Relações hídricas em espinafre (Spinacia oleracea L.) cultivado com águas salobras sob sistemas hidropônico e solo com e sem cobertura

Abstract

Due to the water scarcity, common in arid and semiarid regions, the use of brackish water in irrigation is common. However, the inadequate management of these waters, coupled with the climatic characteristics of the region, leads to soil salinization. This process causes a number of deleterious effects that affect the chemical, physical and biological characteristics of soil and, consequently, of crop itself. In general, vegetables are sensitive to abiotic stresses, while at the same time they play an important socioeconomic. Spinach (Spinacia oleracea L.) has high nutritional contents and is a crops that has been growing in the production of family agriculture, either by conventional or hydroponic cultivation. In this work, the objective was to compare the water, physiological and productive aspects of spinach (Spinacia oleracea L.) cultivated with and without soil, arrogating brackish water in the growing process. For this, an experiment was carried out with a randomized block design, with four replications in a 6 x 3 factorial arrangement, with six (6) levels of sodium chloride concentrations in terms of electrical conductivity of 0; 1.5; 3.0; 4,5; 6 and 7 dSm-1 and 3 (three) cultivation systems, two of them in soil, one with plastic mulching and the other without cover, and the third cropping system was represented by the floating type hydroponic model. The potentials of water in the three cropping systems and in spinach were determined, besides associating them with variables of growth and water consumption (discussed in chapter II), as well as parameters of gas exchange, chlorophyll fluorescence and photosynthetic pigments of spinach (Chapter III). The data were submitted to analysis of variance by the F-test (0.05) and when a significant effect was verified, the regression analysis was performed in relation to the different levels of salinity and the analysis of means comparison by the Tukey test at 5 % probability. The main variables analyzed were soil (osmotic), plant potential (leaf and osmotic water potential) and nutrient solution (osmotic potential), leaf area, biomass, gas exchange parameters, chlorophyll fluorescence and photosynthetic pigments. The results showed that there was a reduction in potentials of spinach and soil with an increase in electrical conductivity, being the smallest reductions for the hydroponic system. The three systems showed increased osmotic adjustment with increased salinity of water. The relative water content reduced linearly for the three systems adopted, while there was an increase in leaf succulence due to the reduction of the systems potentials. The hydroponic system showed higher efficiency of water use followed by soil with plastic mulching and soil without cover. There was a reduction of the photosynthetic pigments, as well as the parameters of gas exchange of the spinach due to the increase of the salinity. The chlorophyll a fluorescence only showed a difference between the systems adopted. The potentials of water in the system and spinach is an important tool for monitoring the water status of the crop and the use of techniques such as hydroponics and plastic mulching are important to reduce the effects of the use of brackish water in spinach, in addition to providing greater efficiencies of water use.