Evapotranspiração de pastagem degradada de capim braquiária na Região de Cruz das Almas, Bahia

Abstract

Brachiaria decumbens belongs to the family Poaceae, widely used as pasture in Brazil, especially in the Northeast region, due to the soil and climate conditions favorable to its cultivation. It is known that the determination of crop evapotranspiration (ETc) is of great importance for the efficient use of water. However, there is still no information on the water requirement of the crop for the region in order to establish an irrigation management. Within this context, it is essential to carry out studies that reveal the real water requirement of Brachiaria decumbens and should be supported by appropriate indications of evapotranspiration, allowing its rational use in the crop. The main objective of the present study was to estimate the wate consumption of Brachiaria decumbens cultivated under conditions of the coastal trays of the Cruz das Almas / BA region. The study was carried out between September 2016 and April 2017. To determine the evapotranspiration, the energy balance methods were used by the Bowen ratio system, soil water balance from the use of TDR probes and via remote sensing from the Model METRIC. The reference evapotranspiration was estimated by the FAO Penman-Monteith method. Calibrations were performed on the moisture sensors TDR hand-held probes and CS 616. Before the data processing of the Bowen ratio system, they were evaluated from validation guidelines. The calibration of the CS 616 hand-held probes and sensors carried out in this research confirms the need for a specific calibration for each type of soil when precise determination is required. The equations for finding inconsistent data from guidelines were employed in the data obtained by Bowen's ratio with success for the area of Bracchiaria decumbens. Comparing the energy balance methods by the Bowen ratio system and soil water balance from TDR probes in the subperiods, the total values obtained were 518 and 438 mm for the energy balance and soil water balance respectively, With a difference of 15%. On the dates when the instantaneous flows were estimated using the METRIC method, it reinforced the confidence of the model. The daily evapotranspiration by the METRIC method obtained a difference of 20 and 12% in relation to the energy balance methods from the Bowen ratio system and soil water balance by TDR probes, respectively.