Temperature-compensated and density-independent moisture content determination in shelled maize by microwave measurements

Moisture content of shelled maize, Zea mays L., was correlated with the attenuation and phase shift of electromagnetic waves travelling through a layer of grain. Several calibration equations are presented in the paper that are based on measurements taken at 15.2 GHz for various grain densities, moisture contents and temperatures. Validation of the calibration equations indicated that moisture content can be predicted with an uncertainty less than +/-0.72% moisture content w.b. at the 95% confidence level. Moisture predictions are largely independent of bulk density variations at temperatures from 4 to 45 degrees C and moisture contents from 9 to 19% w.b. By following one approach described, the grain bulk density can be determined from the same measurements with an uncertainty of less than 25 kg/m(3). With another approach, the grain bulk density cannot be determined, but moisture content is determined independent of the material bulk density and compensated for temperature. No differences among three maize hybrids were observed in the measured data. (C) 1999 Silsoe Research Institute.