Apricot Tree Nutrient Uptake, Fruit Quality and Phytochemical Attributes, and Soil Fertility under Organic and Integrated Management

Abstract

Organic cultivation management has generated a great deal of interest during the last decades. As there are numerous conflicting results in the literature on the superiority of organic cultivation over an integrated one, a trial occurred using two apricot cultivars, i.e., ‘Bebecou’ and ‘Diamantopoulou’, under integrated and organic cultivation (three orchards per cultivation system and cultivar). The trial occurred during a single cultivation period under different soil but the same climatic conditions. Fruit physiological (weight, diameters, skin color), organoleptic (pH, titratable acidity, and total soluble solids), and phytochemical (phenolic compounds, carbohydrates, organic acids, antioxidant activity, and carotenoids) attributes were assessed, along with plant nutrition, soil fertility status, and a sensory evaluation panel. The two cultivation practices exhibited similar effects in many of the parameters studied in this trial as well as small differences. Fruit weight was higher under organic management in ‘Bebecou’ and under integrated in ‘Diamantopoulou’, while copper was found at a higher concentration in the leaves of organically managed trees of both cultivars. The cultivar was found to have the greatest effects on the measured variables, while within each cultivation management, the farm also had a great impact, indicating that the outcome of specific cultivation practice is influenced by so many factors that it is almost impossible to come to a general conclusion about which practice is the best. Therefore, more research is needed, focused not only on the differences between organic and integrated cultivation management but primarily on the influence of specific cultivation practices within the same management system, to be able to elucidate, to some extent, the effects of individual factors on the measured variables.

1. Introduction

During the last decades, it has become apparent that consumers demand high-quality food in terms of taste, appearance, safety, and nutraceutical characteristics [1]. This demand increased during the new millennium when many pesticides were withdrawn from the market, and new cultivars entered with improved quality characteristics. Fruits are considered a natural source of antioxidants and health-promoting substances, with their consumption being linked to the prevention or suppression of chronic diseases, such as cardiovascular problems, cancer, etc. [2,3]. These properties rely on the content of valuable phytochemicals in fruits, such as antioxidants (phenolic compounds, carotenoids, vitamins, etc.), which counter the free radicals produced in the human body, able to damage cellular components and lead to severe health risks [1,2,3].

Among fruits with significant phytochemical content are apricots, with their consumption helping to overcome or mitigate problems, such as vitamin A and trace minerals deficiencies, stress, and anemia, while at the same time, they are considered body defense boosters, maintaining the acid–base balance in the body, and act as a tonic agent for the nervous system [4]. All these properties are attributed to the phytochemicals found in the pulp as well as in the seed.

The content of phytochemicals in fruit is influenced by several factors, with the most significant being the genotype, environmental factors, and cultivation practices [2,5,6].

Three agricultural production systems dominate worldwide: the conventional, the integrated, and the organic management systems [7,8]. The conventional production system is based on the intensive use of synthetic fertilizers and pesticides and, lately, on genetically modified organisms (GMOs) and generally on a narrow base of genetic resources aiming at maximum production at all costs. On the other hand, organic agriculture (OA) does not use synthetic pesticides and synthetic inorganic fertilizers as well as GMOs, but instead, it focuses on the sustainability of the entire system, environment (air, water, soil), farm, crop, biodiversity, and farmers’ and consumers’ health. It relies on renewable resources, natural inputs, greater labor, and generally, practices that restore, maintain, or enhance environmental balance [7,9]. On the other hand, the integrated system (IS) is placed between the two pre-mentioned ones and is characterized by the judicious use of agrochemical inputs along with organic ones, the protection of the environment, and the user (either the farmer or the consumer). It has become the standard management system in Europe since the European Union (EU) Directive 2009/128 [10]. These last two focus on the sustainability of the system, which aims at “meeting the needs of today without compromising the ability of future generations to meet their needs”.

Consumer awareness of the relationship between fruit quality and health benefits as well as environmental protection and sustainability has led to an increasing demand for organically produced fruits [6]. It is a common belief among the community that organic fruits are healthier, due to the practices employed in their production. Nonetheless, this perception is not always supported by research data, as not all studies comparing organic versus integrated management systems have provided consistent results [9,11].

The quality characteristics of a product, in our case the apricot fruit, depend on many variables, such as the pedoclimatic conditions, the cultivation practices, the genotype, etc. Therefore, the present work aimed to assess the effects of organic and integrated practice on soil physicochemical properties, plant nutrition and fruit organoleptic, physiological, and phytochemical properties under the same climatic conditions using two major apricot cultivars. Furthermore, as organic practice is thought to positively affect soil physicochemical properties, plant nutrition and fruit organoleptic, physiological, and phytochemical properties, the objective was to verify any apparent benefit of the organic vs. integrated farming for apricot production and soil properties.

2. Materials and Methods

2.1. Test Site Location—Plant Material

The trial occurred in Mellisi village (38.0473° N, 22.6834° E), Argolida county, central Greece, during the production period 2020–2021. Six orchards were selected, three under organic and three under integrated management. In each orchard, three trees comprised one plot, with a total of three plots per orchard per cultivar (nine trees per cultivar per orchard). All orchards were planted with the two major apricot cultivars for the area, i.e., ‘Bebecou’ and ‘Diamantopoulou’, grafted on Myrobalan 29C rootstock, and trained as opened center cup-shaped trees. Trees were mature, and full-bearing and organic ones were under the inspection of certification organisms for more than ten years.

All the cultural practices in each orchard were recorded, including pruning time, fertilization, and pesticide programs, as well as the mean production per tree (data provided by the farmers—Appendix A).

2.2. Soil and Leaf Sampling and Analysis

Soil samples from each orchard were collected at the end of November at a 0–40 cm depth. A 5 cm diameter auger was used, and soil samples were taken after clearing the soil surface from any plant biomass. Three composite soil samples were collected per orchard and per cultivar.

In mid-July (fruits were already harvested, and new shoots had completed their spring growth), approximately 20 healthy, fully expanded leaves were collected per tree (60 leaves per plot). Leaves were randomly sampled around the canopy of each tree, approximately 1–2 m above ground, from the middle part of non-bearing shoots. Leaves sampled from the three trees of each plot were considered as one sample. The leaves were placed in paper bags and transferred to the laboratory, where they were firstly washed with running tap water and later thrice with deionized water. After drying in an oven at 70 °C until constant weight, the leaves were ground into a fine powder (<1.0 mm) with a centrifugal mill.

