INTRODUCTION
Strawberry is one of the most important berry fruits that is highly consumed and accepted by people worldwide (D’Urso et al. 2015). It has an attractive taste, fine flavor, distinctive aroma, bright red colour, sweetness, and juicy texture, making it a delightful fruit. Moreover, strawberry is rich in essential minerals such as K, Ca, and P, phytochemicals, fiber, antioxidants, and vitamins, particularly vitamins C and B9. Thus, it is beneficial to human health (Fernandes et al. 2012). It can be eaten fresh, and is used for preparing jelly, ice cream, juice, chocolates, and wine (Kumar et al. 2017). In Egypt, strawberry is one of the most important export crops; the cultivated area is 15.836 hectares and the production is 638.842 tons (FAO 2022). However, it is sensitive to high temperature.
Chemical fertilizers are simpler to apply than organic fertilizers; however, they negatively impact naturally occurring soil microorganisms that boost soil fertility (Verma et al. 2014). The overuse of chemical fertilizers has caused significant environmental impacts and increased production costs (Wang et al. 2018; Fang et al. 2021). Besides, they pollute the undersoil water, increase air pollution, and raise soil acidification, which in turn decreases the organic compounds in the soil (Havlin et al. 2005).
Reducing chemical fertilizer use while increasing organic fertilizers represents a forward-looking strategy for balanced agricultural management, and this approach regulates nutrient supply to the soil, enhancing both soil productivity and crop quality (Chen 2006). Sustainable agricultural practices prioritize the health of both soil components and crop plants, along with beneficial microbes (Narula and Dudeja 2013).
Using organic fertilizers can enhance soil nutrient levels and boost soil enzyme activity (Kilic et al. 2021). The usage of organic fertilizers has numerous advantages such as reducing the cost, improving the soil construction, texture, and airing, enhancing the soil water holding capacity and improving the growth root system (Liu et al. 2010), increasing soil organic matter, and consequently improving the soil fertility (Moe et al. 2017; Jin et al. 2022). Additionally, organic fertilizers affect the physicochemical properties of orchard soils and the sugar, acid, and solid content of fruit (Yadav et al. 2016).
Zeolite-coated fertilizers possess a greater capacity to absorb and hold water and retard the rates of nutrient release from the soil, particularly sandy and sandy loam soil (Syukur and Sunarminto 2013). Additionally, natural zeolites are effective soil-improving substances and have a good capacity to hold water and nutrients, and they improve the rates of infiltration, conductivity, cation exchange capacity, and prevent water losses from profound leaking (Enamorado-Horrutiner et al. 2016), and they could be utilized as fertilizer and chelating agents (Tsintskaladze et al. 2016). Moreover, natural zeolites markedly enhance fertilizer efficiency and reduce the environmental impact of chemical fertilizers in agriculture due to their high surface area, porosity, ion exchange capacity, and ability to retain and gradually release nutrients and water (Lahori et al. 2020).
Kaolin (KL) particle film technology has been developed as an efficient, eco-friendly solution to mitigate heat and light stress, reduce water deficits, and promote the cultivation of high-quality fruits and vegetables (Boari et al. 2015) by reflecting solar radiation off the tree canopy surface (Gullo et al. 2020; Ali et al. 2021). Moreover, it is believed to work as an anti-transpirant, enhancing water use efficiency (Brillante et al. 2016), effectively lowering temperature and sunburn, which in turn enhances productivity and improves both the physical and chemical qualities of fruit across various tree species compared to the control (Khalifa et al. 2021). Spraying of KL forms a white film of particles on the leaves, leading to the activation of the photosynthetic rate (Torres-Quezada et al. 2018). KL is a mineral compound characterized by a high amount of kaolinite, and it has been used for alleviating environmental stresses such as heat and drought in different crops. It is also a non-toxic and eco-friendly natural antitranspirant that enhances growth traits, yield, and its components, meanwhile, it can help mitigate the adverse effects of water deficiency, although it may increase leaf temperature if the plant is not under drought stress (Mphande et al. 2020).
