The Evaluation of the Impact of Different Drip Irrigation Systems on the Vegetative Growth and Fruitfulness of ‘Gala’ Apple Trees

Abstract

The consequences of a changing climate in Central Europe are changes in precipitation patterns and the number of rainfall days per year, an increase in the dry summer months, and, most importantly, a reduction in the availability of water resources for orchard production. This study presents a novel evaluation of irrigation systems in commercial apple orchards, highlighting how their installation can improve water use efficiency and orchard productivity. The following systems were used in the experiments: IR+F-A (drip line placed on a wire mesh), IR+F-B (two drip lines placed on both sides of an auxiliary structure), and IR+F-C (two drip lines placed below the soil surface). Among these, the IR+F-C system achieved the best performance, prolonging annual shoot growth by 10.5%, increasing fruit weight by up to 8.5%, and enhancing the proportion of Extra Class fruits by 29%, and yielding 6–10% more per hectare than the other irrigation treatments. These quantitative findings emphasize the novelty of subsurface drip irrigation under Central European conditions and demonstrate its potential to improve water use efficiency and fruit quality, offering a viable strategy for adapting orchard management to climate change.

1. Introduction

The apple tree (Malus domestica Borkh.) is a highly popular and widespread fruit species worldwide. It is grown in different regions with different climatic and soil conditions due to its strong adaptive capacity [1]. According to statistical data, global apple production has increased dramatically in recent years. In 2020, for example, 86 Mt were produced on a harvested area of 4.6 Mha [2]. From a growing perspective, apple trees are particularly demanding in terms of irrigation water due to their high transpiration. The daily water consumption of apple trees ranges from 1.8 to 5 L of water per tree, which corresponds to 0.4 to 1 L per day per m² of leaf area [3]. Thus, the average annual water consumption is 1500–2500 m³ of water per ha of intensive production area [4,5]. Under the conditions of many intensive fruit-growing areas, scarcity of irrigation water is gradually increasing, groundwater levels are declining, the availability of surface water sources is decreasing, and water treatment costs are increasing, for instance, due to pollution [6]. Therefore, sustainable apple production strategies in Central Europe in the coming years will be oriented towards the construction of modern irrigation systems that enable economical and efficient use of irrigation water [7,8,9,10], supporting water saving. Moreover, water-reducing irrigation systems significantly reduce the cost of agricultural management practices [10,11,12,13,14,15,16,17,18,19,20,21,22,23], supporting cost reduction.

In terms of technical aspects, drip irrigation, broadcast spraying, and subsurface irrigation are currently the most commonly used systems in fruit production [24]. Spray irrigation is associated with high consumption of irrigation water, where water is applied to the soil surface or crop by sprinklers [25]. The disadvantages of spray irrigation are inter-row irrigation, wetting of the crop, and an associated higher risk of fungal diseases or hypothermia of the plants and fruits [26]. A basic drip irrigation unit consists of irrigation lines on which drip heads are placed at the appropriate distances, usually respecting the distance between the trees. These hoses are laid parallel to the rows and are most often suspended from a support structure at a height of 0.3–0.8 m above the soil surface. Drip irrigation saves, on average, up to 39% more water than spray irrigation [27,28,29,30]. However, drip irrigation may also have certain drawbacks, including higher initial installation costs, the risk of emitter clogging (especially in areas with poor water quality), and potential damage from animals or external weather conditions. Subsurface irrigation systems most often use water rising from subsurface drips, allowing direct application of water near the roots [4,31]. This system is now preferred in the driest growing areas, such as Israel, Egypt, China, etc. According to foreign experience, the main advantages of the systems include sufficient soil moisture, lossless water management, and minimization of disturbance of the system by the mechanized means [32].

According to FAO [2], the average yield of apples in production orchards is 38.0 t·ha⁻¹ in the USA, 30.1 t·ha⁻¹ in France, 29.5 t·ha⁻¹ in Germany, 40.6 t·ha⁻¹ in Italy, and 16.2 t·ha⁻¹ in the Czech Republic (all orchards included). Economically interesting yields per ha are above 45 t [33], while commonly achieved yields of top producers within Europe are 60 to 70 t [34,35].