Soil and leaf samples were then analyzed following the procedures described by Roussos et al. [12]. Briefly, the soil samples were firstly air-dried and ground to pass 2 mm sieve. The particle size was determined by the hydrometer method, waiting a period of 2 h for the clay concentration estimation [13]. Electrical conductivity (EC) and soil pH were measured in a water-soil suspension (1:1 v-w) [14]. Organic matter was determined according to Walkley-Black wet digestion method [15]. The exchangeable cations as well as the cation exchange capacity (CEC) were determined using the ammonium acetate extraction method [16]. Plant available P was determined according to Olsen et al. [17]. For the determination of available metals 10 g of soil sample were extracted by shaking for 2 h with 20 mL 0.005 M diethylenetriamine-pentaacetic acid (DTPA), previously adjusted to pH = 7.3 [18].

For the leaf mineral analysis, the leaves were carefully washed with running tap water and then thrice with deionized water in order to determine the concentrations of nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), iron (Fe), zinc (Zn), manganese (Mn), copper (Cu) and boron (B). Leaf samples were then dried at 65 °C until constant weight, milled into a fine powder (<1 mm), and dry-ashed in a furnace at 500 °C for 5 h. The ash produced was treated with 5% v/v HCl. For the determination of P concentration, the vanado-molybdo-phosphate yellow color method was used, while azomethin-H was used for B determination. Potassium, Ca, Mg, Fe, Mn, Zn, and Cu concentration was determined by atomic absorption spectrometry (Varian SpectrAA, 240 FS). Nitrogen concentration was measured by the indophenol-blue method in the wet digest [19,20]

2.3. Fruit Sampling

At least 20 healthy fruits were carefully harvested, at the commercial maturity stage (based on their skin ground color, i.e., fully colored) [21] according to an equatorial pattern (East–West–North–South) from the periphery of the canopy of each tree (60 fruits per plot). All orchards of the same cultivar were harvested on the same day. The sampled fruits were put into plastic boxes and transferred immediately to the laboratory, where they were further processed.

2.4. Assessments of Fruit Quality Characteristics

2.4.1. Physiological Attributes

Each fruit was weighed on a calibrated electronic balance (Kern 470, Kern, and Sohn, GmbH, Germany), and its diameter and length were measured by a digital caliper (Starrett, 727 Series, Athol, MA, USA). Skin color was measured at two different points around the equatorial region of each fruit, using a Minolta CR 300 reflectance Chroma Meter (Minolta, Osaka, Japan), providing CIE L*, a*, and b* values. Based on these values the Hue angle degree and Chroma values were calculated. Fruit firmness of 10 fruits was measured on opposite cheeks (after slightly peeling off the skin with a sharp knife), by a hand-held penetrometer with a 6.3 mm diameter conical plunger. The fruits were then de-stoned and the pulp width was measured. The weight of the stone was recorded and the weight of the pulp was calculated. These fruits were further used to determine the percentage of pulp dry matter, after drying them in an oven at 70 °C until constant dry weight.

The remaining fruits were carefully de-stoned and homogenized by a home homogenizer, and the produced pulp was put in 50 mL falcon tubes and 2 mL Eppendorf tubes, which were stored in a freezer (−25 °C) until analysis.

2.4.2. Total Soluble Solids (TSS), Titratable Acidity (TA), and pH Determination

The Eppendorf tubes containing the homogenized pulp were left to thaw at room temperature and centrifuged at 4000 g for 6 min. The supernatant clear juice was used for the determination of TSS, pH, and TA. The total soluble solids were determined with a Hanna HI96801 (270 George Washington Hwy Smithfield, RI 02917, USA) digital refractometer and expressed as ^oBrix. A sample of the juice was diluted 1:20 with distilled water, and the pH of this solution was measured, as well as its titratable acidity (as gram of citric acid 100 mL⁻¹ juice), by titrating to a pH value of 8.2 using 0.05 N NaOH [22].

2.4.3. Phenolic Compound Concentration and Antioxidant Capacity Determination

Approximately 2.0 g of the frozen apricot pulp was extracted with 5 mL 100% methanol for 30 min at 40 °C under periodical stirring and centrifuged at 4000× g for 6 min. The supernatant was transferred to a new tube, and the pellet was re-extracted with methanol under the same conditions. After the second centrifugation, the two supernatants were combined and used to measure the concentration of total phenols, total o-diphenols, total flavonoids, and total flavonols, according to Roussos et al. [22], and the results were expressed as mg equivalent gallic acid (GAE) (total phenols), caffeic acid (CAE) (total o-diphenols), catechin (CtE) (total flavonoids), and catechin (CtE) (total flavonols). Briefly, for the total phenols determination, 50 μL of the supernatant was added to 3.95 mL distilled water, and the solution was vortexed. Afterward, 250 μL of Folin–Ciocalteu reagent was added and vortexed, and then 750 μL of saturated Na₂CO₃ solution and the solution remained at room temperature for 2 h, after which time the absorbance was measured at 760 nm. For the determination of o-diphenols, 100 μL of the supernatant was added to 900 μL water, vortexed, and then 1 mL potassium phosphate buffer (0.1 M pH 5.8) was added, followed by 2 mL of a 5% (w/v) solution of Na₂MoO₄ 5H₂O. The absorbance was measured after 15 min at 370 nm. For the total flavonoids determination, 500 μL of the supernatant was added to 2 mL water, followed by 0.15 mL NaNO₂ (5% w/v in water), and after 5 min, 0.15 mL of AlCl₃ (10% w/v in water) were added. After six minutes, 1 mL of 1 N NaOH was added, followed by 1.2 mL of water, and the absorbance was measured at 510 nm. For the total flavanols determination, 200 μL supernatant was added to 1 mL chromogen reagent (0.1% (w/v) of 4-dimethylaminocinnamaldehyde in 1 N HCl in methanol), the solution was vortexed, and the absorbance was measured after 10 min at 640 nm.

