Vol 110 (1997): Proceedings of the Florida State Horticultural Society


Published December 1, 1997
  • alkaline soil,
  • citrus paradisi macf.,
  • citrus sinensis (l.) osb.,
  • iron chelate,
  • iron chlorosis,
  • optimal leaf iron concentration
  • ...More


In some areas of flatwoods citrus production regions along the east coast and in south Florida, soils are highly calcareous and the trees exhibit iron (Fe) chlorosis symptoms. Currently, Fe-EDDHA (ethylenediiminobis-2-hydroxyphenyl acetic acid) chelate is the most effective source of Fe for high pH soils; however, it is an expensive source. Iron humate, a less expensive by-product of the drinking water decolorization process, was compared with Fe-EDDHA for Fe deficiency correction. Non-bearing 'Ambersweet' orange and 'Ruby Red' grapefruit (Citrus paradisi Macf.) and bearing 'Hamlin' orange (Citrus sinensis (L.) Osb.) and 'Flame' grapefruit trees, all on Swingle citrumelo rootstock, planted in high pH ( 7.6) soils, were used in this study. Iron humate was applied under the tree canopy in spring at rates from 0.07 to 7.0 oz Fe, for the nonbearing trees, or 0.75 to 12.0 oz Fe, for the bearing trees, per tree per year. Application of Fe humate at 0.75 oz Fe/tree/yr significantly increased the Fe concentration in the leaves as well as the fruit yield of both 'Hamlin' orange and 'Flame' grapefruit trees as compared to that of the trees in unamended soil. The fruit yield increase with application of Fe humate was generally very close to that with application of Fe-EDDHA at a similar Fe rate per tree. Modification of the Fe humate with addition of urea or ammonium nitrate did not increase Fe availability. Application of the Fe amendments regardless of rate or sources did not significantly affect the fruit quality. Application of Fe humate to non-bearing trees decreased twig dieback rating and increased flush growth, flush color rating, tree size, and leaf Fe concentration. This study demonstrated significant improvements in growth and Fe availability to non-bearing trees and Fe availability and fruit yield of bearing trees in high pH soils with application of Fe humate as compared to the unamended treatment.