Evaluation of the effect of chelate fertilizer application-based fertilization programs on improving the quantity and quality of date palm fruit of the Estemaran cultivar (Phoenix dactylifera L.) under natural heat stress conditions

A comprehensive review of existing literature indicates the advantageous impacts of nano and chelated fertilizers-based fertilization programs on a variety of fruit crops. However, there is a notable paucity of information regarding the efficacy of advanced chelated fertilizers in enhancing both the productivity and fruit quality of the Estemaran date cultivar, particularly under extreme heat conditions prevalent in Khuzestan province. Consequently, the present study was undertaken to assess the effects of applying an advanced chelated fertilizer on yield, fruit quality, and heat-stress tolerance of the Estemaran cultivar in field conditions. This experiment was conducted during the 2023–2024 growing season, involving date palms (cultivar Estemaran) located in Ahvaz, Khuzestan, Iran. The experiment was designed as a completely randomized block design with three replications. The treatments evaluated included: (1) a control group with no fertilization, (2) fertilization using the conventional method employed in Khuzestan province, (3) Fertilizing with KHAZRA Advanced Nano-chelate fertilizer through deep banding and irrigation, and (4) Fertilizing with Advanced Nano-chelate fertilizer through deep banding and foliar spraying. Analysis of variance revealed statistically significant differences among the various fertilization methods regarding the traits examined. The findings indicated that the treatment involving advanced chelate fertilization applied into the planting deep banding, in conjunction with irrigation, resulted in the highest proportion of active green leaves to total leaves per tree (56.15, 27% increase compared to the control). Additionally, this treatment produced the highest fruit yield of 56.1 kg per palm (30% increase compared with the control), and exhibited an antioxidant capacity of 1.39 mmol Fe(II) per 100 g of fresh weight (7% increase compared with the control). Furthermore, the highest mean leaflet length recorded was 30.67 cm (11% increase relative to the control), as well as an optimal flesh-to-kernel ratio of 8.30 (25% enhancement compared to the control), attributed to the conventional fertilization treatment in Khuzestan province. Given that fruit yield is paramount in date production, it appears that the application of advanced chelate fertilization into the planting deep banding, along with irrigation and foliar spraying, significantly improved growth characteristics, yield, and fruit quality of the Estemaran cultivar under the region’s heat-stress conditions by enhancing nutrient availability to the plant. Consequently, cultivating the Estemaran cultivar under the typical heat-stress conditions of Ahvaz, while employing advanced chelate fertilization in conjunction with irrigation to mitigate the adverse effects of stress, is likely to result in acceptable fruit yields for commercial production. At the molecular level, advanced chelate fertilization produced gene-specific changes in HSP expression. T2 showed the highest expression of PdHSP17.6 and PdHSP22, whereas T3 exhibited the highest PdHSP26.5 expressions. In contrast, the unfertilized treatment showed the strongest induction of PdHSP23.6, together with the highest proline and malondialdehyde contents and the lowest fruit yield. Therefore, considering the results obtained and their implications for yield, which is a primary objective in date production, it appears that fertilization with advanced chelate applied as a pit application and through irrigation (and foliar spray) significantly enhances growth characteristics, yield, and fruit quality by increasing nutrient availability to the plants.