Context Organic amendments (OAs) from agricultural and non-agricultural industries provide an alternative source of nitrogen (N) and other nutrients for crop production, especially with increasing costs of synthetic fertilisers. Aims This study examined the fate of urea in combination with OA in the form of raw mill mud, composted mill mud and high N compost in a maize field experiment on a sandy loam soil in a rain-fed subtropical environment. Methods OAs (346 kg N ha−1) were incorporated at sowing with 15N labelled urea (200 kg N ha−1) applied 28 days later, including a no OA control. Key results Grain yield, aboveground biomass and roots were not significantly different across all treatments, averaging 8.1, 17.4 and 1.3 t ha−1 at harvest. Total N uptake was 249.1 kg N ha−1 (on average) with fertiliser, native soil N and OAs sources accounting for 49.5, 44 and 6.5% of the total N uptake respectively. There was no significant difference in N fertiliser recovery between the OA treatments and the unamended control, with 61.7 and 3.7% of the applied N recovered in the plant and soil (to 100 cm), respectively, at harvest. Nitrogen fertiliser losses were equivalent to 33.6% of the applied N and were attributed to N leaching after extensive rainfall events late in the growing season. Conclusions OAs with high mineral and/or organic N content at time of application can supply significant amounts of plant available N but high levels of soil mineral N at sowing may hinder their full potential. Implications Reducing N loss and cost, and improving overall soil fertility by replacing synthetic N fertilisers with OAs may contribute to more environmentally sustainable crop production.