Document Type : Research Paper
Balanced mineral nutrition is essential for maintaining tree growth, fruit production, and the long-term sustainability of fruit orchards. Nutrient deficiencies and imbalances are particularly common in orchards established on calcareous soils, where high pH, calcium carbonate, low organic matter, and bicarbonate-rich irrigation water can restrict the availability and uptake of phosphorus and micronutrients such as iron, zinc, and manganese. Under these conditions, soil nutrient concentrations alone may not accurately represent the nutritional status of fruit trees, and the combined interpretation of soil, leaf, fruit, and yield data is required.
Integrated nutrient management combines organic, chemical, and biological fertilizers and may help alleviate nutritional constraints through complementary mechanisms. However, conventional diagnostic approaches generally evaluate each nutrient separately and may not adequately account for interactions among nutrients. Compositional Nutrient Diagnosis (CND) evaluates each nutrient relative to the overall nutrient composition of plant tissue and provides standardized indices for identifying nutrient deficiency, excess, and imbalance.
This study was therefore conducted to evaluate the nutritional responses of apple and peach trees to a two-year integrated nutrient management program and to identify potentially yield-limiting nutrients using the CND method under the calcareous soil conditions of Sahneh County, Kermanshah Province, Iran.
The study was conducted during the 2024 and 2025 growing seasons in three apple orchards and three peach orchards. Because the orchards differed in cultivar, tree age, soil properties, and management history, each orchard was considered an independent study unit and was analyzed separately. In each orchard, 30 relatively uniform trees were selected, and the experiment was arranged in a randomized complete block design with two treatments—grower management as the control and integrated nutrient management—and three replications. Each block contained ten trees, including five control trees and five treated trees.
The integrated nutrient management program was implemented from winter 2024 to summer 2025 and consisted of a combination of organic manure, sulfur, Thiobacillus, nitrogen-fixing and phosphate-solubilizing biofertilizers, and chemical fertilizers supplying macro- and micronutrients. Inputs were applied through deep-hole fertilization, soil application, fertigation, and foliar spraying. During the first year, fertilizer rates were adjusted according to the initial soil properties of each orchard. During the second year, nutrient programs were standardized within each fruit species after the nutritional status of the treated orchards had become more similar.
Composite soil samples were collected from depths of 0–30 and 30–60 cm before treatment application and analyzed for major physical and chemical properties. Leaf samples were collected from fully developed leaves during summer 2025, and fruit samples were collected at the appropriate harvest maturity of each cultivar. Nitrogen, phosphorus, potassium, calcium, magnesium, iron, manganese, zinc, and copper were determined using standard laboratory procedures.
Fruit yield was measured separately for each tree. For leaf and fruit nutrient analyses, samples from the five trees assigned to each treatment within each block were combined. Consequently, three independent composite samples were available for each treatment in each orchard. Treatment effects were evaluated separately for each orchard using analysis of variance, and mean comparisons were performed using Duncan’s multiple range test at the 5% probability level.
For the Cate–Nelson analysis and CND calculations, the mean yield of the five trees corresponding to each composite leaf sample was used. The Cate–Nelson method was applied to separate low- and high-yield populations and determine critical yield values. CND norms were derived from the high-yield population, and standardized nutrient indices were calculated to identify potential nutrient limitations.
The two-year integrated nutrient management program increased the concentrations of most measured nutrients in the leaves and fruits of apple and peach trees, and these increases were significant in most orchard–nutrient combinations. In apple trees, leaf nitrogen, iron, and zinc concentrations increased by 10.6–19.6%, 37.4–45.6%, and 41.3–53.0%, respectively, compared with the control. In apple fruits, nitrogen, calcium, and zinc concentrations increased by 21.5–29.8%, 43.2–77.4%, and 51.0–77.3%, respectively.
In peach trees, leaf nitrogen, potassium, and magnesium concentrations increased by 17.4–23.0%, 38.5–49.7%, and 37.5–55.3%, respectively. In peach fruits, nitrogen, calcium, and iron concentrations increased by 45.4–56.7%, 31.3–36.6%, and 25.1–39.1%, respectively, relative to the control. These results demonstrate that the nutritional response to the management program was not restricted to the leaves but was also reflected in fruit nutrient composition.
The observed improvements should be interpreted as the cumulative response to the integrated management package rather than the independent effect of a particular fertilizer or application method. Chemical fertilizers supplied readily available nutrients, whereas organic amendments may have improved nutrient retention and root-zone conditions. Biofertilizers, sulfur, and Thiobacillus may also have contributed to nutrient availability and uptake. Nevertheless, because changes in rhizosphere pH, microbial establishment, soil enzyme activity, and post-treatment nutrient availability were not measured, the contribution of each component could not be quantified separately.
The Cate–Nelson procedure identified critical yield values ranging from 98 to 109 kg tree⁻¹ in apple orchards and from 20 to 51 kg tree⁻¹ in peach orchards. These thresholds were used to distinguish the relatively low- and high-yield populations required for establishing local CND reference values.
The CND indices indicated that zinc, calcium, and phosphorus had the most negative nutritional indices in the apple orchards and were therefore identified as potentially yield-limiting nutrients. In peach orchards, calcium, magnesium, and potassium had the most negative indices and represented the principal potential nutritional constraints. Differences among orchards showed that nutrient limitations were not uniform, even among orchards located within the same geographical area. This finding supports the use of orchard-specific diagnosis rather than uniform fertilizer recommendations.
The CND approach provided additional information beyond the interpretation of individual nutrient concentrations because it evaluated each nutrient in relation to the overall nutrient composition of the leaf tissue. However, the identified nutrients should be considered potential limitations under the conditions of the studied orchards and should be validated through targeted nutrient omission or response experiments.
The two-year integrated nutrient management program improved the nutritional status of apple and peach trees grown under calcareous soil conditions, as demonstrated by increased concentrations of several macro- and micronutrients in leaves and fruits. The response varied according to fruit species, orchard, plant organ, and nutrient.
The Cate–Nelson and CND approaches enabled the differentiation of relatively low- and high-yield populations and supported the identification of orchard-specific potential nutrient limitations. Zinc, calcium, and phosphorus were identified as potential limiting nutrients in apple orchards, whereas calcium, magnesium, and potassium were the main potential constraints in peach orchards. Overall, integrating soil testing, plant analysis, yield data, and CND indices can provide a more comprehensive basis for developing targeted nutrient management programs in fruit orchards. Nevertheless, additional controlled experiments are required to confirm the causal effects of the nutrients identified as potentially limiting.
The study was funded by Agricultural Jihad Organization of Kermanshah.
Conceptualization, F.R.; methodology, F.R., A.B. and I.A.; software, F.R and T.P.; validation, F.R. and I.A.; formal analysis, T.P.; investigation, F.R.; resources, F.R. and A.B.; data curation, F.R. and T.P.; writing—original draft preparation, F.R.; writing—review and editing, F.R.; visualization, F.R. and T.P.; supervision, F.R. and A.B.; project administration, F.R. and A.B.; funding acquisition, F.R. All authors have read and agreed to the published version of the manuscript.
No artificial intelligence tools were used in the article writing process.
Data available on request from the authors.
The authors would like to thank anonymous referees for their constructive comments.
The authors avoided data fabrication, falsification, and plagiarism, and any form of misconduct.
The authors declare no conflict of interest.
