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FIELD SCIENCE 28 SportsTurf | December 2015 www.sportsturfonline.com also results due to external factors such as drought, flooding, or other stress factors. It is therefore, expected that the rate of diffusion of iron into apoplast would be determined by the pH, and accordingly the application of iron compounds should be planned. IRON SOURCES There are three common sources of iron typically used in foliar iron products: Ferrous sulfate, Iron Glucoheptonate where the anion is absorbed and recognized by the turf plant as a key sugar for transport of nutrients, and Iron Citrate which is absorbed and recognized by the turf plant a key component for ATP generation in the Krebs Cycle. CHELATING AGENTS In order for a compound to be called a true chelating agent, it must have certain chemical characteristics. The chelating compound must consist of at least two sites capable of donating electrons to the metal it chelates. For true chelation to occur, the donating atom(s) must also be in a position within the chelating molecule so that a formation of a ring with the metal ion can occur. There are five categories of compounds that are commonly used for foliar applications of iron: synthetic chelates, ligno sulfonates, humic or fulvic acids, organic acids, and protein (amino acids). Synthetic chelating agents. The most common form is EDTA. One popular form is iron EDDHA. Although some debate the effectiveness of synthetic chelating agents for foliar application, it is known that in a nutrient solution, it is essential to have an excess of total mineral in relation to chelating agent so that the chelating agent does not compete for the mineral with the turf plant. Advantages: EDTA chelates are very stable and can be mixed with just about any phosphate containing fertilizer at basically any pH. Disadvantages: EDTA is a synthetic compound, not produced by the turf plant. Ligno sulfonates. Considered to be a water soluble, non- toxic polymer. Polymer usually means the molecule is quite large. Advantage: low cost. Disadvantages: the main disadvan- tage for foliar application is the size of the molecule. Humic or fulvic acids. In foliar applications, fulvic acids may not play a direct role in availability and movement of iron in the turf plant; however, they do act as turf plant stimu- lants and possibly precursors to plant hormones. One of humic acid's known benefits is that it helps the turf plant use applied nutrients more efficiently. Advantages: cost effective. When they are "small enough" to effectively move into the turf plant, they can supply a beneficial source of precursors to important turf plant chemicals. Disadvantages: In foliar appli- cations humic has a definite disadvantage of being too large in size. In trace mineral mixtures humic molecules tend to settle out in the container, largely due to their molecular size and of their poor suspension of these complex colloids in water at lower pH. Organic acids. These compounds are one of two groups of compounds that are essential for the transportation and solubility of divalent elements (two positive charges: Zn++, Mn++, Fe++, Cu++) in turf plants. The organic acids can be called "anionic organic acids" because of the negative charge. One such popular acid used in foliar iron products is citric acid. In foliar sports turf applications, these anionic (negatively charged) organic acids play an important role in converting cationic (positively charged) minerals such as iron into nonionic (neutral) compounds for increased leaf pene- tration and movement into the turf plant. Advantages: organic acids are one of the natural systems a turf plant uses to solubi- lize and translocate minerals such as iron. By neutralizing the charge of minerals, organic acids make mineral uptake more effective. Disadvantages: Commercially produced individual organic acids are quite expensive compared to some other chelating and complexing agents. Compared to synthetic chelating agents and some amino acid chelating compounds, organic acid chelates form weaker bonds with minerals, espe- cially at increasing pH levels. Protein (amino acids). Amino acids are natural com- pounds that the turf plant produces to solublize and translocate minerals such as iron. Turf plants manufacture these compounds to make minerals biologically available in the cell. As with organic acids, amino acid compounds also play a role in mineral uptake into plant tissue because of the increase permeability effect of the amino acid on the cuticle. Another important function of amino acid chelated iron and other minerals is that they are less phytotoxic to the turf plant, especially during stress points in turf plant development. One example of amino acid chelation is by the use of polyamines in chelation. Polyamines are less than l nanometer in size and carry a neutral charge and derived from natural plant extracts consisting of nineteen L-amino acid molecules. One advantage of polyamines, when compared to EDTA, sulfates, citrates, and other synthetic chelates is the turf plant can immediately use the organic acids to maintain charge balance, for an energy source, and for a source of carbon skeletons. Amino acid advantages: Amino acids are one of the natural systems the turf plant uses to translocate and use minerals. By neutralizing the charge of minerals, amino acids make mineral uptake more effective. Disadvantages: Enzymatically hydrolyzed protein is expensive to produce. The actual combination of properly prepared amino acid/peptide compounds and miner- als is not 100% complete with simple tank mix procedures. ■ ST Jeff Haag is Sports Turf Manager at Nova Southeastern University in Davie, FL