Improvement of the Physico-Chemical Properties, Nutritional, and Antioxidant Compounds of Pomegranate Fruit cv. ‘Wonderful’ Using Integrated Fertilization

Abstract

This study comprised of five different integrated fertilizers of calcium nitrate Ca(NO₃)₂ with ammonium sulphate (NH₄)₂SO₄ ratios (0%:100%, 10%:90%, 20%:80%, 30%:70%, and 40%:60%) to enhance the physico-chemical properties, and the antioxidant and nutritional compounds of pomegranate fruits cv. ‘Wonderful’. The results discovered that the application of Ca(NO₃)₂:(NH₄)₂SO₄ in different ratios significantly affected all measured parameters. Among integrated fertilizers, the 30%:70% combination showed an increment of 10.8% in fruit weight, 2.9% in fruit length, 11.8% in fruit volume, and 7.0% in fruit diameter. Similarly, total soluble solids, vitamin C, anthocyanin, total sugars, and reduced sugars, were also increased by 11.2%, 14.6%, 20.2%, 7.4%, and 5.2%, respectively. Likewise, values of both color variations from green to red (a*) and from blue to yellow (b*), and chroma, were also increased by 13.8%, 16.6%, and 14.4%, respectively. Moreover, the application of Ca(NO₃)₂:(NH₄)₂SO₄ at a ratio of 40%:60% showed 25.1% decrease in titratable acidity, and 45.4% and 27.0% increase in maturity index and peel luminosity, respectively. Additionally, the 30%:70% combination showed an increment of 30.9% in total phenolic content, 70.5% in total tannin content, and 43.6% in total flavonoid content. Additionally, it showed 25.8% and 1.7% decrease in pH and moisture content, respectively. Moreover, P, K, Ca, Mg, Na, Fe, Mn, Zn, Cu, and Ni in fruit increased by different increments by application of the 30%:70% with an increasing range of 28% to 175%. A non-reducing sugar increase was observed at an application of Ca(NO₃)₂:(NH₄)₂SO₄ at a ratio of 20%:80% by 47.0%. The findings of this study suggest that using calcium nitrate with ammonium sulphate at a ratio of 30%:70%, using the fertigation approach during the growth season, could be a safe, natural, and novel method for the pomegranate cv. ‘Wonderful’ to improve fruit quality, and its amount of antioxidants—specifically, phenolics, vitamin C, anthocyanin, and fruit minerals—with health benefits at harvest.

1. Introduction

Many regions in the world cultivate pomegranates (Punica granatum L.), particularly in Asian countries and the Mediterranean region [1]. Most pomegranate cultivar trees are deciduous; however, there are numerous evergreen pomegranate cultivars cultivated in India [2]. Pomegranate production is an important contributor to the economy of different countries [3] due to the economic significance of its juice, one of the most potent antioxidants that protects our body from free radicals, the dangerous molecules that can cause cancer, heart disease, and premature aging [4].

Pomegranate fruits include a variety of health benefits, such as dietary fibers, sugars, and a variety of biologically active substances such as vitamin C, anthocyanin, phenolic substances, tannins, flavonoids, and minerals [5], which have a reputation for acting as natural antioxidants. Pomegranate consumption is influenced by both the fresh market and the processing sector, so it is critical to understand all of the fruit’s qualities to satisfy consumer demand for higher-quality fruits [6].

Chemical fertilizer significantly influences both yield and plant growth, in addition to nutritional requirements and fruit quality [7]; therefore, it is necessary, particularly in the poor lands, to enhance pomegranate production. In the future, intensive works will be implemented to enhance fruit quality by applying more successfully cultural practices within pomegranate orchards, including fertilization programs [8]. Conversely, in many areas of the world, information on the optimum dose of chemical fertilizer quantities for maintaining yield potential and fruit quality, is missing [9] and also, modern agricultural production, is dependent on chemical fertilizer quantities [10]; this represents approximately 35% of the agricultural production cost. Prior research regarding the application of the integrated fertilization of ammonium sulphate, together with calcium nitrate to enhance the physico-chemical properties, and the nutritional and antioxidant compounds of the pomegranate fruits of cv. ‘Wonderful’, have not appeared in the literature. Consequently, we may need to create a brand-new type of research. Finding a limitation in this situation might be viewed as a crucial chance to spot literature gaps and highlights the need for more research in the field. In general, pomegranate fertilization is essential in agricultural practice and has a big impact on producing a tree with healthy vegetative development and, in turn, in obtaining fruits that are large and of great quality, which results in increased production and high profits [11]. Furthermore, we believe that proper nutritional strategies based on the needs of plants during the growing season may be more effective than their individual application [12]. Nitrogen application rates and timing had a significant impact on fruit yield [13].

The attributes that represent the fruit quality of the pomegranate may be influenced by orchard cultural practices, in particular, fertilization management, which is the main factor affecting the marketability of fruits [14,15]. The addition of balanced fertilizers to the soil at the right quantity, the right time, source, and scheme, is essential to restore and sustain fruit productivity, and also to assist in checking emerging micronutrient deficiencies [1,16,17,18]. In this direction, nitrogen (N) is measured to be one of the nutrients needed by pomegranate trees, not only for appropriate tree growth and optimum yield, but also to enhance the quality of the fruits [8,19,20]. For the majority of fruit trees growing globally, the N application rate for fertilized, mature trees, varies from 150 to 200 kg/ha/year. Ammonium nitrate, ammonium sulphate, urea, and potassium nitrate, are significant sources of nitrogen [21]. However, prior research [22,23,24,25,26,27] has shown that an appropriate ratio of nitrogen, from nitrate fertilizers to nitrogen from ammonium fertilizers, can affect the solubility and accessibility of other nutrients by altering the pH near the roots, contributing to the increase of yield, plant growth, and fruit quality. The antagonistic relationship between the two cations, which when present in excess competes with other cations such as K⁺, Ca²⁺, and Mg²⁺, results in nutritional problems and reduced biomass production. On the other hand, an excessive concentration of ammonium results in a decrease in calcium concentration in the plant tissues [28,29].

Calcium deficiency can disturb the photosynthetic process in the plant and decrease stomatal behavior, carboxylation efficiency, the capacity of photosynthesis, and, importantly, yield [30,31,32]. It is highest in sandy soils and sandy soil acids, which have a high ratio of aluminum-cation to calcium-cation in the soil solution [33]. Additionally, calcium is a crucial component of many physiological processes, including cell wall, membrane integrity, and enzyme activity [34], which may directly affect fruit quality and growth. As a result, calcium is an important tool for plants to safely and effectively improve fruit quality. Additionally, calcium is advantageous for enzymatic reactions, it provides the balance of anions and cations in plants, and plays a significant role in maintaining cell membranes [35,36]. There is ample evidence that calcium has positive benefits on preserving fruit quality [37].

Consumers are becoming more and more interested in fruit’s nutritional value. Consumer preferences also place emphasis on the existence of compounds that promote health, in addition to visual and organoleptic qualities. The growing focus on fruit quality makes it feasible to better characterize the physical-chemical, nutritional, and biologically active compounds of pomegranate fruits. However, there have not been any field experiments or controlled studies to assess the combined impact of integrated calcium nitrate and ammonium sulphate on the quality of pomegranate fruits. The current study was therefore designed to investigate the impact of integrated fertilization with calcium nitrate and ammonium sulphate on the physical-chemical characteristics, nutritional, and antioxidant components of the pomegranate fruits of cv. ‘Wonderful’.

2. Materials and Methods

2.1. Plant Material and Irrigation Solution Composition

In a commercial pomegranate (Punica granatum L.) cv. ‘Wonderful’ orchard in the Qassim region of Saudi Arabia, the experiment was conducted between the years 2020 and 2021. The region is characterized by an arid climate [38]. The soil properties of the field area at the beginning of the selected orchard are specified in

Table 1. Observed soil parameters at the test site.

