Improving Yield and Quality of ‘Balady’ Mandarin Trees by Using Shading Techniques and Reflective Materials in Response to Climate Change Under Flood Irrigation Conditions

Abstract

Considering climate change predictions, it is logical to anticipate detrimental effects on the mandarin tree, an essential citrus crop. Therefore, scientists should promptly focus on developing methods to enhance its resistance to climatic stress effects such as sunscald. This study assesses the strategies employed in ‘Balady’ mandarin trees when covered by shading nets of varying colors and percentages (white 50%, green 50% or 63%, black 50% or 63%), as well as the application of reflective materials (kaolin at 4% and CaCO₃ at 3%) on the micro-climate of orchards, leaf, and fruit surface temperatures, fruit sunburn%, productivity, and fruit quality. The results indicated that shade nets effectively reduced temperature and enhanced humidity, especially during the period from June to September, when compared to open-field treatments. Black shade nets, particularly those with a shading level of 63%, demonstrated the most notable decrease in canopy temperature and an elevation in humidity, surpassing the performance of green and white shade nets. The present study found that shade nets and reflecting materials like kaolin and calcium carbonate significantly reduced fruit sunburn. Trees without shade had a sunburn rate of 8.74%, while those with shade treatments suffered no sunburn. Kaolin foliar spray at a concentration of 4% and calcium carbonate at a concentration of 3% reduced sunburn incidence to 3.64% and 7.32%, respectively. These treatments also reduced the intensity of sunburn. All treatments increased fruit yield % compared to the control and yield efficiency (kg/m²), especially the trees covered with white shade net of a 50% shading rate provided the highest values (43.70 and 40.17%) and (5.24 and 5.47 kg/m²) compared to other treatments in both seasons, respectively. Trees covered with a white shade net of a 50% shading rate, followed by a green shade net of 50% and a 63% shading rate, as well as a black shade net of 50% and a 63% shading rate, tended to improve the physical and chemical fruit properties. Therefore, it could be recommended that trees be covered with a white shade net of a 50% shading rate or a green shade net of a 50 and 63% shading rate in summer months due to its beneficial impact on mitigating fruit sunburn damage and enhancing the productivity and quality of ‘‘Balady’’ mandarin trees. Hence, shade nets can be a beneficial technology to protect citrus fruits from sunburn without affecting fruit quality in commercial citrus farms.

1. Introduction

Citrus comprises highly popular and extensively cultivated fruit crops. Oranges are the predominant type of citrus fruit trees grown worldwide, comprising over 50% of global citrus production. They are also the most extensively traded citrus fruit, with tangerines, lemons, and grapefruits following closely behind. Global citrus output and exports have experienced consistent growth over the last 30 years. The projected global orange production for the 2022–2023 season is expected to decrease by 5% compared to the previous year, reaching a total of 47.5 million metric tonnes (MMT). The decrease in production in the European Union and the United States is only partially compensated by a larger production in Egypt. The anticipated top producers are as follows: Brazil with 16.5 MMT, China with 7.6 MMT, the European Union with 5.9 MMT, Mexico produced 4.2 MMT, Egypt produced 3.7 MMT, and the United States produced 2.5 MMT. It is projected that Egypt’s orange exports in the year 2023–2024 will grow by 25 percent, reaching an additional record of 2 million tons [1]. This gain can be attributed to improved productivity per unit of land and the expansion into new markets. However, of all citrus fruits, the ‘Balady’ mandarin (Citrus reticulata Blanco) is the second-most widely cultivated and produced fruit in Egypt, following oranges. The mandarin cultivation area stated last year was 53.37 hectares, resulting in a production of 1,174,895 metric tons. It was recently reported by the USDA [1] that the global output of tangerines/mandarins for 2023–2024 is expected to increase by 3% compared to the previous year, reaching a total of 38 million tons. Egypt’s contribution to the global output is 2.25%, which is about equivalent to 989.04 metric tons.

The impacts of global warming will lead to an expansion of heat-induced losses in agricultural economies on a global scale [2]. Climate change-induced heat stress, whether caused by sustained rises in the average annual temperature or by more frequent and intense heat waves, is likely to decrease crop production and ecosystem productivity. Consequentially, it is projected that world average temperatures will rise by 0.3–4.8 °C by 2100, according to the IPCC’s 2014 report. Additionally, some regions are expected to see higher temperature increases than the global average [3].

Plants face various abiotic and biotic stresses due to global warming and environmental contamination. However, there is limited knowledge about their responses to stress combinations. Increased stress events decrease plant growth, survival, and microbiome diversity. This raises concerns about pollution and global warming. Likewise, what raises concern is the way agriculture is negatively affected by stress. Society should focus on reducing pollutants and enhancing agricultural resilience [4]. Admittedly, the majority of Egypt is expected to see a significant increase in temperature due to the effects of climate change. When determining how to adjust to climate change, the citrus industry should primarily consider these observed and projected alterations. Therefore, it is crucial to find effective methods to reduce the adverse impact of temperature fluctuations caused by climate change. Elevated temperatures are frequent sources of stress that restrict the development and output of crops in subtropical areas where citrus trees are cultivated. Excessive solar radiation can have negative effects on physiological processes, including transpiration, photosynthesis, and respiration. Additionally, it can decrease fruit output by causing physiological disorders such as sunburn [5]. Therefore, the occurrence of fruit sunburn, a condition produced by elevated temperatures and intense sunlight, is expected to rise as a result of climate change-induced warmer temperatures [6]. Meteorological factors, plant types, hormonal considerations, nutritional status, and soil moisture levels all have an impact on the frequency and intensity of sunburn, which affects fruit production by varying from 6 to 30%, depending on seasonality and fruit type. Effective sunscald management is essential for minimizing fruit damage resulting from elevated temperatures and excessive light exposure, which can ultimately result in reduced crop yield and compromised fruit quality [7].

To avoid sunburn, producers should use tolerant cultivars, effective irrigation, and proper canopy management. Over-tree spraying, shade netting, fruit bagging, and the use of suppressants (kaolin or calcium carbonate) and chemical protectants can also be beneficial [8]. Recently, numerous agricultural solutions have been aimed at reducing the adverse impacts of intense sunlight and excessive temperatures. One frequently employed method is the utilization of reflective materials such as kaolin and calcium carbonate [9].

Kaolin is an engineered clay that is classified as an aluminum phyllosilicate with the chemical formula Al₂Si₂O₅(OH)₄. It is used as a reflective antitranspirant material and has been the subject of research for the previous 15 years as an environmentally friendly option for organic farming. It helps to reduce heat stress, control insects effectively, and improve the production of fruits and vegetables [10,11].

