Influence of iron pyrites and dicyandiamide on nitrification and ammonia volatilization from urea applied to loess brown earths (luvisols)

Abstract

Laboratory incubation study showed that iron pyrites retarded nitrification of urea-derived ammonium (NH₄ ⁺), the effect being greatest at the highest level (10000 mg kg^–1 soil). Nitrification inhibition with 10000 mg pyrite kg^–1 soil, at the end of 30 days, was 40.3% compared to 55.9% for dicyandiamide (DCD). The inhibitory effect with lower rates of pyrite (100–500 mg kg^–1) lasted only up to 9 days. Urea+pyrite treatment was also found to have higher exchangeable NH₄ ⁺-N compared to urea alone. DCD-amended soils had the highest NH₄ ⁺-N content throughout. Pyrite-treated soils had about 7–86% lower ammonia volatilization losses than urea alone. Total NH₃ loss was the most with urea+DCD (7.9% of applied N), about 9% more than with urea alone.