The right combination of N-P-K fertilization may mitigate salt stress in custard apple (Annona squamosa L.)

Salt stress is the cause of low yield in many arid and semi-arid regions. Strategies to increase crop yields in salt stress conditions are very important, especially in systems with higher production costs, such as irrigated fruticulture. This study proposes to assess the photosynthetic efficiency and growth of Annona squamosa irrigated with saline water under different doses of nitrogen, phosphorus, and potassium fertilization. The assay was conducted in a greenhouse and consisted of two factors, which corresponded to two electrical conductivity of water (ECw) (0.8 and 3.0 dS m−1) and eight combinations of fertilization with nitrogen, phosphorus, and potassium ranging from 100 to 140% of the recommended dose, arranged in a 2 × 8 factorial scheme, with three replicates. Plants were evaluated for growth, chlorophyll a fluorescence, gas exchanges, and production over a period of 1 year. The photosynthetic efficiency in the vegetative stage of A. squamosa plants is the most affected by salt stress. Stomatal closure and damage to the quantum efficiency of photosystem II are the main factors responsible for the reduction of photosynthesis and growth. In the reproductive stage, A. squamosa plants acclimated to salt stress, with no effect of salinity on the photochemical efficiency and stomatal conductance, but the damage to photosynthesis was not reversed and contributed to reducing production. The fertilizer combination C6 (140:100:140% or 56:60:84 g plant−1 year−1 of N:P2O5:K2O) is recommended to mitigate salt stress and increase A. squamosa production.