**5. Conclusions**

The combination of inorganic and organic N substrates reduced the total and mineral N runoff losses compared with inorganic N alone in coarse-textured sand. The higher N uptake by the plant cover provides strong evidence that the combined use of inorganic and organic sources has the potential for increasing NUE by reducing fertiliser losses in surface runoff and synchronising better the N availability with plant requirements. Inorganic N fertiliser can be applied at low rates to provide sufficient N at the early growth stage, with organic substrates, such as composted manures, supplying N at later stages, particularly when the plant growth rate is high.

Furthermore, the potentially slower release of N from organic materials such as CropUpTM may reduce the impacts of other loss pathways (e.g., leaching and sub-surface lateral flow) relative to highly soluble inorganic N fertilisers, particularly when the release rate better matches plant N uptake requirements. These organic materials have widespread applications to sandy soils not only in agriculture, but also in other activities that involve a high N application to sand, such as golf courses and sporting ovals.

**Author Contributions:** Conceptualisation, I.P., C.P.-L. and M.R.; methodology, I.P., M.R. and D.M.; formal analysis, I.P. and D.M.; investigation, I.P.; resources, C.P.-L., I.T., B.S. and B.H.; data curation, I.P.; writing—original draft preparation, I.P.; writing—review and editing, I.P., C.P.-L., M.R., I.T., B.S., D.M. and B.H.; supervision, M.R.; funding acquisition, C.P.-L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Australian Government's Cooperative Research Centres Projects, grant number CRCPFIVE000015.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** We would like to thank the Cooperative Research Centres Projects (grant number CRCPFIVE000015) for funding this project.

**Conflicts of Interest:** The authors declare no conflict of interest.

### **References**

