Effects of Mechanical Pruning on Tree Growth, Yield, and Fruit Quality of ‘Arisoo’ Apple Trees

Win, Nay Myo; Park, Juhyeon; Kim, Seonae; Lee, Youngsuk; Do, Van Giap; Kwon, Jung-Geun; Kwon, Soon-Il; Yoo, Jingi; Kang, In-Kyu; Kweon, Hun-Joong

doi:10.3390/agriculture15202118

Open AccessArticle

Effects of Mechanical Pruning on Tree Growth, Yield, and Fruit Quality of ‘Arisoo’ Apple Trees

by

Nay Myo Win

^1,†

,

Juhyeon Park

^1,†,

Seonae Kim

¹

,

Youngsuk Lee

¹

,

Van Giap Do

¹

,

Jung-Geun Kwon

¹,

Soon-Il Kwon

¹,

Jingi Yoo

²,

In-Kyu Kang

³

and

Hun-Joong Kweon

^1,*

¹

Apple Research Center, National Institute of Horticultural and Herbal Science, RDA, Daegu 43100, Republic of Korea

²

Department of Horticulture & Life Science, Yeungnam University, Gyeongsan 38541, Republic of Korea

³

Department of Horticultural Science, Kyungpook National University, Daegu 41566, Republic of Korea

^*

Author to whom correspondence should be addressed.

^†

These authors contributed equally to this work.

Agriculture 2025, 15(20), 2118; https://doi.org/10.3390/agriculture15202118

Submission received: 2 September 2025 / Revised: 25 September 2025 / Accepted: 10 October 2025 / Published: 11 October 2025

(This article belongs to the Special Issue Advanced Cultivation Technologies for Horticultural Crops Production)

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Abstract

Pruning is labor-intensive and increases production costs, while mechanical pruning offers a promising alternative. However, research on its effectiveness remains limited. To address this gap, we evaluated the effects of mechanical pruning over two consecutive years (2023 and 2024) on tree growth, yield, and fruit quality of ‘Arisoo’ apple trees. The treatment included hand (manual) pruning (HP), mechanical pruning (MP), and combined mechanical and hand pruning (MP + HP) applied during winter pruning in a super-spindle-slender-shaped apple orchard. MP significantly reduced pruning time; however, the amount of plant biomass removed was lower in the MP treatment than in the HP and MP + HP treatments. Canopy volume was higher in the HP treatment than in MP and MP + HP treatments; however, the pruning treatments did not affect trunk cross-sectional area or tree yield. Leaf chlorophyll and nitrogen contents were slightly lower in the MP treatment than in the HP treatment in 2023 but were not affected in 2024. The MP treatment also noticeably reduced light penetration within the canopy and produced smaller fruits with lower soluble solids content and poorer coloration at harvest compared to the HP and MP + HP treatments. In contrast, the HP and MP + HP treatments showed similar effects on light penetration, yield, fruit size, and fruit quality; however, the MP + HP treatment significantly reduced the pruning time compared with the HP treatment. Overall, this study found that MP reduced light penetration and produced smaller and poorly colored fruits, whereas a follow-up combination of HP after MP improved pruning efficiency, light penetration, fruit size, and fruit quality.

Keywords:

pruning; tree canopy; light penetration; tree growth; yield; fruit quality

1. Introduction

Apples are a major crop worldwide, ranking third in global fruit production [1]. In the Republic of Korea, apples are the second most widely cultivated fruit crop. In 2022, the total cultivation area of apple crops was approximately 34,000 ha, and the annual average production was 566,000 metric tons. Domestic consumption of apples was recorded at approximately 10 kg per capita per year [2,3]. According to Korean statistics, the cultivation area of apple crops decreased by approximately 5% in 2023 due to a shortage of skilled workers, labor shortages, and higher labor costs [3]. This labor shortage and lack of skilled laborers could become a major challenge for apple production in the future, potentially leading to reduced apple cultivation areas and decreased fruit yield and economic value. These are pressing issues that require urgent attention.

