Edafología. Volumen 7-2. Mayo 2000. pag 57-66.
Abstract
Iron chlorosis is common in olive trees grown on calcareous soils. In these conditions, olive trees not only reduce yield but also the green color and the size of the olives. Vivianite (Fe3(PO4)2. 8H2O) mixed with a calcareous soil at the rate of 1 g kg-1 was found effective in preventing iron chlorosis in lupin, chickpea and pear trees. The objective of this research was study the effectiveness and persistence of vivianite to correct iron chlorosis in olive trees cv. Hojiblanca and cv. Manzanilla. Vivianite was prepared in the field by precipitating a solution of 2.5 kg of (NH4)2HPO4 and 7.5 kg of FeSO4. 7H2O in a 100 dm3 tank to obtain 5 kg of vivianite. The vivianite was injected into the soil at rates of 1 kg tree-1 (trees<20 years) and 2 kg tree-1(trees>20 years). To determine iron chlorosis degree, chlorophyll index in the youngest leaves, color index of the olives, and the yield were measured. The differences in chlorophyll index between fertilized and control trees, in general, were significant. These differences were also observed the second and the third year after the application of vivianite. The olive color index was significantly higher in the treated than in the control trees. The yield, when measured, was higher in the fertilized than in the control trees. Thus, vivianite was effective to correct Fe chlorosis in olive trees. Moreover, the effect of vivianite persists, at least, for three years. The superiority of vivianite to other Fe salts in correcting Fe chlorosis might be due to the presence of phosphate, which facilitate the formation of amorphous Fe oxides (ferrihydrite) as the alteration product of vivianite. This makes vivianite an interesting alternative to other methods to prevent or correct Fe chlorosis.
Key words: Iron chlorosis, calcareous soils, olive tree, vivianite, ferrous phosphate.