Parameters	Soil Depth (cm)		Average
	0–30	30–60
Sand (%)	57.9	50.3	54.1
Clay (%)	14.9	15.9	15.4
Silt (%)	27.2	33.8	30.5
Soil texture	Sandy loam	Loam	Sandy loam
pH	8.3	7.9	8.1
Electrical conductivity (dS/m)	2.47	1.11	1.79
CaCO3 (%)	3.6	3.9	3.8
Na+ (meq/L)	2.0	4.3	3.2
Ca2+ (meq/L)	9.6	3.6	6.6
Mg2+ (meq/L)	13.0	2.4	7.7
K+ (meq/L)	0.1	0.8	0.45
HCO3− (meq/L)	1.3	2.1	1.7
Cl− (meq/L)	13.3	6.0	9.65
SO42− (meq/L)	10.1	3.0	6.55
Organic matter (%)	0.30	0.21	0.26

. The trees in the orchard area had a height of approximately 2.0–2.5 m, spaced 2.5 × 4 m, and are 8 years old. A drip irrigation system with two lines and four drippers (8 L/h) per tree was used to water the orchard.

In November of both years, organic manure was applied to the soil at a rate of 10 kg per tree. Instructions for the agronomic procedures of the Ministry of Environment, Water and Agriculture, Saudi Arabia, were followed, when cultivating the pomegranate trees in routine cultural practices suited for commercial fruit production. Additionally, phosphorus, potassium, and magnesium, were added as chemical fertilizer in the amounts of 60, 192, and 50 kg/ha, respectively. The chemical fertilizers, which were added by the fertigation approach, included commercial ammonium sulphate (21-0-0+24 S) (Ammonisul), potassium sulphate (0-0-50+18 S) (sulfopotash), magnesium sulphate heptahydrate (15.9% MgO, 47.8% MgSO₄), and Torofert calcium (15-0-0+27 Ca); however, the quantity of N was derived only from ammonium sulphate and Torofert calcium.

In a completely randomized block design with four repetitions for each irrigation solution, the experimental work was carried out utilizing five irrigation solutions. However, 40 trees were selected to be as uniform as possible in vigor and growth, in order to apply fertilization regimens (5 treatments × 4 repetitions × 2 trees per replicate = 40 trees). Different ratios of ammonium sulphate ((NH₄)₂SO₄) and calcium nitrate make up the irrigation solution. The irrigation solution, that was fed to trees through a fertigation system, consisted of five different ratios of Ca(NO₃)₂: (NH₄)₂SO₄ as follows: 0%:100%, 10%:90%, 20%:80%, 30%:70%, and 40%:60%. First, as previous studies showed that the amount of N fertilizer should be 200 kg/ha, we thus preferred to unify this amount. As we applied (NH₄)₂SO₄ (Ammonisul, N percentage 21%), the total amount, which gave 200 kg N/ha, was 952.38 kg/ha of such fertilizer; this amount represented 100% of applied N. For the second treatment, we selected to apply the amount of 90% of (NH₄)₂SO₄ from the total amount, thus, it was 857.14 kg/ha, which gave 180 kg N/ha, and the rest was 10% (20 kg N/ha/200 kgN/ha) to complete 200 kg N/ha. However, the 20 kg N/ha was delivered from the other fertilizer that was (Ca(NO₃)₂ (Torofert calcium, N percentage 15%), and this was equal to 133.33 kg/ha (100 × 20/15), which gave 20 kg N/ha + 36 kg Cao/ha (133.33 × 27/100). For the third treatment, we preferred to apply the amount of 80% of (NH₄)₂SO₄ from the total amount, thus, it was 761.90 kg/ha, which gave 160 kg N/ha, and the rest was 20% (40 kg N/ha/200 kgN/ha) to complete 200 kg N/ha. However, the 40 kg N/ha was delivered from the other fertilizer, and this was equal to 266.66 kg/ha (100 × 40/15), which gave 40 kg N/ha + 72 kg Cao/ha (266.66 × 27/100). For the fourth treatment, we preferred to apply the amount of 70% of (NH₄)₂SO₄ from the total amount, thus, it was 666.67 kg/ha, which gave 140 kg N/ha, and the rest was 30% (60 kg N/ha/200 kgN/ha) to complete 200 kg N/ha. However, the 60 kg N/ha was delivered from the other fertilizer, and this was equal to 400 kg/ha (100 × 60/15), which gave 60 kg N/ha + 108 kg Cao/ha (400 × 27/100). For the fifth treatment, we preferred to apply the amount of 60% of (NH₄)₂SO₄ from the total amount, thus, it was 571.43 kg/ha, which gave 120 kg N/ha and the rest was 40% (80 kg N/ha/200 kgN/ha) to complete 200 kg N/ha. However, the 80 kg N/ha was delivered from the other fertilizer, and this was equal to 533.32 kg/ha (100 × 80/15), which gave 80 kg N/ha + 144 kg Cao/ha (533.32 × 27/100). The details are shown in

Table 2. Irrigation solution composition used in the experiment.

Ca (NO3)2:(NH4)2SO4 Ratio	(NH4)2SO4 from the Commercial Ammonium Sulphate (21-0-0+24 S) (Ammonisul)			Ca (NO3)2 from Torofert Calcium (15-0-0+27 Ca)			Total Application Rate
	Amount (kg)	Application Rate		Amount (kg)	Application Rate
		N (kg/ha)	CaO (kg/ha)		N (kg/ha)	CaO (kg/ha)	N (kg/ha)	CaO (kg/ha)
(0%:100%); control	952.38	200	0	0	0	0	200	0
(10%:90%)	857.14	180	0	133.33	20	36	200	36
(20%:80%)	761.90	160	0	266.66	40	72	200	72
(30%:70%)	666.67	140	0	400.00	60	108	200	108
(40%:60%)	571.43	120	0	533.32	80	144	200	144

.

The control of irrigation solution is composed of a ratio of 100% (NH₄)₂SO₄ and 0% Ca(NO₃)₂. Used commercial fertilizers were diluted with water to create the irrigation solution, which was then provided in separate irrigation water. Nitrogen fertilization in the form of (NH₄)₂SO₄ was firstly applied every two days, and calcium fertilization in the form Ca(NO₃)₂ on the third day was carried out, and repeated this sequence. Each irrigation solution was made with a total application rate of N of 200 kg/ha and the total application rates of CaO differed between 0 and 144 kg/ha of CaO.

2.2. Fruits Measurements

In both seasons, in the third week of October, 20 identical, healthy fruits—10 per tree—were hand-picked at random from each replicate. This was carried out after the fruits had reached the end of the maturing stage and had turned fully colored, based on how they appeared at commercial ripening. To identify chemical properties, nutritional, and antioxidant compounds, pomegranate fruits were split in half and the seeds were manually removed. However, fruit physico-chemical characteristics, nutritional compounds, and antioxidant compounds were determined.

Fruit diameter, fruit volume, fruit weight, fruit length, and peel color were among the criteria that were measured to determine the physical characteristics of the fruit. A digital scale was used to determine the fresh weight (g) (Mettler, Toledo, Switzerland, 0.0001 g accuracy). Using a digital caliper (Mitutoyo, Kawasaki, Japan) with a sensitivity of 0.01 mm, fruit length and fruit diameter (in cm) were measured. The measurement of fruit length was made on the polar axis, i.e., between the apex and the end of stem. The maximum width of the fruit, as measured in the direction perpendicular to the polar axis, is defined as the diameter [39] and fruit volume (ml) was calculated by the liquid displacement method. Peel color was recorded in the CIELab system, using a Minolta CR-400 colorimeter (Konica Minolta Sensing, Inc., Japan) by defining the L* (representing luminosity or lightness), a* (signifying color variation from green to red) and b* (showing color variation from blue to yellow) values [40]. Using a* and b* values, the Chroma, which defined color intensity, can be calculated as follows [41]:

$$\mathrm{Chroma}=\sqrt{{{\mathrm{a}}^{\ast }}^2+{{\mathrm{b}}^{\ast }}^2}$$

(1)

L* lightness ranged from 0 (black) to 100 (white); a* from –60 (green) to 60 (red); and b* from –60 (blue) to 60 (yellow) [42]. The calibration of the Minolta CR-400 colorimeter was performed with a standard white plate, following the manufacturer’s instructions. Color difference ∆E* was calculated as follows [43]:

$${\Delta \mathrm{E}}^{\ast }=\sqrt{{\left({\mathrm{L}1}^{\ast }-{\mathrm{L}2}^{\ast }\right)}^2+{\left({\mathrm{a}1}^{\ast }-{\mathrm{a}2}^{\ast }\right)}^2+{\left({\mathrm{b}1}^{\ast }-{\mathrm{b}2}^{\ast }\right)}^2}$$

(2)

where L1*, a1*, and b1* are the values of color spectra for control treatment defined as integrated fertilizers of calcium nitrate Ca(NO₃)₂ and ammonium sulphate (NH4)₂SO₄ with a ratio of (0%:100%).

