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Abstract
The volatilization of ammonia following applications of urea fertilizers to soils may release significant amounts of N into the atmosphere and reduce the plant available N. This study compared ammonia loss from urea phosphate (170 g N kg−1, 190 g N kg−1), cogranulated urea-urea phosphate (340 g N kg−1, 73 g P kg−1), urea (460 g N kg−1) and ammonium nitrate (350 g N kg−1) granular fertilizers applied to the soil surface at 60, 120 and 200 mg N kg−1 soil. Soil moisture contents were adjusted to 100% and 25% of field moisture capacity at the beginning of the experiment. Ammonia losses from cogranulated urea-urea phosphate and urea were similar, being as much as 7.8% of applied nitrogen in 14 days. Urea phosphate and ammonium nitrate exhibited significantly lower ammonia losses. As the amount of N applied increased, corresponding ammonia loss increased. An initial soil moisture at 25% field moisture capacity caused the fertilizers to lose more ammonia than when the soils were initially at 100% field moisture capacity. The data suggest that urea phosphate has a lower ammonia volatilization potential than urea, but increasing the urea to phosphoric acid mole ratio to achieve a higher N analysis (cogranulated urea-urea phosphate) suppresses the effect of phosphoric acid and raises the ammonia volatilization potential.