Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

Abstract. Water stress directly affects crop growth and is used as a key indicator in evaluating the crop yield. There were several non-destructive approaches suggested to utilize the relationship between water stress and leaf vibration frequency, but the tendency of the frequency due to the dryness was controversial. In addition, we previously observed that the water stress induces either an increase or decrease in vibration frequency even with the same plant species, i.e., soybean plant. Here, we proposed a new perspective of leaf surface curvature effect to vibration frequency in order to understand this discrepancy. To characterize surface curvature changes during the plant drying process, leaves were monitored in both 2D and 3D tracking manner. As well, bending and flexural rigidity tests were conducted with soybean leaves. From video recordings, we found that the curvature of the leaves change​ from a flat surface to an upward curling topology as they grow. It was observed that the cupping shapes appeared randomly. The topological changes influenced the overall stiffness of the leaf and further contributed to increasing the frequency. Thus, the frequency of fluttering leaves can show contrasting results caused by the shape deformation. These results indicate that the morphological feature of leaves is key to the vibration frequency.