Influence of soil copper application and its residual effects on ‘Marisol’ clementine cultivated in sandy soils

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.