The antioxidant capacity of the pulp was assessed in the same methanolic extract of phenolic compound extraction, based on the DPPH (2,2-diphenyl-1-picryl hydrazyl) and FRAP (ferric-reducing antioxidant power) assays as described by Roussos et al. [22], and are both expressed in μmol Trolox equivalents (TE) per g fresh weight. Briefly, 0.1 mL of the supernatant was added to 2 mL of 0.1 mM DPPH solution (freshly prepared each time), and after 15 min in the dark, the absorbance was measured at 517 nm. For the FRAP assay, 50 μL of supernatant was added to 1.5 mL of FRAP reagent previously equilibrated at 37 ℃. The solution remained for 30 min at 37 °C in a water bath, and then the absorbance was measured at 593 nm.

2.4.4. Soluble Sugars and Organic Acids Determination

Soluble sugars were determined in the frozen pulp sample as described by Roussos et al. [14]. The carbohydrates were separated through a Hamilton HC-75 cation exchange column, calcium form (Ca⁺²) (Hamilton, Bonaduz, Switzerland), equilibrated at 80 °C with water as eluent at a flow rate of 0.6 mL min⁻¹ delivered by an isocratic pump (Waters 510 pump) (Waters, Milford, MA, USA). Four carbohydrates were determined, i.e., sucrose, glucose, fructose, and sorbitol, and quantified by the use of authentic standards’ five-point calibration curves.

The sweetness index (SI) of the fruit was calculated based on the relative amount and sweetness perception of each carbohydrate [22,23].

Organic acids were determined in 0.5 g of frozen fruit pulp, which was extracted twice with 5 mL 3% (w/v) aqueous metaphosphoric acid, at room temperature, for 30 min each time, under periodical agitation. After each 30 min cycle, the mixture was centrifuged at 4000 g for 6 min, and at the end, the two supernatants were combined and filtered through a 0.45 m pore size nylon syringe filter. The organic acids were analyzed by an HP1050 HPLC (Agilent, Santa Clara, CA 95051, USA) using a Hypersil ODS 5 μm (250 × 4.6 mm) column (Thermo Fischer Scientific, Waltham, MA, USA). Elution was accomplished isocratically at a flow rate of 1 mL min⁻¹ using 0.02% (v/v) aqueous formic acid as the mobile phase. The organic acids were detected at 200 nm with an HP 1050 DAD detector (Agilent, Santa Clara, CA 95051, USA) based on their retention times compared to those of authentic standards. Four organic acids were determined, namely citric, malic, fumaric, and ascorbic acid, and quantified using authentic standards’ calibration curves. The sourness index (SOURI) was estimated as the quotient of total sugars versus citric acid according to Hasnaoui et al. [24].

2.4.5. Individual Carotenoids Determination

Approximately 2 g of frozen pulp was homogenized with 10 mL of a methanol-ethyl acetate-hexane mixture at a 25-25-50 ratio, containing 0.1% w/v butylated hydroxyl toluene as an antioxidant, using a T10 basic Ultra Turrax (IKA, Janke, and Kunkel-Str. 1079219 Staufen Germany). Carotenoids were extracted in an orbital shaker (IKA, Janke and Kunkel-Str. 1079219 Staufen Germany) working at 400 rpm for 10 min in the dark. At the end of this period, another 5 mL of the extraction solution was added and re-extracted under the same conditions for 10 min, when the pulp was fully discolored. The samples were then put in a freezer for approximately 30 min and then centrifuged at 4000× g for 4 min. An exact volume (8 mL) of the supernatant was removed and dried under a stream of nitrogen at 35 °C. The remaining was diluted in acetone (HPLC grade); it was filtered through a nylon syringe filter and analyzed by a Nexera X2 HPLC system (Shimadzu Kyoto, Japan). Carotenoids were separated by the use of a Supelco Discovery column 5 μm (150 × 4.6 mm) (Bellefonte, PA, USA) using 100% acetonitrile as the mobile phase at a flow rate of 1.5 mL min⁻¹ at 30 °C. Carotenoids were determined by a DAD detector at 450 nm. Two carotenoids were determined, β-carotene and β-cryptoxanthin, and quantified and quantified based on a four-point calibration curve of external standards.

2.5. Taste Panel

To evaluate the sensorial properties of the fruits produced under the two cultivation practices, a taste panel occurred with 15 panelists (with approximately 1:1 women to men ratio, aged 30–45 years) previously trained in the specific sensory evaluation test. The test was based on the evaluation of the following characteristics, on a six-level scale (0, worst or least; 5, best or most): taste, flavor, appearance, firmness, acidity, sweetness, mouth aroma, taste remaining after swallowing (after taste), and general acceptance.

A quality index was produced based on the testers’ opinions about the five most significant traits they seek in an apricot fruit based on the characteristics assessed in the present taste panel. This index was produced after the mean score of each of the five most important attributes was multiplied by the mean significance value and summing the final score as follows:

Quality index = 4.38 × Taste + 2.19 × Sweetness + 1.46 × Mouth aroma + 1.10 × Firmness + 0.88 × Flavor.

2.6. Statistical Analysis

The trial was designed as a pseudo-replicated trial (treatments, i.e., organic versus integrated cultivation practice were not in the same orchard) with three replicates of three trees in each orchard (i.e., three plots of three trees per orchard, three orchards per cultivar, two cultivars, and two management systems). The three plots within each orchard were randomly selected in each orchard’s area (completely randomized in the orchard). Significant differences among cultivation practices for the same cultivar were determined based on the T-test at a = 0.05 after checking the normal distribution of the raw data using standard skewness, standard kurtosis, and the homogeneity of variances. The comparison of the cultivation practices used the data derived from all three orchards of the cultivar managed under the same practice. Data of the taste panels were analyzed based on the Kruskal–Wallis test. Principal component analysis of raw data (on fruit physiological, organoleptic and phytochemical attributes, soil properties, and plant nutrition) was used to describe the characteristics and differences of each orchard management practice as well as to assess possible differences among orchards under the same cultivation practice per cultivar, using a small number of variables. The statistical software Statgraphics Centurion XV (Statgraphics Technologies, Inc. The Plains, VA, USA) was used for the pre-mentioned analyses.

3. Results

3.1. Effect on Fruit Physiological, Organoleptic, and Phytochemical Parameters

Based on the information provided by the farmers (plots were harvested by the farmers “in hands”, and the total yield per plot was calculated), the mean yield of organically grown ‘Bebecou’ reached 46.7 kg per tree, while that of integrated managed trees was 58.5 kg. ‘Diamantopoulou’ trees grown under organic management produced 32.6 kg per tree, while under integrated practice, 40.2 Kg per tree (

Table 1. Effect of cultural management on fruit physiological parameters and pulp carotenoid concentration of the two apricot cultivars.

