Iron is an essential micronutrient for plants and its deficiency is one of the most widespread nutritional problems causing chlorosis in many plant species. Low concentration of available Fe in soil or transformation of Fe to inactive forms in plant tissues may cause iron chlorosis. Chlorosis with the later cause, is called chlorosis paradox, because the Fe concentration in the chlorotic leaves is higher than the green leaves. Different iron containing fertilizers and conditioners may be applied as a major approach to manage the iron chlorosis. Inorganic iron salts, acidifying salts, some industrial wastes and byproducts, iron chelates, organic matter, blood powder and iron sulfate enriched blood powder have been examined by different researchers in this regard. Steel making converter sludge and slag are two byproducts of iron and steel industries, showing high content of iron oxides. Several studies showed the positive effects of these two compounds on iron nutrition of some crops. Since iron deficiency is a major problem in trees, this work is carried out to study the cumulative and residual effects of application of these two compounds, produced by Isfahan iron melting factories, on three ornamental and three fruit tree species as mulberry, acacia, plane tree, apricot, sour cherry and apple, respectively. Different rates of 0.5% and 1.0 % of the sludge and slag were applied to the active root zone of each experimental tree for one and or two years. A blank with no treatment and a 5mg/kg Fe, from iron sequesterin 138, treatment were also considered. The experiment performed in three replicates with a randomized complete blocks design. To monitor the nutritional status of the trees, the newly mature leaves were sampled early and late in the growth season of each year and analyzed for Fe, Zn, Mn, P, Ca and Mg. In the second year, in addition to the leaf samples, fruits were also sampled and analyzed for some elements. In addition to elemental analysis, the annual length growth of tree branches was also measured. The results showed that application of the sludge and slag increased the annual growth of the experimental trees as well as the concentration of Fe, Mn, Mg and Ca in the leaves but had no effect on Zn concentration. The increase was positively related to the number of years of application. It seemed that slag was more efficient in increasing the storage of Fe, Mn, Mg, Ca and P in the plant tissues than sludge. These increases were also observed for the fruit samples suggesting a better fruit quality for the treated plants. Application of two years of 0.5% slag showed bette
