Lowering iron chlorosis of olive by soil application of iron sulfate or siderite

About 70 % of the olive is grown on calcareous soils in Spain, most of which can induce iron (Fe) chlorosis. The main symptoms are interveinal yellowing of the young leaves, leaf necrosis, and reduction of leaf and shoot size, which can lead to major yield losses. Several strategies have been used to avoid Fe chlorosis such as the application of Fe chelates, but they are expensive. Here, we studied the effectiveness of synthetic siderite (FeCO3) and Fe sulfate injected in the form of suspension/solution into the soil for correcting Fe chlorosis in olives. Experiments were established in spring 2009 for four growing seasons in ‘Manzanilla,’ ‘Ocal,’ ‘Arbequina,’ and ‘Picual’ orchards. The treatments were injections of (1) a siderite suspension; (2) a Fe sulfate solution supplied with K2SO4 to make up for the K present in the siderite suspension; (3) a K2SO4 solution, named Control-K; and (4) water, named Control-0. At the start of the experiment, the suspensions or solutions were injected into the soil at 10–20 points around the tree at the depth of maximum root density. Results show that Fe chlorosis was alleviated in ‘Manzanilla’ and ‘Picual’ since leaf chlorophyll concentration (as estimated by the soil plant analysis development (SPAD) value) in the trees treated with siderite or Fe sulfate was increased by 4–7 % relative to the control trees, and leaf weight was increased by 6–9 %, but not in the ‘Arbequina’ and ‘Ocal’ trees. This finding was explained by higher available Fe in Arbequina and Ocal soils. The antichlorosis effect of iron sulfate was persistent and slightly higher than that of siderite. Both iron sulfate and siderite are not susceptible to leaching due to the low solubility of Fe oxide phases. Thus, a single application of these fertilizers constitutes a promising alternative to other Fe fertilizers, which require more than one application per year.