Parameter	Integrated	Organic	Significance
Bebecou
Yield (Kg per tree)	58.5 1	46.7 1	***
Fresh weight (g)	45.46	60.50	***
Diameter (mm)	43.45	48.30	***
Length (mm)	44.40	47.60	*
Firmness (Kg)	1.15	0.99	*
Pulp width (mm)	11.71	13.08	**
Diameter/Length	0.98	1.01	*
Stone weight (g)	2.58	2.92	**
Pulp weight (g)	42.87	57.58	***
Pulp (%)	94.21	95.15	**
Dry matter (%)	10.62	11.07	ns
β-carotene	3.81	3.20	ns
Cryptoxanthin	0.32	0.34	ns
Diamantopoulou
Yield (Kg per tree)	40.2 1	32.6 1	***
Fresh weight (g)	29.32	22.02	*
Diameter (mm)	38.26	34.62	*
Length (mm)	65.82	35.63	ns
Firmness (Kg)	0.59	0.55	ns
Pulp width (mm)	9.22	8.11	*
Diameter/Length	0.92	0.97	ns
Stone weight (g)	2.27	1.75	***
Pulp weight (g)	27.05	20.27	*
Pulp (%)	92.06	91.92	ns
Dry matter (%)	12.31	13.20	ns
β-carotene	15.30	20.62	ns
Cryptoxanthin	0.97	1.28	ns

Asterisks indicate significant differences of means within the same row at probability level *, p < 0.05; **, p < 0.01; ***, p < 0.001, ns, not significant. ¹ Data on yield per tree were provided by the farmers for the specific plots.

).

Organically produced fruits of the ‘Bebecou’ cultivar presented higher values of mean fruit fresh weight, fruit diameter and length, pulp width, a ratio of diameter versus length, stone weight, pulp weight, and percentage of pulp per fruit fresh weight, but a lower value of fruit firmness (Table 1). There was not any significant difference concerning the percentage of dry matter as well as the concentration of β-carotene and β-cryptoxanthin.

In ‘Diamantopoulou’, on the other hand, integrated produced fruits exhibited higher mean fruit fresh weight and diameter, higher pulp width, as well as higher stone and pulp weight (Table 1). There were not any significant differences, though, concerning the fruit length and firmness, as well as the pulp and dry matter percentage and the concentration of the two individual carotenoids determined.

As far as the organoleptic characteristics of the fruit are concerned, the cultivation management exhibited a significant effect only concerning the ratio of TSS versus TA in ‘Bebecou’, where organically produced fruits exhibited greater values (

Table 2. Effect of cultural management on fruit organoleptic characteristics of the two apricot cultivars.

Parameter	Integrated	Organic	Significance
Bebecou
pH	3.54	3.52	ns
TSS (oBrix)	11.41	12.18	ns
TA (% w/w citric acid)	1.47	1.41	ns
TSS/TA	7.73	8.71	*
Diamantopoulou
pH	3.85	3.92	ns
TSS (oBrix)	12.90	14.07	ns
TA (% w/w citric acid)	1.05	1.07	ns
TSS/TA	12.25	13.48	ns

Asterisks indicate significant differences of means within the same row at probability level *, p < 0.05; ns, not significant.

).

Integrated management seems to induce higher values of the CIELab b* parameter of the skin, as in both cultivars, it was found to be higher than that determined in organic fruits (

Table 3. Effect of cultural management on fruit skin color attributes of the two apricot cultivars.

Parameter	Integrated	Organic	Significance
Bebecou
L*	68.38	67.10	ns
a*	4.70	6.42	ns
b*	50.70	48.66	*
Chroma	50.95	49.17	*
Hue	84.69	82.49	ns
Diamantopoulou
L*	66.86	65.09	ns
a*	4.20	5.64	ns
b*	50.59	48.17	*
Chroma	50.80	48.57	ns
Hue	85.62	83.30	ns

Asterisks indicate significant differences of means within the same row at probability level *, p < 0.05; ns, not significant.

). The Chroma index was also higher under integrated management concerning the fruits of the ‘Bebecou’ cultivar.

The carbohydrate concentration of the fruit was not affected by the cultivation management in either cultivar, as can be seen in

Table 4. Effect of cultural management on fruit carbohydrate concentration and sweetness index of the two apricot cultivars.

Parameter	Integrated	Organic	Significance
Bebecou
Sucrose (%)	5.28	5.41	ns
Fructose (%)	0.63	0.59	ns
Glucose (%)	1.32	1.28	ns
Sorbitol (%)	1.19	1.05	ns
Total sugars (%)	8.42	6.35	ns
Sweetness index	10.86	10.81	ns
Diamantopoulou
Sucrose (%)	5.38	5.23	ns
Fructose (%)	0.55	0.64	ns
Glucose (%)	1.29	1.43	ns
Sorbitol (%)	1.32	1.50	ns
Total sugars (%)	8.56	8.80	ns
Sweetness index	10.91	11.17	ns

Asterisks indicate significant differences of means within the same row at probability level, ns, not significant.

. Similarly, the concentration of the organic acids found in fruits of the ‘Bebecou’ cultivar was not affected by the cultivation practice employed, while only ascorbic acid concentration was higher under organic management in ‘Diamantopoulou’ (

Table 5. Effect of cultural management on fruit organic acid concentration (mg 100 g⁻¹ FW) and sourness index of the two apricot cultivars.

Parameter	Integrated	Organic	Significance
Bebecou
Malic acid	589.4	655.4	ns
Citric acid	1690.3	1475.6	ns
Fumaric acid	2.91	3.01	ns
Ascorbic acid	40.93	39.03	ns
Total acids	2324.1	2173.1	ns
Sourness index	3.63	3.88	ns
Diamantopoulou
Malic acid	384.1	388.4	ns
Citric acid	1594.7	1376.2	ns
Fumaric acid	2.75	3.10	ns
Ascorbic acid	39.34	42.78	*
Total acids	2021.0	1810.6	ns
Sourness index	4.23	5.03	ns

Asterisks indicate significant differences of means within the same row at probability level *, p < 0.05; ns, not significant.

).

