Medição e simulação dos fluxos de energia e evapotranspiração em solo cultivado com Brachiaria decumbens na microrregião de Garanhuns – PE

Abstract

The cultivation of grasslands in the state of Pernambuco stands out as the main source of supply of cattle in the region, responsible for the production of 953.2 million liters of milk in 2011. No different from other cultures, knowledge of the amount of water required by grazing at each stage of its development is an important factor for successful crop production. Therefore, quantifying evapotranspiration, even in rainfed agriculture is too important. Thus, the aim of this study was to quantify / estimate the evapotranspiration of Brachiaria grown in rainfed in the micro Garanhuns - PE, employing the methods of energy balance - Bowen ratio equation De Bruin & Holtslag (1982) and model SiSPAT. This work was conducted in the experimental area planted with Brachiaria decumbens in “Riacho do Papagaio” Farm, located in the county of São João - PE, located in the microregion of Garanhuns - PE. Data collection for estimation of evapotranspiration by the various methods proposed for this study was obtained from a micrometeorological tower installed in the experimental area, where they were measured: temperature and relative humidity at two levels above the canopy of pasture, net radiation , solar radiation, soil heat flux, wind direction and rainfall. Were also installed automated sensors for measuring temperature and volumetric soil moisture at depths of 0.10, 0.20, 0.30, 0.40 and 0.50 m. Were also carried out in the pasture the following determinations: height of vegetation (canopy), biomass accumulation, leaf area index and evolution of the root system. Crop evapotranspiration, determined by the energy balance - Bowen ratio and also the model followed SiSPAT variations in rainfall and averaged 1.5 mm d-1 and 1.4 mm d-¹, respectively. By equation De Bruin & Holtslag, evapotranspiration also followed the variations of rainfall and averaged 1.30 and 2.04 mm day-¹, when α was equal to 0.60 and 0.95, respectively. The SiSPAT model showed satisfactory performance by simulating the components of energy balance and evapotranspiration accumulated pasture under different atmospheric conditions and water availability to plants.