Particle film technology is an emerging method to lessen the adverse effects of heat stress and can significantly enhance the photosynthetic rate, stomatal conductance, and transpiration. Additionally, they can lower the heat load on leaves during stressful conditions [12,13,14]. Utilizing kaolin as a method of addressing the rising environmental temperatures resulting from global warming can be an effective approach. Studies have demonstrated that using kaolin particle-film technology can alleviate the negative influences of global warming on plants. This is achieved by lowering canopy temperatures, increasing the accumulation of anthocyanins, and regulating the photochemistry and defence responses of plants [15,16]. Furthermore, the administration of kaolin has also shown an inhibitory impact on the expression of genes associated with heat stress, including VvHSP70, suggesting its protective function against heat stress [16]. Kaolin clay treatment is effective in various fruit species for reducing fruit sunburn and enhancing yield and fruit quality, which was found in research conducted on crops such as orange trees [17,18], ‘Balady’ mandarin [19], and ‘Murcott’ mandarin [20]. Nevertheless, every species exhibits a distinct reaction to the utilization of reflective materials. Plants have been found to benefit from the foliar application of calcium-based films, like calcium carbonate, which helps them function better and deal with environmental stress [14,21]. According to Tsai et al. [7] on ‘Murcott’ mandarins, CaCO₃ was used as particle films, reducing plant temperature and sun damage in fruits. Also, Gullo et al. [9], on sweet orange, found that the application of calcium particle films improved light penetration and photosynthesis, as well as the production of plant pigments, flavor, and the quality of fruits, all of which boosted plant metabolism. The same has also been reported by Ramírez–Godoy et al. [22] on Tahiti lime, and Denaxa et al. [23] on kiwifruit. According to Zaman et al. [24], CaCO₃ enhanced various characteristics of ‘Kinnow’ mandarins, including fruit weight, diameter, juice %, soluble solids content (SSC), ascorbic acid, total antioxidants, total phenolics, total flavonoids, and carotenoids. In addition, a study conducted by Ali et al. [20] demonstrated that the application of calcium carbonate and kaolin clay to the leaves resulted in enhanced fruit quality and reduced sun scales. Furthermore, this treatment increased the output of ‘Murcott’ mandarin fruits per tree in terms of both number and weight when compared to the control group. In addition, there are alternative approaches to alleviate the impact of global warming on agriculture, such as implementing protective coverings. Netting is a crucial tool for protecting crops in areas with high temperatures and intense sunlight. It reduces water consumption and evapotranspiration, as well as light intensity, wind speed, and soil temperature, and it can alleviate stress on trees and fruit sunburn. Installing protective netting in orchards can minimize plant stress and regulate fruit ripening, thereby reducing the negative effects of high temperatures [25].

Various colors of netting exert distinct impacts on soil temperature, with pearl and blue netting notably lowering the temperature of the soil in comparison to red netting, as well as having different effects on the temperature of the fruit’s surface. When used as a protective measure, netting can lower the maximum temperature of the fruit’s surface by 2.6–4.3 °C than when exposed to direct sunlight. Furthermore, pearl and blue netting decrease photosynthetically active radiation by roughly 20%, leading to enhanced fruit quality and a decreased occurrence of sunburn [25]. A separate investigation by Goodwin et al. [26] revealed that the implementation of netting resulted in a 10% decrease in the maximum temperature of the fruit’s surface and a reduction in sunburn damage in red-blushed pears. Additionally, Mupambi et al. [27] found that protective netting in “Honeycrisp” apples enhanced the efficiency of photosynthetic light use at the leaf level, particularly at high ambient temperatures. This resulted in a reduction in photoinhibition and stress. Although netting incurred higher costs, it effectively reduced sunburn compared to alternative treatments, potentially leading to higher profits from unblemished fruit [28]. Kale et al. [29] found that a semi-permanent shade net with 50% black shade net significantly reduced sunburn, which affected 2.9% of fruits compared to 17% in the control treatment. The net also improved fruit color and juice recovery by 20–25%, indicating its positive impact on pomegranate fruit quality in hot and semi-arid regions. The study shown by Narjesi et al. [30] examined the effects of various shade net colors and percentages on the quality and growth of pomegranate fruits. The findings indicated that the use of shade nets resulted in higher leaf water content, lower temperature and light intensity, and enhanced fruit weight and yield. Additionally, they mitigated the occurrence of sunburn. The study suggests using a white shade net that allows 50% of photosynthetically active radiation for better crop productivity, more marketable fruits, and greater fruit quality with increased levels of anthocyanin, phenolics, and vitamin C. The study conducted by El-Naby et al. [31] determined that the use of a white 25% shade net to cover Washington navel orange trees was highly successful in safeguarding the trees. Additionally, this practice resulted in enhanced growth, increased yield, and maintenance of fruit quality.

A study conducted by Mupambi et al. [27] found that using a blue 22% shade net to cover apple trees experiencing heat stress and high light exposure resulted in a decrease in solar radiation, an improvement in the efficiency of photosynthetic light utilization at the leaf level, and a reduction in the symptoms of photoinhibition. Implementing sunscald management techniques, such as employing shade netting and utilizing white paper bagging, can effectively regulate fruit temperature and safeguard against sunburn, ensuring the preservation of fruit quality in commercial citrus fields [7]. In Egypt, shading with a net is a strategy that can be used to reduce heat stress. It involves modifying the microclimate of the crop to enhance plant growth and increase output. Netting is commonly employed to shield crops from intense sun radiation, thereby enhancing temperature conditions. Additionally, this led to a reduction in the incidence of diseases affecting fruit yields [31].

Since elevated temperatures and intense irradiation contribute to enhanced plant stress [32], this study compares shading and reflective sprays as dual strategies to combat climate change’s effects on citrus trees. It is the first to integrate and evaluate their effects on physiological and agronomic aspects of ‘Balady’ mandarin trees. The study’s main goal is to find out how well shading nets and reflective sprays work at protecting these trees from heat stress and too much sunlight. The focus is on determining how these interventions influence key factors such as micro-climatic conditions, leaf and fruit surface temperatures, sunburn occurrence, overall productivity, and fruit quality.

2. Materials and Methods

2.1. Environmental and Experimental Factors

Two successive experiments in 2022–2023 and 2023–2024 were implemented on a private orchard located in the Desouk region, Kafr El-Sheikh Governorate, Egypt (Latitude: N 31°07′39″; Longitude: E 30°40′55″). The orchard involved 10-year-old ‘Balady’ mandarin trees budded on sour orange rootstock (Citrus aurantium L.). Trees were spaced on 5 m centers, with 5 m between rows, on clay soil. The trees in the orchard were subjected to standard agricultural practices, utilizing a flood irrigation system supplied by the Nile River, with annual irrigation requirements estimated at approximately 16,660 m³ per hectare. The meteorological data of the studied period are presented in Figure 1.

Before commencing the investigation, soil samples obtained from the experimental site were examined to ascertain the primary physical–chemical properties of the soil, according to [33].

The representative soil analysis data are listed in

Table 1. Physical properties and soil moisture properties for the experiment site.

Particle Size Distribution (%)			Textural Class	Field Capacity (%)	Wilting Point (%)	Available Water (%)	Bulk Density (g/cm3)
Sand	Silt	Clay
8.37	36.23	55.40	Clay	39.76	20.72	19.04	1.29

and

Table 2. Chemical properties of the experimental soil.

pH	EC (dS m−1)	O.M. (%)	Soluble Cations (meq/L)				Soluble Anions (meq/L)			Available Macro-Nutrients (mg kg−1)
			Na+	Ca2+	Mg2+	K+	Cl−	HCO3−	SO42−	N	P	K
8.13	1.47	1.67	7.6	4.06	3.93	0.16	10.07	3.50	2.18	56.65	25.8	332.5

.

2.2. Plant Materials and Evaluated Treatments

Forty-eight vigorous ‘Balady’ mandarin trees, grafted onto the sour orange rootstock, were meticulously chosen and dedicated for this study. The trees that were chosen were uniform in terms of their growth vigor, size, load, and health. They were then placed in a randomized complete block design (RCBD), with each treatment being reproduced three times and two trees being used for each replicate.

Table 3. Details of treatments used in the study.

Treatment Code	Description
Control	An open field without any treatment
Kaolin 4%	Spraying kaolin at 4% three times
CaCO3 3%	Spraying CaCO3 at 3% three times
W50%	White shade net + 50% shading rate
G50%	Green shade net + 50% shading rate
G63%	Green shade net + 63% shading rate
B50%	Black shade net + 50% shading rate
B63%	Black shade net + 63% shading rate

displays the specific treatments employed in the study.

