Gas exchange and photochemical efficiency of guava under saline water irrigation and nitrogen-potassium fertilization

Abstract

The objective of this study was to evaluate the effects of different combinations of nitrogen and potassium fertilization on gas exchange and chlorophyll a fluorescence in seedlings of guava cv. Paluma irrigated with water of different salinity levels. The experiment was set up in a randomized block design and analyzed in 5 × 4 factorial scheme, with four replicates. The treatments were composed of the combination of the factor electrical conductivity of irrigation water-ECw (0.3, 1.1, 1.9, 2.7, and 3.5 dS m-1), with the factor combinations (C) formed from recommended doses of nitrogen (N) and potassium (K2 O), 70% N + 50% K2 O, 100% N + 75% K2 O, 130% N + 100% K2 O, and 160% N + 125% K2 O. The fertilization combination 130% N + 100% K2 O mitigated the effects of salt stress up to mean ECw of 1.3 dS m-1, resulting in increments in CO2 assimilation rate, transpiration, instantaneous carboxylation efficiency, and electron transport rate. For maximum quantum efficiency of photosystem II, only treatment irrigated with ECw 3.5 dS m-1 under the combination 160% N + 125% K2 O showed damage to the photosynthetic apparatus.