Estratégias de irrigação com águas salinas, adubação nitrogenada e potássica no cultivo de mini-melancieira.

Abstract

The watermelon is a crop that has great importance in Brazil, due to its economic and social return, being cultivated mainly in the Northeast region. However, in this region, problems of water and/or soil salinity commonly occur, which affect the yield of plants. Thus, the use of water salinity management strategies associated with nitrogen and potassium fertilization management stands out as an alternative to reduce the effects of salt stress on watermelon plants. In this context, this research aimed to evaluate the use of salinity management strategies and nitrogen and potassium fertilization in the 'Sugar Baby' mini-watermelon crop. The research was divided into two experiments (I and II), conducted in a protected environment at the Center for Technology and Natural Resources belonging to the Federal University of Campina Grande – Paraíba, analyzed through the experimental design in randomized blocks. In experiment I, six salinity management strategies were evaluated [application of low (CEa = 0.8 dS m-1) and high (CEa = 3.2 dS m-1) waters at different phenological stages of the crop] and two nitrogen doses (50 and 100% of the N recommendation), with five repetitions. In experiment II, eight salinity management strategies were evaluated [application of low (CEa = 0.8 dS m-1) and high (CEa = 4.0 dS m-1) waters at different phenological stages of the crop ] and three doses of potassium (50, 100 and 150% of the K2O recommendation), with three repetitions. In experiment I, mini-watermelon plants cultivated under salt stress successively in the vegetative and flowering phases were more sensitive, with significant reductions, mainly in gas exchange, photosynthetic pigments, yield and postharvest fruit quality, between nitrogen doses , the dose of 50% of N favored the photosynthetic activity, resulting in greater growth of stem diameter and number of leaves, and production per plant, increasing the polar and equatorial diameters of the fruits. The salt stress in the vegetative and flowering phases increases the anthocyanin content in the fruits. For experiment II, in general, gas exchange and growth rates were more sensitive to salt stress in the flowering, fructification and fruit maturation phases; the dose of 50% of K2O provided higher values for these parameters, while for the fluorescence of chlorophyll a, the increase in the doses of K2O associated with salt stress reduced these variables mainly in the vegetative and flowering phases, as for the dry biomass, the salt stress in the vegetative, vegetative/flowering, fructification, flowering/fruiting phases, caused decreases in the accumulation of biomass, for production, irrigation with water with electrical conductivity of 4.0 dS m-1in the flowering and maturation phases of fruits can be a promising alternative for the cultivation of mini-watermelon, as it did not affect this parameter, and in relation to the postharvest quality of mini-watermelon fruits, the salt stress imposed in the vegetative and flowering/fruiting phases associated with increased fertilization reduced fruit quality in terms of soluble solids and ascorbic acid.