Iron and/or acid foliar spray versus soil application of Fe-EDDHA for prevention of iron deficiency in Valencia orange grown on a calcareous soil

A two-year experiment was conducted in an iron(Fe)-deficient orchard with calcareous soil to find out an alternate method for soil application of Fe ethylenediamine-N,N'-bis(2-hydroxyphenylacetic acid) (Fe-EDDHA) in orange trees. Foliar sprays of Fe-EDDHA (5 g l−1, pH = 7.8), sulfuric acid (pH = 3), citric acid (5 g l−1, pH = 2.4), Fe (II) sulfate solutions (250, 500, and 750 mg Fe l−1) with their initial pH (6.5, 6.35, and 6.12) and reduced ones to pH of 3 were compared with soil applied (75 g tree−1) Fe-EDDHA and a control test. Although optimum chlorophyll content, leaf Fe concentration, fruit quantitative and qualitative attributes were resulted from soil application of Fe-EDDHA, repeated sprays of Fe-EDDHA or acidified Fe solutions created suitable results. Acidification of Fe solutions made them more effective in alleviation of leaf Fe concentration and Fe chlorosis, probably due to remobilization of inactive Fe within the plant and prevention of Fe oxidation and precipitation in foliar solutions.