Mapping potential losses of N-urea by volatilization in soils of central Chile

Available soil information from a soil cartography and a soil data base were used to predict the spatial distribution of ammonia volatilization by surface applied granular urea within the central zone of Chile, assuming that the potential losses depends only on soil properties, which are associated with the physical space known as microsite. Relevant properties (cation exchange capacity, urease activity, pH buffering capacity and soil pH post urea hydrolysis or pH(f)) on ammonia loss process were defined according to a conceptual model, determining threshold values for high potential ammonia losses: CEC = 20 cmol((+)) kg(-1), urease activity >= 40 mu g N-urea g(-1) h(-1) and pH(f) >= 8.0. On other hand, considering the use of some simplified pedotransfer functions, these relevant properties were predicted for the cartographic units of 82 soil Series, estimating around of 88,000 ha the area with the highest risk ammonia losses, corresponding principally to Mollisols.