Factors Influencing Ammonia Losses From Urea Applied to Northwestern Forest Soils

Laboratory studies indicated that volatilization losses of NH 3 increased with increasing air movement, temperature, and pH of mineral soils and forest floors. At an air flow rate of 3 liters/min (equivalent to calculated air velocity of approximately 0.01 km/hour) and temperature of 19°C, losses were high—ranging from 6 to 30% of the urea N applied to bare mineral soils and 27 to 46% for mineral soils covered by forest floors. Ammonia losses were less for mixtures of NH 4 Cl and urea crystals than for urea crystals or pellets alone. Losses were not related to urea pellet size.