Mineralization of Manure Nitrogen—Correlation with Laboratory Indexes

Simple and multiple correlations between available N estimated from a 10‐month greenhouse trial with 10 manures and a number of potential laboratory indexes to available N are presented. The best single chemical index to available N was the N extracted by digestion with pepsin. Slightly more than 80% of the variation in available N was related to variations in pepsin N. High correlations were found between available N and the C released as CO 2 during incubations of 1, 2, and 4 weeks. In a multiple correlation using all chemical indexes plus N and C released in 1‐week incubations, the significant indexes were N released by incubation, C released during incubation and the C/N ratio. In a multiple correlation with all indexes, the significant factors were N released in 1‐ and 10‐week incubations, the C/N ratio, and N released to acid KMnO 4 solution. Pepsin digestion and C release during a short period of incubation appear to be useful single indexes.