WATER RELATIONSHIPS OF APPLE TREES ESPECIALLY AT DIFFERENT GROUND WATER TABLE LEVELS
The measurements consisted of the orchard microclimate, soil moisture content up to 120 cm deep with a neutron probe and twig with pressure bombs throughout 4 days of different weather type. The potential transpiration rate of the leaves Eo was calculated by the Penman-Montheith equation.
In the moderately dry summer the infiltration levels caused significant differences in twig on days of different weather type. twig increased with increasing water in the soil profile from the no infiltration (deepest water table levels) to the 70–70 cm level treatment.
Leaf area per tree was strongly affected by infiltration level. As water in the profile decreased leaf area per tree decreased, hence the exposition of the leaves to radiation and wind increased, so Eo increased.
When water content in the soil profile and Eo were taken as the explaining factors for twig in a multiple regression analysis they explained it significantly both in combination and separate.
In another experiment throughout a wide range of evaporation conditions the water potential gradients between leaves and twigs were measured and the resistance to water transport causing these gradients was determined from the transpiration rate of the leaves. The latter was calculated by the Penman-Monteith equation from the synchronously measured microclimate and stomatal diffusion resistance data. The resistance found was approximately 9 bar g-1dm2h and was more than one third of the total resistance in the soil-root-stem-leaf continuum of the transpiration pathway.