Uptake and Partitioning Characteristics of Calcium, Magnesium, and Sulfur in Young Dwarf ‘Fuji’ Apple Trees and Their Relations to the Uptake and Partitioning of Nitrogen, Phosphorus, and Potassium

Although a balanced supply of macronutrients is essential for apple tree growth and orchard productivity, the relationship between macronutrient uptake and partitioning in the entire apple tree remains ambiguous. To address this gap, a 2-year field experiment was conducted from 2019 to 2021 in a newly established dwarf ‘Fuji’ apple orchard in Shaanxi, one of the main apple production areas in China. The results showed that the annual uptake was 11.2−15.0 kg ha–1 for calcium, 1.5−1.9 kg ha–1 for magnesium, and 1.0 kg ha–1 for sulfur. During the 2019–2020 season, trees absorbed most of the calcium, magnesium, and sulfur from the end of spring shoot growth to nutrient withdrawal, accounting for 70.8%, 76.7%, and 80.0% of the annual calcium, magnesium, and sulfur uptake, respectively. During the 2020–2021 season, 57.7%, 61.6%, and 45.5% of the annual calcium, magnesium, and sulfur uptake occurred from the slow growth of the spring shoot to the end of spring shoot growth, respectively. The ratio of nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur absorbed by the tree was 1:0.17:0.82:1.1:0.14:0.092 during the first season, and during the second season, it was 1:0.18:0.60:1.7:0.21:0.11. Regarding the accumulation and partitioning of macronutrients in different organs, calcium accumulation and partitioning were higher than those of the other nutrients in trunks. In coarse roots, branches, and shoots, calcium accumulation was also higher compared to other nutrients. In fine roots, nitrogen accumulation was slightly higher than calcium. In leaves, nitrogen accumulation was higher than the other nutrients, whereas in fruits, potassium accumulation and partitioning were higher than those of the other nutrients. These findings reveal distinct macronutrient requirement patterns across the whole apple tree and specific organs, providing new insights into maintaining nutrient homeostasis in apple trees and optimizing nutrient resource allocation for efficient orchard production.