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Fluid Journal : Fluid Journal 1999-2001
Table 3. Calculating salt index of 6-24-6. ---Salt index--- % Nutrient units per unit in for- Material Nutrient lbs/ton N P2O5 K2O (20 lb)a mulation (1) (2) (3) (4) (5) (6) (7) (8) NH3 82%N 146 6.0 --- --- ---b --- H3PO4 54%P2O5 666 --- 18.0 --- 1.613 10.7 Potassium 22%K2O, phosphate 22%P2O5 546 --- 6.0 6.0 0.097 1.2 Water 642 --- --- --- --- --- ___ __ __ __ __ ___ ___ 2,000 6.0 24.0 6.0 11.9c a Salt index per unit (20 lb) of plant nutrients, listed in Table 1, also called the partial salt index. b Ammoniation of phosphoric acid to a 1-3-0 ratio forms a mixture of MAP and DAP. c 0.32 SI/unit plant nutrient. Table 4. Salt index of some common liquid formulations. Salt index per unit of plant Formulation Salt index nutrient (20 lb) 2-20-20a 7.2 0.17 3-18-18a 8.5 0.22 6-24-6a 11.5 0.32 6-30-10a 13.8 0.30 9-18-9a 16.7 0.48 10-34-0b 20.0 0.45 7-21-7c 27.8 0.79 4-10-10c 27.5 1.18 28%UANc 63.0 2.25 a These grades are formulated using potassium phosphate as the K source. b Use in seed-row placement with caution. c Not suggested for use in seed-row placement. Spring 2001 Fluid Journal 3 5. Total individual SI values of all components in column 8. SI values for a 6-24-6 formulation containing potassium phosphate are shown in Table 3. Phosphoric acid is first ammoniated to a 1-3-0 ratio, which results in an approximate 50-50 mixture of MAP and DAP at about pH 6.8. Potassium phosphate is then added to provide all of the K and remainder of the P. Resulting SI of this grade and SI per unit of plant nutrients are much lower than those for 7-21-7, which contained KCl. Other points to consider are: When K2SO4 is used instead of KCl, the SI is somewhat lower. However, the solubility of K2SO4 is lower than that of KCl, so this must be considered in producing formulations relatively high in K2O. SI values of acids are given as values per 100 lbs of acid rather than a unit of 20 lbs. Also, the SI of H3PO4 varies with P concentration of the acid. SI values calculated differ for formulations when ammoniated phosphate solutions are prepared. SI per unit of N due to the ammoniating solution is not included because its contribution has already been accounted for in the SI per 100 lbs of H3PO4, since it has been converted to ammonium phosphate. The same method is used for calculating the SI of ammoniated H2SO4 formulations. SI values and SI per plant nutrient of some commonly used liquid formulations are listed in Table 4. Note that all formulations containing potassium phosphate have relatively low SI values. The two formulations containing KCl (7-21-7 and 4-10-4) have much higher SI values and are not suggested for use in seed-row placement. These results show that SI of fluid fertilizers varies significantly, depending on the grade and components in the formulation. Dr. Mortvedt, previously with the National Fertilizer and Environmental Research Center, TVA, Muscle Shoals, AL, and Colorado State University, is a consultant with U.S. Borax.
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