Effective Strategies to Correct Iron Deficiency in Florida Vegetable Crops

Abstract

Iron (Fe) deficiency is a frequent nutritional problem in Florida vegetable crops because of leaching of Fe fertilizer from the soil, poor soil aeration, low soil organic matter (SOM), temperature, high soil pH and/or water bicarbonate content, and interactions with high levels of manganese (Mn) and calcium (Ca). Most Fe-deficient plants are yellow and stunted, with symptoms on younger leaves near the top of the plant because of Fe immobility and poor translocation resulting in interveinal chlorosis. Iron deficiency in tomato (Solanum lycopersicum) is characterized by a drastic reduction of leaf chlorophyll content at first at the base of the leaves (bleached leaf) ending in necrotic spots. Iron deficiency can have a significant economic impact depending on the timing of the deficiency during the crop production cycle. Furthermore, crop genotypic variations influence the ability of root systems to acquire Fe. The objective of this article was to describe current methods used by vegetable growers to correct Fe deficiency and to evaluate their effectiveness in tomato, pepper (Capsicum annuum), bean (Phaseolus vulgaris), and eggplant (Solanum melongena) production in Florida. A survey was conducted in the major vegetable production areas in Florida during 2012. Results from the survey indicated that since Fe availability depends on complex soil and environmental factors, there was no reliable soil test method that can predict Fe deficiency on vegetable crops in Florida. Production areas surveyed with calcareous or alkaline soils that are often due to over-liming, Fe becomes unavailable because of significant reduction of Fe. Production practices for those areas were not to use calcitic lime to raise Ca levels, especially if the pH is adequate (6.5). Instead, gypsum or calcium nitrate was recommended for soil Ca. The survey indicated that Fe sulfate (inorganic form) is the most commonly used Fe fertilizer in Florida. However, chelates of Fe were effective but expensive Fe alternative. Among chelate sources, ferric ethylenediaminediaminedi-o-hydroxyphenylacetic acid was frequently the preferred chelate fertilizer for soil application, but it is an expensive option. Soil acidification to lower the soil pH was also used to improve soil Fe availability. Organic matter in animal manures and composts was used as an effective alternative to increase Fe with positive results in Florida tomato production. However, the survey indicated that Fe applied to the soil was converted into unavailable forms especially under high soil pH, thus foliar application was used if Fe deficiency symptoms were observed early in the production cycle.