L2*, a2*, and b2* are the values of color spectra after the application of other integrated fertilizers of Ca(NO3)₂:(NH4)₂SO₄. If 6 > ΔE* > 3, the color difference is visible with medium screen, if 12 > ΔE* > 6, the high color difference is clear, and if ΔE* > 12, different colors are clear, as reported in [44]. However, the biggest change in color was measured in the lightness coordinates (L*).

Fruits were cut longitudinally, the arils manually separated, and the juice containing around 100 g of arils was strained through a metal sieve. To extract the juice, the arils were blended in a commercial juicer. The resulting raw, fresh juice, was then filtered through muslin cloth to measure the juice’s pH, titratable acidity, and total soluble solids (TSS). The pH-meter was used to measure the pH readings (GLP 21; Crison Ltd., Barcelona, Spain). Using a digital hand-held refractometer (Atago Co., Tokyo, Japan), the TSS of juice was calculated by placing a drop of the liquid on the prism, which shows how much a light beam would slow down when it travels through the fruit juice and is recorded as °Brix. By titrating 10 mL of juice with NaOH (0.1 N) to pH of 8.1, titratable acidity (%) was calculated, and the values were reported as a percentage of citric acid (g/L) in accordance with AOAC [45]. The ratio of TSS to titratable acidity was used to calculate the maturity index. However, reducing sugars were estimated in accordance with AOAC [45]; total sugars were calculated using the method outlined by Ranganna et al. [46], and non-reducing sugars were calculated as the difference between the amounts of reducing sugars and total sugars. Furthermore, the residual seed material was freeze-dried to determine its moisture and mineral content. Using the Perkin Elmer 2380 Atomic Absorption Spectrometer, the mineral content of five major elements (P, K, Ca, Mg, and Na) and five trace minerals (Fe, Mn, Zn, Cu, and Ni) was determined. According to AOAC [45], the flame photometer (model PFP7 PFP 7/C, Cole-Parmer Ltd., Staffordshire, UK) was used to determine the contents of the spectrophotometer, with the exception of sodium and potassium.

Antioxidant compounds in the extracted juice were evaluated by measuring the following parameters: vitamin C; total tannin content; total phenols content; total flavonoid content; and anthocyanin content. The vitamin C of the arils juice was estimated in mg ascorbic acid per 100 mL of juice, according to AOAC [45]. Total phenolic content was determined by the Folin-Ciocalteu method, as described in Slinkard and Singleton [47] at 760 nm using a UV-Vis Spectrophotometer (Laxco-Alpha-1102) and gallic acid as a standard, as mentioned by Orak et al. [48]. The total phenolic content was expressed as mg of gallic acid equivalent/100 milliliter (mg GAE/100 mL of pomegranate juice). In addition, total tannin content was calorimetrically determined at a 760 nm, according to Mottaghipisheh et al. [49] using Folin-Denis reagent and expressed as mg of tannic acid equivalent/L ((mg TaE/L) of pomegranate juice). Furthermore, according to Park et al. [50], the total flavonoid content was assessed spectrophotometrically at a wavelength of 430 nm using a UV-Vis Spectrophotometer (Laxco-Alpha-1102, Suite) [50] and was stated as mg catechin equivalents (CaE)/100 mL of juice extract. Meanwhile, two buffer systems, potassium chloride buffer with a pH of 1 (0.025 M) and sodium acetate buffer with a pH of 4.5, were used to determine the total anthocyanin content of the samples using the pH differential method (0.1M) and expressed as (mg/100 g), as described in Ozgen et al. [51].

2.3. Statistical Analysis

The experimental data were examined using one-way analysis of variance and the least significant difference (LSD) at p < 0.05 was used for comparing means. All statistical analyses were conducted using the SAS software version 9.13 [52]. Moreover, correlation analysis among parameters was conducted using the SPSS software using the whole data of two seasons.

3. Results

3.1. Impact of Ca(NO₃)₂: (NH₄)₂SO₄ Proportions on Physico-Chemical Characteristics

Fruit length, fruit diameter, fruit weight, juice pH, fruit volume, titratable acidity, TSS, and maturity index differed significantly among Ca(NO3)₂:(NH4)₂SO₄ ratios, as indicated in

Table 3. Impact of Ca(NO₃)₂:(NH₄)₂SO₄ ratios on the physico-chemical attributes of the pomegranate fruits of cv. ‘Wonderful’ in 2020 and 2021 seasons.

Season	Ca(NO3)2: (NH4)2SO4 Ratio	Physical Attributes				Chemical Attributes
		Fruit Weight	Fruit Volume	Fruit Length	Fruit Diameter	Juice pH	TSS	Titratable Acidity	Maturity Index
		(g)	(ml)	(cm)	(cm)	(-)	(%)	(%)	(%)
2020	(0%:100%)	303.25e	344.25e	7.72e	8.41e	4.32a	15.45d	1.14a	13.6e
	(10%:90%)	313.75d	352.00d	7.79d	8.62d	3.96b	16.30c	1.00b	16.3d
	(20%:80%)	320.25c	364.25c	7.82c	8.74c	3.78c	16.80b	0.94c	17.8c
	(30%:70%)	336.25a	386.25a	7.94a	9.04a	3.19e	17.23a	0.91d	18.9b
	(40%:60%)	326.25b	373.25b	7.86b	8.94b	3.44d	16.85b	0.85e	19.9a
	LSD (5%)	2.87	5.01	0.03	0.05	0.03	0.14	0.01	0.24
2021	(0%:100%)	305.75e	346.00e	7.74e	8.49b	4.22a	15.55d	1.13a	13.8e
	(10%:90%)	316.50d	353.25d	7.81d	8.69d	3.93b	16.35c	0.99b	16.5d
	(20%:80%)	323.50c	367.00c	7.85c	8.78c	3.84c	16.85b	0.93c	18.1c
	(30%:70%)	338.50a	385.75a	7.96a	9.05a	3.14e	17.25a	0.90d	19.2b
	(40%:60%)	327.50b	371.75b	7.88b	8.94e	3.46d	16.90b	0.85e	19.9a
	LSD (5%)	2.44	2.27	0.02	0.02	0.02	0.09	0.01	0.22

Significant differences (p < 0.05) are denoted by values in the same column that are marked with distinct letters.

. The data are presented as the mean of four replicates. It was discovered that, after applying different ratios of Ca(NO₃)₂ fertilizer, the rates of fruit length, fruit weight, fruit volume, and fruit diameter increased obviously, along with the rising concentration of Ca(NO₃)₂ fertilizer ratio, up to 30% under the (NH₄)₂SO₄ ratio of 70%, in both years (Table 3). Among the integrated treatments, the 30%:70% combination showed an increment of 10.8% in fruit weight, 2.9% in fruit length, 11.8% in fruit volume, and 7.0% in fruit diameter; similarly, the TSS was also increased by 11.2%, as an average of two seasons.

