Monitoring Soil Moisture: Comparison Between Neutron Probe and Profiler PR2

Soil moisture monitoring is essential for irrigation management. One of the widely used methods in research is the neutron scattering through a neutron hydroprobe. Although satisfactory accuracy and quite high precision of the soil water content measurement can be obtained, the radioactivity of the neutron probe limits its application in agronomic practices. Capacitance sensors are considered as alternative instruments to measure soil water content due to their much safer characteristics. Calibration of the PR2 for each soil types, or over each soil depth, can significantly improve the accuracy of soil water content measurement. Since this device has been widely used in many studies regardless of its inaccuracy, and at least part of these studies used the default parameters to compute the soil water content, estimating adjusting coefficients would be very helpful to understand the actual soil water content dynamics over the growing season. The objectives of this study were 1) evaluating the method of estimating adjusting coefficients of different soil types and irrigation treatments; 2) making suggestions on how to better use the PR2 readings under the default setup. We found that the volumetric soil water content measured by the PR2 probe can be adjusted using the adjusting coefficients obtained through regression/ ANCOVA, and the adjusting coefficient is better used to adjust the soil water content change instead of absolute volumetric soil water content.