Biophysical controls of evapotranspiration in cowpea cultivation under different water regimes/ Controles biofisicos da evapotranspiracao em cultivo de feijao-caupi sob diferentes regimes hidricos

The objective of this study was to analyze the variations of the decoupling factor and the aerodynamic and stomatal conductances for cowpea subjected to different levels of water availability during the reproductive phenological stages of the crop. The study was conducted in the municipality of Castanhal located in the northeast of the state of Para, Brazil, in an area planted with cowpea, in 2013, 2014 and 2015 with four irrigation treatments: T100--replacement of 100% of the crop evapotranspiration (ETc); T50 replacement of 50% ETc; T25--replacement of 25% ETc; and T0--without any replacement (without irrigation). The interaction between the crop and the atmosphere in water vapor exchange was estimated through the decoupling factor ([OMEGA]), which was between 0.5 and 1, except for the treatment without irrigation, indicating a moderate to high decoupling between the crop and the atmosphere, so that the water vapor exchange process was controlled by the energy supply, instead of stomatal control. Key words: Vigna unguiculata (L.) Walp, decoupling factor, aerodynamic conductance, stomatal conductance Objetivou-se com esse trabalho analisar as variacoes do fator desacoplamento, das condutancias aerodinamica e estomatica para o feijao-caupi submetido a diferentes niveis de disponibilidade hidrica durante os estadios fenologicos reprodutivos da cultura. O estudo foi conduzido no municipio de Castanhal, situado no nordeste do estado do Para, em uma area cultivada nos anos de 2013, 2014 e 2015 com quatro tratamentos de irrigacao: T100--reposicao de 100% da evapotranspiracao da cultura (ETc); T50--reposicao de 50% ETc; T25--reposicao de 25% ETc; e T0--sem reposicao (sem irrigacao). A interacao entre a cultura e a atmosfera na troca de vapor d'agua foi estimada por meio do fator de desacoplamento ([OMEGA]), o qual esteve entre 0,5 e 1, exceto para o tratamento sem irrigacao, indicando um desacoplamento de moderado alto entre a cultura e a atmosfera, de modo que o processo de troca de vapor d'agua foi controlado pelo suprimento de energia, ao inves do controle estomatico. Palavras-chave: Vigna unguiculata (L.) Walp, fator de desacoplamento, condutancia aerodinamica, condutancia estomatica