Although numerous studies have evaluated different irrigation systems in apple orchards, few have quantitatively compared the effect of subsurface and above-ground drip irrigation on both vegetative growth and fruit quality under Central European conditions. Moreover, the long-term adaptation of trees to different irrigation installations and the associated water use efficiency and economic implications remain insufficiently addressed. Therefore, this study aims to fill this gap by providing a comprehensive evaluation of three different drip irrigation systems in Slovak apple orchards during 2019–2021, assessing their impact on shoot growth, fruit yield, fruit weight, and fruit diameter.

2. Materials and Methods

2.1. Experimental Location and Plant Material

The experiment was conducted at Plantex Ltd. (Veselé, Slovak Republic, 48°33′4.72″ N 17°43′40.34″ E; Figure 1) with five-year-old ‘Schinga’ Gala variety apple trees and took place between 2019 and 2021. The altitude of the orchard is 161 m above sea level. The trees were grafted on the weak dwarf apple rootstock M9 T337 (characterized by a shallow root system, with the majority of roots distributed within the upper 0–40 cm of the soil profile), and planted at a spacing of 3.6 × 1 m. In terms of orchard management, the trees were trained as slender spindles, with a total tree height of 3.5 m. The inter-row orchard planting uses cover crops, and the cultivated tree row area is kept weed-free using herbicides.

2.2. Soil and Climate Characteristics

The soil type in the orchard is brown earth on loess, so it is a loam soil; in WRB classification, ha LV [36]. The land under the orchard is flat.

Table 1. Results of the agrochemical testing of agricultural soils for 2018.

Parameter	P (mg·kg−1)	K (mg·kg−1)	Ca (mg·kg−1)	Mg (mg·kg−1)	pH (–)	TOC (%)
Average value	142	441	3737	391	7.2	2.1
Word classification	Good	High	High	High	Neutral	Middle

gives an overview of the results of the soil analyses conducted at the beginning of the experiments (autumn 2018), aimed at determining the nutrient content. The analyses were performed according to the Methodological Instruction n. 9/SZV (Central Institute for Supervising and Testing in Agriculture, Brno, Czech Republic) [37]. The total organic carbon (TOC) was determined using the EN 15936 standard [38].

The orchard is located in the T2 climatic region, warm, slightly humid, and with mild winters. The long-term average air temperature is 9 °C, and the long-term regional average annual rainfall is 550 mm, while the actual precipitation recorded at the experimental site during the study period is presented in

Table 2. The sum of each experimental year in terms of annual temperature, rainfall, and irrigation applied.

Year	Average Annual Temperature (°C)	Sum of Precipitation (mm)	Sum of Irrigation Volumes (mm)	Sum of Water (mm)
Averages of previous years	10.4	673	801	1474
2019	11.3	704	675	1379
2020	11.0	681	449	1130
2021	10.2	631	674	1305

[39].

For the purpose of measuring and recording meteorological data (throughout the experiment), a meteostation with remote data transmission (AMET, V. Bílovice, Czech Republic) was installed in the orchard, but outside the experimental blocks. The reason for this positioning was to make sure the experimental treatments did not affect the meteorological data. Figure 2 and Table 2 show the average monthly temperature, average annual temperature, sum of monthly precipitation and irrigation applied, and sum of annual precipitation and irrigation applied throughout the period under study.

2.3. Drip Irrigation System–Experimental Treatments

During autumn 2018, drip irrigation systems (described below) were installed in the test block and were connected to the whole automated orchard irrigation system (AIS). The AIS controlled the irrigation according to the preset and weather conditions.

The data for the management of the irrigation and individual treatments took into account the moisture content of the soil profile at the limit level, which was measured using a soil moisture content sensor, included in the AIS [40,41] (Hunter Industries Inc., San Marcos, CA, USA), and according to the equation:

V = 0.1 × ρ × h × p × S × Δθ/ψ,

(1)

where

• V—is the volume of irrigation water, L;
• ρ—is the volumetric weight of the soil, 1.45 g·cm⁻³;
• h—is the planned soil wetting depth, 0.8 m;
• p—is the wetting ratio, 0.25;
• S—is the area of the soil surface per 1 apple tree, 3.6 m²;
• Δθ—moisture content of the soil profile;
• ψ—is the coefficient of irrigation water use, ψ = 0.95.
• the constant 0.1 is a unit conversion factor used to express the result in liters, based on the combination of input units (g·cm⁻³, m², m).

