If a fertilizer material containing polyphosphates is applied, the polyphosphate is fairly rapidly converted in most agricultural soils to the orthophosphate form. When an orthophosphate-containing fluid fertilizer is applied or an orthophosphate-containing dry fertilizer dissolves in the soil solution, the plant roots are confronted mainly with two phosphate species (H₂PO₄- and HPO⁻²). First, the phosphorus in most fertilizers is present in the orthophosphate form. So, for most of the growing season, plant roots “see” mainly nitrates unless a source of ammonium nitrogen is supplied during the season.ĭespite the fact that farmers are offered a wide array of phosphorus-containing fertilizers, these farmers are assured that their crops are really confronted with a very limited variety of chemical forms of phosphorus. This is because various soil enzymes rapidly convert urea nitrogen to ammonium forms, and then soil microbiological processes fairly rapidly convert the ammonium forms to nitrate. Although a farmer may apply fertilizer nitrogen as anhydrous ammonia, urea, ammonium nitrate, urea-ammonium nitrate, calcium nitrate or several other forms, the same farmer may be assured that, within a fairly short time, the roots of his crops will be confronted mainly with nitrogen in the nitrate form (NO3). The matter of equality of various physical forms is even more predictable when one considers the limited variety of chemical forms presented to the plant root. The relative equality of fluid and dry fertilizers should not be too surprising in light of the fact that the chemical constituents of the two physical forms are usually identical. For example, concentrated superphosphate, 0-46-0 or CSP, can’t be compared directly with 10-34-0 solution or solid monoammonium phosphate, 11-48-0 or MAP, because the latter two contain nitrogen.įLUIDS AND SOLIDS ARE EQUAL AGRONOMICALLY If data are selected from one study, for one year, at one location, evidence can be cited to prove that solids are better than fluids, or vice versa, or that polyphosphates are better than orthophosphates, or vice versa.Ĭare must be exercised in comparing any solid or fluid fertilizers under field conditions. Essentially, the same conclusions would be reached with dry and fluid NPK mixes.įor valid comparisons, studies should be conducted for several years at the same location using the same experimental design to ensure that the variability inherent in field studies does not lead to faulty interpretations. Similarly, long-term studies have shown solid urea or ammonium nitrate to be virtually equal to nitrogen solutions, such as urea-ammonium nitrate. However, when solids such as diammonium phosphate (DAP), monoammonium phosphate (MAP) or ammonium polyphosphate were compared with fluids such as 10-34-0, 8-24-0 or 11-37-0 under similar conditions, long-term studies have shown these to be essentially equal in nutritive value. For instance, it would not be valid to compare a highly water-soluble phosphate in fluids with a solid phosphate of low water solubility. The last is particularly important when comparing phosphate fertilizers. AGRONOMIC COMPARISONS OF FLUID AND DRY FERTILIZERSĮxperimental data from a wide range of studies overwhelmingly supports the conclusion that there are essentially no differences among the liquid, suspension and dry fertilizers when they are compared over the long term under conditions of similar nutrient rates, placements and chemical forms.
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