Nondestructive measurement of husk-covered corn kernel layer dynamic moisture content in the field

Corn kernel moisture content is the most frequently used indicator for kernel maturity prediction and determination of the appropriate mechanized harvesting time. Corn varieties with lower moisture contents and thus faster dehydration of the corn kernels after physiological maturity are suitable for high plant density and mechanized harvesting. However, nondestructive measurement of the dynamic moisture content of the husk-covered corn kernel layer before physiological maturity in the field remains challenging at present. Therefore, in this study, a nondestructive measurement method based on the vector reflection coefficient measurement technique is proposed and developed for in situ monitoring of the husk-covered corn kernel layer moisture in the field. Based on the one-port calibration procedure used for the handheld moisture detection device, quadratic regression models were established for the corn kernel layer moisture using impedance parameters from 51 husk-covered corn samples. Results showed that this method enabled nondestructive estimation of the husk-covered corn kernel layer moisture (R2=0.62) with a 3.53% root mean square error (RMSE) using a serial capacitor Cs and the husk moisture (R2=0.85) with a RMSE of 7.12%. Additionally, intact corn ears were measured in the field from the dent stage to the maturity stage using this device to investigate the dynamic moisture contents of the kernels and husks. Results showed that the measured moisture content of kernels before physiological maturity followed exponential decay functions with increasing numbers of days, and the mean difference between the measured kernel moisture contents of the intact corn ears and the oven-drying moisture contents of these kernels is 3.72%. In conclusion, the handheld moisture detection device allows us to measure the moisture of husk-covered corn kernel layers nondestructively before maturity in the field. This study thus provides a new way to obtain corn kernel dehydration curves in situ before maturity and estimate the corn maturity time.