Michigan State University Extension
Soils & Soil Management - Fertilizer - 06039722
07/10/97
Tri-state Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa Extension Bulletin E-2567 (New), July 1995
M.L. Vitosh, Michigan State University; J.W. Johnson, The Ohio State University; D.B. Mengel, Purdue University; Co-editors
The three main classes of micronutrient sources are inorganic, synthetic chelates and natural organic complexes. Inorganic sources consist of oxides, carbonates and metallic salts such as sulfates, chlorides and nitrates. Sulfates of Cu, Mn and Zn are the most common metallic salts used in the fertilizer industry because of their high water solubility and plant availability. Oxides of Zn are relatively water insoluble and thus must be finely ground to be effective in soils. Broadcast applications of Zn oxides should be applied at least 4 months before planting to be effective. Oxysulfates are oxides that are partially acidulated with sulfuric acid. Studies have shown granular Zn oxysulfates to be about 35 to 50 percent water-soluble and immediately available to plants. Metal-ammonia complexes such as ammoniated Zn sulfate are also used by the fertilizer industry. Such complexes appear to decompose in soils and provide good agronomic effectiveness.
Chelates can be synthetic (manufactured) or natural organic decomposition products such as organic acids and amino acids, but they all contain known chemical bonds that increase micronutrient solubility. Synthetic chelates usually ~ Have higher stability than natural L chelates. Chelates such as Zn-EDTA are more stable in soils than Zn titrate or Zn-ammonia complexes and thus are more effective in correcting Zn deficiency.
Natural organic micronutrient complexes are often produced by reacting metal inorganic salts with organic byproducts, mainly those of the wood pulp industry. Lignosulfonates, phenols and polyflavonoids are common natural organic complexes. These complexes are often quite variable in their composition and are less effective than the synthetic chelates.
Selecting a micronutrient source requires consideration of many factors, such as compatibility with N-P-K fertilizers, convenience in application, agronomic effectiveness and cost per unit of micronutrient.
(Vis. 26) lists several commonly used micronutrient fertilizer sources. The inorganic sulfates are generally preferred to oxide forms of micronutrients when blending with N-P-K fertilizers because of their greater water solubility and greater effectiveness. Zinc and Mn oxides, however, are acceptable sources of micronutrients when finely ground. Finely ground materials may present segregation problems when used with granular fertilizers, so the use of a fertilizer sticker is highly recommended. Zinc EDTA, a synthetic chelate, has been found to be more effective than Zn sulfate in Michigan and Ohio field trials and may be used at one-fifth the rate of Zn sulfate. Natural organic chelates and complexes such as Zn citrate or Zn lignosulfonate are considered less effective than true (100 percent) synthetic chelates and should be used at the same rate as inorganic sources. Chelated Mn reactions in soil are quite different from chelated Zn reactions. Manganese chelates, when applied to soil, are usually ineffective because of high levels of available Fe in our soils (Fe replaces the Mn in soil-applied Mn chelates). Therefore, they are unacceptable sources of Mn when soil applied. Foliar applications of Zn chelates are effective sources and should be used at their labeled rates.
| Visual title - Visual size | Visual title - Visual size |
|---|
| Micronutrient sources commonly used for correcting micronutrient - 26K |