Water was supplied from a well. An HC-150-FLOW water flow meter (Hunter Industries Inc., San Marcos, CA, USA) was used to measure the amount of irrigation water consumed. The pressure gauge was regulated at 30 psi for the irrigation system. The distance between the drippers was 0.75 m. The diameter of the drip line was 22 mm, and the flow volume of the dripper was 2.1 L·h⁻¹ of water and was controlled by a water flow meter. Three irrigation treatments with the same fertigation were imposed in the experiment (IR+F) (Figure 3):

• IR+F-A: Single aerial suspended dripline—one drip line placed on a wire line 0.5 m above the soil surface in a row—common method
• IR+F-B: Double aerial suspended driplines—two drip lines placed on an auxiliary structure on the left and right side of the trees, 0.35 m from the tree, and 0.5 m above the soil surface
• IR+F-C: Double subsurface driplines—two drip lines placed on the left and right side of the trees, 0.35 m from the tree, and 0.3 m below the soil surface

For the IR+F-B and IR+F-C treatments, irrigation was conducted alternately every two weeks (left to right side).

The treatment sections (each experimental block, including the Control and irrigated variants) were placed in random blocks in the middle of the rows with gaps between individual variants to avoid mutual influence. These sections served as a non-irrigated Control variant (Control). Twenty trees per the experimental variant were used in each replication, and the experiment included 3 replications per treatment, with border trees not used to prevent overlap effects of treatments (Figure 3). Each experimental plot had an area of approximately 70 m² (length × width of the block), ensuring sufficient space for tree growth and accurate measurement of treatment effects.

Irrigation was started as temperatures and growth development allowed from approximately BBCH 01. Intensive irrigation was taking place until BBCH 67, followed by attenuation until BBCH 72. Subsequently, it was again intensively irrigated up to BBCH 81.

A fertilization program based on leaf analysis was applied each year. Leaf samples were collected at the BBCH 72 and BBCH 77 stages. The sampling was performed using the HOL-DRIS version 1.01 software (Research and Breeding Institute of Pomology s.r.o., Hořice, Czech Republic), which determines the need for fertilization on the basis of nutritional diagnostics using DRIS (Diagnosis and Recommendation Integrated System). For fertigation, fully water-soluble fertilizers from Haifa Group (Haifa Negev Technologies Ltd., Haifa, Israel) were used and applied at the same dosages across all irrigation treatments, according to

Table 3. Uniform fertilization program for all irrigation treatments.

Date of Application of the Given Fertilizer in a Specific Year
Type of Fertilizer	2019	2020	2021
Ammonium sulfate,	13.4	29.4	17.4
Iron chelate 6% EDDHA	20.4	3.5	26.4
and Humifirst	27.4	10.5	3.5
Ammonium sulfate	30.5 6.6	16.6 17.6 19.6 22.6 25.6	6.6 13.6 19.6
K2SO4 SoluPotasse and KNO3 multi K	19.6 22.6 27.6 2.7 10.7 16.7 25.7 2.8 9.8 13.8 16.8 19.8	27.6 1.7 7.7 10.7 16.7 20.7 24.7	23.6 30.6 6.7 12.7 18.7 23.7 28.7 2.8 7.8 13.8
Mono potassium phosphate (0-52-34)	21.8 29.8	19.8 27.8	27.8 3.9 10.9
Ammonium sulfate	31.8 3.9 6.9 12.9	–	–

.

2.4. Measurement of Shoot Growth

At the end of the growing season, the length of annual shoot growth was measured using a tape measure. Each treatment included three replicates, with 20 trees per replicate (i.e., 60 trees per treatment in total). From each replicate, 100 shoots were randomly selected (approximately 5 shoots per tree), uniformly distributed between the wires of the support structure—50 shoots from each side of the row. Shoot selection was conducted independently each year, and the same shoots were not measured repeatedly during the study.

2.5. Yield Parameters and Apple Quality

During the evaluation of the experiment, the weight of all the fruit from each tree was recorded. Based on the harvest results from the experimental treatments, the estimated yield per hectare was calculated (t·ha⁻¹).

The fruits were harvested at the stage of commercial maturity. The harvest date was determined based on visual fruit color, ease of detachment from the spur, and internal starch degradation evaluated using an iodine test. Harvesting was conducted in early October, approximately at BBCH stage 87.

