Non-destructive method for root elongation measurement in soil using acoustic emission sensors

A new non-destructive method for the measurement of root elongation in soil was developed using acoustic emission (AE) sensors. Collisions between soil particles caused by the growth of the root tip generated sound pulses that were detected by the AE sensors. In a simulation experiment, using a stainless steel rod (d = 1.3 mm), AE counts increased as the rod approached the sensor. The relative AE count (Ri) calculated from the values obtained from two sensors, vertically placed 15 mm apart, was only slightly influenced by the rod penetration rate and soil conditions, and linearly correlated with the distance between the rod tip and the center of the upper AE sensor. In the experiments using a maize primary root, Ri (Y) was significantly correlated with the distance (X) between the root tip and the center of the upper AE sensor as in the simulation experiment. Accordingly the root tip position could be estimated using the equation Y = 0.994-0.0640X (r = 0.883**). Calculated values for root elongation were comparable to those obtained from actual measurements.