© 1986 Heron Publishing—Victoria, Canada
Precision weighing lysimetry for trees, using a simplified tared-balance design
W. R. N. Edwards
Soil Conservation Centre, Aokautere. Ministry of Works and Development, Private Bag, Palmerston North, New Zealand / Received February 19, 1986
Summary
Four weighing lysimeters (1.8 m diameter, 1 m depth, weight 3.5–4.5 Mg) were used to estimate transpiration from single, isolated
trees. The weighing mechanism incorporated a simple, new system of wire ropes around torsion tubes, producing a lever action
through which most of the weight was tared off with a counter weight. Weight differences measured by load cell under the main
lever arm were unaffected by hysteresis or temperature change. Sensitivity better than 100 g was achieved in windless conditions.
Daily measurements over yearly periods (trees could be regularly replaced using extra pots) revealed both sigmoid seasonal
patterns, and sigmoid diurnal changes closely related to micrometeorological variables, for a range of tree species. Measurements
taken during rainfall demonstrated that an isolated tree intercepts considerably more precipitation than does a uniform crop
covering the same ground area, and that substantial evaporation from the canopy takes place while it is raining.