Total phenolic compounds was not significantly affected by the cultivation practice, as only total o-diphenols and total flavanols concentration presented significant differences in ‘Bebecou’ fruits (

Table 6. Effect of cultural management on fruit phenolic compound concentration and antioxidant capacity of the two apricot cultivars.

Parameter	Integrated	Organic	Significance
Bebecou
Total phenolic compounds	0.31	0.28	ns
Total o-diphenols	0.12	0.096	***
Total flavanols	0.006	0.013	*
Total flavonoids	0.098	0.089	ns
DPPH	0.12	0.08	ns
FRAP	1.67	1.52	ns
Diamantopoulou
Total phenolic compounds	0.47	0.57	ns
Total o-diphenols	0.15	0.22	*
Total flavanols	0.059	0.038	ns
Total flavonoids	0.16	0.19	ns
DPPH	0.46	0.64	ns
FRAP	1.91	2.21	ns

Asterisks indicate significant differences of means within the same row at probability level *, p < 0.05; ***, p < 0.001; ns, not significant. Total phenolic compounds are expressed in mg equiv. gallic acid g⁻¹ FW, total o-diphenols in mg equiv. caffeic acid g⁻¹ FW, total flavanols in mg equiv. catechin g⁻¹ FW, total flavonoids in mg equiv. catechin g⁻¹ FW and DPPH and FRAP are expressed in μmoL equiv. Trolox g⁻¹ FW.

). Total o-diphenols concentration was higher in integrated produced fruits, while the opposite was detected concerning total flavanols. Organically produced ‘Diamantopoulou’ fruits presented higher o-diphenol concentration in the flesh, while no other significant difference was found.

3.2. Effect on Leaf Mineral Nutrient Concentration

High nitrogen concentration was determined in ‘Bebecou’ leaves from integrated cultivated trees, while the opposite stood for the concentration of calcium, magnesium, and copper (

Table 7. Effect of cultural management on leaf nutrient concentration of the two apricot cultivars.

Parameter	Integrated	Organic	Significance
Bebecou
N (g kg−1)	26.61	22.34	*
P (g kg−1)	1.98	1.86	ns
K (g kg−1)	25.2	27.9	ns
Ca (g kg−1)	32.88	38.98	**
Mg (g kg−1)	7.05	7.50	*
Fe (mg kg−1)	85.60	72.67	ns
Mn (mg kg−1)	58.37	70.98	ns
Zn (mg kg−1)	17.05	22.18	ns
Cu (mg kg−1)	8.64	38.46	***
B (mg kg−1)	43.27	42.53	ns
Diamantopoulou
N (g kg−1)	24.72	24.27	ns
P (g kg−1)	1.35	1.55	ns
K (g kg−1)	15.82	19.78	ns
Ca (g kg−1)	30.57	31.2	ns
Mg (g kg−1)	7.20	7.00	ns
Fe (mg kg−1)	81.4	78.7	ns
Mn (mg kg−1)	60.10	66.4	ns
Zn (mg kg−1)	40.61	19.34	***
Cu (mg kg−1)	8.28	36.43	***
B (mg kg−1)	44.20	39.83	ns

Asterisks indicate significant differences of means within the same row at probability level *, p < 0.05; **, p < 0.01; ***, p < 0.001; ns, not significant.

).

In leaves from the ‘Diamantopoulou’ cultivar grown under integrated practices, a high level of zinc was determined, higher than the one in leaves from organically grown trees. On the other hand, the latter exhibited a higher copper concentration.

3.3. Effect on Soil Physicochemical Properties

The soil electrical conductivity of ‘Bebecou’ organic orchards was found to be significantly higher than that of integrated ones, while the opposite stood for nitrogen and phosphorus concentration (

Table 8. Effect of cultural management on soil physicochemical properties of Bebecou orchards.

Parameter	Integrated	Organic	Significance
CEC (meq 100 g−1)	26.18	26.99	ns
pH	7.91	7.86	ns
OM (%)	2.40	2.99	ns
CaCO3 (%)	38.97	40.88	ns
EC (mmhos cm−1)	2.48	3.36	*
Total N (%)	0.28	0.13	*
P (mg kg−1)	26.76	16.28	**
K (meq 100 g−1)	0.85	0.80	ns
Ca (meq 100 g−1)	22.22	22.72	ns
Na (meq 100 g−1)	0.38	0.41	ns
Mg (meq 100 g−1)	4.45	4.81	ns
Fe (mg kg−1)	1.59	1.74	ns
Mn (mg kg−1)	2.27	0.96	ns
Zn (mg kg−1)	0.87	0.81	ns
Cu (mg kg−1)	5.36	8.42	ns

Asterisks indicate significant differences of means within the same row at probability level *, p < 0.05; **, p < 0.01; ns, not significant. CEC, cation exchange capacity, OM, organic matter, EC, electrical conductivity.

). No other significant difference was detected concerning soil physicochemical properties.

In ‘Diamantopoulou’ orchards, the cation exchange capacity of the soil was higher under organic cultivation practice, as well as the organic matter content, total nitrogen, and potassium concentration (

Table 9. Effect of cultural management on soil physicochemical properties of ‘Diamantopoulou’ orchards.

Parameter	Integrated	Organic	Significance
CEC (meq 100 g−1)	20.21	30.59	**
pH	7.9	7.72	ns
OM (%)	2.34	3.67	**
CaCO3 (%)	45.68	29.33	**
EC (mmhos cm−1)	2.77	3.57	ns
Total N (%)	0.13	0.20	*
P (mg kg−1)	30.25	43.35	ns
K (meq 100 g−1)	0.66	1.65	*
Ca (meq 100 g−1)	20.09	22.79	ns
Na (meq 100 g−1)	0.54	0.37	ns
Mg (meq 100 g−1)	4.16	4.85	ns
Fe (mg kg−1)	1.78	1.47	ns
Mn (mg kg−1)	1.89	1.37	ns
Zn (mg kg−1)	1.00	1.17	ns
Cu (mg kg−1)	9.88	8.06	ns

Asterisks indicate significant differences of means within the same row at probability level *, p < 0.05; **, p < 0.01; ns, not significant. CEC, cation exchange capacity, OM, organic matter, EC, electrical conductivity.

). On the other hand, the percentage of calcium carbonate was significantly higher in integrated managed orchards compared to organically managed ones.

