Demanda hídrica do feijão Caupi no nordeste paraense.

Abstract

The knowledge about water needs of crops of great importance for the study of irrigation water management and evapotranspiration are the top main variables of the hydrological cycle. The evapotranspiration of a crop can be measured by lysimeters, or estimated through empirical equations. The use of models related to evapotranspiration allows the establishment of a relationship between the knowledge about the physiological processes that determine yield and irrigation. The main objectives envolve the estimation of the reference evapotranspiration (ETo) for municipalities that produce cowpea, the determination and estimatation of the crop evapotranspiration (ETC) and the crop coefficients (Kc) for the different stages of cowpea. Thereby, a series of data was collected from an automatic meteorological station that belons to the National Institute of Meteorology (INMET). Then, methods of estimation of reference evapotranspiration (ETo) were compared with the Penman-Monteith method FAO 56 for cowpea producers municipalities. The ETC of the cowpea was determined through drainage lysimeters and by the Bowen ratio method. After, it was estimated by the Penman-Monteith indirect method. For the municipalities of Tracuateua, Bragança, Capitão Poço e Castanhal, the Turc method, Blaney-Criddle-FAO24 and the Multiple Regression function presented the best evaluations for all the statistical criteria, requiring no further adjustments; the Priestley-Taylor, Makking and FAO 24 methods presented excellent results after adjustments. Thus, adjusted equations can be used in the study region. The Camargo and Hargreaves-Samani method obtained the worst evaluation for all municipalities and for all criteria comparison with the other methods. The total water consumption of cowpea was, on average, 267.73 mm day¹. On average during the cowpea cycle, the was 0.66, indicating that the cowpea crop does not decouple completely from the atmosphere under the climatic conditions of Castanhal Pará. The Kc of the cowpea presented an average value of 0.8 in the vegetative phase, 1.4 during the reproductive phase, reaching the final stage with an average value of 0.5. The Penman-Monteith model, with a canopy resistance proposed by Ortega-Farias (1993) (rcO), can be used to estimate the evapotranspiration of cowpea cultivated under the edaphoclimatic conditions of Castanhal Pará. On a daily scale, the model presented greater precision and accuracy for LAI conditions ≥ 3. However, the Penman Monteith model achevied a better estimation for the evapotranspiration of cowpea with the canopy resistance (rc1) estimated from the conductance (gf) proposed by Lima et al. (2016, p.547).