From each treatment, one hundred apples were randomly selected using a stratified random sampling method, ensuring proportional representation of fruit from the upper, middle, and lower parts of the tree canopy [42]. The selected apples were then evaluated for diameter, weight, and class according to UNECE STANDARD FFV-50-Apples [43]. Measurements were made using a CAS DB2-60 scale (CAS Corporation, Seoul, Republic of Korea). Class I apples have a diameter of 55–69 mm, Class II apples have a diameter below 55 mm, and Extra Class apples have a diameter of 70+ mm. This classification applies to small-fruited varieties such as Gala. In addition to diameter, fruit skin color was also considered as a primary parameter for classification, following the UNECE STANDARD FFV-50-Apples [43].

2.6. Statistical Analysis

One-way analysis of variance (ANOVA) was conducted separately for each year, and Tukey’s Honestly Significant Difference (HSD) test at a significance level of α = 0.05 was used to determine the differences among the treatments. The results are reported as averages and standard deviations. Significant differences between means within each year are indicated by different letters. The Statistica 14.0 (TIBCO Software Inc., Palo Alto, CA, USA) software package was used.

3. Results and Discussion

It is important to note that the temperature and precipitation patterns of a given year can have a significant impact on the course of individual phenophases in apple trees. This may necessitate supplementary irrigation and fertilization. In terms of water requirements, it is understood that the BBCH scale identifies the following phenophases as being of particular importance: leaf and shoot growth (10–19), flowering (60–69), young fruit growth (70–79), intensive fruit growth (80–89), and ripening (90–99). Apple trees exhibit peak water requirements from May to July, aligning with the BBCH phenological stages 60–89, which encompass flowering, fruit set, and rapid fruit growth. Recent studies have documented that water deficits during this period can lead to reduced fruit size, quality, and increased fruit drop [44,45]. It is during this period that the fruit grows rapidly and increases in size. It has been suggested that a lack of water at this stage can potentially result in smaller fruit, poorer quality, or even fruit drop [46,47]. It has been suggested that a lack of water at this stage can potentially result in smaller fruit, poorer quality, or even fruit drop. As can be seen from the values shown in Figure 2, this period is often associated with limited natural rainfall. It is, therefore, recommended that a sufficient supply of water be ensured during these months through effective supplementary irrigation systems. It is often the case that orchards require supplemental irrigation in order to help minimize plant stress and increase yield and quality [5,7,10,46,47]. It has been suggested that poor tree growth in a newly planted orchard due to water shortage can delay full fruiting by up to several years. Previous studies have indicated that prolonged water shortages can reduce tree growth, delay full cropping, and, if persistent, decrease cumulative orchard profitability by up to 66% over a 20-year period [48].

3.1. Shoot Growth

Ensuring a balanced ratio between vegetative growth and fruitfulness is one of the basic prerequisites for growing apple trees. Increasing fruit set has been shown to induce a vegetative response in fruit trees, associated with a reduction in leaf area and a decrease in growth of roots and trunks [34]. Conversely, encouraging long-lived growth of annual shoots brings the possibility of producing more generative buds and thus increasing fruit yield [49]. Figure 4 shows the average lengths of annual shoot growth for different irrigation treatments.

The values show little difference in the length of the shoots in the first year after the experiment was established, with the average length of the shoots in the Control being 445 mm. The irrigated treatments, however, showed progressively higher values: IR+F-A (491 mm), IR+F-B (514.7 mm), and the highest shoot length in IR+F-C (568.9 mm). In the following year of the experiment, the length of the increments gradually increased in the irrigated variants, while the ranking remained unchanged, with IR+F-C consistently performing best (Figure 4). The results indicate that the average length of shoot growth in the third year was practically double that of the first year, with the IR+F-C treatment showing the most pronounced stimulation of growth. This improvement is likely due to enhanced water availability that stimulates root activity and nutrient uptake, maintains stomatal conductance, and supports higher photosynthetic rates and carbohydrate production—all of which drive shoot elongation. These mechanisms are supported by recent studies: Zhu et al. [50] demonstrated increased shoot and leaf growth, dry matter accumulation, and key physiological parameters (photosynthetic rate, transpiration rate, stomatal conductance) under optimized water–fertilizer regimes; and Plavcová et al. [51] reported that higher stem water potential and stomatal conductance, resulting from irrigation, are closely associated with enhanced vegetative growth and yield in apple trees. Overall, the shortest shoot growth length over the three-year period was observed in the non-irrigated Control variant. This corresponds to the reduction in stress factors affecting the trees due to water shortage, availability, and overall nutrient intake. In summary, irrigation, and particularly the most intensive treatment (IR+F-C), had a clear positive effect on shoot growth.

