Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: August 1, 2004
Publication Date: June 15, 2008
Citation: Griffin, T.S. 2008. Nitrogen availability (chapter in Nitrogen in Agricultural Systems, 3rd edition, American Society of Agronomy). Nitrogen in Agricultural Systems; 3rd Edition. Agronomy Monograph 49; pg. 613-646. Technical Abstract: Soil organic matter N (SOMN) remains a significant source of nitrogen (N) in contemporary agricultural systems, despite the inclusion of numerous inorganic N fertilizers, organic N sources like manures, N-fixing legumes, and direct deposition of atmospheric N. The dual and often contradictory goals of maximizing N use efficiency from all sources, including SOMN, and minimizing the environmental loss of both dissolved and gaseous N necessitates predicting plant available N (PAN) from SOMN. This need has stimulated a decades-long research effort to develop and validate an N availability index that is sufficiently robust to be used as a routine soil test. This chapter reviews research on existing soil-based tests or indices for estimating mineralization of SOMN, including chemical extraction, biological methods like aerobic incubation, and partitioning of soil N pools. The validation of these indices by both long-term aerobic incubation and by field experiment are discussed. The ability of existing methods to account for climatic variability remains a significant challenge.