Reflective particle coatings were utilized during fruit development, specifically two commercial products, purchased from Cornell Lab Company, Cairo, Egypt. One product was composed of kaolin treated to a diameter less than 2 mm (K), while the other product consisted of 97% calcium carbonate. During both seasons, a solution containing 4% kaolin and 3% CaCO₃ was administered three times on the dates of 15 May, 15 June, and 15 July. A 20% Tween surfactant was added to water at a concentration of 0.2 mL per liter. A backpack spray device was used to consistently apply a solution of kaolin and CaCO₃, with a volume of 10 ± 0.5 L, across the entire tree canopy. Shades were manufactured from knitted polyethylene fabric from Al-Amir Shade Net Company, El-Gharbia Governorate, Egypt. Three different types of colored shading nets (white, green, and black) were employed at specific shading percentages. The white shade net was used at 50%, the green shade net at 50% and 63%, and the black shade net at 50% and 63%. The control group comprised trees that were subjected to full sunshine conditions, meaning they were placed in an open field without any further treatments. On 15 May, the nets were placed horizontally at a height of 3 m on each tree, with a rough positioning of around 50 cm over the mandarin trees. The nets stayed in place for 7 months while the fruits ripened and were then picked in mid-December.

2.3. Data Collection and Measurements

2.3.1. Microclimate of Orchards

The air temperature (both maximum and minimum) and relative humidity were measured using a Digital Thermo-Humidity Meter (KT-905; China) every month. The measurements were taken under different shade nets with shading rates, both inside and outside the tree canopy [7]. These measurements were compared with those from other treatments.

2.3.2. Leaf and Fruit Surface Temperatures

The surface temperatures of the leaves and fruits were observed on clear days using an infrared thermometer sensor (IT-122; China). The temperature of 10 leaves and 10 fruits in each of the 4 orientations per tree was measured during midday (11:00–13:00) from June to September on the sunny side of both treated and control trees in both seasons, according to Tsai et al. [7].

2.3.3. Fruit Sunburn

To determine the proportion of fruit sunburn, the number of sunburned fruits per tree was calculated at the time of harvest. The percentage of burnt fruits per tree was then computed using the equation used by Mohsen and Ibrahim [34].

Sunburn% = (No. of sunburned fruits/Total No. of fruits) × 100

2.3.4. Fruit Sunburn Severity

During the harvest period, which occurs in the 2nd week of December, the sunburned fruit on each tree were classified into three groups based on the severity of damage. These categories are light (characterized by mild bleaching), medium (involving tissue damage without necrosis), and high (involving dark necrotic regions and cell death) [19], as illustrated in Figure 2.

2.3.5. Yield and Its Component

The fruit count and yield per tree, measured in kilograms per tree and tons per hectare, were determined during the harvest period on 15 December in 2022–2023 and 2023–2024 seasons.

2.3.6. Fruit Yield Increment

The percentage increase in fruit yield compared to the control was estimated using Abd El-Naby et al. equation [35]:

Fruit yield increment% = [(Fruit yield(kg)/treatment − Fruit yield(kg)/control)/(Fruit yield(kg)/control)] × 100

2.3.7. Yield Efficiency (YE)

The yield efficiency (YE) was calculated by dividing the fruit weight (in kilograms) by the planting distance (in square meters).

2.3.8. Fruit Characteristics

To assess the quality of the fruit, a random sample of 10 mature fruits was collected from each tree (replicate) during the harvest season on 15 December. The fruits were then processed and analyzed to evaluate their physical and chemical characteristics.

The average weight (g) and volume (cm³) of each sampled fruit were determined. The bulk density of the fruit (g/cm³) was estimated using the formula provided by [36], and [37] bulk density (g/cm³) = fruit weight (g)/ fruit volume (cm³), juice volume (mL), fruit length (cm), fruit diameter (cm), fruit shape (L/D ratio), and peel thickness (cm) were measured at median by using Varnier caliper, peel firmness (kg/cm²) was measured on opposite cheeks using Effegi penetrometer (Effegi, Alfonsine, Italy), while pulp weight %, peel weight %, fruit rag weight %, and juice weight were calculated. SSC% was determined with a digital refractometer Milwaukee MA871 (Milwaukee Co., Ltd., Padua, Italy) at 20 °C. Total titratable acidity (mg citric acid/100 mg juice) was evaluated by titrating a known volume of the juice with a 0.1 N sodium hydroxide solution using 1% phenolphthalein as an indicator, following the method outlined in (AOAC) [38]. SSC/acid ratio was estimated from obtained data recorded of fruit juice SSC and total acidity by dividing SSC% over total acidity. The concentration of Vitamin C in the juice was measured using 2, 6-dichlorophenolindophenol and reported as mg/100 mL of juice, as specified by (AOAC) [38]. Chlorophyll and total carotenoid pigment contents in the peel of fruit (three replicates) were spectrophotometrically by using a spectrophotometer (UV/Visible spectrophotometer, Libra SS0PC, Thermo Fisher Scientific, Waltham, MA, USA), determined, according to Wettstein [39], using the following equations.

Chlorophyll (a) (µg/mL) = 9.784 A 662 − 0.99 A 644.

Chlorophyll (b) (µg/mL) = 21.426A 644 − 4.65A 662.

Total carotenoids (µg/mL) = (4.695) A 440 nm − (0.268) (a + b).

where A is the optical density at the specified wavelength.

The results were quantified in mg/100 g of fresh peel weight (FW) using the following formula: [(Value obtained from each equation multiplied by the volume of the extract) divided by (1000 multiplied by FW)], multiplied by 100.

The color flavedo was determined using a portable colorimeter (FRU WR18, Shenzhen, China) on two opposite sides of the equatorial area of five fruits per treatment, based on the specified variables. L*, a*, and b* are three variables. The L* (lightness) values indicate the brightness of the fruit surface, ranging from 0 (black) to 100 (white color). The a* values represent the red color when positive, and the green color when negative. The b* values represent the yellow color when positive and the blue color when negative [40]. The spectrum of color is an amalgamation of three fundamental facets [41].

2.4. Statistical Analysis

Data with eight treatments and three replications of each treatment, in a fully randomized block design (CRBD), were used in this investigation. Using Co-Stat version 6.45, a one-way ANOVA test was performed to assess the data based on [42]. To compare the means, Duncan’s multiple range test was used, with a significance threshold of 0.05 [43].

3. Results

3.1. Microclimate of Orchards

To examine the impact of different shading colors (white, green, and black) and sprays of reflective substances (kaolin and calcium carbonate) on the microclimate of orchards, we conducted measurements and analyses of two key factors: the air temperature and relative humidity both inside and outside the tree canopy during midday (11:00–13:00) from June to September. The results are presented in Figure 3A,B.

In general, the use of B63% resulted in consistently lower air temperatures outside and inside the tree canopy during the examined periods. The reductions ranged from 12.01% to 16.25% compared to the control. In contrast, treatments like G50% and G63% exhibited only slight decreases in temperature, indicating a lower effectiveness in reducing heat exposure. The findings demonstrated that the utilization of shade nets of varying colors had a substantial impact on the microenvironment of the orchard. According to the current research, the shade net’s color and shading rate had a substantial impact on the air temperature both outside and inside the tree canopy at midday. As the level of shading increased, both the air temperature outside and inside the tree canopy decreased (Figure 3A). The study found that the average canopy temperature decreased with the use of different color shade nets, especially during warmer months like June, July, August, and September. Significant changes in mean temperature were observed between different shading treatments, indicating that shading significantly influenced ambient temperature both inside and outside the tree canopy.