3.4. Classification of Treatments, Cultivars, and Farms Based on the Raw Data Collected

The principal component analysis of all raw data resulted in 15 principal components (PC) with eigenvalues above 1, while the first 2 components accounted for only 39% of the total variability in the original data.

Nonetheless, to elucidate the situation, the two PCA graphs are presented, even with such a low cumulative variability explained. The two cultivation practices assessed in the present experiment could not be fully distinguished based on the principal component analysis performed on all raw data collected, irrespective of the cultivar (Figure 1).

On the other hand, the two cultivars could be partly separated, as ‘Bebecou’ was located on the negative side of PC 1, while the majority of ‘Diamantopoulou’ was located on the positive side of PC 1 (Figure 2).

In the following figure where only the raw data of ‘Bebecou’ were used, it can be seen that there was a quite clear separation between the two cultivation systems, as the majority of the raw data of organic farms were located on the positive side of PC1 and those of integrated farms on the negative side (Figure 3).

When only the raw data from the organic farms of ‘Bebecou’ were used, the first two components of the PCA explained together the 47.93% of the variability. It was clear that the farms could be distinguished from each other, as shown in Figure 4.

Similarly, when only the data from the integrated ‘Bebecou’ orchards were analyzed, the first two PCA components could explain 53.48% of the variability of the original data. Again, it was clear that the three integrated ‘Bebecou’ orchards could be separated based on the PCA results (Figure 5).

When the same was performed with the raw data of ‘Diamantopoulou’ orchards, it revealed that orchards could not be separated based only on the cultivation technique applied, on a two principal component scatter plot, where the two components explained only the 39.52% of the variability of the original data (Figure 6).

When only the raw data from the organic farms of ‘Diamantopoulou’ were used, the first two components of the PCA explained 47.93% of the original data. It was clear that one of the farms, number 3 farm, was separated from the other two, as shown in Figure 7.

Similarly, when only the data from the integrated ‘Diamantopoulou’ orchards were analyzed, the first two PCA components could explain 52.49% of the variability of the original data. Again, it was clear that the three integrated ‘Diamantopoulou’ orchards used could be separated based on the PCA results, with farm number 3 being on the opposite side of PC 1 compared to the other two (Figure 8).

3.5. Sensory Evaluation Results

In the following figures (Figure 9 and Figure 10), the results of the taste panel are presented as spider charts. The panelists found significant differences between treatments concerning ‘Bebecou’ fruit quality characteristics, as the fruits produced under organic cultivation management were more appealing in terms of taste and overall acceptance, with the quality index calculated to be 29.8 for the organic and 24.7 for the integrated produced fruits.

On the other hand, the panelists found integrated produced fruits of the ‘Diamantopoulou’ cultivar better than the organic ones in terms of taste, sweetness, acidity, appearance, and overall acceptance (Figure 10). This was also confirmed by the grade the integrated fruits scored in the quality index, which was 29.3 against 24.2 for the organically produced ones.

4. Discussion

As already stated, organic practice is thought to result in improved soil physicochemical properties, plant nutrition, and fruit organoleptic, physiological, and phytochemical properties, with an apparent benefit over conventional or integrated management. Based on the principal component analyses, though, the two cultivation practices employed, irrespective of the cultivar used, had many similar characteristics as reported by other researchers, too [1,25,26]. Additionally, the panelists found few differences between organically and integrated produced fruits in both cultivars, as has been reported by other researchers working with other fruits, too [7,11]. On the other hand, the cultivar exhibited a great influence on the parameters assessed in the present research, similar to that reported in other studies [1,2,25,27], and this was also confirmed by the results of the taste panel, where organically grown ‘Bebecou’ and integrated ‘Diamantopoulou’ fruits were the preferred choice by the panelists.

Based on farmers’ information, the integrated-grown trees presented higher yield than the organically grown ones by almost 25% (in ‘Bebecou’) and 23% (in ‘Diamantopoulou’). Similar results have been reported by other researchers, too, working with different species, regarding the effects of cultivation practice on yield [9,28,29].

Nonetheless, yield is not the only thing a farmer should desire since quality substantially affects a product’s acceptability and market placement. ‘Bebecou’ organic orchards presented significantly higher values in almost all physiological-biometric fruit parameters than the integrated ones, apart from the fruit firmness, which was higher under integrated management. Based on the fact that organically grown trees presented lower yields, it can be assumed that the larger fruits were the result of inter-fruit lower competition for assimilates. On the other hand, smaller fruits tend to present higher firmness in many cases [30,31], probably due to the lower accumulation of water or to a denser mesocarp, as small fruits are characterized by reduced rates of mesocarp cell expansion [31,32]. The differences observed in yield as well as in fruit physiological parameters in the ‘Bebecou’ cultivar can not be solely ascribed to the differences detected in tree nutrient status. Based on leaf analysis, there were few significant differences, while under both cultivation managements, the nutrient levels were within the adequacy range or, in some cases, higher than that [33,34,35,36]. The only exception was the marginal Zn concentration in integrated-grown ‘Bebecou’ [35,36]. However, the aforementioned differences were not able to justify the observed differences in yield and fruit quality components.

Similarly, in the ‘Diamantopoulou’ cultivar, significant differences were not observed in the levels of most nutrients in the leaves, while in most cases, they were found in adequacy levels. The only exception was the low leaf K concentration, mainly in integrated-grown ‘Diamantopoulou’ [35,36], which could be due to the higher fruit yield. Nonetheless, fruit weight, pulp width, and weight were higher under integrated practice, even though the yield was also higher, opposite to that found in ‘Bebecou’. This discrepancy between the two cultivars could be due to the genotype effect, especially regarding the fruit size. ‘Bebecou’ is characterized by large fruits, while ‘Diamantopoulou’ bears small ones, the size and weight of which are less prone to competition for assimilates. On the other hand, integrated-grown ‘Diamantopoulou’ trees presented higher leaf Zn concentrations, which could partly justify the higher yield, as Zn serves as a co-factor for the production of endogenous auxin through tryptophan and stone fruits are species known to positively react to auxin treatment [22]. The opposite trend was observed in integrated-grown ‘Bebecou’ with the marginal Zn concentration and the lower yield. Such discrepancies regarding the effect of the cultivation system on fruit physiological parameters among cultivars have been reported in many species [8,37,38].

