Morphophysiology of mini watermelon in hydroponic cultivation using reject brine and substrates

The objective of the study was to evaluate the growth and physiological aspects of the ‘Sugar Baby’ mini watermelon grown in a hydroponic system with different substrates and mixtures of reject brine in the preparation of the nutrient solution. For this purpose, the experiment was carried out in a plastic greenhouse, using a randomized block design, in a 5 x 4 factorial scheme, corresponding to the combination of five mixtures of reject brine (electrical conductivity EC = 9.50 dS m-1) and tap water (EC = 0.54 dS m-1) and four types of substrates (coconut fiber, sand, 70% sand + 30% rice husk and 40% sand + 60% rice husk), distributed in four replicates. Using the mixture of reject brine and tap water with EC above 4.00 dS m-1 to prepare the nutrient solution of mini watermelon plants markedly reduced their growth. Increments in carboxylation efficiency and activity in the electron transport chain act as tolerance mechanisms to compensate for the net photosynthesis of mini watermelon under salt stress. Coconut fiber promoted the best growth and photosynthetic activity for mini watermelon plants, while the substrate with 100% washed sand led to the lowest performance.