A Sensitive Auxanometer for Field Use

The essential characteristics of an auxanometer designed to measure the extension rates of grass leaves in the field are outlined. The construction, using a linear-variable differential transformer (LVDT) to measure displacement, is described. Laboratory tests showed a linear relation between output and armature displacement, which was independent of changes in temperature between 1 and 24 °C. Field tests on winter wheat leaves showed good agreement between auxanometer and rule measurements of leaf extension made over time periods of 24, 12, and 2 h. The tests and an analysis of the errors, including the thermal expansion of the auxanometer stand, show that this auxanometer can reliably and accurately measure leaf extension rates of between 0·1 and 10 mm h−1 in wind speeds up to 4·5 m s−1.