Foliar iron fertilization: A critical review

Application of foliar iron (Fe) sprays is a common means of correcting Fe deficiency of agricultural crops. However, variable plant responses to iron sprays, ranging from no effect to defoliation, have often been described in the Fe-fertilization literature. Knowledge is still limited concerning the mechanisms of penetration of a leaf-applied, Fe-containing solution and the role of Fe in the leaf. The complex and multi-disciplinary character of the factors determining the effects of Fe sprays hinder the development of suitable foliar fertilization strategies, applicable under variable local conditions and for different plant types. This review describes some key factors involved on the process of penetration of a leaf-applied, Fe-containing solution before briefly analyzing the available foliar Fe-fertilization literature. Iron chemistry, leaf penetration, and plant-nutrition principles will be merged with the aim of clarifying the constraints, opportunities, and future perspectives of foliar Fe sprays to cure plant Fe deficiency.