The decline of N from N-15-labelled mature pea residues was followed in unplanted soil over 16.5 yr. Eight years after residue incorporation, 24% of the residue N-15 input was still present in the soil and, after 16.5 yr, 16% of the residue N-15 input remained. A double exponential model successfully described the decay of N from N-15-labelled pea residues. The total residual N-15 declined with average decay constants of 1.45 yr(-1) for the 30 d to 1 yr period and of 0.07 yr(-1) for the 1-16 yr period. Sixteen years following incorporation of the residues, indicator plants growing in residues-amended soils were obtaining 1.7% of their N from residue N. This is, to our knowledge, the longest study on decay of N in soils from N-15-labelled crop residues. The current study thus provides a unique data set for our empirical understanding of N-dynamics in agricultural systems, which is a prerequisite to parameterize and validate N-simulation models. (c) 2006 Elsevier Ltd. All rights reserved.