Denjam Khadka - MS Defense

Multisensor capacitance probe calibration for temperature correction in tropical soils of Hawaii.

Real-time soil water monitoring systems, i.e., Multisensor capacitance probes (MCPs) are getting attention in recent years as an irrigation management tool. The MCPs are extensively used worldwide to measure volumetric soil water content within and below root zone for better irrigation and nutrient management. A MCP determines soil water content by measuring the frequency change induced by the changing permittivity of the soil-water-air mixture which is mostly dominated by amount of water present in the mixture. These dielectric based soil moisture sensors have advantage of real-time, non-destructive and fast response but previous studies have shown their responses to salinity, and temperature.

The objectives of this study were i) to evaluate the effects of temperature on the performance of MCPs in two tropical soils (Wahiawa and Molokai Oxisols), and ii) to implement a temperature correction procedure using a temperature-dependent scaled frequency. Multi-sensor capacitance probes were logged at one minute intervals in soil columns packet with these two soils and at nine different water contents ranging from dry to saturation (0.00, 0.10, 0.20, 0.25, 0.30, 0.35, 0.40, 0.47 and 0.55 cm3 cm-3). Packed soil columns were placed in a water bath of varying temperature from 5 to 45 oC. There was a highly significant positive soil temperature effect on MCPs readings (p<0.0001) in both soils. In Wahiawa Oxisol, the water content was underestimated below 25oC and was overestimated after 35oC. However, water contents were overestimated in all temperature ranges for Molokai Oxisol. Paired t-tests were used to compare both corrected and default water content readings with actual water contents. This comparison showed that the temperature correction procedure was successful since there no significant difference between temperature adjusted (corrected) and actual water contents for both Wahiawa Oxisol and Molokai Oxisol (p>0.05). Use of the new temperature dependent scaled frequency calibration model was successful in eliminating most of the temperature effect in both soils.

Event Sponsor
NREM, Manoa Campus

More Information
Lois Agena, 956-7530, laagena@hawaii.edu

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