Among the integrated treatments, the 30%:70% combination showed an increment of 28.6% decreased in juice pH. However, Figure 1 depicts the average values of the two years to indicate only the trend of decrease in juice pH values due to fertilizer treatments. It is observed that decreasing the ratio of (NH₄)₂SO₄ results in the decreasing of pH; meanwhile, decreasing Ca(NO₃)₂ results in the increasing of juice pH. The application of Ca(NO₃)₂:(NH₄)₂SO₄ at a ratio of 40%:60% showed 25.1% decrease in titratable acidity and 45.4% increase in the maturity index, as an average of two seasons. Thus, the moderate concentration of Ca(NO₃)₂ fertilizer was more suitable for the quality attributes of pomegranate fruit

3.2. Impact of Ca(NO₃)₂:(NH₄)₂SO₄ Proportions on Fruit Color Values

Fruit peel color attributes (L*, a*, b*, and chroma) differed significantly among Ca(NO₃)₂: (NH₄)₂SO₄ ratios, as indicated in

Table 4. Impact of Ca(NO₃)₂:(NH₄)₂SO₄ ratios on peel color factors of the pomegranate fruits of cv. ‘Wonderful’ in 2020 and 2021 seasons.

Season	Ca(NO3)2: (NH4)₂SO₄ Ratio	Luminosity or Lightness (L*)	Color Variation from Green to Red (a*)	Color Variation from Blue to Yellow (b*)	Chroma	Color Difference (ΔE*)
2020	(0%:100%)	48.80e	43.50e	22.35e	48.90e
	(10%:90%)	52.07d	45.36d	23.23d	50.96d	3.9
	(20%:80%)	56.49c	47.59b	25.44b	53.96b	9.2
	(30%:70%)	59.04b	49.62a	26.22a	56.12a	12.5
	(40%:60%)	61.78a	46.53c	24.68c	52.66c	13.5
	LSD (5%)	0.81	0.48	0.27	0.53
2021	(0%:100%)	49.64e	43.72e	22.70e	49.26e
	(10%:90%)	52.73d	45.69d	23.55d	51.40d	3.8
	(20%:80%)	56.87c	47.80b	25.67b	54.26b	8.8
	(30%:70%)	59.28b	49.62a	26.31a	56.16a	11.9
	(40%:60%)	63.25a	46.74c	24.54c	52.79c	14.1
	LSD (5%)	0.38	0.27	0.21	0.32

Significant differences (p < 0.05) are denoted by values in the same column that are marked with distinct letters.

. No negative values are seen in the present study for a* and b*. The integration of Ca(NO₃)₂ with (NH₄)₂SO₄ yielded better results as compared to control treatment. Among the integrated treatments, the application of Ca(NO₃)₂ at a ratio of 30% and (NH₄)₂SO₄ at a ratio of 70% showed about 13.8% increase in peel a*, 16.6% increase in peel b*, and 14.4% increase in peel chroma (the average of two seasons). Furthermore, changes in external peel color showed a marked increase in peel luminosity (L*) values, over the decrease of (NH₄)₂SO₄ ratio (Table 4). The pomegranate cv. ‘Wonderful’ that received 0% Ca(NO₃)_2: 100% (NH₄)₂SO₄ ratio appeared visually less red and less bright than those that received 30% Ca(NO₃)₂: 70% (NH₄)₂SO₄ ratio, this was confirmed by lower a* and chroma values (Table 4). However, the redness parameter, which is a desirable quality attribute for processing and consumers, is probably due to the fertilization regimes, which led to the condition of a higher increase in anthocyanin responsible for the red color. Furthermore, the application of Ca(NO₃)₂ at a ratio of 40% and (NH₄)₂SO₄ at a ratio of 60% showed about 27.0% increase in peel luminosity (i.e., higher L*), which indicated lighter-colored fruit than those that grew with (NH₄)₂SO₄ as the sole nitrogen source. Additionally, Table 4 indicates the color difference ΔE* between the peel colors of the control treatment and other fertilization ratios. It is observed that ΔE* was in the range from 3.9 to 13.5 in the 2020 season, and it was in the range from 3.8 to 14.1 in the 2021 season.

3.3. Impact of Ca(NO₃)₂: (NH₄)₂SO₄ Ratios on Moisture Content, Total, Reducing, and Non-Reducing Sugar Contents

The fruit moisture content, and total reducing, and non-reducing, sugar contents differed significantly among Ca(NO₃)₂:(NH₄)₂SO₄ ratios, as indicated in

Table 5. Impact of Ca(NO₃)_2:(NH₄)₂SO₄ ratios on moisture content, total reducing, and non-reducing, sugar contents of the pomegranate fruits of cv. ‘Wonderful’ in 2020 and 2021 seasons.

Season	Ca(NO3)2: (NH4)2SO4 Ratio	Fruit Moisture Content	Total Sugar	Reducing Sugar	Non-Reducing Sugar
		(%, wb)	(%)	(%)	(%)
2020	(0%:100%)	83.0a	12.85d	11.81e	1.04c
	(10%:90%)	82.3b	12.88d	11.88d	1.00c
	(20%:80%)	81.5d	13.57b	12.03c	1.54a
	(30%:70%)	81.0e	13.79a	12.44a	1.36b
	(40%:60%)	82.2c	13.23c	12.21b	1.02c
	LSD (5%)	0.04	0.05	0.04	0.07
2021	(0%:100%)	83.0	12.88e	11.83e	1.05c
	(10%:90%)	82.3	12.92d	11.90d	1.02c
	(20%:80%)	82.2	13.59b	12.05c	1.54a
	(30%:70%)	82.0	13.84a	12.46a	1.37b
	(40%:60%)	82.1	13.26c	12.22b	1.04c
	LSD (5%)	0.01	0.03	0.03	0.04

Significant differences (p < 0.05) are denoted by values in the same column that are marked with distinct letters.

. The integration of Ca(NO₃)₂ with (NH₄)₂SO₄ yielded better results, as compared to control treatment. Among the integrated treatments, the application of Ca(NO₃)₂ at a ratio of 30% and (NH₄)₂SO₄ at a ratio of 70% showed about 7.4% increase in total sugar, and 5.3% increase in reducing sugar; additionally, it showed 1.7% decrease in moisture content as an average of two seasons (Table 5). Moreover, non-reducing sugar increasing was observed at the application of Ca(NO₃)₂:(NH₄)₂SO₄ at a ratio of 20%:80% by 47.0%, as an average of two seasons.

3.4. Impact of Ca(NO₃)₂:(NH₄)₂SO₄ Ratios on Antioxidant Compounds

The vitamin C, anthocyanin, total tannin content, total phenolic content, and total flavonoid content differed significantly among Ca(NO₃)₂:(NH₄)₂SO₄ ratios, as indicated in Figure 2, Figure 3, Figure 4, Figure 5 and Figure 6. Among the integrated treatments, the 30%:70% combination showed an increment of 14.6%, 20.2%, 30.9%, 70.5%, and 43.6%, in vitamin C, anthocyanin, total phenolic content, total tannin content, and total flavonoid content, respectively, as an average of two seasons. The TSS, vitamin C, anthocyanin, total phenolic content, total tannin content, and total flavonoid content in the fruits decreased with the increasing proportion of (NH₄)₂SO_4, when (NH₄)₂SO₄ reached 100%. The TSS was lowest compared to fruits in other treatments containing Ca(NO₃)₂. This means that irrigation solutions containing a larger percentage of Ca(NO₃)₂ (up to 70%) caused the most sugar and starch to accumulate. The fruits’ anthocyanin content declined as the concentration of (NH₄)₂SO₄ rose at 100%; it was lowest when compared to fruits from other Ca(NO₃)₂-containing treatments. Additionally, when the ratio of Ca(NO₃)₂ to (NH₄)₂SO₄ was increased, it was evident that the anthocyanin in the fruits would increase. This means that the maximum amount of anthocyanin was accumulated when the irrigation solution had a larger proportion of Ca(NO₃)₂ (up to 70%).

