Field evaluation and error analysis of soil water content measurement using the capacitance probe method

The volumetric water content of a silty clay loam soil was measured using the capacitance probe method (CPM) for three successive winter-spring periods. The results were compared with those obtained using the neutron scattering method (NSM). The CPM was calibrated using gravimetric water content measurements, whereas the NSM was calibrated using a theoretical calibration which requires chemical analysis of soil samples. The calibration curves of CPM were linear for volumetric water content ranging from 0.25 to 0.40 m(3) m(-3). The correlation coefficients (r) ranged from 0.87 to 0.98. The advantages of the CPM were discussed, and it was demonstrated that, for low differentiated soils, this method can be a better alternative to the NSM, which is commonly used for the determination of soil water content. The CPM and NSM measurements were compared and root mean squared errors between these two methods ranged from 0.0098 to 0.0159 m(3) m(-3). The precision of NSM and CPM in a field calibration exercise was calculated. For CPM, this study discusses unbiased and biased statistical treatments to establish the calibration curves. The unbiased treatment greatly decreased the total variance in volumetric water content. The standard deviation of volumetric water content ranged from 0.0194 to 0.0248 m(3) m(-3) and from 0.0108 to 0.0136 m(3) m(-3) for biased and unbiased statistical method, respectively. Finally, the soil water storage and associated errors were calculated using CPM and NSM.