Use of the Dixon-Tyree stem hygrometer in a rubber tree plantation

The Dixon-Tyree stem hygrometer has hitherto been used primarily indoors in controlled conditions. We used it, and the leaf pressure chamber, to measure water potentials in plantation rubber trees outside in the Cote d’Ivoire (May and September 2004). Measurements of stem and root xylem water potentials were considered to be reliable, provided they complied with technical constraints that we specify. The stem hygrometer is non-destructive if the sensor is well installed, and provides measurements for two to three weeks without intervention, although the initial measurements are sometimes erroneous.