Termometria por infravermelho como indicador de estresse hídrico em plantas de feijão-caupi

Abstract

The objective of this study was to evaluate the use of infrared thermometry as an indicator of crop water stress to cowpea, from the difference between the temperature of the crop canopy and air temperature. Two experiments were conducted, one under controlled conditions, and the other, the field, both with four cowpea cultivars (BRS Potengi, BRS Nova Era, BRS Guariba e BRS Itaim). The test in the greenhouse was held in Dourados, MS, Brazil, in a completely randomized design with treatments arranged in a 4x2 factorial design, with four cultivars of cowpea and two water status (with and without water stress), with six replicates. To simulate the drought, there was the absence of irrigation. We evaluated the stomatal conductance, transpiration, intercellular carbon dioxide concentration, photosynthetic rate, efficiency of water use, leaf temperature, ambient temperature, the deficit of saturation pressure of vapor in air and solar radiation incident . In the field experiment, besides the above variables, we calculated the index of crop water stress in a drought period of fifteen days after rainfall, with readings at 38, 43, 48 and 53 days after sowing. According to the results, it can be concluded that water deficit in cowpea plants results in decreased stomatal conductance, transpiration, photosynthetic rate and intercellular carbon concentration, with a decrease to values close to zero for first three variables; stomatal closure in plants under water deficit is offset by the increase in instantaneous efficiency of water use; infrared thermometry can be used for indirect estimation of soil water availability in cowpea plants, based on the difference between leaf temperature and air; model water stress index for growing cowpea should take into consideration, besides the difference between leaf temperature and air temperature, the deficit of the saturation pressure of vapor in air and sunlight global incident, and that the proposed formula for the index of crop water stress of cowpea is valid for indirect measurement of plant water conditions.