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Water scarcity is a major constraint in arid and semi-arid regions. Crops that require less irrigation water and those, which are considered drought-tolerant such as date palm (Phoenix dactylifera L.), are dominant in these regions. Despite the tolerance of these crops, the development of technologies that ensure efficient use of irrigation water is imperative. Taking these issues into consideration, the study was conducted to investigate the impact of limited irrigation water using a new subsurface irrigation system (SSI) on gas exchange, chlorophyll content, water use efficiency, water productivity, fruit physicochemical characteristics, and yield of date palm (cv. Sheshi). The impact of the SSI system was compared with two surface irrigation systems, namely, surface drip irrigation (SDI) and surface bubbler irrigation (SBI). The field experiment was carried out during 2018 and 2019 at the Date Palm Research Center of Excellence, King Faisal University, Kingdom of Saudi Arabia. The annual crop evapotranspiration (ETc) was 2544 mm. The applied irrigation water was set at 50%, 75%, and 125% of ETc for SSI, SDI, and SBI, respectively, which were based on the higher crop water productivity recorded in an initial field study. The total annual volume of water applied for SSI, SDI, and SBI was 22.89, 34.34, and 57.24 m3 palm−1, respectively. The crop water productivity (CWP) at the SSI system was significantly higher, with a value of 1.15 kg m−3, compared to the SDI (0.51 kg m−3) and SBI systems (0.37 kg m−3). The photosynthetic water use efficiency (WUE) was 10.09, 9.96, and 9.56 μmol CO2 mmol−1 H2O for SSI, SBI, and SDI, respectively. The maximum chlorophyll content (62.4 SPAD) was observed in SBI, followed by SSI (58.9 SPAD) and SDI (56.9 SPAD). Similarly, net photosynthesis and the transpiration rate were significantly higher in SBI and lowest in SSI. However, the SSI system substantially increased palm yield and enhanced fruit quality. The new SSI system, through its positive impact on the efficiency of irrigation water use and enhancement on fruit yield and fruit quality of date palm, seems quite suitable for the irrigation of palm trees in arid and semi-arid regions.

Water scarcity is very common in the arid region due to the low yearly rainfall. The cost of water for agricultural usage is extremely high in dry locations. Date palm is a high water-demanding tree throughout the year in arid regions. Therefore, the application of deficit irrigation strategies for date palm cultivation may significantly contribute to conserving irrigation water. The present study aimed to assess the effects of controlled deficit irrigation using two modern micro-irrigation systems on water use efficiency (WUE), gas exchange, fruit yield, and quality of date palm (Khalas cv.). The irrigation systems included drip irrigation (DI) and subsurface irrigation (SI) systems. The study was conducted during the 2020 and 2021 seasons at the Date Palm Research Center of Excellence, King Faisal University, Saudi Arabia. The meteorological variables of the study area were real-time monitored using cloud-based IoT (Internet of Things) to calculate the evapotranspiration reference (ETo) and control the irrigation scheduling. Three irrigation treatments (50, 75, and 100% ETc) were applied using DI and SI systems compared with the traditional surface bubbler irrigation (Control). The actual applied water at the deficit irrigation treatments of 50, 75, and 100% ETc were 27.28 ± 0.06, 44.14 ± 1.07, and 55.55 ± 0.37 m3 palm−1, respectively. At all deficit irrigation treatments, the leaf chlorophyll and gas exchange were significantly higher in the SI compared to the DI system. The yield of date palms did not differ significantly between the control and SI systems at both the level of 100 and 75% ETc. The WUE under the SI (1.09 kg m−3) was significantly higher than the DI system (0.52 kg m−3) at the 50% level. There was no significant difference regarding the fruit quality parameters between SI at 50% ETc and control at 100% ETc. Therefore, adopting deficit irrigation strategies using the SI system at 50% ETc level throughout the year could be suggested for date palm irrigation to save water, improve WUE, and maintain fruit quality.

Date palm is widely propagated through conventional offshoots. It is also produced through a tissue culture technique due to the limited number of offshoots produced throughout the course of a palm’s life. Being dioecious, it is a cross-pollinated tree that can be naturally or artificially pollinated. Tissue-cultured plants often have abnormal epigenetic or genetic changes that affect specific phenotypic characteristics. The growth of parthenocarpic fruits in date palms is mostly induced by hormonal imbalances in certain tissues. The major hormones in parthenocarpic fruits are auxins (IAA), gibberellins (GA3), and abscisic acid (ABA). Parthenocarpic, or abnormal fruit development, is an undesirable trait for date palm growers since it drastically reduces farm income. The current study was therefore conducted over two seasons to confirm previous observations and included conventional offshoot-derived trees (CO) and tissue culture-derived ones (TC) of the cultivar Barhee. According to the observed ratio of the fruiting abnormalities, two date palm tree ages were selected, i.e., 6 and 13 years. Two pollination interventions were used: pollination of naturally open female spathes (NOP) and pollination of forced open female spathes (FOP). Plant hormones, IAA, GA3, and ABA were identified just before pollination and at specific intervals after pollination for up to 85 days. The ratio of the abnormal fruit set was identified 5 days after pollination. Significant differences were observed in hormonal levels between tree ages as well as between tree propagation sources. Young TC trees (6-year-old) had high abnormal fruit sets compared to CO date palm trees that were the same age. During the early fruit growth and development phases, CO date palms had much higher amounts of IAA and GA3 than TC date palms. However, ABA concentrations were surprisingly higher in the TC trees during the early fruit growth stages, while it immediately decreased after pollination in the CO date palms. The ratio of abnormal fruits was significantly reduced in the 13-year-old TC date palms, and no differences were observed compared to the CO ones. The levels of IAA, GA3, and ABA hormones in both young and old date palms derived through CO or TC followed similar patterns. The critical observations regarding the ABA pattern in the old TC date palms (13-year-old) gradually dropped after pollination, which was identical to the CO ones, whereas it was the opposite in the young 6-year-old TC date palm plants.

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