RAINFALL INTERCEPTION AND EVAPORATION FROM SOIL BELOW A WHEAT CANOPY

Components of the seasonal pattern of water use by a wheat crop at Wag ga 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 evapora tion from soil below the canopy. Evaporation of intercepted rain was c alculated using an aerodynamic technique in conjunction with a canopy storage coefficient. Detailed measurements of soil evaporation and rai nfall interception commenced 80 days after sowing (DAS), when L approx imately 1, until 165 DAS. Interception losses accounted for 33% of rai n during this period (114 mm), while soil evaporation was 48% of rainf all. Combined interception and soil evaporation losses for the whole g rowing season accounted for 49% of total evapotranspiration. Scope exi sts to reduce soil evaporation by managing crops for early canopy clos ure, but this will mean greater rainfall interception losses and reduc ed replenishment of soil water.