No differences were detected concerning carotenoid concentration in both cultivars, with the main one being β-carotene, as has been reported in the literature [25,39,40]. It was interesting, though, that ‘Diamantopoulou’ fruits presented higher β-carotene concentration compared to ‘Bebecou’, a clear sign of the effect of cultivar on carotene content, as has been reported earlier [25,40,41,42,43]. Similar to the present findings, Park et al. [5] found no significant effect of the cultivation system on carotenoid concentration in kiwifruits.

Fruit size and shape are among the desired characteristics a consumer seeks, but the taste itself also plays an important role in his choice. Organoleptic characteristics of the fruits were not significantly affected by the cultivation system. No significant effects of cultivation management on pH and TA have also been reported in several other species [29,44]. Only the ratio of TSS versus TA in ‘Bebecou’ was higher under organic cultivation. This could be partially ascribed to the higher fruit load of the cultivar under integrated management, which could have affected the accumulation of carbohydrates in the fruits due to higher competition. The same also stood for ‘Diamantopoulou’ fruits, which presented higher TSS under organic cultivation without any significant difference in all other measured organoleptic characteristics. According to Milosevic and Mladenovic [45], chemical fertilization seems to reduce the soluble solid content in apples, while there are several reports on organically produced fruits with higher TSS content and lower TA [46,47,48], as was shown in the present trial, without though significant differences. Other researchers have reported similar results, too [49,50,51]. Both cultivars exhibited TSS higher than 11.2 ^oBrix, which according to the European Commission on apricots marketing (Commission Regulation (EC) n. 112/2001), is the threshold of the minimum degree of ripeness at packing [52].

Skin color also plays a significant role in the consumer’s preference for an apricot fruit. In the present trial, skin color under integrated management exhibited higher b* (in both cultivars) and Chroma (only in ‘Bebecou’) indexes, indicating that the yellow coloring was advanced compared to organic management. A similar higher Chroma index has been reported in orange skin under integrated management [49], while on the contrary, Peck et al. [8] reported better skin blush of organically produced apple fruits. There are also reports where no significant effect of the cultivation management on strawberry [29] and apple skin [48] color has been detected, revealing the complexity of the effects of the management system employed each time on color indexes.

Apart from fruit size and color, pulp sweetness and, therefore, the carbohydrate content of fruit is also important, as it determines its overall sweetness and appreciation. Fruit carbohydrates were found at similar concentrations under both cultivation practices in both cultivars used in the present trial, indicating that fertilization and phytosanitary programs had few effects on sugar accumulation in the fruit. Similar results have been reported in other species, too [7,26,53]. It seems that under the specific fruit yield of each tree, under both cultivation practices, there was not any restriction on carbohydrate supply, even though differences in fruit size were detected. Nonetheless, one must take into consideration not only the yield and fruit weight produced but also the fruit load (as the number or weight of fruits per trunk cross-sectional area) as well as the number of leaves providing assimilates to the fruit [8]. Based on Roussos et al. [54], the higher number of leaves per fruit results in higher carbohydrate concentrations determined in apricot fruit. Assuming that the lower fruit yield under organic cultivation is based mainly on the differences in fruit number per tree, it seems reasonable to assume that the leaf-to-fruit ratio under organic cultivation would be enough for a sufficient carbohydrate supply to the fruits. On the other hand, though, the use of chemical fertilizers in integrated cultivation practice seems to result in faster and better shoot development or greater canopy growth in many species [29,55], ensuring that the leaf-to-fruit ratio, even under higher yields, will be sufficient for the unhindered carbohydrate supply to the fruits. Thus, the similar carbohydrate concentration in the fruits under both cultivation systems could be based on the adequate carbohydrate allocation to the fruit under any fruit load.

Apart from carbohydrates, organic acids also play an important role in fruit taste as well as the balance between sugars and acids. In the present trial, the major organic acids detected were citric and malic acid, in accordance with the literature [43,52,54]. Organic acids concentration seemed not to be significantly affected by the cultivation practice employed in the orchards. Only ascorbic acid in organic ‘Diamantopoulou’ fruits was found to be in higher concentration than in integrated produced fruits. A similar concentration of organic acids in organic and integrated produced fruits has been reported in many species [5,7,29,56], although there are also reports of higher organic acid concentrations under organic cultivation [11]. The superiority of organic cultivation versus integrated or conventional one regarding ascorbic acid concentration has been reported in various species [3,5,30], although there are also reports where no such superiority was found [10,29,57]. Thus, the present results on both ‘Diamantopoulou’ and ‘Bebecou’ cultivars are supported by the literature, indicative of the complexity of the influence of cultivation practice on fruit nutraceutical characteristics.

Although appearance and taste have a major impact on consumer acceptance, the functional properties of the fruit have been considered a greatly appreciated attribute for some decades now. Among the compounds conferring the nutraceutical character of fruit are the phenolic compounds, a class of potent antioxidant, antibacterial, and anticarcinogenic agents. Several factors affect the concentration of phenolics in fruits, such as the genotype, cultivation management, pedoclimatic conditions, etc. [6]. In the present trial, the concentration of total flavanols was higher in organically grown and that of total o-diphenols in integrated-grown ‘Bebecou’ fruits, while total o-diphenols were determined in higher concentrations in organically grown ‘Diamantopoulou’ fruits compared to those produced under integrated practice. No differences were detected between the two cultivation practices regarding antioxidant capacity (assayed by both FRAP and DPPH methods) in both cultivars. One would expect that phenolic compounds would have been found consistently in higher concentrations under organic cultivation practice since they are involved in the defense mechanism of the plant against biotic factors (insect infestation and fungi or bacterial infections) [6,58], although opposite results or no differences have also been presented [7,8,29,59]. Nonetheless, when no significant problem is caused by any biotic factor, it seems logical to assume that the plant does not need to engage any defense mechanisms, as it is reported by Roussos et al. [29]. In the present trial, all farmers successfully controlled biotic factors, keeping the plants and fruits healthy and free from attacks. According to Young et al. [60], it is not the organic cultivation per se that increases the phenolic compound concentration but the higher probability for and sensitivity to biotic attacks, which may trigger the biosynthesis of phenolic-based defense arsenal [9,29]. According to Almaliotis et al. [34], the fertilization program also plays a significant role in phenolic compounds biosynthesis since low N availability in apricot resulted in increased total phenol content under organic management, as has been reported in other species too [38,44]. This was attributed to the slow release rate of nitrogen from the organic sources used as fertilizers [34]. Furthermore, according to Roussos and Gasparatos [38], the protein competition model could justify the higher phenolic concentration in organically produced fruits since the high nitrogen concentration would result in increased dry mass production with higher protein requirements, leaving thus limited space for the partitioning of available carbon skeletons to phenolic biosynthesis. Thus, as in the present trial, no safe conclusion can be drawn regarding the effect of the cultivation system on phenolic compounds concentration and antioxidant capacity of the fruit, especially if biotic stress factors are successfully controlled [44].