Neilsen and Neilsen [52] also consider that the length of annual shoot growth depends on a number of factors, such as pre-spring pruning, fertility (even from the previous year), and the sufficiency of water and nutrients in the soil. Nazari et al. [33] have stated that the type of irrigation chosen, as well as the total amount of water supplied by irrigation, can significantly affect the vegetative growth of trees. In our study, the IR+F-C treatment consistently produced the longest shoot growth, which can be explained by the higher and more stable water input. This not only reduced plant stress caused by seasonal water shortages but also enhanced nutrient uptake efficiency, making IR+F-C superior to the other irrigation variants and the non-irrigated Control.

3.2. Fruit Growth

The average fruit size and weight are the parameters with the greatest effect on total yield, which are influenced by both irrigation intensity and the total yield load of fruit trees [26,53]. Moreover, Tanasescu and Paltineanu [54] have stated that fruit weight, together with fruit diameter, is one of the most important harvest parameters of apples, which, besides varietal and other characteristics, also depends on irrigation and fertilization.

The results (Figure 5), especially from 2021, clearly demonstrate the significant positive effect of subsurface irrigation (IR+F-C) compared to standard irrigation (IR+F-A) and the non-irrigated (Control). The difference between the average fruit weight of the IR+F-C and IR+F-A treatments was 5% in 2019, 6% in 2020, and 8.5% in 2021, and similar results have been obtained in similar trials around the world, as Nazari et al. [33], Ebel et al. [11]; Mpelasoka et al. [12,35]; Liao et al. [10]; Boland et al. [13] and Iqbal et al. [14].

The 8.5% increase in average fruit weight observed in 2021 for the IR+F-C treatment compared to IR+F-A represents a substantial agronomic improvement. Comparable studies conducted in arid and semi-arid regions report gains ranging from 5% to 10% under optimized irrigation regimes; e.g., 6% in Ebel et al. [11] and 9% in Nazari et al. [33]. Therefore, our results fall at the higher end of this spectrum, suggesting that subsurface irrigation is not only statistically but also practically effective, even in temperate climatic conditions.

The year-on-year difference in the IR+F-C treatment reflects an average fruit weight of 33 g for 2019–2020 and 12 g for 2020–2021. As reported by Mert et al. [55], blossom thinning significantly affects the resulting fruit size. Nevertheless, the effect of irrigation on fruit weight is clear.

However, despite these differences in fruit weight, no statistically significant difference was observed in fruit diameter between the drip-irrigated and non-irrigated treatments (

Table 4. The effect of the irrigation system on fruit diameter and quality class distribution.

Variant	Year	Fruit Diameter (mm)	Extra Class (%)	Class I (%)	Class II (%)
IR+F-A	2019	65.9 ± 7.0 a	31.5	65.0	3.5
	2020	71.6 ± 6.1 a	57.1	36.7	6.2
	2021	69.2 ± 5.7 a	67.1	29.7	3.2
IR+F-B	2019	66.9 ± 6.9 a	39.2	58.5	2.3
	2020	72.2 ± 6.3 a	60.7	34.9	4.4
	2021	70.3 ± 5.3 a	71.2	26.4	2.4
IR+F-C	2019	67.5 ± 7.4 a	48.3	50.7	1.0
	2020	73.7 ± 7.5 a	68.4	29.1	2.5
	2021	71.7 ± 6.7 a	75.9	22.8	1.3
Control	2019	63.1 ± 4.2 a	29.6	62.1	8.3
	2020	68.3 ± 4.9 a	38.9	53.7	7.4
	2021	65.7 ± 5.1 a	42.9	49.8	7.3

Note: Data representing Fruit Diameters are expressed as mean ± standard deviation. Means with different letters within a column are significantly different according to Tukey’s test (p < 0.05).

). This lack of difference can be attributed to sufficient natural rainfall during the growing seasons, which may have met the water requirements for fruit expansion, thus minimizing the additional effect of supplemental irrigation on fruit diameter. Furthermore, the ‘Gala’ variety used in this study is known to tolerate moderate water stress without a strong impact on fruit size. Additionally, factors such as nutrient availability, tree vigor, and pruning practices likely influenced fruit diameter, potentially overshadowing the effect of irrigation alone. This interpretation is consistent with findings from other studies in similar climatic conditions.

