Irrigation requirements and transpiration coupling to the atmosphere of a citrus orchard in Southern Brazil

Abstract

► Kc values varied from 0.65 during the summer to 0.24 during the winter due to the role of interrow vegetation and seasonal physiological changes of acid lime orchards. ► The transpiration represented 35% of overall orchard evapotranspiration , a value near the orchard area occupied by acid lime trees. ► The strong transpiration coupling to the atmosphere causes crop coefficients for tall orchards to reduce as ETo increases. ► The acid lime leaves reduced the stomatal conductance under high temperature, DPV and solar radiation and the strong transpiration coupling to the atmosphere enhanced this response pattern. Crop evapotranspiration (ETc) was measured as evaporative heat flux from an irrigated acid lime orchard ( Citrus latifolia Tanaka) using the aerodynamic method. Crop transpiration (T) was determined by a stem heat balance method. The irrigation requirements were determined by comparing the orchard evapotranspiration (ETc) and T with the reference evapotranspiration (ETo) derived from the Penman–Monteith equation, and the irrigation requirements were expressed as ETc/ETo (Kc) and T/ETo (Kcb) ratios. The influence of inter-row vegetation on the ETc was analyzed because the measurements were taken during the summer and winter, which are periods with different regional soil water content. In this study, the average Kc values obtained were 0.65 and 0.24 for the summer and winter, respectively. The strong coupling of citrus trees to the atmosphere and the sensitivity of citrus plants to large vapor pressure deficits and air/leaf temperatures caused variations in the Kcb in relation to the ETo ranges. During the summer, the Kcb value ranged from 0.34 when the ETo exceeded 5 mm d −1 to 0.46 when the ETo was less than 3 mm d −1 .