Multi-nutrient fertilization-based analysis of fruit quality and mineral element composition during fruit development in Merlot wine grapevines

Mineral elements play a crucial role in plant growth and development. Ensuring the proper supply of these elements in soil and maintaining an optimum range within plants is necessary for achieving optimal fruit yield and quality. Unfortunately, the application of NPKCaMg fertilizers to fruit trees is often either insufficient or excessive, leading to both environmental degradation and reduced fruit yield and quality. To assess the impact of different fertilizers on the biological-related traits of grape fruit and its response to nutritional elements, Merlot grapevines were subjected to multi-nutrient fertilization over four consecutive growing seasons from 2018 to 2021 in Penglai District, Yantai, China. Principal component analysis revealed that T11 treatment, consisting of N3P3K1Ca2Mg4, was the most suitable fertilizer type and application design for this experiment. The application of T11 resulted in a significant decrease (24.29%–35.20%) in fertilizer usage, and it resulted in an increase in several important traits such as 100 grain weight (HGW), number of seeds (SN), total soluble solids (TSS), total seed phenols (SP), seed flavanols (SFI), and seed tannins (ST) by 3.28%–12.84%, 3.76%–20.03%, 1.11%–14.95%, 2.16%–23.69%, 11.00%–32.78%, 1.07%–23.35%, respectively, compared to T14 (N4P2K3Ca1Mg4), T16 (N4P4K1Ca3Mg2), T13 (N4P1K4Ca2Mg3), and T15 (N4P3K2Ca4Mg1) treatments. Flowering and fruiting behavior exhibited a considerable demand for NPK, with a higher requirement for K and B during fruit growth and development compared to the other mineral elements. Excessive K in soil was found to enhance the competitive inhibition of Ca uptake by Merlot grapevines. The optimum ranges of mineral element content for total peel phenols (PP), peel flavanols (PFI), total peel flavonoids (PFD), total seed phenols (SP), and seed tannins (ST) were primarily influenced by grape variety and nutritional analysis method. In conclusion, the careful selection of NPKCaMg fertilizer and its meticulous application to soil at an optimum range of mineral elements are critical for grapevine growth and development.