Brackish water irrigation strategies and potassium fertilization in the cultivation of yellow passion fruit

The high concentration of salts in water sources in the semi-arid region of the Brazilian Northeast stands out as one of the limiting factors for the expansion of irrigated cultivation of fruit crops. Thus, the search for a strategy capable of mitigating the effect of saline stress on plants is of paramount importance. In this context, the objective of this study was to evaluate the gas exchange and yield of yellow passion fruit cultivated under brackish water irrigation strategies and potassium fertilization in two production cycles. The experiment was conducted under field conditions, using the randomized block design in a 6 x 2 factorial scheme, corresponding to six strategies of irrigation with brackish water applied in the different phenological stages of the crop: WS - without stress, irrigation with low-salinity water throughout the crop cycle; irrigation with high-salinity water only in the vegetative stage - VE; flowering stage - FL; fruiting stage - FR; and successively in the vegetative and flowering stages - VE/FL; and vegetative and fruiting stages - VE/FR, and two potassium doses (60 and 100% of the recommendation), with four replicates and three plants per plot. In irrigation, water with high (4.0 dS m(-1)) or low (1.3 dS m(-1)) electrical conductivity was used. The potassium dose of 100% recommendation corresponded to 345 g of K2O per plant per year. The yellow passion fruit 'BRS GA1' was more sensitive to salt stress applied successively in the vegetative and flowering stages and vegetative and fruiting stages, showing reductions in the intercellular CO2 concentration, CO2 assimilation rate, instantaneous water use efficiency, number of fruits, and yield. Irrigation with water of 4.0 dS m(-1) in the fruiting stage is a promising strategy, as it does not compromise production. The dose of potassium equivalent to 60% was better than 100% of recommendation in terms of gas exchange and yield.