Optimizing fertilization timing and composition for young ‘Medjool’ date palms in a hyper-arid environment

Fertilization guidelines for young ‘Medjool’ date palms during the 4–5 year establishment phase remain poorly defined, particularly where saline groundwater supplies substantial potassium (K). We conducted a six-year field experiment (2018–2024) in the southern Arava Valley, Israel, with tissue-cultured palms receiving five treatments: unfertilized control (NF), nitrogen+phosphorus without K (NP), nitrogen+K without phosphorus (NK), continuous full fertilization (NPK), and delayed NPK beginning in year 4 (NF+). Soil and leaf nutrients, vegetative growth, inflorescence production, and yield were monitored. Fertilization containing nitrogen was associated with the strongest response: NP and NK produced 65% and 75% higher cumulative yield than NF across the first three bearing seasons (2022–2024; p < 0.001), while NP and NK did not differ (p = 0.16). K fertilization provided no yield benefit because irrigation water supplied 1.9–2.6 kg K per tree annually during bearing years; soil and leaf K remained adequate without K fertilizer. Delayed NPK produced rapid leaf-N recovery, but reproductive recovery lagged: in 2022, NF+ leaf N matched NPK whereas inflorescence production reached only 53% of NPK. Annual yield converged by 2024, but NF+ cumulative yield remained 20% below NPK over 2022–2024 (p = 0.006). These results indicate that K-rich irrigation water can remove the need for K fertilization, but early N-containing fertilization should not be delayed because early N stress can reduce cumulative yield during the first bearing years.