In Egypt’s arid and semi-arid lands where the main olive production zone is located, evapotranspiration is higher than rainfall during winter. Limited research has used nanomaterials, especially nano-silicon (nSi) to improve the growth, development, and productivity of drought-stressed fruit trees, amid the global water scarcity problem. To assess the role of nSi on drought-sensitive ‘Kalamata’ olive tree growth, and biochemical and physiological changes under drought conditions, a split-plot experiment was conducted in a randomized complete block design. The trees were foliar sprayed with nSi in the field using nine treatments (three replicates each) of 0, 150, and 200 mg·L⁻¹ under different irrigation regimes (100, 90, and 80% irrigation water requirements ‘IWR’) during the 2020 and 2021 seasons. Drought negatively affected the trees, but both concentrations of nSi alleviated drought effects at reduced irrigation levels, compared to the non-stressed trees. Foliar spray of both concentrations of nSi at a moderate level (90% IWR) of drought resulted in improved yield and fruit weight and reduced fruit drop percentage, compared to 80% IWR. In addition, there were reduced levels of osmoprotectants such as proline, soluble sugars, and abscisic acid (ABA) with less membrane damage expressed as reduced levels of malondialdehyde (MDA), H₂O₂ and electrolyte leakage at 90% compared to 80% IWR. These results suggest that ‘Kalamata’ olive trees were severely stressed at 80% compared to 90% IWR, which was not surprising as it is classified as drought sensitive. Overall, the application of 200 mg·L⁻¹ nSi was beneficial for the improvement of the mechanical resistance, growth, and productivity of moderately-stressed (90% IWR) ‘Kalamata’ olive trees under the Egyptian semi-arid conditions.

Plant growth, development, and productivity are adversely affected under drought conditions. Previous findings indicated that 5-aminolevulinic acid (ALA) and 24-epibrassinolide (EBL) play an important role in the plant response to adverse environmental conditions. This study demonstrated the role of ALA and EBL on oxidative stress and photosynthetic capacity of drought-stressed ‘Williams’ banana grown under the Egyptian semi-arid conditions. Exogenous application of either ALA or EBL at concentrations of 15, 30, and 45 mg·L⁻¹ significantly restored plant photosynthetic activity and increased productivity under reduced irrigation; this was equivalent to 75% of the plant’s total water requirements. Both compounds significantly reduced drought-induced oxidative damages by increasing antioxidant enzyme activities (superoxide dismutase ‘SOD’, catalase ‘CAT’, and peroxidase ‘POD’) and preserving chloroplast structure. Lipid peroxidation, electrolyte loss and free non-radical H₂O₂ formation in the chloroplast were noticeably reduced compared to the control, but chlorophyll content and photosynthetic oxygen evolution were increased. Nutrient uptake, auxin and cytokinin levels were also improved with the reduced abscisic acid levels. The results indicated that ALA and EBL could reduce the accumulation of reactive oxygen species and maintain the stability of the chloroplast membrane structure under drought stress. This study suggests that the use of ALA or EBL at 30 mg·L⁻¹ can promote the growth, productivity and fruit quality of drought-stressed banana plants.

Organic fertilization improves soil fertility and ameliorates the deleterious effects of accumulated salts in soil for sustainable agricultural production. This research was carried out on thirteen-year-old Mexican lime trees to study the effect of humic acid (HA), applied as soil (10, 20 or 30 mL·tree⁻¹) and foliar (0.1 or 0.2%) applications, on soil fertility, tree growth, productivity and fruit quality. The experiment was conducted during the 2020 and 2021 seasons in a randomized complete block design of twelve treatments with three replicates with two trees each. Soil and foliar applications of HA were performed once and twice a month in Marsh, May and July, respectively. HA enhanced the soil’s N, P, K, Ca, Mg, Fe, Mn, Zn, Cu and B availability and microbial activity, in addition to improved tree growth, canopy size, leaf chlorophyll and nutrient contents with reduced proline levels. The total yield and number of fruit per tree were increased with increased HA levels. Fruit weight, juice and soluble solids were also increased. The best results were achieved with the combined soil (30 mL·tree⁻¹) and foliar (0.2%) applications of HA, which indicated a great potential to alleviate the effects of salinity stress on Mexican lime growth and productivity.

Evolved in South Africa and released to market in 2009, the ‘African Rose’ plum has been introduced and grown under the Egyptian semi-arid conditions since 2010. Within that time, this cultivar has faced significant fruit quality issues, mainly poor color and low total soluble solids (TSS). Several trials using foliarly applied growth regulators have been conducted, but with little conspicuous results on fruit yield and quality. There is very limited information about the relationship between irrigation regime and fruit quality for this cultivar. Therefore, a field experiment was conducted to study the effect of deficit irrigation on the quality of the ‘African Rose’ plum during the 2019 and 2020 seasons. Five-year-old hedge growing trees were subjected to three deficit irrigation regimes: 100% (control), 80%, and 60% of the crop evapotranspiration (ETc) after the pit hardening stage until the end of the harvest season (May to June period) were evaluated. Results indicated that deficit irrigation positively enhanced the levels of abscisic acid (ABA), total phenols, and anthocyanins with improved fruit TSS and maturity index, although fruit yield, acidity, size, and firmness were decreased. Deficit irrigation could be suggested as a sustainable novel solution to improve the fruit quality of the ‘African Rose’ plum grown under the semi-arid conditions of Egypt. Although the total yield and some quality characteristics were not improved, the early harvested fruit with enhanced color and taste could be a good start for additional research to solve other quality-related issues under such conditions.

Water scarcity, especially in countries like Egypt, is one of the biggest challenges facing agricultural development. Pomegranate (Punica granatum) is drought-resistant but only if the irrigation can be optimized. This can be a crucial approach toward the country’s agricultural development. The impact of deficit irrigation on pomegranate growth, yield, and overall fruit quality was observed during this study, which focused on two consecutive years from 2023 to 2024 at a private farm located in El Khatatba, Egypt. It was determined that deficit irrigation of pomegranate was able to achieve a high level of water productivity whilst also achieving a reasonable yield. Trees receiving moderate deficit irrigation had a yield decrease of 10% in comparison to full irrigation; however, this yield decrease did not have a huge overall impact because the level of water saved during the process made up for the reduced yield. Moreover, fruit soluble solids content (SSC) was high when trees received moderate deficit irrigation. Trees that were given severe deficit irrigation had the lowest fruit yields with less juice content, which limits targeted uses like the juice market. Still, these trees produced the highest SSC indicating that sugar becomes concentrated in the fruit when plants are water-stressed. In general, the most efficient treatment was moderate deficit irrigation as it balanced the yield and quality parameters with less water. The resulting data provide assurance that moderate deficit irrigation can be effectively and suitably implemented for pomegranate production in arid regions where water conservation and market quality standards must be satisfied in order to be economically viable. There is also a need to examine the longer-term effects of DI on economic sustainability, plant physiology, and soil biomes.