Foliar iron sulphate-organic acids sprays improve the performance of oriental plane tree in calcareous soil better than soil treatments

Oriental plane tree (Platanus orientalis) is among the much-used elements of urban decoration in Iran. Many thousands-of-years-old plane trees are still viable in different cities. In recent years, because of the changes in management practices of urban areas, like widespread use of asphalt for streets pavement and use of concrete in water canals together with the polluted water and air, the growing condition is worsened causing a widespread occurrence of chlorosis symptoms. In this study, we assessed the effect of foliar sprays (3000 ppm or 6000 ppm humic acid, 4 or 8 mM of malic acid, citric acid or l-glutamine and a control blank treatment) in comparison to soil treatments (a localized placement method in which a mixture of sulfur, FeSO4 and decomposed manure is placed under the topsoil and a standard sequestrene Fe 138 application), for improving the performance of plane trees. All the sprays contained 0.7% FeSO4 as Iron source. The leaf area, leaf SPAD value, leaf thickness and trichome presence on leaves, the color of the newly emerged leaf and the current season shoot growth were recorded. The concentration of key leaf elements were also determined. Glutamine treated plants showed elevated acquisition of boron, manganese, zinc and copper. In all treatments, the leaf chlorophyll index (SPAD) significantly increased compared to the control treatment. Glutamine, citric acid, and sequestrene treatments were superior in improving the color of the young leaves. Treatments containing glutamine and citric acid had more trichomes on the leaf surface compared to the control and the leaf necrosis index was reduced by all applied treatments. Sequential Equations Modeling (SEM) is used to examine the path of noted responses to applied treatments.