On the other hand, the results showed that the average relative humidity outside and under the tree canopy rose under all color shade nets compared to the open field, particularly during the warmer months (June, July, August, and September). This is illustrated in Figure 3B. The greatest average relative humidity was seen both outside and inside the tree canopy when covered with a black shade net with a shading rate of 63%. This was followed by other shade net treatments, while the lowest values were recorded in the open field without any treatment.

3.2. Leaf and Fruit Surface Temperatures

Both seasons’ data showed a notable disparity in the average temperature of the leaf and fruit surfaces in the four tree orientations (north, south, east, and west) from June to September. The findings indicated that using color shade nets and sprays of reflective materials resulted in lower temperatures on the leaf and fruit surfaces compared to the control group. This is illustrated in Figure 4 and Figure 5. The data depicted that black shade nets have a significantly superior impact on reducing the temperature of both leaves and fruits compared to green and white shade nets, particularly when employing a shading rate of 63%. It was also noted that the leaf and fruit surface temperature of ‘Balady’ mandarin trees under the conditions of this experiment recorded the highest values in the southern and western sides, followed by the rest of the trends in both seasons. Furthermore, the fruit surface temperature exhibited greater values compared to the temperature observed on the leaf during both seasons.

3.3. Fruit Sunburn and Severity

Data in

Table 4. Effect of shading and sprays of some reflective materials on fruit sunburn and severity of sunburned fruits of ‘Balady’ mandarin trees.

Treatments	Fruit Sunburn %		Severity % of Sunburned Fruit
			Light %		Medium %		High %
	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024
Control	9.31 a	8.17 a	13.10 c	12.68 c	32.75 c	32.40 c	54.15 a	54.94 a
Kaolin 4%	4.00 c	3.28 c	49.52 a	53.83 a	36.46 a	36.27 a	14.02 c	9.89 c
CaCO3 3%	7.58 b	7.05 b	39.99 b	41.66 b	33.85 b	33.34 b	26.16 b	25.00 b
W50%	-	-	-	-	-	-	-	-
G50%	-	-	-	-	-	-	-	-
G63%	-	-	-	-	-	-	-	-
B50%	-	-	-	-	-	-	-	-
B63%	-	-	-	-	-	-	-	-

Means followed by different letters are significantly different within columns by Duncan’s multiple range test, p ≤ 0.05.

clearly show the effect of shading and sprays of some reflective materials on fruit sunburn percentage and severity % of sunburned fruits of ‘‘Balady’’ mandarin trees in the 2022–2023 and 2023–2024 seasons.

In terms of fruit sunburn percentage, in both seasons, it was observed that all treatments were successful in reducing the percentage of sunburn in ‘Balady’ mandarin fruit. The use of shading nets of different colors was found to be particularly effective as it eliminated sunburn symptoms. However, a low rate of sunburn (4.00% and 3.28%) was observed in fruits sprayed with kaolin at 4%, followed by the treatment of CaCO₃ at 3% (7.58% and 7.05%). In contrast, control fruits, which were grown without any treatments, showed a significant incidence of sunburn (9.31% and 8.17%) in both seasons, respectively (Table 4). Concerning the severity % of sunburned fruits, the data shown in Table 4 indicated that the percentage of fruits with a high level of sunburn severity (see Figure 2) was more notable in control fruits than in untreated fruits. The findings demonstrated that the use of colored shading nets, foliar spraying with kaolin at 4%, and applying CaCO₃ at 3% effectively decreased sun damage on scorched fruits of ‘Balady’ mandarin trees in the 2022–2023 and 2023–2024 seasons, as compared to the control group in the open field. Nevertheless, there were no instances of sun damage detected on the fruits that were covered by the various colored shade nets. The application of 4% kaolin spray resulted in a decrease in solar injuries in the mild and medium categories, whereas the use of a 3% CaCO₃ spray also showed a reduction compared to the control group. The sunburn injuries on fruits obtained from the control were the most severe in the high category in both seasons.

3.4. Yield and Its Components, Fruit Yield Increment in Relation to the Control and Yield Efficiency

Data listed in

Table 5. Effect of shading and sprays of some reflective materials on yield components, fruit yield increment, and yield efficiency of ‘Balady’ mandarin trees.

Treatments	Yield Components						Fruit Yield Increment %		Yield Efficiency (kg/m2)
	Number of Fruits/Tree		Yield (kg/Tree)		Yield (ton/ha.)
	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024
Control	819.73 f	868.89 f	91.17 g	97.50 h	36.74 g	39.31 h	0.00 g	0.00 h	3.65 g	3.90 h
Kaolin 4%	893.00 d	924.67 e	104.67 e	112.50 f	42.20 e	45.36 f	14.80 e	15.39 f	4.19 e	4.50 f
CaCO3 3%	857.55 e	850.49 g	100.33 f	103.00 g	4.45 f	41.52 g	10.06 f	5.64 g	4.01 f	4.12 g
W50%	1031.51 a	1055.93 a	131.00 a	136.67 a	52.82 a	55.10 a	43.70 a	40.17 a	5.24 a	5.47 a
G50%	985.03 b	1007.80 b	124.00 b	129.33 b	49.99 b	52.147 b	36.02 b	32.65 b	4.96 b	5.17 b
G63%	964.18 bc	991.20 c	119.33 c	125.00 c	48.12 c	50.400 c	30.90 c	28.21 c	4.77 c	5.00 c
B50%	979.00 b	979.48 c	119.00 c	122.00 d	47.98 c	49.19 d	30.54 c	25.13 d	4.76 c	4.88 d
B63%	952.01 c	948.67 d	112.33 d	117.00 e	45.29 d	47.17 e	23.23 d	20.00 e	4.49 d	4.68 e

Means followed by different letters are significantly different within columns by Duncan’s multiple range test, p ≤ 0.05.

showed the effect of shading and sprays of some reflective materials on yield, yield components, and fruit yield increment % in relation to the control and yield efficiency of ‘Balady’ mandarin trees in the 2022–2023 and 2023–2024 seasons. Concerning the number of fruits per tree, data in Table 5 showed that, in comparison to the lowest number recorded by the control in the 2022–2023 and 2023–2024 seasons, the number of fruits per tree was significantly increased under color shading nets and reflecting materials (kaolin at 4% and CaCO₃ at 3%). In comparison to the lowest number of fruits per tree obtained under the open field, the maximum number of fruits per tree of ‘Balady’ mandarin trees were obtained under the white shade net at 50% shading rate, followed by the green shade net and the black shade net at 50% shading rate. The data reported in Table 5 demonstrate the impact of shade and sprays of certain reflecting materials on yield (kg/tree). There were statistically significant differences among the treatments in both the 2022–2023 and 2023–2024 seasons.

The highest yield per tree (131.00 and 136.67 kg/tree, respectively) was achieved under a 50% white shade net for both seasons, followed by other colored shade-net treatments. In comparison, the lowest yield per tree was observed in the open-field treatments (control, kaolin at 4%, and CaCO₃ at 3%) over both seasons of the study. The results from Table 5 indicate that there were significant differences in the yield (ton/ha) of ‘Balady’ mandarin fruits due to shading and sprays of reflective materials during the 2022–2023 and 2023–2024 growing seasons. Concerning fruit yield increment % compared to the control, there was a noticeable improvement in the increased-yield ratio in all the treatments. The study utilized yield efficiency, measured in kg/m², to assess the effectiveness of shade and spraying with reflective materials in maximizing the utilization of ‘Balady’ mandarin trees. The trees covered with a white shade net with a 50% shading rate had the highest yield efficiency values (5.24 and 5.47 kg/m²) compared to the control, which had the lowest values (3.65 and 3.50 kg/m²) in both seasons. The green shade net with a 50% shading rate also resulted in higher yield efficiency values. All differences were statistically significant, except those between the green shade net with a 63% shading rate and the black shade net with a 50% shading rate in the first season (Table 5).

