Respostas fisiológicas, nutricionais e produtivas em plantas de feijão-de-corda cultivadas sob fontes de adubos

Abstract

The aim of this study was to evaluate the biometric, physiological, productive aspects and the nutrients accumulation in cowpea shoot (Vigna unguiculata), grown under different fertilization. The experiment was carried out in a greenhouse, it was arranged in a randomized block design , in a factorial scheme (4 x 5 + 2), and consisted of four organic fertilizers: (composed of sewage sludge, green coconut shell, carnauba straw and sewage sludge biochar), at 100, 200, 300, 400 and 500 g vase-1, and two additional control treatments (without fertilization and with chemical fertilization), with five replications, totalizing 110 plants. We evaluated biometric variables: height, stem diameter, leaf area, dry mass (shoot: SDM and root dry mass: RDM), and relative chlorophyll index (RCI); gas exchange variables: photosynthetic rate, stomatal conductance, transpiration, instantaneous carboxylation efficiency and water use efficiency; production variables: pod length, number of pod, pod weight, seed number per pod and production; and nutrients accumulation (macronutrients, micronutrients and heavy metals). Biometric variables were increased, mainly by carnauba straw and green coconut shell, it was found that the highest values obtained for these treatments were, respectively, for height (98.75 and 89.98 cm); stem diameter (5.61 and 5.88 mm); leaf area (3867 and 3497 cm²); relative chlorophyll index (50.32 and 53.84) and shoot dry mass (50.66 and 50.21 g) as well the most representative dose for these results was 300 g vase-1, except to RCI and SDM which 500 g vase-1 were the best dose. In relation to physiological variables, carnauba straw and green coconut shell were higher than the other ones, including the chemical treatment, which presented during the crop cycle, decreases in the gas exchanges. It is noteworthy that both in the biometric aspects and in the gas exchanges the treatment with biochar caused reduction in most of the variables evaluated. The productive aspects were increased by about 60%, mainly for the treatment with sewage sludge, green coconut shell and carnauba straw when compared with the one without fertilization. The order of nutrient accumulation in the shoot was Ca>N>K>Mg>S>P for macronutrients and Fe>Mn>B>Zn>Cu for micronutrients. Compounds from carnauba straw and coconut green promoted satisfactory results for growth, physiology, nutrition and production in cowpea culture, and are therefore viable alternatives that could substitute or complement chemical fertilization, when 300 g vase-1 of these treatments were used.