe output increased by only about 1%. Soil volume sampled by the probe was about 15 cm3. The change in probe response was negligible when soil cores up to 0.95 cm in diameter near the probe surface were removed. Probes responded well to changes in soil water content in the field. The EC-5 probe output increased noticeably when bulk density was increased from 1.1 to 1.6 Mg m–3. Probe-to-probe output signal and response to bulk density variations can affect the estimation of field water content unless necessary correction factors are utilized. These probes can be useful for monitoring soil water movement, estimating soil water content, and scheduling irrigation.

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