Although water-use efficiency (WUE) was not directly measured in this study, several findings point toward improved resource efficiency in the IR+F-C treatment. These include increased yields, a higher share of Extra Class fruit, and the targeted delivery of water and nutrients with minimized surface evaporation. This interpretation aligns with Liao et al. [10], who reported a 20–30% improvement in WUE using subsurface drip irrigation in apple orchards under similar conditions. Moreover, a recent global meta-analysis by Tong et al. [5] indicates that regulated deficit irrigation strategies can simultaneously maintain fruit yield while improving water-use efficiency by approximately 5–6 % in fruit trees, supporting the agronomic importance of optimized irrigation regimes.

The results can be attributed to the direct delivery of water and fertilizers via subsurface drip irrigation to the roots of the trees, removing surface evaporation and a shorter time for water to soak into the soil, which has the positive effect of faster response to irrigation in comparison to aerial suspended dripline [56].

The diameter of the fruit is the main determinant of its classification in terms of quality classes and, consequently, of the purchase price. In the case of the ‘Gala’ variety, for the first harvest, the emphasis is on fruit with a diameter of 70+ mm, which, according to UNECE STANDARD FFV-50-Apples [43], belong to the Extra Class (superior quality), with a skin color of at least 80%. From the grower’s perspective, this quality class is the most attractive in terms of price. For the second harvest, apples that fall into Class I are harvested, with a diameter of 55–69 mm and a skin color of at least 40%. For the third harvest, mainly Class I apples are harvested. For the last harvest, Class II apples are harvested. This includes apples with a diameter below 55 mm and with less than 40% skin color. Subsequent sorting, also by weight, usually occurs before the apples are placed into storage. Interestingly, the average fruit diameter in 2022 was slightly higher despite lower irrigation volume and precipitation compared to previous years. This can be attributed to seasonal climatic factors, such as temperature and solar radiation, which influence fruit expansion independently of water supply.

According to Table 4, no statistically significant differences in the diameter were found. However, this result is positive as different treatments did not have a negative impact on the size of fruits, which is crucial for the price of apples. The largest fruit diameter was achieved in 2020. What was reflected, though, was a higher percentage of the Extra Class depending on the irrigation treatment used, as shown in Table 4. Correspondingly, there was a decrease in the representation of Class I and, even more so, Class II. This resulted in higher income for producers and lower costs. Once again, these results are consistent with those of similar experiments [33]. A more detailed analysis of the results shows that in 2019, less than 50% of fruit was in this Extra Class.

The differences between 2020 and 2021 refer primarily to variations in fruit skin coloration, which were not directly measured in this study. These variations are largely caused by the annual differences in day and night temperatures, a factor well known to affect apple skin coloration and overall fruit quality. The differences between 2020 and 2021 are mainly due to the different skin colouration of the fruit, which is caused by the annual difference in temperature between day and night. Cool nights help the fruit to color better and thus fall within the higher quality class. In 2020, the temperature differences between day and night during the harvest period averaged 10 °C, and the lowest night temperature was 11 °C. Year 2021 was characterized by greater differences in temperature between day and night during the harvesting period, with an average of 16 °C, and the lowest temperature at night being 7 °C.

The IR+F-C treatment consistently outperformed all other irrigation treatments across the years. Although IR+F-B showed some localized improvement in soil water infiltration, the overall shoot and fruit growth was highest under IR+F-C. The alternation of irrigation from one hose to the other in this treatment over an interval of two weeks resulted in a partial drying in the soil on the non-irrigated side of the row, which contributed to better water management of the plant, the development of the root system in width, and thus better utilization of rainfall. In combination with vertical cutting (with blades) of the soil in the root zone twice a year, a water-logging furrow is to be created, and water infiltration into the soil will be improved.

3.3. Production

Economically interesting yields are considered to be above 45 t·ha⁻¹ [57], and top producers in Europe reach 60–70 t·ha⁻¹ [33,53]. In our study, the best-performing treatments (IR+F-C) approached these levels, indicating that proper irrigation can help bridge the gap between current and potential yield. Wang et al. [58] have reported that yields are often limited by water and nutrient availability (yield-limiting factors), as well as pest and disease damage (yield-reducing factors); thus, the actual yield is often far below the potential. This comparison supports the practical relevance of the irrigation treatments tested in this study. Differences in yield levels for the same crop in different regions and with different management are, therefore, mainly related to crop genotypes, prevailing environmental conditions, and technological practices applied in cultivation [53].

