Cultivo de hortaliças em substrato de fibra de coco sob estresse salino e aplicação foliar de ácido ascórbico

Abstract

The global shortage of water resources and the necessary food production induce the use of water of low quality in irrigation of crops or in hydroponics systems , even with losses of production. These losses are a consequence of the osmotic and ionic stress which in turn are directly related to the excess of salts in the soil solution or hydroponic nutrient solution. In addition, part of this loss is also attributed to oxidative stress, which occurs secondary. To minimize such losses, the use of exogenously applied antioxidants is cited in the literature as an alternative, with ascorbic acid (AsA) being one of the most important antioxidants. In this sense, the objective was to evaluate the effect of the interaction between the application of ascorbic acid via leaf and the salinity of the water used in the preparation of the nutrient solutions on the production of the crops. The works were developed in a protected environment at the Federal Rural Semi-Arid University, in the city of Mossoró-RN, in the cultivation of four vegetables (crisp lettuce, american lettuce, arugula and coriander) in a hydroponic production system using coconut fiber as a substrate. Two stress conditions were obtained with and without the addition of NaCl in the preparation water of the nutrient solution. An application of AsA per cycle was performed in five different concentrations (0, 0.25, 0.50, 0.75 and 1.00 mol L -1 ), the AsA was sprayed on the leaves, so that all were completely Wet. At the end of the production cycles the plants were harvested and the following variables were analyzed in each culture: crisp and American lettuces: fresh plant mass (FPM), stem length (LENG), number of leaves (NL), diameter of Stem (DS), leaf area (LA) and dry mass of plants (DMP); Arugula: fresh plant mass (FPM), plant height (HEIG), dry mass of plants (DMP) and leaf area (LA); Coriander: fresh plant mass (FPM), plant height (HEIG), number of stems per plant (NSP) and dry mass of plants (DMP). The response of the foliar application of ascorbic acid on the production variables was dependent on the culture, the stress condition and the concentration of AsA used. For the crisp lettuce in the plants under stress, it was observed that the production variables behaved increasing form to the concentration of 0.5 mol L -1 . The interaction of the factors on the American lettuce culture influenced the FPM, LA and DMP, but in a negative way, thus reducing the production. The application of AsA in the arugula culture provided increases in the FPM and HEIG variables up to the concentration of 0.6 mol L -1 . The beneficial effect of AsA was observed up to the concentration of 0.5 mol L -1 in the FPM, HEIG and DMP, only in non-stressed coriander plants.