To study the main soil, climatic and management factors that affect N losses due to NH3 volatilization in volcanic ash soils of southern Chile.

1.- To evaluate soil, climatic and management factors that affect NH3 emissions following the application of mineral and organic fertilizer. 2.- To evaluate the implementation of best mitigation practices to reduce NH3 volatilization and the efficiency of N use in grassland soils. 3.- To validate a simple process-based model for estimating NH3 emissions from grasslands soils following N applications