Nonetheless, only in ‘Bebecou’ leaves the nitrogen concentration was found to be higher under integrated practice, compared to that under organic one, which would partly justify, based on the former protein competition model, the higher o-diphenols concentration but not, the lower total flavanols under integrated management. In general, there were few significant differences regarding leaf nutrient concentration between the two cultivation practices in both cultivars, as has been reported in other species too [37,61,62], not able to fully justify any phytochemical differences found in the fruits. The sole similar trend between the two cultivars was the excessive concentration of leaf copper under organic practices, way beyond the adequacy limits (5–16 ppm) [33,34,35,36], without any visible symptoms of toxicity. This is fully justified, though, by the use of copper fungicides in organic cultivation as one of the few registered fungicides-bactericides. The majority of the studies on the effects of the cultivation system on leaf nutrient concentration report higher nutrient concentration in the leaves of plants grown under integrated practice [29,44,63], while non-significant differences regarding some macro and micronutrients have also been reported [8,51,61]. It must be noted, though, that the majority of the nutrients in apricot leaves were detected in adequate concentration in the leaves irrespective of the cultivation practice, supporting thus shoot and fruit growth. As already mentioned, the higher yield under integrated management could be ascribed to the development of a larger canopy, resulting in an equal or even better leaf-to-fruit ratio. This larger canopy, though, does not seem to be the result of a better plant nutrient status, as nutrient concentrations under both practices were within the adequacy range. This could be partly justified by the faster and simultaneously adequate availability of nutrients in chemical fertilizers compared to those in organic ones, thus being absorbed earlier, supporting earlier as well as higher growth rates and final larger tree mass, without any apparent deficiency symptom. Assuming that this is the case, then the overall nutrient content per tree (mass of nutrient per tree) should be higher under the integrated practice while at the same time being in adequate concentration in the leaves, comparable to those determined under organic practice.

Soil physicochemical properties did not present many significant differences due to cultivation practice. Organic matter was either slightly higher (in ‘Bebecou’ orchards) or significantly higher (in ‘Diamantopoulou’ orchards) under organic cultivation, which is rather expected due to the continuous and sole use of organic materials as nutrient sources. The cation exchange capacity was also higher under organic practice (in ‘Diamantopoulou’ orchards only), probably due to the higher concentration of organic matter found in the soil, which contributes to cation exchange sites [64,65]. Total nitrogen was higher under integrated practice in ‘Bebecou’ while the exact opposite stood for ‘Diamantopoulou’. This may rely on the differences in fertilization practice among farmers employing integrated practices between the two cultivars. Furthermore, the organic matter concentration in ‘Diamantopoulou’ orchards may also explain the observed higher total nitrogen in the soil. High organic matter has been linked to high total nitrogen content since proteins and amino acids found in organic matter contribute to the increase in total soil nitrogen through organic matter mineralization [65]. Available P concentration was higher under integrated practice in ‘Bebecou’, while in ‘Diamantopoulou’, the solubilization of native phosphates due to the release of organic acids by the microbial decomposition of organic matter counterbalance the P content and, therefore, no significant differences were observed between the two cultivation practices. Significantly higher exchangeable K was observed in the organic than in the integrated system (in ‘Diamantopoulou’), supporting the hypothesis that in soils under organic management, the organic amendments, besides acting as a significant source of K, also release organic colloids that attract K from the nonexchangeable fractions increasing the available K. According to the critical limits of DTPA-extractable Fe (4.5 mg kg⁻¹), Mn (3.5 mg kg⁻¹), Zn (0.6 mg kg⁻¹), and Cu (0.2 mg kg⁻¹) [66], Cu and Zn concentration were above the critical limit for the two management practices.

The differences observed in soil nutrient concentrations seem to be relevant, at least to some extent, with the nutrient concentration found in the leaves. The leaf nitrogen concentration was higher in ‘Bebecou’ orchards under integrated practice, whereas potassium was found in a slightly higher concentration in the leaves of organically grown ‘Diamantopoulou’ trees. The latter reveals the close relationship between soil and leaf nutrient concentration. According to Duan et al. [67], the application of manure for a long period of time could result in reduced or even zero addition of potassium fertilizers in rice and wheat culture, while at the same time, manure enhances nutrient availability and thus nutrient use efficiency [68]. In general, contrasting effects of management practice on soil properties have been reported in the literature [61], ascribed probably to the differences in pedoclimatic conditions, water management, cultivars, etc.

5. Conclusions

Consumers’ awareness of healthier food and environmental protection has led agriculture to new pathways, searching for more sustainable ways to produce the necessary quantities of high-quality agricultural products. In the present trial, it became evident that there are some differences concerning specific parameters assessed (regarding plant nutrition, soil physicochemical properties, and fruit physiological, organoleptic, and phytochemical properties). Nonetheless, these differences were not enough to distinguish the two cultivation practices, as has been seen in the relative PCA analysis. The cultivar plays an important role in the parameters measured, probably more important than the cultivation practice itself. One of the most significant findings, though, was the fact that the individual farms (orchards) of the same cultivar, assessed under the same cultivation practice (integrated or organic), had a significant impact on the parameters measured. This fact clearly indicates that the practices employed by each farmer greatly influence fruit organoleptic, physiological, and phytochemical characteristics, as well as tree nutrient status and soil physicochemical properties. Therefore, these practices, along with the climatic conditions of the region, should be recorded, and their influence on the measured variables should be separately determined. Thus, the outcome of organic or integrated agricultural management depends on a multi-parameter system, which cannot be completely controlled, and this is probably the reason for the conflicting results found in the literature. Something that we can be sure about, though, is the zero levels of pesticide residues in organically produced foods, assuming the farmer strictly follows the directions of organic management. Further work is needed to fully elucidate the significance of the management practice on fruit quality attributes, seeking which component(s) of this specific practice, apart from cultivar’s influence, exerts the greatest influence.