Evapotranspiration and irrigation requirements of a coffee plantation in southern Brazil

Crop evapotranspiration (ETc) was measured as evaporative heat flux from a drip-irrigated coffee (Coffea arabica) plantation with 5-year-old trees using the Bowen ratio-energy balance technique. Crop transpiration (T) was determined with the stem heat balance method. Irrigation requirements were determined by comparing the ETc and T with reference evapotranspiration (ETo) derived from the Penman-Monteith equation and expressed as the ETc/ETo (Kc) and T/ETo (Kcb) ratios. Also, relationships were established between ETc and T and class A pan evaporation (ECA). The influence of inter-row vegetation on ETc was analysed, since the measurements were taken in a period of transition between dry-wet seasons. The average Kc value obtained was 1.00. The strong Coupling Of coffee plants to atmospheric conditions and high sensitivity of coffee plants to large vapour pressure deficits and air/leaf temperatures caused variations in Kcb in relation to ETo. Kcb ranged from 0.67, when ETo exceeded 4 mm d(-1), to 1.27 when ETo was less than 2 mm d(-1). When vegetation did not occupy the inter-row ground spaces, T represented about 0.87ETc, but 0.68ETc when ground vegetation filled the inter-row spaces.