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The research was carried out during the 2015–2017 in an organic certified hazelnut (cv. ‘Çakıldak’) orchard established at 6 × 5 m spacing with ‘ocak’ system (multi-stemmed bush) in Samsun, Türkiye. The aim was to determine effects of plant density on nut traits, nut yield, cluster distribution, kernel oil content, fatty acid composition, total phenolics content (TPC), total flavonoids content (TFC) and total antioxidant activity (TAA) in ‘Çakıldak’ hazelnut cultivar. Plant density (D) in orchard was arranged as 5 (D5), 6 (D6), 7 (D7), 8 (D8), 10 (D10), 12 (D12) and 14 (D14) plants per ocak, respectively. The highest nut yield per hectare was achieved with 2344 ± 129.1 kg in D14, and the highest nut yield per plant was determined with 534 ± 2.0 g in D8. Depending on the plant density, nut weight, kernel weight and kernel ratio ranged from 2.06 ± 0.01 g (D10) to 2.26 ± 0.02 g (D8), 1.18 ± 0.02 g (D10) to 1.27 ± 0.01 g (D8) and 55.10 ± 0.55% (D14) to 57.47 ± 0.40% (D7), respectively. The number of nuts per cluster also varied between 2.24 ± 0.03 and 2.41 ± 0.08. ‘Çakıldak’ kernels contained oil between 58.0 ± 0.02% (D14) and 63.5 ± 0.40% (D8). TPC was determined between 9.10 ± 0.64 and 13.09 ± 0.76 mg GAE g−1. TFC varied from 8.62 ± 0.06 to 13.17 ± 0.32 mg QE 100 g−1. TAA was measured between 39.05 ± 1.24 and 70.27 ± 2.13 mmol TE kg−1by FRAP test and between 25.54 ± 1.49 and 37.37 ± 0.12 mmol TE kg−1by DPPH assay. Results indicated that nut traits, nut yield, oil content, fatty acids, TPC, TFC and TAA were affected by plant density in Çakıldak cultivar.

This study was conducted to determine the effects of microclimatic conditions, which directly and indirectly affect the yield and quality of hazelnuts, on physiological characteristics. The study was carried out on ‘Tombul’, ‘Palaz’ and ‘Kalınkara’ hazelnut varieties (Corylus avellanaL.), which are important commercial varieties, in three complete hazelnut orchards with different microclimatic conditions in two vegetation periods in 2021 and 2022 in Yalıköy town of Fatsa district of Ordu province (Türkiye). The experiment was designed according to the randomized block trial design with 3 replications. The results of the research revealed that the changes in physiological parameters vary depending on the orchards and the varieties. As sun exposure increased in the ‘Tombul’ variety, the chlorophyll value and tissue relative water content decreased on July 25, and the number of stomata increased. The change in chlorophyll value and number of stomata on July 25 in the ‘Palaz’ variety was similar to the ‘Tombul’ variety. In ‘Kalınkara’ variety, unlike the other two varieties, the change in leaf temperature on July 10 according to orchards was significant and the change in the number of stomata was found to be similar to the other two varieties. On the other hand, the highest leaf temperatures in all three varieties were determined in 2021 and the highest chlorophyll values in 2020. Unlike ‘Palaz’ and ‘Kalınkara’, the tissue relative water content on August 3 in the ‘Tombul’ variety was determined to be higher in 2021. As a result, it can be said that important physiological parameters in hazelnuts may vary primarily depending on the variety, but also according to the sunshine duration of the orchards, years, and therefore, the microclimatic conditions of the orchards should also be taken into account in the evaluations regarding yield and quality.

This research was carried out to determine the effects of supplementary irrigation in the last cluster drop period by the drip irrigation method on yield and yield components in a conventional rain-fed ‘Tombul’ hazelnut orchard in Giresun province (Turkey) in 2015 and 2016. The experiment was designed as randomized plots with three replications. The plants in the ocak (multi-stem bush) were irrigated with drip irrigation in July and early August. In the study, irrigation water application was planned to be watered when 40% of the available water was consumed. Conventionally rain-fed plants were used in the control group. The results showed that the yield, kernel size, internal cavity, good kernel and kernel defects were significantly affected by last cluster drop period irrigation treatments in both years. The yield (grams per ocak with five stems) varied from 1520.36 g (control) to 2436.95 g (irrigation) in 2015 and from 765.06 g (control) to 1443.72 g (irrigation) in 2016. Kernel size was significantly higher in irrigated plants than in control plants in both years. The lowest internal cavity values were found in irrigated plants in both years. The rate of good kernel was higher in irrigation treatment than in control. In the study, the lowest defective kernel rates were determined in the irrigated plants in both years. As a result, irrigation during the last cluster drop period in ‘Tombul’ hazelnut had significant positive effects on yield and important quality parameters compared to conventionally rain-fed hazelnut orchards.