In apple orchards, pruning is one of the most intensive tasks, requiring a large number of laborers and significant time, accounting for over 22% of total fieldwork in apple production [4]. Pruning is a fundamental and essential practice for maximizing fruit production [5]. In recent decades, traditional hand (manual) pruning (HP) has become the most widely used method in apple orchards. Mechanical pruning (MP) has been developed as an alternative to HP [6,7]. MP, also referred to as mechanical hedging, is a non-selective pruning method in which a cutting tool is attached to a tractor to cut branches at a predetermined distance along the sides of the trees [8]. This pruning method has shown positive effects on fruit yield and quality, resulting in lower pruning costs for citrus and olive trees [9,10]. However, it has been shown to limit shoot growth, yield, and quality in peach and apple trees [11]. Therefore, the efficiency of MP can vary depending on the training system, canopy structure, and crop [12,13]. In contrast, the MP method can be beneficial when apple trees are trained into tall or spindle leaders with narrow, vertical canopy structures in high-density apple orchards [14,15]. However, some studies have reported that HP is required as a follow-up practice after the use of MP [4]. Particularly, there is limited information about the combined effects of MP and HP on pruning efficiency and physiological changes in the apple trees.

In addition, pruning often alters the structure, canopy, and light distribution of trees [16]. Consequently, pruning can modify the microclimate around trees, directly influencing productivity and fruit quality [17]. For example, inadequate pruning can lead to unbalanced tree growth and reduced light penetration, whereas excessive pruning can lower fruit yield and productivity [8]. In apple production, sufficient light intensity is required not only for maintaining tree health, photosynthesis, and vegetative and reproductive growth but also for ensuring the desired shape and size, and reducing susceptibility to pathogens [18,19,20]. Additionally, the production of high-quality fruits, considering external (size, color, and visual appearance) and internal (texture, sugars, and acidity) qualities, is considerably influenced by pruning intensity and light availability [21,22]. Despite the positive effects of MP in reducing labor costs and fieldwork, its impact on the physiological responses, growth, yield, and fruit quality has been rarely reported. Moreover, HP is widely used in many apple orchards, possibly due to limited availability or information on MP techniques.

To address this gap in the literature, this study aimed to evaluate the effects of MP on vegetative growth, yield, and fruit quality of apple trees. A combined MP + HP treatment was also used to investigate its effects in comparison to MP or HP alone.

2. Materials and Methods

2.1. Experimental Design and Treatments

This study was conducted at an experimental station at the Apple Research Center, Gunwi-gun, Daegu, Republic of Korea (36.28 N, 128.47 E), over two consecutive years: 2023 and 2024. Apple trees planted under the same soil conditions (clay loam soil and pH 6.8) and an experimental block were selected. The detailed nutrient conditions of the soil are presented in Supplementary Table S1. Additionally, the average annual air temperatures and precipitation were 13.6 °C and 14.3 °C, and 1359 mm and 1265 mm for 2023 and 2024, respectively. The daily temperature and precipitation of the experimental orchard are presented in Supplementary Figure S1.

‘Arisoo’ (Malus domestica Borkh.), a mid-season apple, is a hybrid population of a cross between ‘Yoko’ and ‘Senshu’ [23]. ‘Arisoo’ is a low-vigor tree type with adequate numbers of tree branches, and its bearing type is on spurs and long shoots. ‘Arisoo’ is a relatively high-premium cultivar in the Republic of Korea due to its high-quality attributes (shape, taste, and color). Therefore, this apple cultivar was chosen in this study. The selected apple trees were grafted onto M.9 rootstocks and trained in a super-slender-spindle shape. All selected apple trees were four years old and planted at a spacing of 3.0 m × 1.0 m. The selected trees were uniform in canopy structure and height. The orchards were managed using an integrated pest management system and irrigated using a drip irrigation system.

Three pruning treatments were performed in this study: HP, MP, and a combination of mechanical and hand pruning (MP + HP). For the MP + HP treatment, MP was performed first, followed by HP. A completely randomized block design was used. Each block consisted of 20 apple trees per treatment, with three replicates (a total of 180 apple trees across all treatments). For HP, pruning shears (Hwashin Metal Co., Ltd., Daegu, Republic of Korea) were used following the orchard pruning techniques [24]. These techniques involved removing both internal and external parts of the trees, including dead and damaged branches, suckers, downward growing shoots, and water sprouts to open the canopy structure and light penetration of the trees by professional, skilled laborers with more than 10 years of experience in apple tree pruning. MP was performed using a CRF-340 mechanical pruning device (Rinieri, Forlí, Italy). This device consists of a trimmer-type fixed blade attached to a tractor that cuts branches vertically. The device and its characteristics are shown in Supplementary Figure S2. The branches were cut at a predetermined distance of approximately 40 cm from the trunk of the tree (Figure 1).

