A modified urea based NP fertilizer: urea-TSP-MAP combinations
Applying urea with acidic phosphate fertlizer increases urea fertilizer efficiency by reducing ammonia volatilization and toxicity to crop from urea hydrolysis. However, urea and triple superphosphate (TSP) are not recommended to be cogranulated because blends might become wet and sticky. Monoammonium phosphate (MAP) is a less acidic P source than TSP, but is compatible with urea. The objective of this study was to evaluate compound NP fertilizer products made from MAP and TSP combinations as P sources with urea. Fertilizer mixtures were pelletized from commercial urea, TSP and MAP with different N:P2O5 ratios and MAP/TSP combinations. Moisture changes during storage, pH of fertilizer solutions, and ammonia volatilization from surface applied fertilizer pellets were measured. Using MAP with TSP in urea-P mixtures reduced moisture increases during storage. Increasing MAP in urea-TSP-MAP combinations increased fertilizer solution pH by over 1 unit as the MAP/TSP-P2O5 ratio increased from 0/100 to 100/0. Adding MAP as 50% of P in urea-MAP-TSP mixtures at 3:1 and 1.5: (N:P2O5) ratios reduced ammonia loss from urea 50% to 60% compared to urea alone; and ammonia loss was similar to that of urea-TSP combinations. A urea-TSP-MAP fertilizer combination could make efficient use of urea-N by crops by reducing ammonia loss from urea hydrolysis.