The impact of five different nets—conventional black, grey, white, and photoselective red and yellow—on the performance of “Gala Redlum” apples was evaluated over a five-year period (2020–2024) and compared to an uncovered control. The cumulative production over this period, ranked from highest to lowest, was as follows: white net (182.4 t/ha), grey net (178.5 t/ha), yellow net (175.8 t/ha), black net (175.5 t/ha), red net (169.5 t/ha), and uncovered control (138.8 t/ha). Vegetative growth results were inconsistent among the studied years. The cumulative photosynthetic rate (An) was slightly higher under the white net (57.9 µmol m⁻² s⁻¹). Fv/Fm values remained closest to optimal levels under the black and grey nets. Netting effectively protected fruits from elevated temperatures, particularly under the grey net, and reduced sunburn damage, with the grey, black, and yellow nets performing best in this regard. Overall profitability was increased by netting: the black net provided the highest cumulative income per hectare over a five-year period (EUR 72,315) alongside the second-lowest sunburn loss (0.69%), while the yellow net also showed strong economic performance (€64,742) with a moderate sunburn loss (1.26%) compared to the red net. Fruit dry matter and soluble solids content (SSC) were generally higher in the uncovered control, whereas °Hue values tended to be higher under the red and yellow nets. In summary, the black and yellow nets provided more balanced microclimatic conditions that enhanced tree performance, particularly under heat stress, leading to improved yield and profitability. However, the economic feasibility of each net type should be evaluated in relation to its installation and maintenance costs.

The MOPLUS project, funded by the Portuguese Recovery and Resilience Plan (PRR), aims to enhance soil organic matter, soil structure, and water retention in apple orchards located in the “Maçã de Alcobaça” Protected Geographical Indication area through organic fertilization based on locally available livestock effluents, thereby reducing reliance on synthetic fertilizers under Mediterranean climatic conditions. This study evaluated the physiological and biometric responses of apple trees subjected to four fertilization strategies (M1–M4) in three commercial ‘Gala’ orchards in central Portugal over three growing seasons (2023–2025). Measurements included leaf functional traits, gas exchange, chlorophyll fluorescence, spectral indices, vegetative growth, fruit production per tree and mean fruit weight. Interannual climatic variability and orchard-specific conditions were the dominant drivers of tree response, while fertilization effects were smaller and mainly expressed through interactions with year and orchard. When analyzed within the same orchard, fertilization strategies M2 and particularly M3 maintained physiological performance, vegetative growth, and fruit production per tree at levels comparable to full mineral fertilization. Among treatments, M3 showed the most consistent responses across sites and years, indicating that partial mineral substitution with pig slurry can sustain tree functioning while maintaining or enhancing fruit production per tree. The most restrictive strategy (M4) occasionally showed reduced photosynthetic performance under specific orchard–year combinations, suggesting a threshold effect associated with stronger mineral reduction, but without evidence of generalized physiological stress. Overall, these findings demonstrate that partial substitution of mineral fertilizers by organic amendments—especially pig slurry (M3) and, to a lesser extent, composted cattle manure (M2)—is agronomically viable, allowing apple tree performance and productivity to be maintained while enhancing system resilience under Mediterranean climatic variability. These results also provide practical decision support for site-adapted fertilization management in commercial drip-irrigated apple orchards, supporting reduced mineral fertilizer dependence without compromising productivity.

Fruit sunburn is a major abiotic stress limiting apple production worldwide, with losses potentially reaching 50% due to climate change-driven heat events. This study aimed to evaluate sustainable strategies to mitigate or reduce sunburn on ‘Gala Galaxy Selecta’ apple trees. Field trials conducted in summer 2021 compared eight treatments: silicon-based application (Eckosil^®), foliar fertilization with algae extracts, macro- and micronutrients, and amino acids, increased irrigation (+35% ET_c), mineral particle films (Surround^®, Vegepron Sun^®, Agrowhite^®, Sunstop^®), and an untreated control. Randomized block designs with replicates were used. Agronomic parameters, including particle film coverage, trunk cross-sectional area, yield, and fruit quality (color, sunburn incidence, firmness, soluble solids content, dry matter, starch), were measured at harvest. Physiological responses, such as net photosynthesis, maximum quantum yield of Photosystem II, specific leaf area, fruit surface temperature, photoprotective pigments, antioxidants, and heat shock protein gene expression, were also assessed. Foliar fertilization, Agrowhite^®, and water reinforcement produced the highest yield per trunk cross-sectional area, with increased soluble solids content and enhanced red pigmentation. Surround^® minimized sunburn incidence but reduced photosynthetic activity, as did Vegepron Sun^®. Agrowhite^® balanced sunburn protection with maintenance of fruit quality and physiological function. These findings provide practical guidance for growers to select effective treatments, balancing sunburn mitigation, fruit quality, and tree physiological performance, while offering researchers insights into integrating agronomic and physiological strategies for climate-resilient apple production.

