## 4 Conclusions  
This study showed that all three BBFs are safe to use as a replacement for mineral fertiliser or slurry manure in potato growing on sandy soil, although there are still some practical issues related to the application of BBF to be solved. Environmentally, refined BBFs AS and KC performed, in terms of N\({}_{2}\)O emission, slightly worse compared with the less refined BBF LFD, whereas agromically the crop yield was slightly better in the case of AS. However, in combination with manure, the BBFs AS and LFD did not show significant differences in crop yield. The hypothesis that refined BBFs perform environmentally and agromically better compared with less refined BBFs was therefore rejected. Compared with MF, all BBF had lower N\({}_{2}\)O emissions but also slightly lower crop yields (except the field that was treated with AS only). Overall, we conclude that agricultural circularity can be stimulated by (i) solving the practical issues that occurred during the application of LFD, (ii) making sure BBFs are on the list of RENURE materials so they can legally replace mineral fertiliser, and (iii) reducing the surplus of slurry manure to stimulate the use and fair pricing of BBF products. Conceptualization, C.M.J.H., I.S., J.P.L., E.M. and R.v.N. ; data curation, C.M.J.H., V.S., I.S. and Z.Y. ; formal analysis, C.M.J.H., V.S., I.S. and Z.Y. ; investigation, V.S. ; methodology, C.M.J.H., V.S., I.S. and R.P.J.J.R. ; visualization, C.M.J.H. and V.S. ; writing--original draft, C.M.J.H. and V.S. ; writing--review and editing, C.M.J.H., V.S., I.S., J.P.L., E.M., R.v.N., Z.Y. and R.P.J.J.R. All authors have read and agreed to the published version of the manuscript. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Quantity Required** & **Product Costs** & **Application Costs** & **Total Costs** \\ \cline{2-5}  & **(kg/ha)** & **(\(\ell\) kg\({}^{-1}\) N Application ha\({}^{-1}\))** & **(\(\ell\) kg\({}^{-1}\) N Application ha\({}^{-1}\))** & **(\(\ell\) kg\({}^{-1}\) N Application ha\({}^{-1}\))** \\ \hline \multirow{3}{*}{Manure + CAN} & Manure: 80,000 & \multirow{3}{*}{5.7} & \multirow{3}{*}{30} & \multirow{3}{*}{35.7} \\  & MF: 200 & & & \\ \cline{1-1} \cline{4-4} \cline{5-5}  & Manure: 80,000 & & & \\ \cline{1-1} \cline{4-4} \cline{5-5}  & LFD: 10,900 & & & \\ \cline{1-1} \cline{4-4} \cline{5-5}  & Manure: 80,000 & & & \\ \cline{1-1} \cline{4-4} \cline{5-5}  & AS: 600 & & & \\ \cline{1-1} \cline{4-4} \cline{5-5}  & LFD: 64,778 & & & \\ \cline{1-1} \cline{4-4} \cline{5-5}  & AS & 35,82 & & \\ \hline \hline \end{tabular} \({}^{*}\) Trial specific due to the labour-intensive application of large amounts of LFD on small plots.  
\end{table} 
Table 6: The purchase and application costs of the bio-based fertilisers liquid fraction of the digestate (LFD) and Ammonium sulphate (AS) and the mineral fertiliser CAN. **Funding:** This research was funded by the Nutri2 Cycle project who receives funding from the European Union's Horizon 2020 Framework Programme for Research and Innovation under Grant Agreement no 773682 and from the Dutch Ministry of Agriculture (AF-EU-18030). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Data are available on request due to restrictions, e.g., privacy or ethical. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy. **Acknowledgments:** This research was carried out in collaboration with Van den Borne Potatoes, Practice Center for Precision Agriculture, a pig farmer, and VP-Hobe. We are very grateful for their contributions. **Conflicts of Interest:** The authors declare no conflict of interest. * [PERSON] et al. (2015) [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON] Biochar amendment to soils with contrasting organic matter level: Effects on N mineralization and biological soil properties. _GCB Bioenergy_**2015**, \(7\), 135-144. [CrossRef]
* [PERSON] et al.