15N labelling of cattle manure reveals the distribution of organic fertiliser nitrogen in a winter wheat system

15N tracer technology can be used to study the distribution of fertiliser N in the soil–plant system. However, few studies have used 15N tracer to directly label organic fertiliser such as livestock manure. Therefore, we analysed the distribution of N derived from cattle manure labelled with15N in winter wheat plants and the soil. An unlabelled large-plot experiment and 15N-labelled micro-plot experiment were performed using five fertilisation treatments: M (30 t ha–1 manure) without additional N fertiliser, M+N75 (75 kg N ha–1), M+N150 (150 kg N ha–1), M+N225 (225 kg N ha–1) and M+N300 (300 kg N ha–1). The amounts of manure-derived N in crop plants and the soil were determined over a 2-year period (2019 and 2020). The wheat yield of M+N150 treatment plots was close to the highest wheat yield obtained in the M+N225 treatment plots (6311 kg ha–1 in 2019 and 6523 kg ha–1 in 2020). A large amount of manure-derived N was distributed in the whole plants treated with M+N150, being 78.4% (2019) and 58.3% (2020) higher than that in the plants treated with M+N300. The N use efficiency of manure in the M+N150 treatment plots was 8.1%, not unlike the highest N use efficiency observed in the M+N75 treatment plots (8.4%, sum of 2019 and 2020). The manure-derived total N at 0–40 cm soil depth in the M+N150 treatment plots was lower than that in the M treatment plots, whereas the manure-derived mineral N in the M+N150 treatment plots was similar to that in the M treatment plots and lower than that in the M+N300 treatment plots. These results suggested that the application of 30 t ha–1 of cattle manure with 150 kg ha–1 of N fertiliser was the optimal fertilisation treatment in the soil–wheat system, which could obtain high crop yield and improve N use efficiency by increasing the distribution of manure-derived N in whole plants and reducing manure-derived N in the soil.