Soil moisture depletion in summer by an eucalyptus grove in a desert area

Abstract

The soil moisture depletion in the principal root zone of a 12-year-old eucalyptus grove in a desert area has been analyzed. The contributing factors to the total soil moisture loss or actual evapotranspiration could be separated during the dry summer months, with a high evaporative demand following a deep but partial recharge of the soil profile by run-off from an adjacent watershed. Under these circumstances the ratio of the water extraction by roots to free-water evaporation was about 1.35 as long as soil moisture suction in the root zone was less than 1 3 atm . An almost linear reduction in the ratio was observed when soil moisture suctions increased from 1 3 to 4 atm . Above 4 atm soil moisture suction, the ratio quickly decreased to an asymptotic curve with further drying out of the soil profile. Soil moisture upward flow from the wetted profile below the root zone was an important factor to be considered over a relatively long period when determining the rate of moisture extraction by roots. Soil moisture loss by direct evaporation from the soil surface was a factor only during a short period after flooding, but continued to deplete the surface soil layer at slower rates to below wilting point moisture content. The cumulative amount of water lost by actual evapotranspiration of the grove was 48% of that lost by a free-water surface with an average evaporation rate of 8.6 mm/day over a period of 5 months.