Fruit yield of citrus is largely regulated by the N fertilization. Adequate nutrient management of citrus trees is related to efficient use of nitrogen (N) fertilizers. However, losses of N through volatilization of ammonia (NH3) can be very significant due to the characteristics of different N sources. Research reports conducted in orange groves in Florida and Brazil have demonstrated the potential for NH3 losses following application of urea and ammonium nitrate to the soil surface without incorporation of the fertilizer.