During MP, the tractor was operated at 1 km/h by a skilled driver. In the combined pruning treatment, HP was performed in the internal parts of apple trees following the orchard pruning techniques after MP. All pruning treatments were performed during late winter, in the first week of March in both years (Figure 1 and Figure 2). The flowers fully bloomed in the experimental orchard on 22–24 April 2023 and 2024, respectively.

2.2. Measurement of Pruning Capacity and Plant Biomass Removal

The pruning capacity of HP was calculated based on the time required to prune an entire tree (minutes of pruning per tree per laborer) using both a handsaw and manual pruning shears, and was calculated as hours per hectare (h/ha) [13]. The pruning time for MP was calculated in a similar manner, determined by the tractor’s forward speed and the time needed to prune both sides of a single tree, and expressed as h/ha. For the determination of plant biomass removal, the cut branches of each apple tree by each pruning method were separately collected, and the collected branches were measured as the fresh plant biomass removal by pruning treatments, and the results are expressed as kg per tree (kg/tree). For the combined MP + HP treatment, the cut branches after MP and HP were combined and weighed.

2.3. Measurement of Flower Set and Tree Growth Characteristics

The number of flower sets was recorded for each apple tree during the full bloom stage in 2024 and 2025 to analyze the effects of pruning treatments on flower density. Shoot length and canopy width (canopy diameter measured along and across rows) were measured using measuring tape (Digikey Co., Ltd., Suwon, Republic of Korea), and canopy height was measured using a tower ruler (Levenhuk Co., Ltd., Prague, Czech Republic) (Figure 2). Canopy volume was determined using the equation by Lodolini et al. [25]: canopy volume = canopy height × canopy width along the row × canopy width across the row. The trunk cross-sectional area (TCSA) was measured approximately 10 cm above the graft using digital calipers (CD-15APX, Kawasaki, Tokyo, Japan).

2.4. Measurement of Sunlight Penetration, Leaf Chlorophyll and Nitrogen Contents, and Photosynthetic Parameters

Sunlight penetration inside the tree canopy was assessed as photosynthetically active radiation (PAR) using a light sensor meter (3415FX; Spectrum Technologies Inc., Aurora, IL, USA). PAR was measured approximately 1 m above the ground on both sides of each apple tree on a sunny day in July, following the method described by Win et al. [26]. Leaf chlorophyll content was measured on 10 randomly selected mature apple leaves per tree, located in different positions within the middle canopy, using a chlorophyll meter (SPAD-502 Plus, Konica Minolta, Tokyo, Japan). Leaf nitrogen content was measured after SPAD assessment using an elemental analyzer (Kjeltec 8400, Fisher Scientific, Hoganas, Sweden), following the method outlined by Lee et al. [27].

Photosynthetic parameters, including assimilation rate (P_n) and stomatal conductance (G_s), were determined on fully expanded and mature leaves located on the 6th or 7th leaf from the tip of a growing shoot in the outer canopy [28]. Measurements were conducted using an open gas exchange system (LI-COR 6400, Li-COR Inc., Lincoln, NE, USA) equipped with a leaf chamber and a red–blue LED light source, set to a light intensity of 1000 μmol m⁻² s⁻¹ and a CO₂ concentration of 400 μmol m⁻² s⁻¹ during the measurement. Analyses were conducted from approximately 8:00 to 9:00 a.m. on a clear day in August 2024. Ten leaves (five per side of the canopy) per tree were used to measure photosynthetic parameters. For all measurements of chlorophyll, nitrogen content, and photosynthetic parameters, leaves located 100 cm above the ground were selected, following the method outlined by Bhusal et al. [28].

