Effects of the frequency of iron chelate supply by fertigation on iron chlorosis in citrus

A field experiment was carried out in a drip-irrigated orchard of Clementine (Citrus clementina Ort. ex. Tan) grafted on Troyer citrange (C. sinensis x Poncirus trifoliata) rootstock located in the Valencian Citrus area (Spain). The trees received a single iron (Fe) EDDHA (ethylene diamine diorthohydroxyphenyl acetate) rate (3 g Fe tree(-1)) supplied in different application frequencies from April to September (8-, 4-, 2-, or I-week intervals). Leaf chlorophyll (Ch1) concentrations were estimated every month by using an SPAD-502 meter. The foliar contents of Fe were also evaluated with time. Mineral composition of leaves, total Ch1 concentration, yield, and fruit quality were also evaluated at the end of the assay. SPAD readings, Ch1, N, K, Mg, Fe, and Mn concentration in leaves increased as a result of Fe application. The concentration of Zn, however, significantly decreased in comparison to the control trees. Iron treatment increased yield and some of the fruit quality parameters, like total juice, sugar, and acid contents. Iron application frequency had not a consistent effect on the concentrations of macro and micronutrients in leaves, yield, and fruit quality. The highest values of SPAD readings and the leaf Ch1 content were obtained when Fe was applied at 4-week intervals along the year. These results suggest that soil Fe-EDDHA application with a moderate frequency could be recommended to the Citrus farmers in the area for a more rational Fe application along the growth cycle in Citrus orchards.