Iron chlorosis in olive in relation to soil properties

Chlorosis due to iron (Fe) deficiency is becoming severe in olive (Olea europaea L.) trees growing on some highly calcareous soils in southern Spain. We investigated the relationships between the incidence of Fe chlorosis in three olive varieties (`Hojiblanco', `Manzanillo' and `Picual') and soil properties. Leaf chlorophyll content, estimated by the mean value of three SPAD measurements during the growing season, was poorly correlated with soil carbonate content and reactivity. In contrast, it was significantly correlated with the clay content and with the amounts of Fe extracted with oxalate (Fe_ox), citrate/ascorbate (Fe_ca), and diethylendiaminepentaacetid acid (Fe_DTPA). This suggests that the content and reactivity of poorly crystalline Fe compounds play an important role in Fe nutrition. The three olive varieties did not differ significantly in their susceptibility to Fe chlorosis. Soil test critical levels separating chlorotic and non-chlorotic trees were 300 g clay kg^–1 soil and 0.35 g Fe_ox kg^–1 soil.