3.5. Impact of Ca(NO₃)₂:(NH₄)₂SO₄ Ratios on Mineral Content

The mineral content of P, K, Ca, Mg, Na, Fe, Mn, Zn, Cu, and Ni, in fruit differed significantly among Ca(NO₃)₂:(NH₄)₂SO₄ ratios, as indicated in

Table 6. The impact of Ca(NO₃)_2: (NH₄)₂SO₄ ratios on P, K, Ca, Mg, and Na, of the pomegranate fruits of cv. ‘Wonderful’ in 2020 and 2021 seasons.

Season	Ca(NO3)2:(NH4)2SO4 Ratio	P	K	Ca	Mg	Na
		(g/kg)
2020	(0%:100%)	1.51e	8.08e	0.43e	0.49e	0.29d
	(10%:90%)	1.64d	8.58d	0.68d	0.65d	0.32c
	(20%:80%)	1.75c	9.53b	0.94c	0.77c	0.33b
	(30%:70%)	2.14a	10.50a	1.14a	0.92a	0.38a
	(40%:60%)	1.84b	9.23c	1.07b	0.87b	0.34b
	LSD (5%)	0.03	0.15	0.03	0.02	0.02
2021	(0%:100%)	1.53e	8.20e	0.41e	0.48e	0.29d
	(10%:90%)	1.77d	8.75d	0.71d	0.66d	0.32c
	(20%:80%)	1.85c	9.63b	0.95c	0.79c	0.33b
	(30%:70%)	2.23a	10.60a	1.17a	0.95a	0.38a
	(40%:60%)	1.85b	9.35c	1.09b	0.88b	0.34b
	LSD (5%)	0.02	0.12	0.02	0.02	0.02

Significant differences (p < 0.05) are denoted by values in the same column that are marked with distinct letters.

and

Table 7. The impact of Ca(NO₃)₂: (NH₄)₂SO₄ ratios on Fe, Mn, Zn, Cu, and Ni, of the pomegranate fruits of cv. ‘Wonderful’ in 2020 and 2021 seasons.

Season	Ca(NO3)2:(NH4)2SO4 Ratio	Fe	Mn	Zn	Cu	Ni
		(mg/kg)
2020	(0%:100%)	9.0d	4.50c	8.25d	5.5d	0.21d
	(10%:90%)	12.5c	5.50c	11.0c	6.0c	0.28c
	(20%:80%)	15.0b	7.50b	13.25b	7.0b	0.32b
	(30%:70%)	18.0a	9.25a	14.25a	8.0a	0.35a
	(40%:60%)	15.5b	8.00b	13.75b	7.25b	0.33b
	LSD (5%)	1.19	1.01	0.9	0.49	0.01
2021	(0%:100%)	8.5d	4.25d	8.3d	5.25d	0.22d
	(10%:90%)	12.75c	5.75c	11.5c	6.00c	0.29c
	(20%:80%)	15.5b	7.50b	13.5b	7.25b	0.33b
	(30%:70%)	18.75a	9.50a	14.8a	8.25a	0.36a
	(40%:60%)	15.75b	8.25b	13.8b	7.50b	0.33b
	LSD (5%)	0.86	0.81	0.9	0.67	0.01
Anon [53]				150	10
FAO/WHO [54]						70
Pomegranate fruits [55]		80.54	34.56	22.19	4.51	26.87

Significant differences (p < 0.05) are denoted by values in the same column that are marked with distinct letters.

. Among the integrated treatments, the 30%:70% combination showed increments with an increasing range of 28% to 175% for P, K, Ca, Mg, Na, Fe, Mn, Zn, Cu, and Ni, as an average of two years, as exposed in Figure 7, compared to ratio 0%:100%. The highest increment belonged to Ca content at 175%, and the lowest increment belonged to K content in fruits at 28%.

3.6. Correlation Analysis

The correlation coefficients between nutrient concentrations of pomegranate fruits and fruit quality attributes, using the whole data of the two seasons, are presented in

Table 8. Correlation coefficients among investigated parameters in pomegranate fruits.

Fruit Macro- and Micronutrients Content		Fruit Quality Attributes
		Vitamin C	Anthocyanin	Total Phenolic Content	Total Tannin Content	Total Flavonoid Content
P	Pearson Correlation	0.933 **	0.872 **	0.904 **	0.940 **	0.875 **
	Significant (2-tailed)	0.000	0.000	0.000	0.000	0.000
	No. of observations	40	40	40	40	40
K	Pearson Correlation	00.926 **	0.941 **	0.938 **	0.960 **	0.898 **
	Significant (2-tailed)	0.000	0.000	0.000	0.000	0.000
	No. of observations	40	40	40	40	40
Ca	Pearson Correlation	0.973 **	0.959 **	0.979 **	0.975 **	0.984 **
	Significant (2-tailed)	0.000	0.000	0.000	0.000	0.000
	No. of observations	40	40	40	40	40
Mg	Pearson Correlation	0.985 **	0.947 **	0.971 **	0.974 **	0.986 **
	Significant (2-tailed)	0.000	0.000	0.000	0.000	0.000
	No. of observations	40	40	40	40	40
Na	Pearson Correlation	0.914 **	0.878 **	0.904 **	0.919 **	0.880 **
	Significant (2-tailed)	0.000	0.000	0.000	0.000	0.000
	No. of observations	40	40	40	40	40
Fe	Pearson Correlation	0.962 **	0.946 **	0.948 **	0.961 **	0.957 **
	Significant (2-tailed)	0.000	0.000	0.000	0.000	0.000
	No. of observations	40	40	40	40	40
Mn	Pearson Correlation	0.944 **	0.930 **	0.953 **	0.961 **	0.929 **
	Significant (2-tailed)	0.000	0.000	0.000	0.000	0.000
	No. of observations	40	40	40	40	40
Zn	Pearson Correlation	0.934 **	0.938 **	0.933 **	0.932 **	0.965 **
	Significant (2-tailed)	0.000	0.000	0.000	0.000	0.000
	No. of observations	40	40	40	40	40
Cu	Pearson Correlation	0.916 **	0.906 **	0.922 **	0.935 **	0.908 **
	Significant (2-tailed)	0.000	0.000	0.000	0.000	0.000
	No. of observations	40	40	40	40	40
Ni	Pearson Correlation	0.957 **	0.946 **	0.949 **	0.948 **	0.972 **
	Significant (2-tailed)	0.000	0.000	0.000	0.000	0.000
	No. of observations	40	40	40	40	40

** Correlation is significant at the 0.01 level (2-tailed).

. The highly positive correlation was found among all fruit quality attributes (vitamin C, anthocyanin, total phenolic content, total flavonoid content, and total tannin content), with macro- and micronutrient concentrations in pomegranate fruits. The obtained results on the relationship of fruit macro- and micronutrient content with fruit quality attributes are in agreement with those reported in [56,57,58].

4. Discussion

Water availability, fertilizer requirements, and crop management during pomegranate fruit growth have been stated to affect physico-chemical characteristics, fruit ripening, and fruit quality [8,59]. In the current experiments, climatic environments were similar for 2020 and 2021 and all trees were under similar climatic and agronomic conditions. Thus, differences among fertilization treatments on the physico-chemical, nutritional, and antioxidant attributes of the pomegranate fruits of cv. ‘Wonderful’ may be due solely to the effects of fertilization treatments.

