Correction of iron chlorosis by foliar sprays

Iron chlorosis is a widespread agricultural problem in crops that grow in calcareous soils worldwide. In the Mediterranean area,. Fe chlorosis is one of the major abiotic stresses affecting fruit tree crops. Treatments used to control iron chlorosis are generally aimed to provide plants with external iron supplies. These treatments include soil iron treatments as well as foliar sprays and trunk and branch solid implants. This work is aimed to review the current status of foliar fertilization procedures to correct iron chlorosis. First, the rationale of using foliar Fe sprays to correct Fe chlorosis in fruit tree crops is discussed. We also briefly summarize the quite large number of studies published on foliar spray iron treatments in crops. A large number of results are available in the literature, covering most of the crops affected by iron chlorosis. The foliar fertilization practices currently being carried out by fruit tree growers are discussed. We also describe the range of products currently available in the market for carrying out iron foliar spray treatments, taking as an example the particular case of Spain in the year 2000. The characteristics of these commercial products are very diverse. We discuss the field of chlorosis-correcting spray treatments in view of the recent knowledge gained on the mechanisms of iron trafficking in plants. Until recently, knowledge on iron traffic was mostly related to iron uptake by roots. Although Fe chlorosis is mainly caused by low Fe availability in high pH soils, root uptake is not the only limiting step in Fe utilization by plants. Given that the major Fe destination is the chloroplast, leaf mesophyll cells must acquire Fe taken by roots or applied to shoots. Possible ways to continue research in foliar spray management techniques to correct Fe chlorosis are also discussed.