2.5. Measurement of Tree Production, Yield, and Fruit Quality Characteristics

All fruits were harvested on 4–5 September 2023 and 2024, respectively. Fruits were harvested by estimating the starch pattern index (SPI) of apples between 7.5 and 8.0, following Cornell’s 8-point SPI scale method [29]. At harvest, the tree production (fruits/tree) and the tree yield were recorded for each apple tree. The individual weight of all harvested fruits was also measured. Fruit size (length and diameter) was assessed using a digital caliper, and fruit shape was calculated as the length-to-diameter ratio. Fruit color was measured using a chroma meter (CR-400; Konica Minolta, Tokyo, Japan). The fruit color index was calculated using the following equation [30]: fruit color index = 1000 × a*/(L* × b*). Flesh firmness was measured using a firmness tester (TR-327; Forlí, Italy). Soluble solid content was measured using a refractometer (PR-201, Atago, Tokyo, Japan). Titratable acidity was measured using the malic acid reduction method described by Win et al. [26]. For all pruning treatments, five individual fruits per apple tree (300 fruits/treatment) were randomly taken and used for determination of fruit color, firmness, SSC, and TA values.

2.6. Statistical Analysis

The data were subjected to analysis of variance (one-way ANOVA), and the means of the pruning treatments for each experimental year were compared using Tukey’s HSD test at p < 0.05. Data are presented as mean ± standard error. All analyses were performed using SPSS software (Version 26, IBM Corp. Inc., Armonk, NY, USA).

3. Results

3.1. Pruning Time and Plant Biomass Removal

In 2023, the pruning time for HP and MP + HP was approximately 88.9 h and 42.9 h, respectively, whereas MP required only 5.9 h per ha, reducing pruning time by 82.9 h (14.8 times) and 36.9 h (7.2 times) compared to HP and MP + HP, respectively (Table 1). The MP + HP method saved 46.0 h of pruning time compared with HP. The non-selective MP method removed approximately 1.5 kg/tree of plant biomass, whereas the HP method removed 2.8 kg/tree, and the MP + HP method removed 2.5 kg/tree.

In 2024, the pruning time for HP and MP + HP was approximately 92.6 h and 46.8 h per ha, whereas MP required only 6.0 h per ha, saving 86.6 h (15.4 times) and 40.8 h (7.8 times) compared to HP and MP + HP, respectively. The MP + HP method saved 45.8 h of pruning time compared with HP. However, the MP method removed approximately 1.7 kg/tree of plant biomass, whereas the HP method removed 3.0 kg/tree, and the MP + HP method removed 3.2 kg/tree of plant biomass (Table 1).

3.2. Tree Growth Characteristics

In both 2023 and 2024, TCSA was not statistically affected by the pruning treatments (Table 2). In 2023, shoot length was longer in the MP treatment than in the HP treatment; however, it was not statistically different from that in the MP + HP treatment. In 2024, shoot length was longer in the MP treatment than in the MP + HP treatment; however, it was not statistically different from that in the HP treatment. In both years, shoot lengths did not statistically differ between the HP and MP + HP treatments (Table 2).

Canopy height was slightly shorter in the MP treatment in both years; however, the results were not statistically different from those of the other treatments (Table 2). The canopy diameter (along the row) was longer in MP than in HP in 2023; however, no differences were observed among treatments in 2024. However, the canopy diameter (across the rows) was greater in the HP treatment than in the MP and MP + HP treatments in both years. Additionally, the canopy volume was larger in the HP treatment than in the MP and MP + HP treatments in both years (Table 2).

3.3. Light Penetration, Leaf Chlorophyll and Nitrogen Content, and Photosynthetic Parameters

PAR was used as an indicator of sunlight penetration inside the tree canopies (Table 3). PAR was mainly affected by pruning treatment and was significantly lower in MP than in HP and MP + HP in both years. Leaf chlorophyll content (measured by SPAD) and leaf nitrogen content were lower in the MP treatment than in the HP treatment in 2023; however, these results were not statistically different among pruning treatments in 2024. No significant differences in SPAD or leaf chlorophyll content were observed between the MP + HP and MP or HP treatments in either year (Table 3).

Photosynthetic parameters (P_n and G_s) were measured on mature leaves of apple trees in 2024 (Figure 3). Although both P_n and G_s values were slightly lower in the MP, the results were not statistically different from those of the other pruning treatments (Figure 3).

3.4. Flower Set, Tree Production, Yield, Fruit Weight, and Size

The number of flower set per tree were counted during the full bloom stage, but the results were not statistically different among pruning treatments in both years (Table 4). Production (fruit per tree) and yield per tree were assessed at harvest. In 2023, apple trees produced approximately 14.6 kg/tree (71.0 fruits/tree) under HP, 14.3 kg/tree (74.7 fruits/tree) under MP, and 13.7 kg/tree (65.0 fruits/tree) under MP + HP. Except for higher production in MP than in MP + HP treatments, yield was not statistically different among pruning treatments. In 2024, apple trees produced approximately 16.0 kg/tree (68.3 fruits/tree) under HP, 15.4 kg/tree (78.3 fruits/tree) under MP, and 15.7 kg/tree (63.4 fruits/tree) under MP + HP.

