RAINFALL INTERCEPTION AND EVAPORATION FROM SOIL BELOW A WHEAT CANOPY

Components of the seasonal pattern of water use by a wheat crop at Wagga Wagga, N.S.W. are presented. Total evapotranspiration was estimated using a combination of Time Domain Reflectometry and Neutron Moisture Meter measurements. Miniature lysimeters were used to measure evaporation from soil below the canopy. Evaporation of intercepted rain was calculated using an aerodynamic technique in conjunction with a canopy storage coefficient. Detailed measurements of soil evaporation and rainfall interception commenced 80 days after sowing (DAS), when L approximately 1, until 165 DAS. Interception losses accounted for 33% of rain during this period (114 mm), while soil evaporation was 48% of rainfall. Combined interception and soil evaporation losses for the whole growing season accounted for 49% of total evapotranspiration. Scope exists to reduce soil evaporation by managing crops for early canopy closure, but this will mean greater rainfall interception losses and reduced replenishment of soil water.