Yield and fruit quality responses of ‘Kabkab’ date palm (Phoenix dactylifera L.) to potassium and iron fertilization under calcareous soil conditions

This two-year field study (2021–2022) evaluated the effects of soil-applied potassium sulfate (K₂SO₄; 45% K₂O) and trunk-injected ferrous sulfate heptahydrate (FeSO₄·7 H₂O) on yield, fruit quality, and leaf mineral composition of ‘Kabkab’ date palm under calcareous, semi-arid conditions. Forty-eight 20-year-old palms were arranged in a factorial randomized complete block design with K₂O at 0, 400, 800, and 1200 g palm⁻¹ and FeSO₄·7 H₂O at 0, 11, and 23 g L⁻¹ (1.0 L per palm per application). Injections were performed once per season (two injections in total over the study). Potassium and iron each affected fruit set, total yield, bunch traits, fruit weight, and sugar indices, and several traits exhibited K × Fe interactions. A representative treatment (400 g K₂O combined with 11 g L⁻¹ FeSO₄·7 H₂O) achieved up to 64.4 kg palm⁻¹ in total yield and a mean fruit weight of 17.1 g. Higher K inputs tended to increase total soluble solids and sugars, whereas responses of some physical attributes plateaued at the upper rates. Leaf K, Fe, Zn, and Cu generally increased with fertilisation, while Mn decreased at higher rates. Within the limits of this study, moderate nutrient rates can support productivity and selected quality attributes of ‘Kabkab’ date palm on calcareous soils. Outcomes are site- and cultivar-specific and should be verified across additional locations, seasons, and Fe formulations before broad recommendation.