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Fluid Journal : Fluid Journal 2002-2004
3 Fluid Journal Spring 2002 Manganese uptake and corn yields wereoftheorderMn+AST>Mn+ DAP> Mn + SNT Soil pH in the starter band was lowest with AST and highest with SNT. The acid starters (AST and DAP) applied in a band without Mn were more effective in increasing Mn uptake than SNT with Mn. Extractable soil Mn, Mn uptake, and average response to Mn increased with increasing water solubility of the Mn fertilizer. Other studies have reported improved micronutrient uptake by combination with acid phosphates, sulfuric acid, and elemental sulfur. Results with elemental sulfur seem to be less consistent than results with ammonium sulfate and acid phosphates. This is probably related to varying biological oxidation of S with variations in the soil environment. Advantages of fluids Fluid fertilizers offer special advantages in enhancing micronutrient availability. Because micronutrients are used at low rates distribution in the soil is poor. Fluid bands enhance micronutrient distribution because they are: 1. More or less continuous 2. Provide better distribution 3. Generally eliminate spaces occurring between granules. It has been proposed that much of the advantage of chelated and complex forms applied in fluids results from superior distribution and root interception in addition to nutrient chemistry. Zinc sources banded in suspension with ammonium polyphosphate suspensions have been studied. Suspending zinc materials in fluids produced similar responses among products, eliminating the disadvantages of the insolubility of some zinc carriers such as zinc oxide. Watch compatibility Compatibility of micronutrient fertilizers with starters is typically only a problem when mixing solutions. Probably the greatest concern for dry blended materials is blend uniformity and adequate distribution of a very small amount of micronutrient in the blend. Mixed solutions, however, create intimate contact between nutrient compounds in the various carriers combined. Many chemical reactions are possible in the solution. Compatibility with liquid phosphate sources is usually the greatest problem. As a general rule of thumb, the true chelates are most compatible and inorganic salts are the least compatible. Compatibility is in order of the stability constant of the nutrient compound. A variety of fluid carriers may be used, but compatibility should be checked and the final solution grade may be limited by the compatibility of the carriers. In a number of studies, polyphosphate solutions have produced somewhat better responses than orthophosphate solutions. Polyphosphates are essential for sequestering many inorganic micronutrients. For example, low polyphosphate products cannot hold as much zinc in solution. Chelates provide greater compatibility, but are much more costly. A higher rate of a lower cost material may be more economical if compatibility problems are accounted for. Dr. Blaylock is agronomist for Agrium U.S. Inc., Denver, Co.
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