Ammonia volatilization from ammonium nitrate, urea and urea phosphate fertilizers applied to alkaline soils

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.