RATIONALE: The combination of plant residues with inorganic fertiliser-N provides the potential to increase N-use efficiency in agricultural fruit production systems, such as olive orchards. The development of weeds in the inter-canopy area of olive orchards is encouraged as a novel strategy to reduce soil erosion. However, little is known about soil N retention or N₂O production following the combined application of inorganic-N with the mulched weed residues. METHODS: Emissions of ¹⁵N-N₂O and soil mineral ¹⁵N retention were measured following combined applications of ¹⁵N-labelled fertiliser and a range of olive crop weed residues to a silty loam soil under controlled conditions. These plant residues differed in their C:N ratios, lignin and polyphenol contents. RESULTS: The magnitude of soil ¹⁵N-NO₃ ^- retention from combining plant residues and fertiliser-N was highly dependent on potential N mineralisation (r = -0.96) and the (lignin + polyphenol)-to-N ratio (r = 0.98) of the residues. Fertiliser-N-derived retention was zero for a legume-based mulch but up to 80% in the treatment containing plant residues with a high (lignin + polyphenol)-to-N ratio. N₂O emissions increased after the addition of residues, and increased further (up to 128%) following the combined application of inorganic fertiliser and residues. Fertiliser-derived ¹⁵N-N ₂O was <1.4% of the total ¹⁴⁺¹⁵N-N₂O emission and <0.01% of the applied ¹⁵N-NO₃ ^-. Enhanced N₂O emissions following the application of residues and the fertiliser-N values were positively correlated with the C:N ratio of the residue. Thus, combining organic- and inorganic-N immobilised a significant proportion of the inorganic N with little increase in N₂O, especially in low C:N ratio residues. CONCLUSIONS: The results demonstrate that whilst there is potential for N₂O emissions to be controlled by combining weed residues and inorganic fertilisers, this is not easy to achieve as the magnitude and direction of interactions vary between different species due to their varying substrate qualities.