## 3 Results
### Soil N\({}_{2}\)O Fluxes  
Our hypothesis that plots treated with urea fertilizer would have the highest N\({}_{2}\)O fluxes was not supported by our results. Instead, there was no significant difference in N\({}_{2}\)O fluxes, even while the urea fertilizer and hydrochar treatment plots had lower mean N\({}_{2}\)O emissions. Noticeably, there were no N\({}_{2}\)O fluxes recorded for about 80% of the sampling weeks, and only occasional effluxes in the control and urea treatment plots. Baseline soil flux measurements before applying treatments were made on 14 June and there was no N\({}_{2}\)O flux detected in any of the treatments. After the treatment application, the urea treatment plots produced the highest N\({}_{2}\)O fluxes (0.25 \(\upmu\)g m\({}^{-2}\) h\({}^{-1}\)) at site A on the first sampling week and 2.14 \(\upmu\)g m\({}^{-2}\) h\({}^{-1}\) at site B. These fluxes were clearly a result of the application of the fertilizer as no fluxes were detected in the control treatments that week. Out of the 17 weeks of sampling, fluxes of N\({}_{2}\)O in the hydrochar treatment plots were detected on only five sampling weeks at site A, and these all showed the soils acted as a small sink on average. There was no N\({}_{2}\)O flux recorded at site B for hydrochar-treated soils. Generally, studies investigating the effects of hydrochar on N\({}_{2}\)O emissions report a reduction in N\({}_{2}\)O emissions [36; 37; 50; 54]. [PERSON] et al. [36] however observed a subsequent increase in N\({}_{2}\)O emissions of 302%. Hydrothermal carbonization usually results in an increase in the C of the material that was pretreated resulting in an increase in C content of soil when used as an amendment [3]. Higher C:N ratios (17:1 in the case of hydrochar used in this study) are correlated with higher immobilization of organic N in soil, which reduces mineralization and nitrification. This likely led to the suppression of denitrification in hydrochar-treated soils. N\({}_{2}\)O fluxes in the digestate treatment at site A occurred on only two sampling weeks one month apart and resulted in the site acting as a weak net source of N\({}_{2}\)O. The release of N\({}_{2}\)O on these two sampling weeks could be caused by an accumulation of organic C in the soil from the digestate [33] which [PERSON] and [PERSON] [57] claim stimulates N\({}_{2}\)O production from soil through denitrification. After applying digestate at a rate of 170 kg N ha\({}^{-1}\) to soil, [PERSON] [32] reported a release of N\({}_{2}\)O fluxes for several days after application. They explain that this initial increase resulted from denitrification induced by the reduction in oxygen concentrations caused by microbial respiration. This study used a lower N application rate (100 kg N ha\({}^{-1}\)) which may explain why N\({}_{2}\)O was only released on two occasions. Similarly, [PERSON] [58] observed that digestate released significantly greater N\({}_{2}\)O fluxes compared to N fertilizer but the release was rather short term. Their study used application rates ranging from 202 to 254 kg N ha\({}^{-1}\)[58] which is more than twice the application rate used in this current study which implies N\({}_{2}\)O fluxes are dependent on the N application rate. Site B had four weeks of N\({}_{2}\)O fluxes that resulted in the site acting as a weak net source of N\({}_{2}\)O fluxes, although mean cumulative fluxes were not significantly different from zero. One sampling time point stood out as showing a very high flux of N\({}_{2}\)O in the control treatment at site A (i.e., 103.22 \(\mu\)g m\({}^{-2}\) h\({}^{-1}\)). No explanation could be given for such a detection of this flux on a day when the temperature was low and there was no precipitation; hence, this was most likely the result of an anomalous event in the soil on that sampling day (e.g., animal defecation or soil disturbance).