The results of the three-year irrigation experiment show that the yield of apples in the evaluated treatments ranged from 62 to 85 t·ha⁻¹. The results clearly show a positive effect of irrigation for the IR+F-C treatment, which had a 6–10% higher effect on each year than the IR+F-A treatment and 4–5% higher than the IR+F-B treatment, and 12–15% higher than the non-irrigated Control treatment (Figure 6). The superior performance of subsurface drip irrigation can be attributed to the direct delivery of water and nutrients to the root zone, reducing surface evaporation and ensuring faster and more efficient water uptake by the trees. This improves plant water status, enhances root development, and promotes better nutrient absorption, resulting in higher fruit yield and quality [24,57,58]. Moreover, a clear synergy was observed among all monitored parameters (yield, percentage of Extra Class fruits, and fruit weight), further supporting the advantage of subsurface irrigation.

The total yields recorded in our study (62–85 t·ha⁻¹) significantly exceed the national average (16.2 t·ha⁻¹) and are comparable to or higher than those typically achieved in Europe’s top-producing regions, 60–70 t·ha⁻¹ [33,53]. This confirms that modern irrigation technologies offer benefits not only in water-scarce areas but also in temperate climates, where they contribute to production stability and high fruit quality.

3.4. Results Applicable to Practice

Based on the results of the three-year trial, the IR+F-C treatment showed the longest annual shoot growth, the highest fruit weight, and contributed to a higher percentage of Extra Class fruit by an average of 29%. Yield per ha increased by 6–10% compared to other treatments. From an operational point of view, the main disadvantages of this system are the higher demands for the installation of the irrigation pipes and their placement in the soil (higher labor intensity and material consumption).

A suitable alternative is the IR+F-B treatment, which increased annual shoot growth and fruit weight, improved the representation of Extra Class fruit by an average of 12%, and increased yield per ha by 2–5%. This treatment represents an improvement of the classic irrigation line and is less investment-intensive.

Further research will aim to determine the longer-term effects of the selected treatments and better understand the dynamic physiological responses of apples and trees, for example, the chlorophyll index or NDVI, transpiration, parameters affecting fruit storage, or the reaction of different varieties and rootstocks.

4. Conclusions

The presented research results show that the different irrigation systems had varying degrees of positive effects on selected parameters in the cultivation of Gala apple trees, with subsurface irrigation (IR+F-C) showing the most significant impact. Based on the results, the IR+F-C treatment can be recommended as the best irrigation strategy for shoot and fruit growth and overall yield. The results also demonstrate the gradual adaptation of trees to the installed irrigation system over the course of a three-year evaluation.

The best effects were achieved by the IR+F-C variant: double subsurface driplines increased the representation of Extra Class by an average of 29% and increased the yield per ha by an average of 6–10%. Subsequently, the variant IR+F-B: Double aerial suspended driplines increased the representation of the fruit Extra Class by an average of 12% and increased the yield per ha by an average of 2–5%. From a practical perspective, the results suggest that subsurface drip irrigation with double laterals (IR+F-C) is the most efficient option for achieving high fruit quality and yield, particularly in regions with limited water resources where water use efficiency is crucial. Aerial suspended drip irrigation (IR+F-B) may be recommended as a cost-effective alternative for orchards with higher installation or maintenance constraints. The choice of system should, therefore, depend on the grower’s economic possibilities and site-specific conditions, such as soil type, water availability, and orchard design.

This study contributes novel field-based evidence on the comparative performance of subsurface and aerial drip irrigation systems over multiple seasons, in a temperate climate context where such long-term data are still limited. The clear demonstration of the irrigation system's impact on fruit class distribution and overall yield provides a valuable reference for modern orchard management.

In addition to the agronomic benefits, the subsurface irrigation system showed potential environmental advantages, such as reduced surface evaporation, more efficient water delivery directly to the root zone, and likely improved water conservation at the system level. These aspects are especially relevant in the context of increasing climatic variability and the need for sustainable horticultural practices.

Nevertheless, certain limitations of the study must be acknowledged. Only one apple cultivar (‘Gala’) and a single rootstock were used, which may limit the generalizability of the results across different genetic backgrounds. Furthermore, no direct measurements of soil moisture dynamics were taken during the experiment, which restricts the ability to analyze water movement and retention in more detail. Future work should aim to integrate soil moisture monitoring, additional cultivars, and economic cost–benefit analysis to build on the findings presented here.