4.1. Fertilization Treatment Effects on the Physico-Chemical Characteristics of the Pomegranate Fruit of cv. ‘Wonderful’

Our findings showed that the Ca(NO₃)₂ and (NH₄)₂SO₄ fertilizer interactions or cooperative effects, which may result in a combined effect greater than the sum of their individual effects, may be responsible for an increase in the fruit weight of the pomegranate cv. ‘Wonderful’. Abd-Ella et al. [60] noted this phenomenon, but attributed gains in pomegranate yield and fruit characteristics to the synergistic interaction between organic and mineral amendments. As stated by Li et al. [61], and Itoo and Manivannan [62], they believed the improvement in pomegranate growth was caused by the improvement of soil physio-chemical characteristics and the available nutrients. These factors consequently promote plant growth, fruit yield, and quality. Increased cell division and expansion, leading to more photosynthates being accumulated in the fruit and improved photosynthate translocation permitting optimal source, could be the cause of the increase in fruit weight [63]. Additionally, calcium fertilization typically results in a rise in the concentration of apoplastic calcium, which affects a number of processes, including the composition and operation of cell-walls and membranes, as well as specific elements of cell metabolism [64,65]. The different values of fruit weight of the pomegranate cv. ‘Wonderful’ were reported by numerous studies [66,67,68,69,70,71]. By weight, the pomegranate cv. ‘Wonderful’ fruit in this study belonged to medium-sized fruits; however, according to criteria presented by Cadze et al. [72], the fruit belonged to large-sized fruits. Regardless, the average weight of the pomegranate cv. ‘Wonderful’, in both seasons, ranged from 304.5 g to 337.38 g.

According to our findings, the two seasons of testing saw a considerable increase in fruit volume, fruit length, and fruit diameter, when the fertilization application rate consisted of the quantity of N and CaO at 200 kg/ha and 108 kg/ha, respectively. These nutrients’ involvement in several metabolic processes, and the movement of metabolites, may be the reason for this impact [73]. Moreover, different values of fruit volume of the pomegranate cv. ‘Wonderful’ were reported in [67,70], as well as fruit length in [47,58,66]; additionally, fruit diameter recorded different values in [74,75].

In the current study, the rise in fruit weight, volume, length, and diameter rests on the specific treatment, and the rises were larger in 2020, than in 2021. Moreover, the differences in fruit properties of the pomegranate cv. ‘Wonderful’ among growing locations may be attributed to the humidity levels during the fruit growing season [70]. Even with trees of the same genotype, cultivated under similar management procedures, the size of the fruits produced within commercial orchards can be quite diverse [67]. In this study, 200 kg/ha of N was considered a constant level, with a varying of CaO application rate, so the benefits of Ca(NO₃)₂ fertilizer, which had noticeable effects, were detected in trees grown under only (NH₄)₂SO₄ fertilizer. However, calcium regulates the enzymes and photosynthesis activities [76,77]. Moreover, in our experiment, moderate and excessive calcium, and a fixed nitrogen application rate of kg/ha in the irrigation water, resulted in the high volume, weight, length, and diameter of the pomegranate fruits of cv. ‘Wonderful’ (Table 3). In both seasons, the TSS level increased from quite a low level of just 15.45% to 17.23% in the first season, and just 15.55% to 17.25% in the second season, in fruit grown under the ratio combination of Ca(NO₃)₂:(NH₄)₂SO₄ from 0% to 30% and 100% to 70% (Table 3). For the production of any of the pomegranate cultivars, the cultivar owns high TSS contents in juice, and is considered to be an ideal cultivar; however, Ben-Arie et al. [78] reported that TSS more than or equal to 17% is recommended for the cultivar ‘Wonderful’.

All data from the fertilization regimes analyzed showed that the TSS values are above the minimum value (12° Brix) required for commercial pomegranate fruit use [79]. However, Karav et al. [80] reported that the TSS values of the pomegranate cultivars were found within the range of 12.1–18.1° Brix. Additionally, Mohamed et al. [81] reported that TSS in fruits are around 15 to 17° Brix for most pomegranate cultivars. Moreover, Abbas et al. [82] found that the TSS values of pomegranate juices were in the range between 14.79 and 15.81%. The variation in TSS values among studies could originate from the cultivar and agro-climatic, as well as the environmental conditions [83]. The lower TSS levels under control treatment ((Ca(NO₃)₂:(NH₄)₂SO₄; 0%:100%) in the irrigation solution can be clarified by the lower transport of carbohydrates from the leaves into the fruit, as suggested previously [84,85]. In addition, the reduction observed in the value of TSS with the use of a higher portion of (NH₄)₂SO₄, may be related to the competition of ammonium and other cations for absorption sites, such as calcium, which has its absorption and, consequently, its content, reduced at high concentrations of ammonium [86]. This is because calcium is positively related to germination, giving a higher physiological quality of the fruits [87]. The increase in TSS in fruits with calcium may be due to the effect of it in improving tree growth, which includes leaf area, the total chlorophyll of the leaves, the absorption of water, nutrition, and increasing the food synthesized that translocate to fruits [88]. The lower transfer of sugar, from the leaves into the fruit, can account for the lower TSS levels under low nitrogen fertilization circumstances, as predicted by Paul et al. [84] and Hermans et al. [85]. These results could be ascribed to increasing the soluble matter in the juice, by the penetrated calcium [64].

The juice pH is a crucial factor in determining how sour fruit is. The values of all compared fertilization regimes were higher in 2020 (ranging from 3.19 to 4.32) than in 2021 (ranging between 3.14 and 4.22), as shown in Table 3. When comparing fertilization regimes, the highest values of juice pH were noted in both years for the integration of Ca(NO₃)₂ with (NH₄)₂SO₄ fertilizers 0%:100%. Our range data were similar to that of another study [89], who noted the lowest juice pH value was measured in cv. ‘Wonderful’ of 3.32. Meanwhile, Abdulrahman et al. [90] reported juice pH value of 4.02 in cv. ‘Wonderful’ cultivated in Iraq. The pomegranate fruit with a lower pH showed correspondingly higher acid content [91].

Drinking the juice of pomegranate fruit is considered to be the most usual way for consumers to consume it [92]. However, sensorial parameters including sweetness, sourness, and astringency, which are the flavors of pomegranate juice, are affected by sugar content, acidity content, and phenolic compounds, respectively [93]. Here, we found that the titratable acidity range was from 0.85 to 1.14 in season 2020, while it was from 0.85 to 1.13% in season 2021; however, Mohamed et al. [81] reported that titratable acidity ranged from 0.3 to 3.0 for most cultivars of pomegranate. Additionally, Ben-Arie et al. [78] reported that titratable acidity of less than 1.85% is recommended for cultivar ‘Wonderful’. Abdulrahman et al. [90] reported 1.09% titratable acidity for the ‘Wonderful’ cultivar cultivated in Iraq. In our study, titratable acidity was higher in the treatment with 0%:100% of Ca(NO₃)₂:(NH₄)₂SO₄, with 1.14% and 1.13% in both seasons of 2020 and 2021, respectively, as depicted in Table 3. As shown in Table 3, the integration of Ca(NO₃)₂ with (NH₄)₂SO₄ fertilizers, in different ratios, enhanced the fruit quality of the pomegranate cv. ‘Wonderful’ by decreasing the titratable acidity, in comparison with 0%:100% of Ca(NO₃)₂:(NH₄)₂SO_4, as pomegranate juice sourness is affected by acidity content [92]. Therefore, a lower Ca(NO₃)₂:(NH₄)₂SO₄ ratio application level could enhance consuming pomegranate fruit. As in higher plants, ammonium (NH₄) and nitrate (NO₃) are the two forms of inorganic nitrogen necessary for biochemical and physiological processes [94].

From the viewpoint of the consumer, the maturity index or (TSS/titratable acidity) ratio is a superior display of taste and flavor quality for most fruit species, rather than the individual content of sugars or acids. It has been stated to play a significant role in appraising pomegranate fruit as it balances tartness and sweetness, and controls the taste [95]. However, each pomegranate cultivar requires a certain maturity index at harvest time. Moreover, calculating this ratio permitted us to appraise the satisfactoriness of the store-bought pomegranates. Based on the literature, mature pomegranates have a TSS value above 15% and a titratable acidity value less than 1.85% in citric acid equivalents, resulting in a maturity index of 8.1 or higher, and these standards were used for quality valuation [96]. In this study, the maturity index varied from 13.6% to 19.9% in the 2020 season, and in the 2021 season it varied from 13.8% to 19.9% (Table 3). However, Ben-Arie et al. [78] reported that the TSS/titratable acidity ratio between 11% and 16% is recommended for cultivar ‘Wonderful’. Some values of the maturity index in our study were much higher than those reported in Ben-Arie et al. [78]; however, the desired maturity index of 18.5 of TSS/titratable acidity for commercially available ‘Wonderful’ is recommended. If it is less than 18.5%, a significant pomegranate quality problem is considered [96].

