article · Journal of Plant Nutrition
Sandy soils often suffer from copper deficiency, yet the immediate and lasting effects of copper fertilisers on citrus cultivation are not well understood. An evaluation of Marisol clementine trees grown in sandy soil assessed five soil copper application rates during flowering in 2015, alongside residual impacts across the subsequent two years. Copper treatments did not significantly alter overall fruit yield or quality markers, including juice content, acidity, soluble solids, and maturity index. However, in the initial season, fruit size showed a modest three percent increase at an optimal rate of 0.58 milligrams of copper per kilogram of soil, though this benefit did not persist into following seasons. Leaf copper levels rose linearly with treatment, showing that three milligrams per kilogram is sufficient to avoid deficiency and sustain productivity, challenging established guidelines.
Citrus growers in sandy Mediterranean soils often rely on established fertiliser guidelines to prevent nutrient deficiencies. By demonstrating that Marisol clementines remain productive at lower leaf copper levels than standard industry benchmarks recommend, this research highlights that excessive fertiliser application provides minimal return. Understanding precise nutrient limits helps growers avoid unnecessary input expenses whilst preventing over-fertilisation.
This field research provides applied data directly relevant to citrus orchard managers, agronomists, and fertiliser manufacturers formulating nutrient programmes for Mediterranean sandy soils. The findings are ready to inform updated agronomic guidelines and soil-management practices. By indicating that lower copper thresholds are sufficient, the work enables producers to optimise micronutrient purchases and reduce application costs, functioning as an immediately applicable guidance tool rather than requiring further product development.
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Copper (Cu) deficiency frequently occurs in sandy soils, but the immediate and residual effects of soil Cu application on citrus production remain poorly documented. This study evaluated the impact of soil Cu application and its residual effect on the clementine trees. Five Cu rates were supplied to the “Marisol” variety planted on a sandy soil: 0 (control), 0.1,0.3,0.6, and 1 mg of Cu per kg of soil. It was applied at the flowering stage of the 2015 season. Its residual effect was evaluated in two subsequent seasons (2016 and 2017). The results showed that soil Cu application did not significantly improve yield and fruit quality parameters (juice content, total soluble solids, acidity, and maturity index), over the three years of experimentation. However, a positive quadratic response of fruit size was recorded during the first year of evaluation (2015), with an optimal increase of 3% (58.4 mm) at 0.58 mg kg − 1 of Cu compared to the control (56.8 mm). No residual effect of Cu application on fruit size was observed in the following two seasons. A positive linear response of Cu concentration in leaves with Cu supply was recorded. The leaf Cu concentration of 3 mg kg−1 appeared sufficient to prevent Cu deficiency, thereby maintaining adequate productivity. The uptake of N, P, K, Ca, Mg, Zn, Mn, Fe, and B was not influenced by Cu application. Therefore, the commonly cited Cu deficiency threshold of 5 mg kg−1 in leaf tissue may overestimate the actual requirement for clementine grown on sandy soils of Mediterranean areas.
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DOI: 10.1080/01904167.2026.2723975
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