Appling of chitosan (Cs) has been demonstrated as a strategy to alleviate the negative effect of abiotic stress, stimulate plant growth, and improve the yield and quality of crops (Jabeen and Ahmad 2013). It also can improve plant tolerance to abiotic stresses such as salt, drought, and low temperatures (Hassan et al. 2021; Kocięcka and Liberacki 2021; Wang et al. 2021). The impact of Cs may be attributed to the release of nitrogen, which is then utilized in the synthesis of components for the photosynthetic system (Shangguan et al. 2000). It acts as a growth promoter by enhancing nutrient absorption capacity in plants (Malekpoor et al. 2016; Balal et al. 2017). Additionally, Cs is a natural, low toxic, and economical compound, consisting of an amino polysaccharide obtained by alkaline deacetylation from chitin and other decomposable substances of crabs and shrimp shells. Therefore, it is considered an eco-friendly product (Mohamed et al. 2018). Cs is favored for its various properties; water-soluble (Golkar et al. 2019), bioactive (Turk 2019; Bakhoum et al. 2020), antimicrobial (Gerami et al. 2020), and non-toxic characteristics (Sen et al. 2020) to enhance stress tolerance and boost plant performance by activating multiple stress-related enzymes. Therefore, this study focused on studying the influence of zeolite combined with different combinations of KL + Cs as to improve the growth, productivity, and fruit quality attributes of strawberry.
EXPERIMENTAL
Applied Treatments, Location, and Experimental Design
The experiments were conducted using a split-plot design with three plots (replicates) on the festival strawberry variety, where each plot contained ten plants. The plants were cultivated in rows. The distance between rows was 40 cm and between plants in the same row 25 cm under drip irrigation. Strawberry plants were planted at the start of October 2022 and 2023 seasons in a private orchard in the Nubaria region, Beheira governorate, Egypt. Each plot was fertilized with zeolite with 0, 2, and 3 kg at the start of the plantation as the main factor, then they were sprayed with the combinations of 2% g/L KL + 500 ppm Cs, 4% KL + 1000 ppm Cs, and 6% KL + 1500 ppm Cs as a submain factor compared to untreated trees as a control (Table 1). The plants were sprayed four times: mid-November 2022 (vegetative growth and flowering period), December 01, 2022 (flowering and fruiting period), March 01, 2023 (fruiting period), and April 01, 2023 (fruiting period). The same treatments were performed again in the second season of 2023/2024, where the total volume of the spraying solution was 2 L. Physical and chemical analysis of the experimental soil is given in Table 2, and the weather data in Table 3.
O.M: organic matter
Vegetative Growth Attributes
After 120 days from transplanting throughout the two experimental seasons, in the two growing seasons, plant height (cm), number of leaves per plant, and leaf area were measured. Leaf chlorophyll content was measured in fresh leaves by taking an average of ten readings. The flower number and the number of crowns were estimated.
Fruit Yield
The yield per plant (g) was determined as the weight of all harvested fruits from each plot during February and March over the harvested season up to mid May, and then the total yield per hectare was calculated.
Fruit Quality
Fruit physical characteristics
The average fruit weight was calculated as the average of 40 fresh fruits. Fruit firmness was measured using a Chatillon Pressure Meter Equipped with a Plunger (Hongqi Instrument (Changxing) Company, Zhejiang, China). Fruit length and diameter were measured using a digital Vernier caliper.
Fruit chemical characteristics
Twenty ripe fruits were chosen randomly from each experimental plot at a full ripe stage to measure the percentage of total soluble solids content (TSS) using the hand re-fractometer. Titratable acidity (TA%), samples of 100 g fruits from each experimental plot at a full ripe stage were randomly chosen to determine the titratable acidity of juice by titration with 0.1 NaOH solution, according to the method described in (AOAC 2005). The content of vitamin C (mg/ 100 mL juice) was determined by titration using 2,6-dichloro phenol indophenol (Nielsen 2017). Anthocyanin content (mg/100 g F.W.) was determined according to Nangle et al. (2015). The phenol-sulfuric acid method was used to estimate the total sugars using 1.0 mL of sample treated with 1.0 mL of 5% phenol and 5.0 mL of concentrated H2SO4 and measured at 485 nm, while reduced sugars were estimated using the 3,5-dinitro salicylic acid (DNS) method using 2.0 mL of the sample and 1.5 mL of DNS at 80 °C for 10 min and measuring at 510 nm (Lam et al. 2021). Non-reduced sugars were the difference between them.
Mineral Content in the Leaves
At the end of seasons 2022/2023 and 2023/2024 seasons, 40 leaves from each plot (Arrobas et al. 2018) were dried at 70 °C until constant weight and then ground and digested using H2SO4 and H2O2 until the solution became clear to determine nitrogen content using the micro Kjeldahl method (Wang et al. 2016), phosphorus content using the Vanadomolybdo method (Wieczorek et al. 2022), and potassium content was determined using a flame photometer (Asch et al. 2022). Micronutrients, such as iron, manganese, and zinc, were determined using atomic absorption spectrophotometry.
