Assessing sugarcane evapotranspiration based on a biophysical approach

Brazil is the largest producer of sugarcane in the world; due to the increased use of irrigation systems in sugarcane fields, it is important to search for methods to assist with the rational use of irrigation water. Among the methods used to quantify transpiration, the Penman-Monteith (PM) method is based on a strong biophysical approach. The study aimed to use the PM method as a basis for estimating the crop transpiration of sugarcane. The experiment was conducted in an experimental area of 2.5 ha, irrigated by center pivot. To use the PM model, it was necessary to use sub-models for estimating the crop aerodynamic resistance (ra), the canopy energy balance (Rnef), vapor pressure deficit in the crop environment (Δe), and canopy resistance (rc). When relating Rg with Rnef and net radiation from above the cane field, there is an R2 of 0.85 and 0.84, respectively. Ra was strongly influenced by the wind speed and the proposed rc sub-model performed well, with an R2 of 0.62. To quantifying the temperature of the canopy can determine Δe variable of PM model and the sub-model used to estimate the temperature of the canopy presented an R2 of 0.84. PM model was relating with transpiration measured by sap flow sensors and presented a R2 of 0.72 and relating the evapotranspiration measured with the method of the Bowen ratio (BRM) with the ETc model proposed, there is an R2 of 0.54, and an angular coefficient of 1.09.