ChileanJAR

A research was developed during 2003 and 2004 at an avocado (Persea americana Mill.) orchard cv. Hass grafted on Mexicola rootstock. The orchard was located in the V^th Region of >Chile (32°53’ lat. S; 71°16’ long. W). The orchard was under optimal water and nutritional condition. Several experiences were carried out to optimize midday stem water potential (Ψxmin) measurements, effected by means of pressure chamber techniques: effect of vapor pressure deficit (DVP), leaf age, time of equilibrium of leaf and stem water potential after leaf envelopment, minimum time between leaf detachment and stem water potential (Ψx) measurement in the pressure chamber, leaf location on the tree and the effect of high humidity conditions on detached leaves prior to measurements. The results showed that in avocado trees Ψx were stable between 12:30 and 17:30 h. The less variability of measurements was obtained using 10 to 12 months old leaves, under exposure to sunlight.. The pressure chamber measurements should be carried out 15 min after the leaf was enveloped. Ψx should be measured no longer than 1 min after the leaf is detached from the tree; however, this time could be longer if the leaves are kept in high humidity conditions before measurements.