Statistical Analysis
The results were statistically analyzed by using a Split Plot Design in three replicates, where soil addition of zeolite was the main factor and spraying of KL + Cs combination was the submain factor using CoHort Soft-ware 6.311 (Pacific Grove, CA, USA). The least significant difference at 0.05% (LSD0.05) was applied to compare the treatment means (Snedecor and Cochran 2021).
RESULTS AND DISCUSSION
Vegetative Growth Parameters
Spraying strawberry plants with the combination of KL + Cs solely or combined with the soil addition of zeolite greatly improved the leaf chlorophyll content, numbers of flowers, and crowns compared to untreated plants (Fig. 1). Additionally, the results significantly improved the leaf chlorophyll content by the addition of 3 kg of zeolite combined with 6 % KL + 1500 ppm Cs, which is the superior treatment rather than the other treatments. Numbers of flowers and crowns were statistically improved by the addition of 3 or 2 kg zeolite to the soil combined with the exogenous spraying of 6% KL + 1500 ppm Cs, 4% KL + 1000 ppm Cs, and 2% KL + 500 ppm Cs compared to untreated plants.
Enlarge this image.Table 4. Effect of the Zeolite Soil Addition Combined with the Spraying of KL and Cs on the Leaf Number, Plant Height, and Leaf Area of Strawberry
Note: Treatments with the same letter in each column indicate no significant differences between them.
Fruit Weight and Fruit Yield
The results showed that there was an improvement in individual fruit weight, fruit yield were obviously improved by the soil addition of zeolite at 3 or 2 kg combined with the spraying of 6% KL + 1500 ppm Cs or 4% KL + 1000 ppm Cs respectively, compared to untreated plants (Fig. 2). Additionally, the spraying of 6% KL + 1500 ppm Cs and 4% KL + 1000 ppm Cs also were more effective in improving the same parameters than the spraying of 2% KL + 500 ppm Cs compared to untreated trees. The results indicated that the most efficient treatment was the application of 3 kg of zeolite to the soil combined with the spraying of 6% KL + 1500 ppm Cs compared to the other applied treatments.
Fruit Physical Characteristics
Spraying strawberry plants fertilized with zeolite by the mixture of KL + Cs positively increased the fruit length, fruit diameter, and fruit firmness compared to nontreated plants (Table 5). The best results in fruit length, fruit diameter, and fruit firmness were noted by the addition of 3 kg zeolite and spraying the plants with the 6% KL + 1500 ppm Cs. Additionally, the fruit length and fruit diameter were also greatly improved with the addition of 3 kg zeolite combined with the spraying of 4% zeolite + 1000 ppm Cs in the two experimental seasons.
Table 5. Effect of the Zeolite Soil Addition Combined with the Spraying of KL and Cs on the Fruit Length, Diameter, and Fruit Firmness of Strawberry
Spraying of 6% KL + 1500 ppm Cs and 4% KL + 1000 ppm Cs greatly increased the fruit content from TSS %, anthocyanin, and vitamin C, and their effect was greatly increased by the soil addition of zeolite at 3 or 2 kg. Meanwhile, they greatly reduced the fruit content from acidity compared to untreated trees (Fig. 3). Additionally, the results demonstrated that the most positive influence was obtained by the 3 kg zeolite combined with 6% KL + 1500 ppm Cs, which is the best treatment compared to nontreated plants during the testing period. Moreover, the spraying of 6% KL + 1500 ppm Cs was more effective in improving these parameters than the spraying of 4% KL + 1000 ppm Cs or 2% KLl + 500 ppm Cs.
The soil addition of 3 or 2 kg from zeolite combined with the spraying of 4% KL + 1000 ppm Cs and 6% KL + 1500 ppm Cs improved the total, reduced, and non-reduced sugars compared to untreated plants (Fig. 4). The spraying of 6% KL + 1500 ppm Cs was higher in its effect than the spraying of 4% KL + 1000 ppm Cs or 2% KL + 500 ppm Cs. The soil addition of 3 kg from zeolite was more effective than the usage of 2 kg. The combined application of zeolite with the spraying of KL + Cs was more effective than the sole application of each one of them.
Nutritional Status
The data in Tables 6 and 7 indicate that the soil addition of zeolite of 3 or 2 kg combined with the foliar spraying of 6% KL + 1500 ppm Cs and 4% KL + 1000 ppm Cs significantly improved the leaf content of nitrogen, phosphorous, potassium, iron, manganese, and zinc compared to untreated plants. Additionally, the results showed that the individual spraying of 6% KL + 1500 ppm Cs was more effective in its positive effect than the spraying of 4% KL + 1000 ppm Cs or 2% KL + 500 ppm Cs compared to untreated plants.
