Crescimento, trocas gasosas e produtividade da beterraba em função de doses de substâncias húmicas e salinidade hídrica

Abstract

Beta vulgaris L. is one of the main vegetables grown in Brazil, being rich in vitamins, fibers, anticancer and anti-oxidants agents. The development of strategies to mitigate the effects of saltwater irrigation on agricultural production may be a viable alternative to increase crop productivity in the Brazilian semiarid region. The objective of this study was to evaluate the effects of the humic substance to reduce the effects of irrigation water salinity on growth, physiological responses and beet production. The experiment I was arranged in randomized blocks, adopting the factorial scheme of 6 x 4, referring to the electrical conductivities (CEa of 0.5, 1.5, 2.5, 3.5, 4.5, 5.5 dS m-1 ), and four rates of humic substance (SH) (0; 10; 20; 30 ml per plant) with 3 replicates. SH was applied via fertigation at 15, 45 and 75 days after emergence. Experiment II was arranged in randomized blocks, adopting the factorial scheme of 6 x 4, referring to the electrical conductivities (CEa of 0.5, 1.5, 2.5, 3.5, 4.5, 5.5 dS m-1 ), and four SH rates (0, 30, 70, 140 ml per plant) with 3 replicates. SH was applied via fertigation at 7, 26 and 45 days after transplantation. For the data processing, the statistical package SAS® . The variables evaluated in experiment I and II were: EC and soil pH, growth (height, number of leaves and leaf area), physiological responses (stomatal conductance, rate of carbon assimilation, transpiration and internal carbon concentration), and yield (tuber diameter, tuber weight, total soluble solids, pH, fresh and dry shoot and root matter). In experiment I, the beet tolerated the salinity of the irrigation water until the electrical conductivity of 5.5 dS m-1 demonstrating that it presents good maintenance of the photosynthetic activity under low salinity exposure, producing satisfactorily until the salinity 5.5 dS m-1 , thus being a plant resistant to the salinity of irrigation water. Humic substances up to the 30 ml rate did not provide satisfactory results in attenuating the effects of salinity on the beet crop. In experiment II, the beet tolerated irrigation water salinity up to the electrical conductivity of 5.5 dS m-1 , with no derogatory growth response, gas exchange, shoot and root length, and shoot and root fresh and dry matter, thus being a plant tolerant to the salinity of irrigation water. The use of humic substances in adjusted doses can be used to attenuate the effects caused by the salinity of the irrigation water in the beet crop.