BY-PRODUCT IRON-HUMATE INCREASES TREE GROWTH AND FRUIT PRODUCTION OF ORANGE AND GRAPEFRUIT

Citrus trees planted in alkaline soils typically show iron (Fe) defici ency chlorosis. Currently, Fe-EDDHA (ethylenediiminobis-2-hydroxypheny l acetic acid) chelate is the most effective source of Fe for high pH soils. Iron humate (FeH), a by-product of the drinking water decoloriz ation process, was compared with Fe-EDDHA for Fe deficiency correction on nonbearing 'Ambersweet' orange and 'Ruby Red' grapefruit Citrus pa radisi Macf., and bearing 'Hamlin' orange Citrus sinensis and 'Flame' grapefruit trees, all on Swingle citrumelo rootstock, planted on high pH (>7.6) soils. Iron humate was applied under the tree canopy in spri ng at rates from 2 to 200 g Fe (nonbearing trees), or 22 to 352 g Fe ( bearing trees) per tree per year. Application of FeH to nonbearing tre es decreased twig dieback rating and increased flush growth, flush col or rating, tree size, and leaf Fe concentration. Addition of urea or a mmonium nitrate to FeH did not increase Fe availability. Iron amendmen ts (22 g Fe per tree per year) increased fruit yield after the 1st yea r of application. Further increases in the rate of Fe, from 22 to 352 g Fe per tree per year as FeH, did not significantly increase tree gro wth, fruit yield, or fruit quality, This study demonstrated that FeH w as an effective Fe source for citrus trees planted on alkaline soils.