Table 6. Effect of the Zeolite Soil Addition Combined with the Spraying of KL and Cs on Leaf Content of Nitrogen, Phosphorous, and Potassium in Strawberry
Note: Treatments with the same letters in each column indicate no significant differences between them
DISCUSSION
The soil application of zeolite positively affected soil fertility, which improved the vegetative growth, yield, and fruit quality of strawberry. Previous authors have stated that the addition of zeolites to the light texture of soil minimizes the bulk density, which improves the soil air porosity (Ramesh and Reddy 2011). Zeolite addition to sandy soil increased the water- holding capacity by at least 10% and the available water to plants by 15% (de Campos Bernardi et al. 2013), or by 50% (Sangeetha and Baskar 2016) and delayed reaching the permanent wilting point (Torkashvand and Shadparvar 2013).
Enlarge this image.Table 7. Effect of the Zeolite Soil Addition Combined with the Spraying of KL and Cs on the Leaf Content from Iron, Zinc, and Manganese in Strawberry
Note: Treatments with the same letters in each column indicate no significant differences between them.
Zeolites act as fertilizers and chelating agents, enhancing soil properties by reducing water leaching, improving water efficiency through increased soil water-holding capacity, and supporting a slow, consistent release of essential nutrients like nitrogen, potassium, calcium, and magnesium, which boosts crop growth, enhances nutrient efficiency, and reduces fertilizer costs across growing seasons (Eroglu et al. 2017; Cataldo et al. 2021). In addition, zeolite promotes rapid rewetting and lateral water distribution throughout the root zone during irrigation, reducing the time needed for water application, and enhancing the soil moisture retention for extended periods, especially during dry times, helping to alleviate drought stress and enable the plants to endure dry conditions (Nakhli et al. 2017). Additionally, it improves the usage of fertilizers and water efficacy and minimizes the pollution of the environment by lessening the leaching of nitrate and emissions of nitrous oxides and ammonia, thereby significantly improving crop growth, productivity, and quality (Mondal et al. 2021). Zeolites enhance plant yield by serving as fertilizers with high cation exchange capacity, large reactive surface area, effective water retention, and strong adsorption properties, gradually releasing key nutrients such as nitrogen and potassium to meet crop needs, improve phosphorus availability, and boost nitrogen uptake (Bibi et al. 2024). This addition of zeolite at 1, 2, and 3 kg to mango cv. ‘Ewaise’ positively improved the soil characteristics, which led to improving the tree trunk thickness, shoot length and thickness, inflorescence number, fruit set and fruit retention percentages, fruit number, fruit yield, fruit weight, fruit dimensions, fruit size, fruit firmness, peel and pulp weights, fruit content of TSS, VC, carotene, total, reduced and non-reduced sugars, as well as the minerals content in the leaves, including N, P, K, Fe, Zn, Mn, Cu, Mo, and B compared to nontreated trees. Additionally, these applied treatments minimized the percentages of fruit drop and fruit content from the acidity (Harhash et al. 2022).
The results showed the positive influence of KL in mitigating the undesirable influence of heat on strawberry and improving the growth, productivity, and fruit quality. These results are in harmony with the findings of many authors, who have stated that KL is a natural clay mineral that serves as a reflective agent and antitranspirant, enhancing plant performance by reducing stomatal conductance under abiotic stress in some plant species, reflecting solar radiation to lower plant temperature, improving gas exchange and photosynthetic efficiency, and providing a protective barrier against disease by hindering pathogen penetration (Ramírez-Godoy et al. 2018; Brito et al. 2019a; Luciani et al. 2020). Moreover, it can reduce leaf temperature by up to 6.7 °C, inducing the opening of stomata, and this improves the process of photosynthesis and raises the plant adaptation to excessive light and temperatures (Abreu et al. 2022). The foliar application of K releases nutrients and helps retain soil moisture, enhances growth parameters, reflects radiation, reduces leaf temperature and significantly minimizes water loss from cells, promoting cell expansion and elongation (Vani et al. 2023). Additionally, KL reduces the negative impacts of combined stress by minimizing leaf damage and abscission and inhibiting carotenoid degeneration. Meanwhile, it increases the proline content, the physiological and gas exchange percentage, chlorophyll content, and regulates the levels of hormones such as abscisic, salicylic, indole-3-acetic, and jasmonic acids, which raise the plant stress tolerance (Terán et al. 2024). KL concentrations of 2 to 4% are recommended for improving the rates of photosynthesis and transpiration and protecting fruits from sunburn in apples (Glenn, 2010), grapevines (Dinis et al. 2016), and olive trees (Brito et al. 2019b). Segura-Monroy et al. (2015) reported that the application of KL on cape gooseberry noticeably boosted plant height, dry weight, and water-use efficiency, and improved the opening rates of stomata under stresses. Meanwhile, it lessened the rates of transpiration, the temperature of the leaves, and leaf thickness. Applying KL greatly improved the fruit quality, such as total soluble solids, color, and fruit size in mango (Baiea et al. 2018), and reduced the fruit drop, sunburn, and cracking percentages in Persian walnut (Gharaghani et al. 2018). Spraying of KL at 2, 4, and 6% greatly improved the fruit set percentages, productivity, fruit weight and firmness, and reduced the fruit sunburn percentage in pomegranate (Al-Saif et al. 2022), leaf surface area, tree volume, photosynthesis process, chlorophyll, and carotenoids content in the leaves, productivity, and the fruit quality in mango, meanwhile these treatments significantly reduced the sunburned fruits number, and 6% was the most recommended concentration (Hamdy et al. 2022).
