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Abstract
Polyphosphate consists of phosphate chains linked by oxygen bridges. When applied to soil, they gradually hydrolyze into orthophosphates through the action of phosphatase enzymes or chemical reactions. This process enabled a more sustained release of phosphorus compared to monoammonium phosphate (MAP) or diammonium phosphate (DAP). Consequently, ammonium polyphosphate fertilizers and NPK formulations containing polyphosphate have attracted considerable attention as a promising strategy in modern agriculture. This study aimed to evaluate the polyphosphate content in NPK 16-16-8 produced using polyphosphate technology by Petro Vietnam Ca Mau Fertilizer JSC and compare it with other common NPK fertilizers 16-16-8 produced by different technologies. The experiment was conducted at the Soil chemistry laboratory, Can Tho University, using water extraction, FeSO₄ precipitation, and molybdophosphate blue colorimetry to determine the contents of ortho- and polyphosphate. The results showed that Ca Mau NPK 16-16-8 fertilizer had the highest proportion of polyphosphate in water-soluble phosphorus (89.7%), significantly higher than other products. The polyphosphate content reached 9.66% P₂O₅, while other NPK fertilizers ranged from 4.97% to 8.28%. This production technology reduced phosphorus fixation with Fe, Al, and Ca, thereby maintaining phosphorus availability under unfavorable soil conditions such as acid sulfate and alkaline soils. These findings indicated the distinctive polyphosphate composition in Ca Mau NPK 16-16-8 compared to other currently available NPK 16-16-8 fertilizers in Vietnam.
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