In both years, the HP and MP + HP treatments produced heavier fruits than the MP treatment did (Table 4). In 2023, fruit diameter was smaller in the MP treatment than in the MP + HP treatment. However, fruit length and the L/D ratio were not statistically different among treatments. In 2024, both fruit length and diameter were smaller in the MP treatment, particularly compared to the MP + HP treatment. Additionally, fruit length was smaller in the MP treatment than in the HP treatment (Table 4).

3.5. Fruit Quality Characteristics

Fruit quality attributes were evaluated at harvest (Table 5). In 2023, SPI scores at harvest ranged from 7.4 to 7.8 scales; however, the results were not statistically different among treatments. L* was not statistically affected by the pruning treatments; however, lower b* values were observed in the HP treatment than in the MP and MP + HP treatments. The a* value and fruit color index were significantly higher in the MP treatment than in the HP and MP + HP treatments.

In 2024, the SPI scores at harvest were nearly 8.0 across treatments. The SPI and titratable acidity (TA) values were not statistically different among treatments. However, fruit firmness in the MP treatment was lower than in the MP + HP treatment, but not statistically different from that in the HP treatment. Additionally, soluble solids content (SSC) was lower in the MP treatment than in the other treatments. L* and b* values were not statistically affected by pruning treatments. The color index and a* values were significantly lower in the MP group than in the HP and MP + HP groups (Figure S3, Table 5).

4. Discussion

The application of automation in the agricultural sector is necessary not only for reducing fieldwork and timing but also for increasing crop quality and orchard profitability. In this study, MP significantly reduced pruning time, particularly when compared to HP. Additionally, this result was also consistent in MP treatment in both experimental years. A reduction in pruning time and fieldwork can help address labor storage and reduce pruning costs [31]. Lehnert [32] also reported that MP is a time-saving technique that can offer additional benefits in cause-and-effect development. However, the difference in pruning time between MP and HP can vary based on pruning intensity, orchard density, orchard type, tree age, canopy size, and the type of pruning device used. The removal of plant biomass with the MP method was considerably lower than that observed with other pruning treatments. This is likely because the MP device used in this study was non-selective, only trimming at a predetermined distance along the tree branches. Therefore, the extent of plant biomass removal from trees largely depends on the predetermined distance between the trees [8]. Additionally, the removal of plant biomass can also vary depending on the canopy size and the duration of MP application [7,13]. Moreover, the excessive removal of plant biomass by MP can negatively affect the vegetative and reproductive growth of trees, leading to reduced yield and productivity [33]. Therefore, MP should be carefully adjusted according to the canopy structure and training system of the trees, as not all crops are suitable for MP [4]. Additionally, the combined MP + HP treatment significantly reduced pruning time compared to HP, and the plant biomass removed under MP + HP was similar to that of HP. Because MP is not a complete replacement for HP, follow-up HP should be considered after MP to improve pruning efficiency [4].

Shoot length was greater under MP than HP in 2023 and greater under MP than MP + HP in 2024. The increase in shoot length observed under MP may have resulted from the removal of shoots and buds along the sides of the tree canopy, which then stimulated the production of longer shoots from the remaining buds. Similarly, Mika et al. [7] reported that MP trees produced longer shoots than HP trees. Canopy height did not differ among treatments in both years. However, canopy diameter along the row was greater under MP than under HP in 2023. This outcome may reflect the effects of cutting along the sides of trees under MP, which promoted the production of longer canopy diameters along the tree intervals. Conversely, a longer canopy diameter across rows was observed under HP than under MP or MP + HP. This may be attributable to the vertical cutting effect of MP along the sides of trees, resulting in a shorter canopy diameter across row intervals [32].