The applied treatments from Cs effectively reduced the heat stress and consequently improved the growth and yield of strawberry. These results are in the same trend as those obtained by many studies that reported that applying Cs to the aerial parts of plants, such as leaves, stems, and fruits has been shown to increase the nitrogen content in the fruits. This increase could be due to the release of nitrogen from Cs (polysaccharides-NH2) by promoting the growth of xylem vessels, which enhances nutrient absorption and improves the plant’s nutritional status, particularly in nitrogen for amino acid synthesis (Khan et al. 2015; El Amerany et al. 2020). Studies have reported that the application of Cs has increased the indole-3-acetic acid concentration, which induces cell division (Saharan and Pal 2016; Lopez-Moya et al. 2017) and enhances the rates of ascorbic acid and sugars (Moha et al. 2021). Additionally, Cs application to shoots affects fruit metabolome by raising the rates of sucrose and minimizing the rates of organic acids, particularly citrate (Choudhary et al. 2017). Shaheen et al(2017) reported that spraying onion with Cs at 5 cm/L three times at 15-day intervals greatly increased the proportion of large mother bulbs, resulting in a higher weight of onion seeds. Ahmad et al. (2019) reported that foliar application of Cs at a concentration of 0.75 mg mL−1 enhanced growth, number and area of leaves, and the fresh and dry weights of shoots and this improvement is because of improving the chloroplast function, leading to increased O2 production and CO2 fixation compared to untreated plants (Ahmad et al. 2019). The application of Cs stimulates carbon and nitrogen metabolism and enhances nitrogen and phosphorus uptake, leading to increased sucrose production, and it also influences various plant processes like stomatal conductance, division and developing of cells, ripeness of fruits, intake of elements, and defense responses. It also increases the accumulation of chlorophyll, and nutrient uptake (Ahmed et al. 2020; Maluin and Hussein 2020) and improves chlorophyll fluorescence, increases CO2 assimilation, and boosts the plant’s photosynthetic activity (El Amerany et al. 2022). Additionally, Cs is quite effective at promoting plant development, and this could be connected to how it affects the osmotic pressure in cells and stimulates the absorption of water and vital minerals (Chakraborty et al. 2020). Applying nano Cs at 50 ppm to onion remarkably raised the growth attributes, yield, and yield components compared to untreated plants (Geries et al. 2020). Additionally, Cs improves the productivity and agro-environmental sustainability by boosting plant defense systems against biological and environmental stresses, acting as an inducer the plant growth by increasing stomatal opening rates and reducing the rates of transpiration, aiding nutrient delivery by preventing leaching and enabling slow nutrient release, and improving soil properties and plant resistance to both abiotic and biotic stresses (Shahrajabian et al. 2021). Applying nano Cs to bean at 50 ppm improved the vegetative growth, parameters, bulb weight, marketable bulbs percentage and productivity, bulb diameter and TSS%, compared to the control (Khalil et al. 2022; Bayar et al. 2024).
CONCLUSIONS
1. The results of the present study showed that the soil addition of zeolite positively improved the vegetative growth of strawberry plants, productivity, fruit physical and chemical characteristics, and leaf mineral content from macro and micronutrients, and the positive influence was greatly increased by the spraying of KL and Cs, in particular 6% KL + 1500 ppm Cs and 4 % KL + 1000 ppm Cs.
2. The best results were obtained by 3 kg zeolite combined with 6% KL + 1500 ppm Cs followed by 2 kg zeolite combined with 4% KL + 1000 ppm Cs in the experimental period compared to untreated plants or the other treatments.
Data Availability Statement
All the required data are included in the manuscript.
ACKNOWLEDGMENTS
The authors extend their appreciation to the Researchers Supporting Project number (RSPD2025R561), King Saud University, Riyadh, Saudi Arabia.
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