3.5. Fruit Physical Properties

Data reported in

Table 6. Effect of shading and sprays of some reflective materials on fruit weight (g), fruit volume (cm³), fruit density (g/cm³), and juice volume (ml) of ‘Balady’ mandarin fruits.

Treatments	Fruit Weight (g)		Fruit Volume (cm3)		Fruit Density (g/cm3)		Juice Volume (mL)
	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024
Control	111.22 e	112.22 e	125.33 g	131.11 h	0.89 a	0.86 b	35.72 e	36.67 e
Kaolin 4%	117.22 d	121.67 d	139.44 e	141.11 f	0.84 b	0.86 b	39.49 cd	41.67 cd
CaCO3 3%	117.00 d	121.11 d	131.56 f	135.56 g	0.89 a	0.89 a	38.72 d	40.00 d
W50%	127.00 a	129.44 a	171.67 a	173.33 a	0.74 d	0.75 e	46.52 a	48.89 a
G50%	125.89 a	128.33 a	161.44 b	164.44 b	0.78 c	0.78 d	45.45 ab	47.78 ab
G63%	123.78 b	126.11 b	160.44 b	162.22 c	0.77 c	0.78 d	44.71 b	46.67 b
B50%	121.56 c	124.56 c	154.11 c	156.67 d	0.79 c	0.80 c	40.61 c	42.78 c
B63%	118.00 d	123.33 c	141.67 d	144.44 e	0.83 b	0.85 b	39.64 cd	41.67 cd

Means followed by different letters are significantly different within columns by Duncan’s multiple range test, p ≤ 0.05.

,

Table 7. Effect of shading and sprays of some reflective materials on fruit length (cm), fruit diameter (cm), fruit shape (L/D ratio), peel thickness (mm), and peel firmness (g/cm²) of ‘Balady’ mandarin fruits.

Treatments	Fruit Length (cm)		Fruit Diameter (cm)		Fruit Shape (L/D Ratio)		Peel Thickness (mm)		Peel Firmness (g/cm2)
	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024
Control	5.22 f	5.24 g	6.58 f	6.68 e	0.79 a	0.79 a	2.39 g	2.50 f	782.58 h	790.00 h
Kaolin 4%	5.33 e	5.39 e	7.19 d	7.23 d	0.74 e	0.75 c	2.51 f	2.63 e	832.47 f	841.11 f
CaCO3 3%	5.33 e	5.34 f	7.15 e	7.23 d	0.75 de	0.74 c	2.50 f	2.61 e	815.48 g	823.33 g
W50%	5.85 a	5.90 a	7.64 a	7.72 a	0.77 b	0.77 b	2.77 e	2.88 d	848.78 e	857.78 e
G50%	5.70 b	5.72 b	7.57 b	7.69 a	0.75 c	0.74 c	2.97 d	3.11 c	865.33 d	875.00 d
G63%	5.53 c	5.55 c	7.55 b	7.62 b	0.73 f	0.73 d	3.02 c	3.14 c	892.45 c	902.78 c
B50%	5.50 d	5.54 cd	7.36 c	7.45 c	0.75 d	0.74 c	3.18 b	3.27 b	910.22 b	918.89 b
B63%	5.48 d	5.51 d	7.20 d	7.27 d	0.76 b	0.76 b	3.25 a	3.36 a	944.33 a	950.00 a

Means followed by different letters are significantly different within columns by Duncan’s multiple range test, p ≤ 0.05.

and

Table 8. Effect of shading and sprays of some reflective materials on pulp weight (%), peel weight (%), fruit rag weight (%), and juice weight (%) of ‘Balady’ mandarin fruits.

Treatments	Pulp Weight (%)		Peel Weight (%)		Fruit Rag Weight (%)		Juice Weight (%)
	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024
Control	67.83 de	69.27 c	32.17 ab	30.73 b	36.06 a	36.01 ab	31.77 c	33.26 e
Kaolin 4%	70.05 b	70.47 bc	29.95 d	29.53 bc	36.36 a	36.87 a	33.69 b	33.60 e
CaCO3 3%	66.86 e	67.03 d	33.14 a	32.97 a	33.90 b	33.66 d	32.96 bc	33.37 e
W50%	71.13 a	72.42 a	28.87 e	27.58 d	34.53 ab	34.43 cd	36.61 a	37.99 a
G50%	69.07 bc	70.58 bc	30.93 cd	29.42 bc	34.60 ab	33.54 d	34.47 b	37.04 b
G63%	69.34 bc	70.99 ab	30.66 cd	29.01 cd	35.05 ab	35.05 bc	34.29 b	35.94 c
B50%	68.77 cd	71.02 ab	31.23 bc	28.98 cd	34.47 ab	35.30 bc	34.30 b	35.72 c
B63%	69.59 bc	70.34 bc	30.41 cd	29.66 bc	35.21 ab	35.36 bc	34.38 b	34.98 d

Means followed by different letters are significantly different within columns by Duncan’s multiple range test, p ≤ 0.05.

showed that shading and sprays of reflective materials treatments enhanced the physical characteristics of ‘Balady’ mandarin fruits in this experiment, in both seasons.

Data from both seasons demonstrated statistically significant variations in fruit weight (g), fruit volume (cm³), fruit density (g/cm³), and juice volume (mL) across the different shading and sprays of reflecting materials treatments compared to the control group (Table 6). The data indicates that ‘Balady’ mandarin trees, when covered with a white and green shade net at a 50% shading rate, experienced a notable increase in the average weight of their fruits (specifically the heaviest ones) and the highest volume of juice. These results were significantly better compared to other treatments, with no significant differences observed among them. In contrast, the control group yielded the lowest values in both seasons. The white shade net at a 50% shading rate had the highest fruit volume, followed by the green shade net at a 50% shading rate, as well as other treatments. In comparison, the control group had the lowest values in both seasons. Regarding fruit density (g/cm³), the application of a 3% CaCO₃ spray and the control group increased fruit density (g/cm³) during the first season, with no significant differences observed between the two. In the second season, trees that were treated with a 3% CaCO₃ spray had the highest fruit density. This was in contrast to the lowest fruit density, which was observed in the first season with a white shade net that had a 50% shading rate, and in the second season with a green shade net that had shading rates of 50% and 63%.

Data presented in Table 7 indicate notable variations across treatments in both seasons regarding fruit length (cm), fruit diameter (cm), fruit shape (L/D ratio), peel thickness (mm), and peel firmness (g/cm²). In all seasons, the white shade net with a 50% shading rate resulted in the highest fruit length (cm) and fruit diameter (cm) compared to the control and other treatments.

The fruit shape, as influenced by all treatments, exhibited considerable variations in both seasons. The control treatment had the highest L/D ratio, whereas the green shade net with a 63% shading rate had the lowest values. The trees treated with a black shade net with a 63% shading rate showed the highest values for both peel thickness (mm) and peel firmness (g/cm²). This was followed by the trees treated with a black shade net with a 50% shading rate. In comparison, the control treatment and other treatments had significantly lower values for peel thickness and peel firmness in both seasons. In addition, there were significant differences observed among the treatments about the four qualitative attributes of ‘Balady’ mandarin fruit: pulp weight (%), peel weight (%), fruit rag weight (%), and juice weight (%) (Table 8). The fruit samples with a white shade net at a 50% shading rate exhibited the highest percentages of pulp weight (71.13% and 72.42%). No significant differences were observed in the other shading treatments compared to the open-field condition. Nevertheless, the treatment involving the application of CaCO₃ produced the lowest minimal values (66.86% and 67.03%) for both seasons. The application of CaCO₃ resulted in the highest percentage of peel weight (33.14 and 32.97) compared to the other treatments. Balady mandarin trees under the white shade net at a 50% shading rate recorded the lowest values (28.14 and 27.58) in both seasons. Applying kaolin at a concentration of 4% and using control treatments resulted in a significant increase in fruit rag weight percentage. There were no significant differences between these treatments in both seasons. However, the lowest values were observed when using CaCO₃ at a concentration of 3% in the first season, and when using a white shade net with a shading rate of 50%, followed by spraying CaCO₃ at a concentration of 3% in the second season. Furthermore, there were no notable distinctions observed among the remaining shade net treatments. A notable disparity in the juice weight percentage was seen in the fruit of trees under the white shade net with a shading rate of 50%, as well as in the other treatments, as compared to the control. The ‘Balady’ mandarin fruit had the maximum juice weight (36.61% and 37.99%) when shaded with a white shade net at a 50% shading rate. Under other conditions, the average juice weight ranged from 34.47% to 32.96% and 37.04% to 33.37% (both seasons).

