Ammonia volatilization following dairy slurry application to a permanent grassland on a volcanic soil

Agriculture is the largest source of ammonia (NH3) emission to the atmosphere. Within the agricultural sector, the application of slurry to grasslands as fertilizer is one of the main emission sources. This is a common practice in southern Chile, where most dairy production systems are grazing-based. In Chile, there are few published data of gaseous emissions following slurry application to grassland. The aim of this study was to evaluate NH3 volatilization following dairy slurry application to a permanent grassland on an Andosol soil. Ammonia volatilization was measured in four field experiments (winters of 2009 and 2011 and early and late springs of 2011) using a micrometeorological mass balance method with passive flux samplers following dairy slurry application at a target rate of 100 kg total N ha−1. The accumulated N loss was equivalent to 7, 8, 16 and 21% of the total N applied and 22, 34, 88 and 74% of total ammoniacal nitrogen (TAN) applied for winters 2009 and 2011, and early and late spring 2011, respectively. Ammonia emission rates were high immediately after application and declined rapidly with time, with more than 50% of the total emissions within the first 24 h. Losses were highly influenced by environmental conditions, increasing with temperature and lack of rainfall. Taking into consideration the low N losses via leaching and nitrous oxide emissions reported for the study area, results indicate that NH3 volatilization is the main pathway of N loss in fertilized grasslands of southern Chile. However, dairy slurry application could be an important source of nutrients, if applied at a suitable time, rate and using an appropriate technique, and if soil and climate conditions are taken into consideration. This could improve N use efficiency and reduce N losses to the wider environment.