Effects of drip fertigation parameters on apple growth and fruit quality

【Objective】Drip fertigation has been increasingly utilized in orchard farming in northwest China. This study is to investigate the combined effects of water and fertilizer application, as well as fertigation parameters, on apple growth and fruit quality.【Method】A field experiment was conducted from 2022 to 2023 in a Fuji apple orchard located in Jingning, Gansu Province. The study used a three-factor, two-level complete block design. The experiment included two fertilization frequencies: 15 days (T15) and 30 days (T30), two inter-row dripper spacings: 30 cm (D30) and 50 cm (D50), and two drip pipeline arrangements: one pipe per row (P1) and two pipes per row (P2). In each treatment, plant height, stem diameter, spring shoot length, leaf area index (LAI), fruit yield, fruit weight, longitudinal and transverse fruit diameters, titratable acidity, soluble sugar content, sugar-acid ratio, fruit firmness, and vitamin C (Vc) content were measured. Subordinate function analysis was used to evaluate and rank the treatments.【Result】The fertigation design parameters significantly impacted physiological and fruit quality traits. Compared to T30, T15 significantly increased LAI by 0.71, but decreased single fruit weight by 17.25 g, soluble sugar by 1.76 g/kg, sugar-acid ratio by 0.44, and Vc by 0.44 mg/100 g. Compared to D50, D30 significantly increased LAI by 0.63 and soluble sugar by 1.76 g/kg, but reduced fruit weight by 30.51 g, sugar-acid ratio by 2.16, and Vc by 1.22 mg/100 g. Compared to P2, P1 increased LAI by 0.38, fruit weight by 16.11 g, soluble sugar by 4.26 g/kg, and sugar-acid ratio by 0.78, but decreased Vc by 1.82 mg/100 g. The interaction between fertilization frequency and dripper spacing significantly affected LAI, soluble sugar content, and sugar-acid ratio. The three-way interaction among fertilization frequency, dripper spacing, and pipe arrangement significantly influenced fruit weight, soluble sugar, and sugar-acid ratio. The combination of T15, D50, and P2 was optimal, resulting in improvements in stem diameter (2.03 mm), leaf area (2.97 cm2), fruit yield (7 224.27 kg/hm2), fruit weight (36.91 g), transverse fruit diameter (5.77 mm), and Vc content (2.79 mg/100 g) compared to other treatments.【Conclusion】Comprehensive evaluation using the membership function method showed that the optimal combination of drip fertigation parameters for improving apple growth, fruit yield, and quality in the studied region was: fertilization frequency of 15 days, dripper spacing of 50 cm, and two drip pipes per row.