## 5 Conclusions  
Liquid ammonium sulfate from processed animal manure (AS) was produced according to the proposed technologies [1] in the European Nitrate Directive [13]. The field demonstrations showed that AS can be applied with a low-NH\({}_{3}\)-emission technique on sandy and clay soils under two crops (grass and maize), and result in similar yields without damaging the crops. In both the field and greenhouse experiments, full N fertilization was carried out using ammonium sulfate, which produced much more S than the fertilization recommendation for S. The greenhouse experiment showed that for most soil-crop combinations tested, there was no evidence that AS is less effective as a nitrogen fertilizer than CAN. There were only two exceptions in the greenhouse experiments: dry matter yield of grass on both clay and sandy soil, and crop N uptake for maize on clay soil. Since N loss through NH\({}_{3}\) or N\({}_{2}\)O was very low in the greenhouse experiment we have no explanation for the lower efficiency of AS for maize on clay soil. The sheltered flux chamber experiment showed no NH\({}_{3}\) emission from AS in sandy soil. AS can be applied to supplement the use of commonly used livestock manure and mineral N fertilizer to meet the crop's S requirement. However, the goal of using processed manure products, to make nutrient fertilization more balanced with crop needs than the original animal manure, is only achieved if AS is applied in line with the recommendation of both N and S, and not by applying more. Applying S at higher doses than the recommendation for S does not fit into any strategy because increased S content in grass can be toxic to cattle and sheep [30] and excess S can leach into (1) surface waters leading to eutrophication in P-rich systems [39] and (2) groundwater leading to elevated sulfate concentrations in drinking water. The field demonstration in grass showed that sulfur uptake can be increased when extreme amounts of AS are used. To avoid toxicity to livestock when used as feed material, these elevated levels should be accounted for in their complete diet. The greenhouse experiment provided no evidence for significant differences in NH\({}_{3}\), N\({}_{2}\)O, or CH\({}_{4}\) emissions caused by fertilizer type, because the achievable measuring accuracy was not sufficient to distinguish between the overall low emissions. The low amount of N emissions is consistent with the N balance, which shows that the amount of uptake by the plant was higher than the amount taken up by the control, implying that the crop was able to utilize all or most of the applied N in addition to some N available in the soil, and that there was very little loss via emissions. The greenhouse experiment was conducted under controlled conditions; in contrast, the field demonstrations provide insight into emissions in a less controlled environment. Here, the N\({}_{2}\)O emissions showed higher levels from the CAN fields compared to the AS fields after rainfall. **Author Contributions:** Conceptualization, R.R., O.S. and K.v.D. ; methodology, R.R. ; validation, R.R. ; formal analysis, R.R. ; investigation, R.R. ; resources, O.S. and K.v.D. ; data curation, R.R. ; writing--original draft preparation, R.R. ; writing--review and editing, R.R., K.v.D. and O.S. ; visualization, R.R. ; supervision, O.S. ; project administration, O.S. ; funding acquisition, O.S. All authors have read and agreed to the published version of the manuscript. **Funding:** This research received funding from the EU Horizon 2020 Research and Innovation Programme under grant agreement No. 862849, \"Innovative nutrient recovery from secondary sources--Production of high-added value Fertilizers' from animal MANURE\", project acronym: FERTIMANURE. www.fertimanure.eu (accessed on 30 May 2024). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The raw data supporting the conclusions of this article will be made available by the authors on request.