Development of non-destructive measuring systems for root growth based on AE method

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Continuous measurement of plant root development is important for evaluating its contributions to water and nutrient uptake, as well as is responses to changes in the soil environment. However, there has been no method to measure the root system continuously in soil.Through this study, we have developed a new non-destructive method for measurements of spatial root elongation in soil, using Acoustic Emission (AE) sensors. AE is defined as "the phenomenon of the energy, which is released, as sound pulses, from destroyed and/or deformed materials". We tried to detect AE pulses generated in the collisions between soil particles and a growing root in order to deduce how roots are developing.There sensors were placed vertically at 15mm intervals on each of thefour side walls of a rectangular stainless steel container (15*14*200mm). Spatial root tip position was expressed by the three axs. Relative AE counts on x and y-axis, obtained from three sensors on the same and oppsite planes, were linearly related to root tip position on x and y-axis. Root tip positions (X) on the x and y-axis can be calculated from the equation Y=0.740-0.042X (r=0.861^<****>) which was developed by regressing relative AE counts (Y) on actual measurements of root tip position. Thus spatial root tip position can be estimated at any time. The trajectory of maize primary root tip postion estimated by AE sensors was almost consistent with that obtained from actual measurements. This method can be used to give continuous, three-dimensional measurement of root tip position and direction of growth. A wide range of root elongation rates and direction angles can be detected.