This study is Part II of a five-year (2018–2022) field trial in western Portugal evaluating the effects of three microbial biofertilizers—Mycoshell^® (Glomus spp. + humic/fulvic acids), Kiplant iNmass^® (Azospirillum brasilense, Bacillus megaterium, Saccharomyces cerevisiae), and Kiplant All-Grip^® (Bacillus megaterium, Pseudomonas spp.)—applied at different dosages alongside two mineral fertilizer regimes, T100 (full dose) and T70 (70% of T100, alone or combined with biofertilizers), on the physiological performance of ‘Gala Redlum’ apple trees. Part I had shown that Myc4 (Mycoshell^®, 4 tablets/tree), iNM6, and iNM12 (Kiplant iNmass^®, 6 and L ha⁻¹, respectively) consistently enhanced fruit growth, yield, and selected quality traits. While Part I showed clear agronomic gains, Part II demonstrates that these improvements occurred without significant alterations in seasonal photosynthetic performance, canopy reflectance, or chlorophyll fluorescence parameters over five years, highlighting the contrast between observed yield improvements and physiological stability. Seasonal monitoring of physiological traits—including specific leaf area (SLA), chlorophyll content index (CCI), gas exchange (A_n, g_s, E, C_i), spectral indices (NDVI, OSAVI, SIPI, GM2), and chlorophyll fluorescence (OJIP). It is clear that physiological values remained largely stable across biofertilizer treatments and years. Importantly, this stability was maintained even under a 30% reduction in mineral fertilizer (T70), indicating that specific microbial biofertilizers can sustain physiological resilience under reduced nutrient inputs, thereby providing a physiological basis for the yield-enhancing effects observed and supporting their integration into fertilizer reduction strategies in Mediterranean orchards.

Biofertilizers are sustainable alternatives to mineral fertilizers in perennial crops, reducing the need for mineral inputs. This five-year field study evaluated three biofertilizers—Mycoshell^® (Glomus spp. + humic/fulvic acids), Kiplant iNmass^® (Azospirillum brasilense, Bacillus megaterium, and Saccharomyces cerevisiae), and Kiplant All-Grip^® (Bacillus megaterium and Pseudomonas spp.)—at different dosages alongside two mineral fertilizer regimes, T100 (full recommended dose) and T70 (70% of T100, alone or combined with biofertilizers), in an apple orchard under Mediterranean conditions. Biofertilizers maintained or increased soil nutrient availability by 5–15% and leaf N, P, K, Mg, and Zn concentrations by 5–12% compared with T100. Trees under biofertilizers, particularly Myc2 and Myc4, exhibited greater shoot growth (up to 30.4 m/year), trunk cross-sectional area (TCSA: 11.9 cm² in 2022), and canopy volume (2.21 m³), representing 10–20% increases. Selected biofertilizer treatments produced 6–7.5 kg/tree, 130–145 g average fruit weight, 66–74 mm diameter, 13.9–18.7 °Brix, and 13–18% dry matter, maintaining >90% of yield and fruit size relative to T100, with more balanced medium- and large-sized fruit distribution. Principal Component Analysis explained 66–72% of soil and leaf nutrient variance, confirming their multivariate impact. Overall, biofertilizers applied at recommended doses and timings can partially replace mineral fertilizers, sustaining productivity and quality, enhancing nutrient availability, and supporting long-term orchard sustainability. While climate remains the main driver of annual production, these findings provide evidence for integrating biofertilizers into environmentally friendly fertilization strategies.

Protective net systems are increasingly used in Mediterranean apple orchards to mitigate climate-related production risks, yet their long-term agronomic and economic performance remains insufficiently documented. This study evaluated five protective net systems (black, grey, white, red, and yellow) and an uncovered control over six consecutive growing seasons (2020–2025) in a Mediterranean ‘Fuji’ apple orchard. Vegetative growth, reproductive development, yield, fruit quality, sunburn incidence, and economic performance were assessed under contrasting seasonal conditions. Yield ranged from 27 to 69 t ha⁻¹ and was strongly correlated with fruit number per tree (r = 0.90, p < 0.001), whereas net type did not significantly affect fruit number, mean fruit weight, or yield. Black nets reduced predicted sunburn incidence by 64% relative to the uncovered control (from 25.7% to 9.3%), promoted the greatest cumulative annual shoot growth (39.4 m tree⁻¹), and achieved the highest average final revenue among the evaluated treatments (€28,038 ha⁻¹ yr⁻¹). Under two assumed hail-damage scenarios (moderate and severe), estimated payback periods for the black net were 3.1 and 1.8 years, respectively. Overall, black nets combined the lowest predicted sunburn incidence, the greatest cumulative shoot growth, and the highest mean final revenue among the evaluated treatments, while yields remained comparable to the uncovered control, suggesting that they may represent a promising climate-adaptation strategy for Mediterranean ‘Fuji’ apple orchards.