In fruit trees, TCSA is closely associated with fruit yield and productivity, as a larger TCSA can support a greater fruit load and higher yield [34]. Additionally, TCSA is responsible for transporting water and nutrients from the roots to the canopy [35]. In this study, TCSA was not considerably affected by the pruning treatments. Generally, pruning intensity can negatively affect TCSA, as severe pruning can reduce TCSA, leading to decreased fruit yield [8,22]. Therefore, the non-significant effect of MP on TCSA observed in this study may be linked to the lower pruning intensity and reduced plant biomass removal, resulting in TCSA values similar to those of the other pruning treatments. Moreover, MP treatment had no significant effect on TCSA and canopy height in both years, indicating that the differences in climatic conditions had little impact on vegetative growth under MP. The lower canopy volume observed in the MP and MP + HP treatments in both years may be attributed to the pruning effect of MP on the external parts of the tree, which limited canopy expansion.

PAR within the tree canopy was noticeably reduced under MP, whereas HP and MP + HP maintained higher PAR values across both years. The SPAD value was lower in MP trees than in MP + HP trees in 2023, but no difference was observed in 2024. Additionally, leaf nitrogen content was lower under MP than under HP in 2023. Light penetration and distribution inside the tree canopy are essential for improving photosynthesis [18,36]. Reduced light penetration under MP can limit photosynthesis and air circulation, resulting in reduced plant growth and health, and the production of low-quality fruits [21]. However, P_n and G_s did not differ significantly among treatments, consistent with the absence of significant differences in SPAD and leaf nitrogen content observed in 2024. Moreover, the reduction in PAR in this study may be linked to the solid-hedge structure created by MP. Follow-up pruning with HP after MP helped improve PAR. Thus, MP using a non-selective cutting bar creates a dense outer layer of the tree, which can become a barrier to sunlight penetration [37]. Consistent with our results, previous studies have reported that MP reduces light penetration into the interior parts of trees [7].

The tree production and yield were slightly increased in the MP treatment; however, fruit weight was significantly lower in the MP treatment than the HP and MP + HP treatments. In mandarins, MP produced a yield comparable to that of HP [33]. In olive trees, MP showed a non-significant reduction in yield over eight years, whereas combined MP + HP did not increase yield [38]. However, in citrus, follow-up HP after MP increased yield compared to HP alone [39]. Interestingly, the alternative annual use of MP and HP in mandarins resulted in a higher yield than the consecutive application of MP alone [31]. This indicates that the effect of MP may vary depending on the crop and the timing of application. The increase in fruit size is highly dependent on the relationship between the crop load and TCSA [40]. Unpruned trees typically produce smaller fruits than pruned trees, although fruit size can vary depending on pruning strategies and intensity [12,17]. Krueger et al. [41] reported that MP trees had greater fruit density and yield and produced more fruits than HP trees, but with smaller fruit size. Mika et al. [7] also reported that MP apple trees produce small or industrial fruit, as observed in this study. Additionally, the production of smaller fruits in the MP treatment was consistent across both experimental years, indicating that reduction in fruit weight and size of apples was mainly affected by pruning treatments and was not influenced by climatic conditions. Moreover, the absence of HP in the internal parts of trees in the MP treatment led to higher crop loads and the production of smaller fruits. Therefore, follow-up application of HP may be an effective approach to maintain crop load balance and ensure the production of marketable fruits [4].

In 2024, SSC was lower in the MP treatment than in the HP and HP + MP treatments, whereas the color index and a* value in fruit skins (2023 and 2024 years) were significantly higher in the HP and MP + HP treatments than in the MP treatment. In this study, the production of poor-colored fruits was consistent across both experimental years, indicating that the improvement in red-blush color in fruit was primarily attributable to pruning treatments. Consequently, the improvement in fruit color in the MP + HP trees in this study may be attributed to the follow-up application of HP after MP treatment. Fruit firmness was higher in the MP + HP treatment than in the MP treatment in 2024, whereas TA and SPI were unaffected by the treatments. Both SSC and red blush color are important indicators of marketability, and lower values of these indicators indicate reduced marketability [42]. Generally, the development of red pigments in fruit skin is closely associated with light availability to the fruits [43,44]. Additionally, natural light and solar radiation promote not only fruit color but also sugar accumulation in fruits [45]. Therefore, the lower light intensities in the interior parts of trees in this study may have contributed to the reduced development of red-colored pigments and sugars in the fruit, resulting in the production of poor-colored and low-quality fruits, similar to MP trees [7]. Madhumala et al. [46] also reported that pruning enhanced fruit color and sugar accumulation by improving light penetration into fruits, similar to that observed in HP trees. Additionally, some studies also reported that the variations in climatic conditions can influence the quality of apples [47]. Therefore, the lower flesh firmness and SSC observed in MP treatment in 2024 may be attributed to difference in average daily temperature and precipitation during the fruit development and maturation stages.

