## 3 Results
### CO\({}_{2}\) Fluxes  
Prior to the application of the treatments, baseline GHG fluxes from the soil in all plots were measured. Both the highest (0.092 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\)) and lowest (\(-\)0.012 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\)) baseline soil CO\({}_{2}\) fluxes occurred in site A. The highest flux of CO\({}_{2}\) in the week following treatment application was measured in site A (0.959 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\)) in the digestate treatment (Figure 2b). In the samples collected during the week following application of the fertilizer treatments, soils in all the treatment subplots were a source of CO\({}_{2}\), with the exception of the digestate treatment at site B, which instead acted as a very weak sink (\(-\)0.023 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\)) from the atmosphere (Figure 3b). Figure 3: Time series CO\({}_{2}\) fluxes measured from June to October 2018 at site B in mg m\({}^{-2}\) h\({}^{-1}\) by treatment: (**a**) control, (**b**) digestate, (**c**) hydrochar, (**d**) urea. Values show a mean across two replicated plots with error bars representing the standard error. Figure 2: Time series CO\({}_{2}\) fluxes measured from June to October 2018 at site A in mg m\({}^{-2}\) h\({}^{-1}\) by treatment: (**a**) control, (**b**) digestate, (**c**) hydrochar, (**d**) urea. Values show a mean across two replicated plots with error bars representing the standard error. Generally, soil CO\({}_{2}\) fluxes in all the treatments were higher in the month of August (Figures 2 and 3). The absolute highest CO\({}_{2}\) flux occurred on the 7 th week of sampling from the control treatment plot at site A with 1.45 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\), and the lowest flux occurred in the hydrocarbon treatment at site A on 6 August (\(-\)0.092 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\)). The month of October brought a decrease in CO\({}_{2}\) fluxes in all treatments as temperatures dropped below 15 \({}^{\circ}\)C.  
Cumulative CO\({}_{2}\) fluxes were not affected by fertilizer treatment (Figure 4) or site when tested with the linear mixed model. There was no significant interaction between treatment and site. There was however a statistically significant difference between hydrochar treatments at site A than site B (\(p<0.01\)) detected with a post-hoc Mann-Whitney test. For repeated measures comparisons, test results suggest there was a statistically significant effect of sampling date on CO\({}_{2}\) fluxes in the four treatments (\(p<0.001\)). A Bonferroni multiple comparison test showed that CO\({}_{2}\) fluxes in week 7 of sampling were significantly greater than CO\({}_{2}\) fluxes in weeks 1, 3, 4, 5, 6, 9, 10, 11, 12, 13, 14,15, 16, and 17 (\(p<0.05\)). CO\({}_{2}\) fluxes in weeks 2, 4, 6, 7, and 8 were significantly greater than CO\({}_{2}\) fluxes in week 1 (\(p<0.05\)). CO\({}_{2}\) fluxes in week 2 were significantly greater than CO\({}_{2}\) fluxes in weeks 12 and 17 (\(p<0.05\)). Finally, CO\({}_{2}\) fluxes in week 8 were significantly greater than CO\({}_{2}\) fluxes in weeks 12, 16, and 17 (\(p<0.05\)). Mean instantaneous and mean cumulative fluxes were statistically similar in across all treatments when tested with the linear mixed model, but CO\({}_{2}\) fluxes generally were lower in the hydrochar treatment plots. Mean instantaneous fluxes were 0.246 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\) in the hydrochar-treated soils (0.198 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\) in site A, and 0.294 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\) in site B), 0.340 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\) in the urea-treated soils, 0.342 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\) in the digestate-treated soils, and 0.374 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\) in the control treatment soils. The average cumulative CO\({}_{2}\) fluxes across all four blocks in each treatment were: control (1068.21 mg m\({}^{-2}\)), digestate (977.24 mg m\({}^{-2}\)), hydrochar (702.20 mg m\({}^{-2}\)) and urea (970.11 mg m\({}^{-2}\)).