3.6. Fruit Chemical Properties

Shading and reflecting material sprays affected several fruit chemical characteristics of ‘Balady’ mandarin fruits in the 2022–2023 and 2023–2024 seasons (

Table 9. Effect of shading and sprays of some reflective materials on SSC %, total acidity %, SSC/acid ratio, vitamin C, and pH juice of ‘Balady’ mandarin fruits.

Treatments	SSC %		Total Acidity %		SSC/Acid Ratio		Vitamin C (mg/100 mL Fresh Juice)		pH Juice
	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024
Control	8.43 h	8.47 e	1.069 a	1.088 a	7.89 h	7.78 g	45.87 g	46.93 d	3.53 d	3.63 c
Kaolin 4%	9.35 f	9.35 d	0.879 c	0.960 b	10.63 f	9.73 f	46.93 ef	47.87 d	3.63 bc	3.73 bc
CaCO3 3%	8.52 g	8.60 e	0.955 b	0.896 c	8.92 g	9.60 f	46.33 fg	46.93 d	3.57 cd	3.70 bc
W50%	11.18 a	11.28 a	0.745 f	0.753 f	15.00 a	14.98 a	56.73 a	57.60 a	3.77 a	3.87 a
G50%	10.48 b	10.69 b	0.746 f	0.761 f	14.05 b	14.05 b	55.93 b	57.33 a	3.70 ab	3.80 ab
G63%	10.30 c	10.53 b	0.818 e	0.821 e	12.60 c	12.82 c	53.53 c	54.13 b	3.67 b	3.77 ab
B50%	9.77 d	10.00 c	0.829 de	0.832 de	11.79 d	12.02 d	49.53 d	50.13 c	3.67 b	3.77 ab
B63%	9.59 e	9.64 cd	0.838 d	0.843 de	11.44 e	11.44 e	47.07 e	48.00 d	3.63 bc	3.77 ab

Means followed by different letters are significantly different within columns by Duncan’s multiple range test, p ≤ 0.05.

).

Data exhibited that there were statistically significant variations among treatments in both seasons for parameters such as SSC%, total acidity%, SSC/acid ratio, vitamin C, and pH of the juice. In both seasons, trees that were covered with a white shade net at a 50% shading rate had the greatest values for SSC % and SSC/acid ratio when compared to the control. However, the control exhibited the highest percentage of juice acidity compared to the lowest values achieved by the white and green shade nets with a shading rate of 50%, which were similar to one another in this regard. White shade net with a 50% shading rate had a significant impact on increasing the vitamin C content during the first season. Similarly, in the second season, the white shade net with a 50% shading rate, followed by the green shade net at a 50% shading rate, also showed significant increases in vitamin C content compared to the lowest values observed in the control group during the first season and the control group and spraying kaolin at 4% during the second season. The pH of the juice had a higher value when the fruits were placed under the color shade netting, in comparison to the fruits that were left uncovered. The juice with the greatest pH values (3.77 and 3.87) was obtained while using a white shade net at a 50% shading rate in both seasons, respectively. This was followed by the use of a green shade net with a 50% shading rate, which resulted in pH values of 3.70 and 3.80. There were no significant differences between these two conditions in both seasons. On the other hand, the control group had the lowest pH values in both seasons, averaging 3.53 and 3.63 (Table 9).

3.7. Chlorophyll Pigments, Total Carotenoids, and Color Parameters (L*, a*, and b*)

Table 10. Effect of shading and sprays of some reflective materials on chlorophyll and total carotenoids of ‘Balady’ mandarin fruits.

Treatments	Chlorophyll A (mg/100 g Fresh Fruit Peel)		Chlorophyll B (mg/100 g Fresh Fruit Peel)		Total Chlorophyll (mg/100 g Fresh Fruit Peel)		Total Carotenoids (mg/100 g Fresh Fruit Peel)
	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024
Control	2.90 a	2.80 a	3.63 a	3.56 a	6.53 a	6.37 a	21.10 g	20.44 f
Kaolin 4%	2.48 b	2.34 c	2.11 c	2.06 c	4.59 c	4.40 c	21.68 f	21.11 e
CaCO3 3%	2.50 b	2.49 b	2.84 b	2.69 b	5.33 b	5.18 b	21.38 fg	20.89 e
W50%	1.08 e	0.99 g	1.32 e	1.19 f	2.40 g	2.17 h	28.53 a	27.12 a
G50%	1.15 e	1.02 g	1.40 e	1.32 f	2.54 g	2.34 g	25.97 b	25.45 b
G63%	1.31 e	1.18 f	1.63 d	1.56 e	2.94 f	2.75 f	23.85 c	23.38 c
B50%	1.70 d	1.61 e	2.09 c	1.89 d	3.79 e	3.50 e	22.68 d	21.99 d
B63%	2.03 c	1.87 d	2.22 c	2.16 c	4.24 d	4.03 d	22.31 e	21.82 d

Means followed by different letters are significantly different within columns by Duncan’s multiple range test, p ≤ 0.05.

shows that, for both seasons, the amount of carotene and chlorophyll pigments in the fruit peel was significantly affected by shade nets and sprays of reflecting materials. The control group, consisting of open fields without any treatment, exhibited the highest levels of chlorophyll pigments (chlorophyll a and b). This was followed by calcium carbonate treatment at 3% and kaolin treatment at 4%. In comparison, the lowest levels were observed in trees grown under a white shade net with a shading rate of 50%, as well as in the other covering treatments, during both seasons. In contrast, the white shade net at a 50% shading rate produced the highest levels of carotene content, followed by the green and black shade nets and reflecting material, when compared to the control treatment in both seasons. As shown in

Table 11. Effect of shading and sprays of some reflective materials on fruit color parameters of ‘Balady’ mandarin fruits in 2022–2023 and 2023–2024 seasons.

Treatments	L*		a*		b*
	2022–2023	2023–2024	2022–2023	2023–2024	2022–2023	2023–2024
Control	56.30 e	57.22 d	8.78 e	9.19 e	49.35 c	50.82 d
Kaolin 4%	56.82 cde	57.92 cd	14.81 c	15.75 c	52.84 b	53.57 c
CaCO3 3%	56.55 de	57.74 cd	11.67 d	12.80 d	52.63 b	53.47 c
W50%	59.66 a	60.68 a	18.91 a	19.75 a	57.63 a	58.98 a
G50%	58.65 ab	59.36 b	18.50 a	19.03 a	56.54 a	57.11 ab
G63%	58.32 ab	59.14 b	17.76 ab	18.44 ab	55.94 a	56.76 b
B50%	58.13 bc	59.07 b	16.33 bc	17.14 bc	55.83 a	56.36 b
B63%	57.87 bcd	58.64 bc	15.61 c	16.51 c	53.58 b	54.33 c

Means followed by different letters are significantly different within columns by Duncan’s multiple range test, p ≤ 0.05.

