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Many citrus species and cultivars are grown successfully in tropical and subtropical countries, as well as in arid and semi-arid regions with low levels of organic matter and low cation exchange, resulting in lower nutrient uptake by the plant. The essential nutrients needed for citrus flowering and fruit set are limited in winter due to a reduction in transpiration rate, negatively effecting vegetative growth, flowering, yield, and fruit quality. The present investigation was carried out to assess the nutritional status, fruit yield parameters, and fruit quality of Valencia orange trees after foliar spraying of seaweed extract (SW) combined with calcium chloride and boric acid and their combinations in the 2020/2021 and 2021/2022 seasons. The treatments were arranged in a split-plot design (three levels spraying seaweed extract × four levels spraying calcium chloride and boric acid and their combinations × four replicates × one tree/replicate). The results indicated that all of the characteristics measured, including leaf chlorophyll, leaf mineral contents, fruit yield parameters, fruit physical properties, and fruit chemical properties, were significantly affected by the foliar spraying of seaweed extract (SW) combined with calcium chloride and boric acid and their combinations. Although all treatments increased the productivity and the physical and chemical properties of Valencia orange fruits compared to the control, a treatment of 10 g/L SW combined with 0.5 g/L boric acid and 1 g/L calcium chloride produced superior results. This ratio of SW, boric acid, and calcium chloride is therefore recommended to enhance productivity and improve the physico-chemical properties of Valencia orange for greater fruit yield.

The present study was conducted during the two successive seasons, 2017 and 2018, at King Saud University, Saudi Arabia, to investigate the effects of foliar sprays on Ziziphus jujuba trees by yeast extract at 1% and 2% and potassium nitrate (KNO3) at 1% and 2%. All treatments were foliar applied twice (December 15–January 15) in both seasons. Yield and fruit quality were studied. Treatments significantly improved yield, physical fruit and fruit chemical characteristics, moisture content, chlorophyll a, b and total chlorophyll by most tested treatments in both seasons than the control (water only). Yeast spray treatments significantly decreased juice content vitamin C (mg/100 g), while KNO3 spray treatments increased juice content vitamin C in both seasons. It can be concluded that foliar application with KNO3 at 2% recorded the best treatment to obtain the highest yield, fruit weight, flesh weight, fruit volume, fruit length and fruit diameter, while yeast extract at 2% treatment gave the highest TSS% and total sugar contents in this study.

The current investigation represents of the synergistic effects of application of potassium nitrate (KNO3) in combination with putrescine (Put) on flowering, productivity, and fruit quality on Ewais mango (Mangifera indica L.) trees during the seasons 2021/2022 and 2022/2023. The selected trees were sprayed at three different stages, including flower bud differentiation, full bloom, and beginning of the fruit set, with one of the following treatments: control, 2% KNO3, 4% KNO3, 50 ppm Put, 75 ppm Put, 2% KNO3 + 50 ppm Put, 2% KNO3 + 75 ppm Put, 4% KNO3 + 50 ppm Put, 4% KNO3 + 75 ppm Put. Results showed that all treatments were successful in improving the productivity of mango trees by increasing flowering terminal shoots, fruit set, fruit retention, number of fruits/tree, yield, and fruit yield increment while reducing the percentage of fruit drop, as well as improving the quality of mango fruits cv. Ewais by increasing fruit length, fruit diameter, TSS, total sugars, V.C, and total phenol and carotenoid content, but at the same time, diminishing the total acidity, as compared with control. Based on this research, the application of 4% KNO3 in conjunction with 75 ppm Putrescine has shown the most prominent advances in enhancing Ewais tree productivity and fruit quality. The investigation successfully highlighted the synergistic effect of using KNO3 and putrescine to improve mango fruit yield and quality.

Using biofertilizers has been a good method in this respect. Field experiments were conducted in 2014 and 2015 on 6-year-old grapevine cv. “Flame Seedless” grown under arid conditions (Riyadh, Saudi Arabia) to evaluated the effects of foliar application with natural sources and chemical of fertilizer on yield and fruit quality. Eight different foliar spray treatments were applied at 4 weeks after fruit set and repeated after another 4 weeks. These treatments were yeast at 4, 6 or 8%; seaweed extract at 1 or 2%; potassium nitrate at 2%; potassium hydrogen phosphate at 2%, and the control (water only). Results indicated that the application of 8% yeast had improved fruit chemical characteristics (soluble solid content, reducing sugars and total sugars) and some physical characteristics (cluster width and weight of 100 berries). Application of 2% potassium nitrate had a significant effect on yield, cluster weight, cluster length, and volume of 100 berries.

The effect of foliar spray with algae extract and/or potassium nitrate on the quantity and quality of Barhee date palm yields was investigated during the 2017 and 2018 seasons. Inflorescences of Barhee date palms were sprayed twice, after pollination (1st April of each season) and one month later, with algae extract at concentrations of 0.5% and 1.0% and with potassium nitrate at concentrations of 1% and 2% applied individually or in combinations. The obtained results showed that all of the sprayed treatments enhanced the yield and fruit properties when compared to the controls. Spraying inflorescences of Barhee date palms with algae extract and/or potassium nitrate had a significant effect on the yield and on the physical and chemical properties of the fruit when compared with the untreated palms. The increase in yield and qualitative properties was associated with increasing concentrations of both materials (algae extract and potassium nitrate). The best results were detected with spray containing high rates of combined treatment (1% algae extract + 2% potassium nitrate) applied twice in both seasons studied because this treatment resulted in the highest value of fruit and bunch weight, increased the yield per palm compared to the control by about 60.2%, and improved the fruit physical properties (fruit length, fruit diameter, fruit shape index, flesh weight, and seed weight) and fruit chemical properties (total soluble solids (TSS); acidity; TSS/acid ratio; tannins; and reducing, nonreducing, and total sugars) of the Barhee date palm given the experimental conditions.

The influence of salicylic acid (SA) on growth, yield, fruits’ quality and enzymes’ activities was monitored in strawberry plants cv. Camarosa grown under salinity stress via two pot experiments in two successive years of 2018 and 2019. The examined concentrations of SA were 30, 60, and 90 ppm, which foliary applied in addition to control (sprayed with water), while the used levels of salinity were 20, and 40 mM as NaCl as irrigation application in addition to control (without salinity). The results showed a significant effect of salinity at 40 mM where the mean values of shoot fresh and dry weights, chlorophyll, leaves’ NPK, yield plant−1, yield ha−1, and fruits’ ascorbic acid were significantly decreased. However, the 40 mM salinity resulted in a significant increase in leaves’ content of Na and proline as well as catalase (CAT) and peroxidase (POD) enzymes’ activity and the fruits’ TSS and acidity. The application with 90 ppm SA was found to be the most significant positive treatment for all of the studied characters except the Na leaves’ content. Regarding tolerance index percentages (STI%), the high values of CAT, POD, and proline referred to the ability to use them as indicators for strawberry salinity response in other physiological and plant breeding studies. The findings of this study suggest that the 90 ppm SA foliar application can ameliorate the negative effect of salinity on the growth of strawberry cv. Camarosa.