|Jabro, Jalal "jay"|
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/1/2004
Publication Date: 6/10/2005
Citation: Jabro, J.D., Lieb, B.G., Jabro, A.D. 2005. Estimating soil water content using site-specific calibration of capacitance measurements from sentek enviroscan systems. Applied Engineering in Agriculture. 21(3):393-399 Interpretive Summary: Newly developed sensors, including the EnviroSCAN capacitance system have the potential to estimate soil moisture content continuously at various depths. Average water content values of the soil profile estimated by the EnviroSCAN capacitance system were used to develop a site-specific calibration equation. A calibration equation was developed using the 1998 soil water content and sensors' scaled frequencies. The calibration equation was then statistically validated using both 1999 and 2000 soil water contents. The statistical analysis also supports considerable discrepancies between soil water contents estimated by the site-calibration and manufacturer's default equations. The developed site calibration equation accurately estimated volumetric soil water content values for all three years, compared to those estimated by the manufacturer's default equation. Therefore, site-specific calibration is essential for the most precise soil moisture content measurements as well as to improve the sensor's accuracy and performance.
Technical Abstract: Newly developed sensors, including the EnviroSCAN capacitance system have the potential to monitor and estimate soil moisture content continuously at various depths. A simple site calibration of these sensors is required to obtain absolute accurate soil water content because these sensors are shipped with a default (uncalibrated) equation to the user. Therefore, our research objectives were: 1) to calibrate the EnviroSCAN capacitance system versus soil water contents estimated by a neutron probe calibrated with gravimetrically measured water contents, then 2) statistically compare the calibrated soil water content results with those estimated by the uncalibrated equation using three years of field data. Both the EnviroSCAN capacitance and the neutron probe were installed in a Warden silt loam soil planted to alfalfa. The average water contents of the soil profile estimated by the EnviroSCAN capacitance was used to develop a site specific calibration equation by comparing the sensors' scaled frequencies for 1998 with the soil water content of the neutron probe. The site calibration equation was then statistically validated using both 1999 and 2000 soil water contents. The statistical analyses indicated that discrepancies existed between the site calibration equation and those estimated by the manufacturer's default equation for soil water contents. For instance, the RRMSE values of soil water content produced from the calibrated equation were 7%, 41%, and 40%, compared with uncalibrated RRMSE values of 68%, 59%, and 66%, for 1998, 1999, and 2000, respectively. These results support that the site calibration equation was found to give more accurate estimates of individual values of volumetric soil water content compared to those obtained from the uncalibrated equation.