4.2. Fertilization Treatment Effect on Color Characteristics of the Pomegranate Fruit of cv. ‘Wonderful’

We found that the increase in brightness changes due to the reduction of (NH₄)₂SO₄ ratio probably refer to a shiny appearance on the surface of the fruit, formed by the reduction of (NH₄)₂SO₄ ratio in the irrigation solution [97]. In the present study, the L* value that represents the brightness of the peel of the fruit varied between 48.80 and 61.78 for season 2020, and for season 2021 the values are between 49.64 and 63.25 (Table 4). In various other studies, the fruit peel L* value of the ‘Wonderful’ variety differed; for example, Abdel-salam et al. [68] found that the L* was 54.61 and Passafiume et al. [69] found that L* was 39.1 ± 14.6. It can be concluded that changes in the color of the peel of the pomegranate cv. ‘Wonderful’ was mostly as a result of seasonal variation, as well as growing area [98]. Generally, pomegranate fruits with deep red color tend to have greater consumer appeal on the market. Our findings agreed with the findings of many studies, which showed a large diversity in the physical properties of pomegranate fruits among cultivars due to genotype, growing regions, climatic conditions, the degree of maturity, and agricultural practice [99,100].

Significant differences in the intensity (chroma value) of fruit color per season were recorded (Table 4), and varied across the five fertilization treatments in the range from 48.90 to 56.12, and from 49.26 to 56.16, across 2020 and 2021 seasons, respectively. Our results were lower than those reported by Durgac et al. [101] in Turkey, and Mellisho et al. [102] in Italy, with values ranging from 9.2 to 19.9 and from 40.6 to 42.5, respectively. An accumulation of anthocyanin pigments and a rise in chroma value in the peel could be the causes of the vivid red hue [68]. Overall, the findings showed that the red coloring (a*) and intensity (chroma) of fruit peel were better preserved under the fertilization combination ratio of 30% Ca(NO₃)₂:70% (NH₄)₂SO₄, when these values were noticeably greater than the observed fruit color at other ratios. However, ΔE* had higher values for a ratio of 30% Ca(NO₃)₂:70% (NH₄)₂SO₄ (Table 4) fertilization combination, compared to other treatments; this is due to higher values of L*.

4.3. Fertilization Treatment Effect on Moisture Content, Total, Reducing, and the Non-Reducing Sugar Content of Pomegranate Fruit of the cv. ‘Wonderful’

Fruit water is an important attribute as it affects harvesting, transportation, marketing, packaging, and storage; additionally, the ‘Wonderful’ cultivar can lose 20–25% of the initial fruit weight within 4 weeks at a temperature and relative humidity of 22 °C and 65% [103,104]. Thus, our goal was to maintain high fruit moisture content at harvest. Significant differences in the fruit moisture per season were recorded (Table 5), and varied across the five fertilization treatments in a range from 81.5% to 83%, and from 82.1% to 83%, across 2020 and 2021 seasons, respectively. The high variability in the fruit moisture content of pomegranate fruit from the ‘Wonderful’ cultivar used under different combinations of Ca(NO₃)₂: (NH₄)₂SO₄ in the present study, may be of interest to the food industry for the development of different products. Abdulrahman et al. [90] reported 82.269% wb for the pomegranate fruit of the cv. ‘Wonderful’ cultivated in Iraq.

The total sugar content was reported to be maximum between 13.79% and 13.84%, by the application of treatment Ca(NO₃)₂:(NH₄)₂SO₄; 30%:70% in the first and second years of study, respectively, as compared to all the remaining treatments. The minimum total sugar (12.85%) was recorded under Ca(NO₃)₂:(NH₄)₂SO₄; 0%:100% treatment combination in the first year, while the similar treatment combination recorded the minimum total sugar content in fruits (12.88%) in the second year. Our values of total sugar in the ‘Wonderful’ cultivar juice generally differed to those reported by Abdulrahman et al. [90], who reported that the ‘Wonderful’ cultivar cultivated in Iraq recorded 5.31% in juice. This is may be due to number of factors, including climatic factors, species, cultivars, and processing techniques.

It was clear from Table 5 that the treatment Ca(NO₃)₂:(NH₄)₂SO₄; 30%:70% produced fruits with significantly more reduced sugars, between 12.44% and 12.46%, in the first and second years of study, respectively, compared to all the remaining treatment combinations; whereas the minimum reduced sugars were recorded under the Ca(NO₃)₂: (NH₄)₂SO₄; 0%:100% treatment combination of between 11.81% and 11.83% during the first and second years, respectively. However, during the second year, the treatment of Ca(NO₃)₂: (NH₄)₂SO₄; 40%:60% significantly decreased both total sugar and reduced sugar, compared to the treatment of Ca(NO₃)₂: (NH₄)₂SO₄; 30%:70% combinations. Due to the dilution of soluble solids and sugar, the decrease in total sugar and reduced sugar over both study years, with the increased ratio of (NH₄)₂SO₄ may be anticipated [73]. Furthermore, non-reduced sugars had a range from 1% to 1.54% in the 2020 season, and from 1.02% to 1.54% in the 2021 season (Table 5). Additionally, high values were recorded at the treatment of Ca(NO₃)₂: (NH₄)₂SO₄; 20%:80% of 1.54%. This may be due to the amount of both total sugar and reduced sugar.

4.4. Fertilization Treatment Effect on Antioxidant Compounds

Consuming pomegranate fruit is said to have health benefits because of its antioxidant activity [105]. The vitamin C content of fruits was observed to be maximum with the application of treatment Ca(NO₃)_2: (NH₄)₂SO₄; 30%:70% in the first and second years of study, between 17.01% and 17.13%, respectively, over all the remaining treatment integrations; whereas the minimum vitamin C contents in fruits, between 14.78% and 15.02%, were recorded under a Ca(NO₃)₂:(NH₄)₂SO₄; 0%:100% treatment combination, in the first year and second year, respectively. Our vitamin C measurements in the ‘Wonderful’ cultivar juice usually differed from those reported by Abdulrahman et al. [90], who stated that the ‘Wonderful’ cultivar juice contained 48 mg of vitamin C per 100 mL. Most likely, a number of factors, including climatic factors, species, cultivars, processing techniques, etc., affect the amount of chemical components in fresh juice [90]. However, higher ascorbic acid concentration in such fruit may primarily be caused by the fact that calcium has a precursory influence on the vitamin C content [106]. This study found that adding calcium enhanced the content of ascorbic acid. In order to prevent physiological problems, delay ripening, and improve the quality of different fruit crops, calcium is given both before and after the harvesting period [107,108]. The anthocyanin range was from 23.6 mg/100 g to 28.4 mg/100 g in season 2020, and it was from 23.84 mg/100 g to 28.6 mg/100 g in season 2021, based on the integration of Ca(NO₃)₂:(NH₄)₂SO₄ ratios. A rapid increase in anthocyanin pigment concentration with increasing Ca(NO₃)₂ from 0% up to 30%, and decreasing (NH₄)₂SO₄ from 100% to 70%, may be attributed to the maturation level [109]. Our values of anthocyanin content in the ‘Wonderful’ cultivar juice generally differed to those reported by Abdulrahman et al. [90], which noted a ‘Wonderful’ cultivar content of 19.50 mg/100 mL juice. Generally, the application of calcium increased ascorbic acid content in this study; however, according to the cultivar, pomegranate juice typically has an anthocyanin level ranging from 10 to 700 mg/L [110]. As a result of their positive preventative effects on human health, dietitians advise preserving these components during the preparation of fruit juice [111].