, all treatments statistically significantly raised the values of skin color parameters (L*, a*, and b*) compared to the control. The green shade net and the white shade net, both at a 50% shading rate, had the same statistically significant relationship concerning the greatest lightness (L*) values compared with the control. Contrarily, all treatments affected the a* and b* values. Accordingly, the white shade net with the maximum shading rate of 50% proved to have the highest a* and b* values statistically in both seasons. Notably, compared to the control treatment, the application of kaolin at 4% and CaCO₃ at 3% resulted in marginally higher L* and b* values, suggesting a paler and more yellowish look of the fruits.

3.8. Economic and Agronomic Comparison of Shading Technologies vs. Kaolin Spraying for ‘Balady’ Mandarin in Egypt

The comparison between shading technologies and kaolin spraying on Balady mandarin trees in Egypt provides valuable insights into both the economic and agronomic aspects. This discussion integrates the findings from the experimental results and economic evaluations to highlight the relative advantages of each approach.

• Initial Costs: Shading technologies incur significantly higher initial costs, ranging between EGP 126,000 and 189,000 per feddan, due to the installation of shade nets. However, their effectiveness in completely eliminating fruit sunburn and improving microclimatic conditions justifies the investment, particularly for large-scale operations. In contrast, kaolin spraying has a lower initial cost (EGP 2520 to 6300 per feddan annually) but requires repeated applications each season to achieve a significant reduction in sunburn (down to 3.28%).
• Operational Costs: Shading technologies, once installed, present low operational costs (EGP 2520 to 6300 per feddan annually) mainly related to maintenance. In contrast, kaolin requires a higher operational expense due to multiple applications per season, with each application costing EGP 2520 to 5040 per feddan.
• Impact on Yield and Quality: Shading nets, particularly the white shade net with a 50% shading rate, led to the highest yield (up to 136.67 kg/tree) and superior fruit quality, with the best results in terms of juice content and fruit weight. Kaolin spraying resulted in a lower yield (up to 121.67 kg/tree) and slightly reduced fruit quality compared to shading treatments.
• Long-Term Benefits: The long-term benefits of shading technologies include not only full sunburn protection but also consistent improvements in fruit yield and quality. Kaolin spraying, while flexible and adaptable, incurs higher long-term costs.
• Market and Environmental Considerations: Shading technologies reduce the need for chemical treatments and water usage, offering sustainability, while kaolin spraying remains environmentally friendly and accepted in organic farming but offers lower returns.
• Economic Return: Shading technologies provide higher long-term returns due to consistent impact on yield and quality. Kaolin, while cheaper initially, offers lower returns due to its recurring expenses (

  Table 12. Feasibility study of the applied treatments.

  Aspect	Shading Technologies (Cost per Feddan, Agronomic Results)	Kaolin Spraying (Cost per Feddan, Agronomic Results)
  Initial Costs	High (e.g., EGP 126,000–189,000 per feddan)—No fruit sunburn under shade net treatments	Low (e.g., EGP 2520–6300 per feddan annually)—Reduces sunburn to 3.28%
  Operational Costs	Low (e.g., EGP 2520–6300 per feddan annually)	High (e.g., EGP 2520–5040 per application per feddan, 3–5 applications per season)
  Impact on Yield and Quality	Highest yield under white shade net 50% (up to 136.67 kg/tree) with superior fruit quality (highest juice content)	Improves yield (up to 121.67 kg/tree), though lower than shading treatments, and enhances fruit quality
  Long-Term Benefits	High, with consistent fruit quality over time and total sunburn elimination	Flexible, with recurring costs each season, reduces sunburn but is less effective than shading
  Market and Environmental Considerations	Sustainable, reduces water/chemical use, high initial investment, highest fruit yield and quality	Environmentally friendly, well-accepted in organic farming, reduces sunburn and improves quality
  Economic Return	Highest long-term returns, especially for large-scale operations due to consistent yield and quality	Lower initial costs but higher recurring expenses; effective but less impactful than shading on yield

  ).

4. Discussion

4.1. Microclimate of Orchards

This study assesses the importance of agronomic methods, including shade netting and spraying reflecting materials such as kaolin and carbonate calcium, in adapting to the climate and maintaining the quality of mandarin fruit in the Mediterranean area, as well as becoming standard practices for protected horticulture in many countries. In Egypt, netting is a method used to reduce heat stress in crops by modifying their microclimate. It enhances plant growth and output by shielding them from intense sun radiation, thereby improving temperature conditions and reducing disease incidence in fruit harvests [44]. Our results, shown in Figure 3, indicate that using black shade nets on trees effectively reduced air temperature, with a maximum difference of up to 4 °C, while green shade nets and white shade nets also reduced temperatures. Additionally, colored shading nets and reflective material treatments reduced the surface temperatures of leaves and fruits, especially when using black shading nets with different ratios. Our research aligns with the findings of Kalcsits et al. [25], which revealed that the use of netting resulted in a reduction of around 20% in the mean daily maximum light intensity in rows that were not covered. Furthermore, our findings were consistent with the results reported by [45,46,47]. These studies demonstrated that shade nets can lower canopy temperature and increase relative humidity, depending on the specific type of shade nets and the climatic region, when compared to open field conditions. Glenn [11] showed that reflectors, such as kaolin, can lower canopy temperatures by reflecting infrared and ultraviolet radiation, as well as photosynthetically active radiation.

Applying the idea put forward by Narjesi et al. [30] to pomegranate trees, they found that by lowering the temperature and light intensity, shade nets produced an environment that was favourable for the physiological activities that plants engage in, such as photosynthesis. Regarding the effects on the orchard micro-climate, controlling the temperature and relative humidity of the shaded area is possible by modifying the net’s type, color, and texture. According to Tinyane et al. [48], red shading nets had the lowest relative humidity, while white shading nets had the highest. The canopy temperature was lowered by 7.6 and 7.3 degrees Celsius, respectively, by white and blue shade nets.

4.2. Leaf and Fruit Surface Temperatures

An analysis comparing the use of shade nets and reflective materials reveals that the use of these materials often leads to a decrease in leaf and fruit temperature in the environment, as shown in Figure 4 and Figure 5. Generally, these results are in harmony with those obtained by Tsai et al. [7], who determined that the use of black nets and calcium carbonate resulted in a reduction in fruit temperature as a result of the interception of radiation by the nets, and shade treatments had a substantial impact on reducing leaf surface temperatures compared to the control group. The study by Lee et al. [49] observed a notable decrease in the surface temperatures of both the leaves and fruits of ‘Ponkan’ mandarin trees when white shade nets were employed, as compared to the control. These findings align with our research on the decrease in fruit temperature achieved by using shading nets. Another study by Kalcsits et al. [25] found that using pearl 20% shading nets significantly reduced maximum leaf temperature by 4 °C in apple orchards, while pearl and blue nets also effectively reduced fruit surface temperature during high heat periods. The greatest difference in fruit surface temperature between the exposed control and shelter net was 2.6 to 4.3 °C under full-sun conditions. Other investigations by Narjesi et al. and Tinyane et al. [30,48] demonstrated that fruits’ average temperatures were significantly lower under colored shade nets than they were under control trees. The shade nets had a more pronounced impact on reducing leaf and fruit temperature. Our findings are in agreement with those of Jifon and Syvertsen and Melgarejo et al. [50,51], which also discovered that kaolin-treated grapefruit and pomegranate trees had cooler leaves and fruits than untreated trees. In the study by Rodriguez et al. [5], it was shown that reflection lowered the temperatures of grapefruit trees’ fruit by 0.2 °C and their leaves by 0.21 °C when compared to the control group. The use of kaolin as a foliar treatment resulted in a considerable reduction in leaf and fruit surface temperature when compared to the control [19]. One possible explanation for the observed reduction in fruit and leaf temperatures after kaolin treatment is its higher reflectivity of both visible and ultraviolet light, as well as of direct solar radiation [11].

