PREDICTING THE INCIDENCE OF IRON CHLOROSIS IN CALCAREOUS SOILS OF SOUTHERN SPAIN

Iron chlorosis is a serious crop production problem in many calcareous soils of Southern Spain. The objective of this study was to determine which indigenous soil properties (i.e., those which are essentially permanent) were related to Fe chlorosis. Experiments, using two chickpea (Cicer ariethinum L.) cultivars and a sunflower (Helianthus annuuus L.) cultivar, were carried out in a growth chamber with 25 calcareous soils representing widespread Xerofluvents, Xerorthents, Xerochrepts, Haploxeralfs, Rodoxeralfs, Chromoxererts, and Pelloxererts of Southern Spain. The average chlorophyll contents for the three cultivars were significantly correlated with several properties of the carbonate and Fe oxide phases, such as calcium carbonate equivalent (r = 0.69***), "active lime" (r = 0.58**), acid NH4-oxalate extractable Fe (r = 0.68***), Tiron-extractable Fe (r = 0.61**), and DTPA-extractable Fe (r = 0.55**). The present and other studies indicate that the soil property most consistently related to Fe chlorosis is acid NH4-oxalate extractable Fe (Feo). The Feo critical level separating soils with a high probability from those with a low probability of responding to Fe fertilization was 0.63 g/kg soil a value similar to those found in other studies. This further supports the use of Feo as a key property to predicting the appearance of Fe chlorosis.