Water balance and pattern of root water uptake by a Quercus coccifera L. evergreen srub

The water balance of a Quercus coccifera evergreen scrub was studied over 7 consecutive years. This scrub grows on hard limestone. Soil water content was measured with a neutron meter. Calibration curves were calculated from (1) the thermal neutron macroscopic cross-sections of soil (<2-mm fraction) and rock samples, and (2) the profile of wet bulk density measured with a subsurface gamma-ray gauge. The annual and seasonal patterns of actual evapotranspiration and of deep drainage were calculated using field-measured drainage characteristics. The soil water content data were used to compute water uptake rates and pattern for the root zone over a 4-month drying period. The 906 mm of mean annual precipitation yielded 603 mm of actual evapotranspiration (AET) and 296 mm of drainage. No drainage occured with precipitation less than 578 mm. The average AET values for the months from April to September were 57, 74, 89, 96, 70, and 42 mm respectively. It was found that Quercus coccifera consumed considerable quantities of water from the soil-rock complex. Roots could extract 270 mm of water in the first 470 cm of soil. The results showed a gradual downward shift of the zone of maximum root water uptake as the soil dried.