5. Conclusions

In conclusion, MP significantly reduced pruning time, and a combination of MP + HP reduced pruning time compared with the HP treatment in both 2023 and 2024. The plant biomass removal was lower in MP than in HP and MP + HP. MP noticeably reduced the canopy volume of apple trees, although it did not affect TCSA and canopy height compared with HP. Furthermore, MP did not reduce flower set and tree yield, while remarkably reducing light distribution inside the tree canopies. Additionally, MP negatively affected fruit weight and size and resulted in poorly colored (reduced fruit color index and a* value) and low-quality fruits. However, combining MP with HP improved these effects, resulting in large fruits with high-quality attributes. Moreover, the MP + HP treatment showed similar effects on tree yield and fruit quality. Overall, this study suggests that MP alone reduces light penetration, fruit size, and quality of apples. A combined MP + HP can partially reduce pruning time and field workloads and improve fruit quality. Therefore, MP should be followed by HP to improve pruning efficiency and fruit quality. However, the results obtained in this study were focused on the ‘Arisoo’ apple, and continuous studies are required on other apple cultivars to observe the potential variability of the results. Moreover, the long-term effects of MP on plant health, hormone levels, and nutrient metabolism should be considered in future studies.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agriculture15202118/s1. Table S1: The detailed nutrient conditions of the soil; Figure S1: Daily air temperature and precipitation of the experimental orchard; Figure S2: A Rinieri CRF-340 mechanical pruning device: Front view and lateral view; Figure S3: Fruit samples of ‘Arisoo’ apples harvested from trees subjected to hand pruning, mechanical pruning, and mechanical + hand pruning in 2024.

Author Contributions

Conceptualization, N.M.W., J.P. and H.-J.K.; methodology, N.M.W., J.P. and H.-J.K.; software, N.M.W.; validation, N.M.W.; formal analysis, N.M.W.; investigation, N.M.W. and J.P.; resources, H.-J.K.; data curation, N.M.W.; writing—original draft preparation, N.M.W.; writing—review and editing, N.M.W., J.P. and H.-J.K.; visualization, S.K., Y.L., V.G.D., J.-G.K., S.-I.K., J.Y. and I.-K.K.; supervision, H.-J.K.; project administration, J.P. and H.-J.K.; funding acquisition, H.-J.K. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the “Cooperative Research Program for Agriculture Science and Technology Development (RS-2021-RD009831)” of the Rural Development Administration of the Republic of Korea. This work was supported by the 2025 RDA Fellowship Program of the National Institute of Horticultural and Herbal Science, Rural Development Administration, Republic of Korea.

Data Availability Statement

Data are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Tree canopy and spacing along (A) tree and row intervals, and (B) canopy height and canopy diameter across and along the row of apple trees.

Figure 2. Mechanical pruning of apple trees using (A,B) a CRF-340 mechanical pruning device during winter pruning, (C) apple trees after mechanical pruning in March, and (D,E) in May of 2023.

Figure 3. Photosynthesis rate (P_n) (A) and stomatal conductance (G_s) (B) of mature apple leaves from trees subjected to hand (HP), mechanical (MP), and mechanical + hand (MP + HP) pruning in 2024. Same lowercase letters indicate non-significant differences between treatments according to Tukey’s HSD test at p < 0.05.

Table 1. Pruning time and plant biomass removal of ‘Arisoo’ apple trees subjected to hand (HP), mechanical (MP), and mechanical + hand (MP + HP) pruning treatments during winter pruning.

Pruning Treatments	Experiment Year	Pruning Time (h/ha)	Plant Biomass (kg/tree)
HP	2023	88.9 ± 3.1 ^z a ^y	2.8 ± 0.6 a
MP		5.9 ± 0.1 c	1.5 ± 0.4 b
MP + HP		42.9 ± 1.6 b	2.5 ± 0.3 a
HP	2024	92.6 ± 4.9 a	3.0 ± 0.4 a
MP		6.0 ± 0.1 c	1.7 ± 0.3 b
MP + HP		46.8 ± 6.9 b	3.2 ± 0.5 a