Prediction of Soil Nitrogen Availability in Forest Ecosystems: A Literature Review

Abstract The increasing interest in the use of N fertilizers to stimulate forest growth is prompting consideration of laboratory soil testing methods to predict the probability of N response. However, even in tilled agricultural systems, laboratory tests for N availability are not widely accepted. To be successful in predicting N response in the forest ecosystem, many additional factors than those used in agriculture must be considered. These include the sources and sinks of N and the internal redistribution of N in the trees, as well as intensity of management. Problems also exist with selection of the sample, since the forest floor litter oftentimes constitutes a major reservoir of N. Availability of this N will be difficult to estimate. Spatial variability also presents formidable obstacles in obtaining a valid sample. However, some success with N availability tests has been reported in the Douglas-fir ecosystems of western United States, particularly with the anaerobic incubation method. Further progress will require considerable research effort and careful attention to the N cycle. Forest Sci. 26:159-171.