Fruits and vegetables include phenolic chemicals that are significant for sensory qualities, as well as having potential health advantages [95]. The total phenolic content values are affected by different combinations of Ca(NO₃)₂:(NH₄)₂SO₄ in the present study. The total phenolic content of fruit ranged from 548.8 to 723.8 mg of gallic acid equivalent/100 mL of pomegranate juice in the first season, and from 561.3 to 728.8 mg of gallic acid equivalent/100 mL of pomegranate juice in the second season, suggesting that the total phenolic concentration of pomegranate juice may be affected by fertilization treatment. Among the integrated fertilization treatments, the Ca(NO₃)₂:(NH₄)₂SO₄ of 30%:70% combination gave the highest total phenolic content in both seasons, compared to the Ca(NO₃)₂: (NH₄)₂SO₄ of 0%:100% combination. When compared to other values for pomegranate fruits, the cv. ‘Wonderful’ total phenolic content, measured as gallic acid equivalents, the value was 1494 (mg GAE)/L by Adiletta et al. [89]; the value was 800 (mg GAE)/L and for ‘Wonderful’ fruit from California (obtained from a local store in Tifton, Georgia), and the value was 2468 (mg GAE)/L [112]. Weerakkody et al. [113] found that total phenolic content in juice from ‘Wonderful’ in Australia, during fruit development, varied from 1710 mg GAE/L (immature fruit) to 790 mg GAE/L (mature fruit). Abdulrahman et al. [90] reported a total phenolic content of 353.11 mg/100 mL for the ‘Wonderful’ cv. Cultivated in Iraq. The variation among total phenolic content values may be due to fruit maturity and production process, in addition to environmental conditions before harvest [112]. Additionally, Saenz et al. [114] observed that events occurring during juice production, such as hydroxylation, methylation, isoprenylation, dimerization, and/or glycosylation, may be the reason for the variability in the total phenolic component, and the values of total tannin content were affected by different combinations of Ca(NO₃)₂:(NH₄)₂SO₄ in the present study. The total tannin content of fruits ranged from 3.1 to 5.2 mg of tannic acid equivalent/L of pomegranate juice in the first season, and from 3.2 to 5.3 mg of tannic acid equivalent/L of pomegranate juice in the second season, suggesting that the total tannin concentration of pomegranate may be affected by fertilization treatment. In an earlier study, the total tannin content was 32.60 ± 0.240 mg TaE/100 g in ‘Rabab-e-Fars’ [115], and 0.540–2.531 mg TaE/mL in Chinese cultivars [116]. Among the integrated fertilization treatments, the Ca(NO₃)₂:(NH₄)₂SO₄ of 30%:70% combination gave the highest total tannin content in both seasons, compared to the Ca(NO₃)₂:(NH₄)₂SO₄ of 0%:100% combination.

Total flavonoid content values were affected by different combinations of Ca(NO₃)₂: NH₄)₂SO₄ in the present study. The total flavonoid content of fruits ranged from 218.8 to 317.5 mg catechin equivalents (CaE)/100 mL of juice extract in the first season, and from 228.8 to 325.0 mg catechin equivalents (CaE)/100 mL of juice extract in the second season, suggesting that the total tannin concentration of pomegranate may be affected by fertilization treatment. The ‘Mollar de Elche’ pomegranate cultivar’s juice, which was taken from the fruit at a medium-high stage of ripening, had the most flavonoids (165 mg of QE per 100 mL) [117]. Among the integrated fertilization treatments, the Ca(NO₃)₂: (NH₄)₂SO₄ of 30%:70% combination gave the highest total flavonoid content in both seasons, compared to the Ca(NO₃)₂:(NH₄)₂SO₄ of 0%:100% combination. As a result, such treatment would increase pomegranate cultivar, with excellent international market commercialization, antioxidant capabilities, and health-promoting effects. Regarding the fertilization treatment effect, the different behaviors of total phenolic content, total tannin content, anthocyanin, and total flavonoid content, could be clarified, at least in part, by genetic factors [59].

4.5. Fertilization Treatments Effect on Mineral Contents

Although many fruits are abundant in mineral nutrients vital to human health, cultivar-specific fruit mineral nutrient concentrations were required to propose the pomegranate as a food source [118]. The regulation of the concentrations of heavy metals in food should be a crucial component of food quality, since national and international standards on food quality specify the maximum allowable limit of harmful metals in human food [119,120].

Among the integrated fertilization treatments, the Ca(NO₃)₂:(NH₄)₂SO₄ of 30%:70% combination gave the highest P, K, Ca, Mg, Na, Fe, Mn, Zn, Cu, and Ni, concentration in fruit in both seasons, compared to the Ca(NO₃)₂:(NH4)₂SO₄ of 0%:100% combination in both seasons, as shown in Table 6 and Table 7. It is clear also that Na and Ni had no changes in both years. The concentrations of the mineral elements P, K, Ca, Mg, Na, Fe, Mn, Zn, Cu, and Ni, in pomegranate juice determined in this study, were consistent with the results of [118], indicating that pomegranate is a good source of these elements. Inconsistencies in fruit macro- and micronutrient concentrations between the current study and earlier studies may be due to cultivar differences, or the availability of different nutrients in the soil at various study sites [118]. Moreover, the comparison of macro- and micronutrient element concentrations in the arils of healthy fruit of the ‘Malase Saveh’ pomegranate cultivated in Markazi Province, Iran, were P, K, Ca, and Mg were 1.5, 10.5, 1.4, and 0.9 g/kg, respectively, and of Fe, Mn, Zn, and Cu, were 37.4, 6.5, 26.4, and 25.2 mg/kg, respectively [121]. The mean concentration of heavy metals in fruit shows the following decreasing trend: Fe > Zn > Mn > Cu > Ni for Ca(NO₃)₂:(NH₄)₂SO₄ ratios of (30%:70%), in seasons 2020 and 2021, as shown in Table 7. These concentrations of Fe, Mn, Zn, Cu, and Ni, in fruit samples were within the recommended level set by Anon [53], the FAO/WHO [54,55].

The consistency of such macro- and micronutrient element concentrations in juice with the treatment Ca(NO₃)₂:(NH₄)₂SO₄ of 30%:70% combination showed that excessive Ca(NO₃) application, until 30%, and lower (NH₄)₂SO₄ application, until 70%, could enhance the concentration of such elements in the juice, and this fertilization level should be sufficient for fruit development. The Ca concentration was enhanced under such fertilizer regimes (Table 6 and Table 7), but its concentration remained relatively low, and thus does not have a significant impact on human health. However, a balanced calcium intake is essential for good root system growth, a healthy fruit set, and the development of high-quality fruit; it also increases photosynthesis and improves the efficiency of nitrogen usage [122]. Furthermore, when fertilizer calcium is sprayed, the apple leaves’ potential for photosynthetic activity and the chloroplast pigment levels rise [123], thus the mineral content, sugar–acid metabolism and the fruit quality of ‘Fuji’ apples are improved.

5. Conclusions

In general, applying integrated fertilization from calcium nitrate and ammonium sulphate (Ca(NO₃)₂:(NH₄)₂SO₄) ratios improved the quality of pomegranate fruits of the cv. ‘Wonderful’. The integrated Ca(NO₃)₂:(NH₄)₂SO₄; 30%:70% was more conducive to increase fruit weight, fruit length, fruit volume, fruit diameter, total soluble solids, vitamin C, anthocyanin, phenolic compounds, total tannin content, total flavonoid content, sugar content, and to decrease titratable acidity. The calcium fertilizer improved the photosynthetic function of pomegranate leaves, increased the P, K, Ca, Mg, and Na contents, and also increased the Fe, Mn, Zn, Cu, and Ni contents in pomegranate fruit. For the pomegranate fruits of the cv. ‘Wonderful’, the effects of integrated fertilization containing N application rate 200 kg/ha plus 108 kg/ha application rate of CaO was more desirable than the integrated fertilization containing other application rates of CaO.