Evapotranspiration and Transpiration Coupling To The Atmosphere Of Sugarcane In Southern Brazil.

Some of the traditional sugarcane areas and most of the expanding regions in Brazil, water stress is a limiting factor and irrigation is usually needed to assure economically viable yields. As around the world, agriculture is under pressure for improving the water use efficiency. Despite the great social and economic importance of sugarcane irrigation, few studies have been done in Brazil. This paper evaluated the water requirements of a sprinkler-irrigated sugarcane crop based on three different spatial scales: the whole field evapotranspiration, plants and leaves transpiration. The Bowen ratio method (BRM) was used to evaluate the mass and energy exchanges over the field, further computing the field evapotranspiration (ETc). Sap flow by heat balance methods installed in four representative stalks was used to evaluate the water use at the plant scale, and an infra-red gas analyzer (IRGA) 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 were observed under conditions of strong crop-atmosphere coupling together with high solar radiation. The stomatal conductance ranged from 0.01 and 0.40 mmol/m²s daytime in dry and wet seasons respectively, showing a remarkable sensitivity to the vapour deficit pressure and wind speed. BRM gave ETc ranging from 3.7 to 4.4 mm/day, sap flow varied from 0.3 to 0.6 L/stalk/day and leaf transpiration among 3.4 and 4.2 mm/day. This study provides a new theoretical basis to improve crop water management of sugarcane in Brazil.