Cultivo hidropônico de pimentão com águas de rejeito de dessalinizadores e com biofertilização

Abstract

The rejects of desalinators installed in the region are an alternative, since they can be used in production systems with appropriate technologies for promoting the mitigation of injuries caused by the excess of salts. Accordingly, the use of hydroponics can join this scope, considering the possibility of facilitating the leaching of the excess of salts by increasing the drainability of the substrates, in addition to the accurate control of the salinity of the nutrient solution supplied to the plants. Furthermore, the inclusion of organic matter through the biofertilizer in cultivation systems may potentiate crop tolerance to salt stress, for example. The biofertilizer composition can promote chemical, physical and biological improvements in the substrates, favoring the nutritional balance, the water absorption and the tolerance to diseases. Therefore, this research was designed aiming at evaluating the salinity concentrations in water and the biofertilizer dosages and interactions in pepper cultivation in an open hydroponic system. The study was conducted at the Teaching, Research and Extension Unit (in Portuguese, Unidade de Ensino, Pesquisa e Extensão - UEPE), an area which belongs to the Federal Institute of Education, Science and Technology of Ceará – (in Portuguese, Instituto Federal de Educação, Ciência e Tecnologia do Ceará – IFCE), located in Limoeiro do Norte, Ceará, Brazil. The experimental design was a randomized block in a factorial 5 x 4, for five different saline water concentrations (0.5, 1.5, 3.0, 5.0 and 7.5 dS m-1); three doses of biofertilizers in the nutrient solution (50, 100 and 150% of the recommended dosage) and one additional solution (the recommended one for hydroponics in pepper culture) with 4 replications, totalizing 80 experimental units, with three plants being used per plot. Growth and production variables, the measurement of water requirements for the drainage lysimeter, the efficient use of water and the gas exchange in fully mature leaves through a portable infrared gas analyzer were investigated. It has been found that the growth and production variables and the gas exchange suffered a significant influence of the increased salinity and of the interaction with the biofertilizer. It was possible to observe a linear decline in all variables with the increasing salinity. Likewise, the more the level of salinity of the irrigation water increased, the bigger was the decrease in crop evapotranspiration. In contrast, there was an increased efficiency in water use. It was found further increase in the salt content in the water drained from the application of the biofertilizer. In the conditions in which this study occurred, the biofertilizer did not attenuate the deleterious effects of salinity as far as the production variables and the gas exchange are concerned. It is believed that the osmotic stress has been largely responsible for reducing the growth, the production and the gas exchange caused by the salinity to the peppers; and it is also responsible for the ability to perform with a certain efficiency the compartmentalization of ions at a cellular level.