Root-derived carbon is a major input fuelling soil organic carbon stock. However, root sampling generally omits a considerable fraction of this input. Here, we used isotopic tracing, performed on 12 crops, to quantify this carbon pool and to evaluate its persistence through an 18-month field incubation experiment. We highlighted that it represents a large share of root-derived carbon (27 %) with differences between plant families, and that its persistence in the soil might exceed that of roots.