4.3. Fruit Sunburn and Severity

It is important to note that high temperatures and strong solar radiation are the primary causes of sunburn and the severity percentage of sunburned in citrus crops [52,53]. Exposing citrus seedlings to sunlight can be reduced by using net shading to increase water use efficiency, photosynthesis, and fruit quality. Jifon and Syvertsen and Otero et al. [52,54] demonstrated that the presence of net shade can reduce the intensity of sunlight, retain soil moisture, decrease wind speed, and lower temperatures. Furthermore, Ilić et al. [55] found that color shade nets can reduce the intensity of light during the summer compared to the natural environment. Additionally, shading techniques, specifically the use of black shade nets, significantly enhanced fruit quality by reducing temperature and photosynthetic photon flux [7]. Mahmood et al. and Tinyane et al. [45,48], as well as Shaban et al. [56], conducted a study on pomegranate, avocado, and mango, respectively, to elucidate the efficacy of shade nets, such as white and blue shading nets, in safeguarding fruit trees from sunburn. The researchers found that all treatments markedly reduced the incidence and severity percentage of fruit sunburn damage.

In their study, Ali et al. [20] examined various nanoscale compounds, including calcium carbonate and kaolin clay, to determine their effectiveness in protecting fruit trees against sunburn. The researchers discovered that all treatments significantly decreased the occurrence of fruit sun scales. Our research, as shown in Tale 4, aligns with the findings of Tsai et al. [7], which confirmed that methods such as CaCO₃ spraying, shade nets, and bagging effectively decreased sunscald incidence without causing notable variations in fruit quality. Another study has shown that the main effect of kaolin is to increase the reflection of solar radiation, which in turn helps to reduce the temperature of exposed leaves and fruits during the hottest hours. This can greatly reduce the incidence and severity percentage of sunburn, as demonstrated in this study [19,53] in citrus. According to Glenn [11], kaolin can reduce sunburn by lowering the light intensity and temperature of leaves and fruits. The observed reduction in sunburn percentage and severity percentage might be explained by lower heat stress and fruit surface temperature. Our data support this idea, as seen in Table 4. Another study by Cronjé et al. [57] examined the effects of using 20% white shade nets on the quality of ‘Nadorcott’ mandarin fruit and demonstrated that shade netting significantly reduced the occurrence of sunburn and suggested that shade netting could be a promising solution for maintaining the excellent fruit quality.

4.4. Yield and Its Components, Fruit Yield Increment in Relation to the Control and Yield Efficiency

The utilization of shade nets resulted in increased yield, yield efficiency, and yield components in comparison to the cultivation of trees without net cover [44,58] on orange and [59] on lime. The fruit size difference shown in Table 6 was influenced by the shade net treatment. It is probable that the increased vegetative growth under the shade net, as observed by Brown [60], contributed to this difference. This finding contradicts the results of Wachsmann et al. [61], who found no influence of shade net on the fruit size of “Orri” mandarins. Overall, the application of shade consistently led to reduced air temperatures both outside and under the tree canopy during the observed periods. Our research corroborates the findings of Kaalcsits et al. [25], who showed that the utilization of netting led to a decrease of around 20% in the average daily maximum light intensity in uncovered rows. The shade net’s reduction in light intensity had an impressive effect on fruit size and, therefore, yield and its components, as demonstrated in Table 5. The findings of this study align with those of previous research conducted by Ennab et al., Zaghloul et al. [19,62], and El-Tanany et al. [53] on citrus. These studies reported that applying kaolin at three different times resulted in increased yield and improved yield components, particularly when using concentrations of 3% and 4%. Research conducted by Ali et al. [20] found that the use of synthetic chemicals, namely calcium carbonate and kaolin clay, resulted in a considerable increase in the production of ‘Murcott’ mandarin fruits and their components compared to the control.

4.5. Fruit Characteristics

According to research by Tsai et al. [7] on ‘Murcott’ mandarin trees shaded by black netting produced heavier and larger fruit than trees shaded by other types of netting. Blue shade nets with 70% light transmittance placed 0 cm above plants 30 days after flower fading improved pineapple fruit quality (size, firmness, yield, and total solids) [63]. In a study by Narjesi et al. [30], it was found that pomegranate trees under a white shade net allowed 50% photosynthetically active radiation, which resulted in the highest fruit quality and juice percentage among the shading treatments. Furthermore, shaded lemon fruits exhibited slightly higher fresh mass and equatorial diameter than open fruit [59]. Also, Mditshwa et al. [64] discovered that fruits produced under 25% white nets had substantially higher SSC/TA ratios than fruits grown under 7% transparent nets. Based on Ennab et al. and El-Tanany et al., [19,53] it was found that spraying kaolin improved the fruit quality of Balady mandarin fruits. Ali et al. [20] showed that several treatments, including calcium carbonate and kaolin clay, effectively decreased the acidity of ‘Murcott’ mandarin.

4.6. Chlorophyll Pigments, Total Carotenoids, and Color Parameters

Out of all the shading treatments, the white shade net at 50% shading rate consistently showed the most notable decrease in chlorophyll levels as compared to the control treatment. Similarly, the shading treatments, specifically using a white shade net and shading rate of 50%, had a more pronounced effect on the color parameters (L*, a*, and b*). Previous studies by Mditshwa et al. [64] and Mira–García et al. [59] found that fruit trees grown under shade nets had enhanced color development compared to those grown in the open field. These authors contended that the shade net’s ability to produce a cooler microclimate resulted in a favourable environment for the breakdown of chlorophyll and the buildup of carotenoids in the fruit peel. Thus, they deduced that the reduction in canopy temperature, caused by the use of shade netting, improves the degreening process. While nets serve as a physical barrier against unfavourable environmental conditions, it can be contended that they have a significant impact on the production of carotenoids. Furthermore, the results suggest that applying kaolin at a concentration of 4% resulted in minor alterations in color parameters. In the study, Dinis et al. and Hamdy et al. [65,66] discovered that using kaolin spray resulted in an augmentation of photochemical reflectance and photosynthetic pigments in plants.

5. Conclusions

Heat stress caused by high temperatures in the summer months and interaction with direct solar radiation and excess light causes sunburn in the leaves and fruits of ‘Balady’ mandarin. Compared with the leaves, fruits are more susceptible to sunburn, primarily because they have inefficient processes of utilizing and/or dissipating solar radiation. Sunburn causes important fruit losses in Balady mandarin yield, as well as income loss to farmers. According to the study, it is vital to balance growth and quality while avoiding overexposure to abiotic stress in places with high light intensity and air temperatures. Implementing netting to protect fruit cultivation can effectively alleviate stress, buffer elevated temperatures, and regulate fruit development. Netting additionally mitigates wind damage and lowers the occurrence of fruit sunburn, resulting in a decrease in overall losses caused by sunburn. To summarize, the results presented here show that using different types of nets and reflecting materials has positive benefits on the yield and quality of Balady mandarins, as well as reducing sunscald. Therefore, it could be recommended that trees be covered with a white shade net with a 50% shading rate or a green shade net with a 50 and 63% shading rate in summer months because it has a positive effect on preventing fruit sunburn damage and improving yield and fruit quality of ‘Balady’ mandarin trees. Hence, shade nets can be a beneficial technology to protect citrus fruits from sunburn and improve fruit quality in commercial citrus farms.