Sugarcane evapotranspiration and irrigation requirements in tropical climates

Irrigation is necessary to help meet the high demand for water by sugarcane in several countries including Brazil and Australia. The crop irrigation requirements are typically estimated using the crop coefficient-reference evapotranspiration (Kc-ETo) procedure. Sugarcane evapotranspiration rates were measured in three different sugarcane-producing regions of the world, and crop coefficients (Kc) were derived for those diverse environments, irrigation methods, and farming systems, therefore representing a robust basis for irrigation management. We also verified the occurrence of the inverse relation between Kc and ETo found in previous studies. Two experiments in Brazil and one in Australia were used for the analysis. Our data showed that Kc for a full canopy cover was lower than 1.0 in the three experimental sites and that sugarcane evapotranspiration (ETc) seems to be limited and exceeds ETo only when this is below 4 mm day−1. In one of the Brazilian experiments, Kc declined at higher rates than in the other two experiments, and for the three sites, average Kc was 0.77 and 0.87, respectively, for initial and full cover phase when ETo > 6 mm day−1. The increase of aerodynamic and other upstream resistances to water transport of plants appears to be one of the reasons for Kc to decrease at high levels of ETo. Based on our data and the literature, the Kc values provided by Allen et al. (1998) could overestimate the irrigation needs of sugarcane under high evaporative demand conditions. Irrigation management based on Kc should use the average ETo from the preceding 3 days before irrigating to save water and energy while maintaining high yield levels.