Evapotranspiration and Transpiration Coupling to the Atmosphere of Sugarcane in Southern Brazil: Scaling Up from Leaf to Field

Abstract

In some of the traditional areas growing sugarcane and in most of the expanding regions in Brazil, water deficit stress is a limiting factor and irrigation is usually needed to assure economically viable sugarcane yields. This research evaluated the water requirements of a drip-irrigated second ratoon sugarcane crop based on three different spatial scales: field, plant and leaf. The Bowen ratio method (BRM) was used to evaluate the mass and energy exchanges over the field, further computing the crop evapotranspiration (ETc). Sap flow by heat balance method installed in four representative stalks was used to evaluate the water use at the plant scale, and an infra-red gas analyser was used to evaluate leaf transpiration and stomatal conductance at the leaf scale. Comparing ETc and reference evapotranspiration we found that the crop coefficients for dry and wet seasons were 0.81 and 0.98, respectively. Evapotranspiration peaks of 7 mm day⁻¹ were observed under conditions of strong crop-atmosphere coupling and high net radiation values. The stomatal conductance ranged from 0.09 to 0.19 mmol m⁻² s⁻¹ in dry and wet seasons respectively, showing sensitivity to the atmospheric conditions, notably the vapour deficit pressure and wind speed. BRM ranged from 3.7 to 4.4 mm day⁻¹ and leaf transpiration ranged among 3.4 and 4.2 mm day⁻¹. In an irrigated sugarcane production area in Brazil, water consumption of the sugarcane crop was highly correlated with atmospheric conditions.