Actual evapotranspiration and response factors of the cowpea in Amazonian edaphoclimatic conditions¹

Evapotranspiração real e fatores de resposta do feijão-caupi nas condições edafoclimáticas Amazônica

HIGHLIGHTS:

For the cowpea cultivar BR3-Tracuateua, the phenological stage with the greatest water demand was the flowering stage.

The flowering phenological stage showed the highest sensitivity to water deficit, with a response factor of dry biomass of 2.03.

Cowpea BR3-Tracuateua showed high sensitivity to water deficit, with a Ky of 1.48.

ABSTRACT

Due to the sensitivity of the cowpea to water deficit during the dry season in the Amazonian environment, there is a need for studies related to water management and the optimization of annual yield. Thus, the objective was to estimate the crop evapotranspiration (ETc) and the actual evapotranspiration (ETr), whilst also evaluating the effect of different irrigation depths on the yield response factor (Ky) and dry biomass (Kss) of the cowpea cultivar BR3-Tracuateua under edaphoclimatic conditions in the Amazon region. The experiment was carried out in randomized blocks, with six replicates and four treatments: T1 (100% ETc), T2 (50% ETc), T3 (25% ETc), and T4 (0% ETc), commencing in the reproductive phase with a drip irrigation system. The total evapotranspiration recorded for the cowpea cultivar BR3-Tracuateua across the four treatments was 337.5, 284.35, 258.62, and 219.82 mm with an average consumption of 4.6, 3.90, 3.54, and 3.01 mm d^-1 for T1, T2, T3, and T4, respectively. The emergence phase showed evaporation rate of 5.19 mm d^-1 and the reproductive, vegetative, and senescence ETc phases showed evaporation of 4.87, 4.84, and 3.32 mm d^-1, respectively. The flowering stage had the greatest water demand (5.88 mm d^-1). There was a significant difference in the crop yield among all treatments, with decreases of 18.91, 33.12 and 57.17% for T2, T3 and T4 in the grain yield, with a Ky of 1.48, and Kss of 2.03, 1.08, and 0.87 for the flowering, grain filling, and physiological maturation stages, respectively.

Key words:
Vigna unguiculata (L.) Walp; sensitivity coefficient; water deficit; water balance; water demand