## 2 Materials and Methods
### N Release Rate of Bio-Based Fertilisers  
An incubation experiment was set-up to test the mineralisation rate of BBFs. Prior to the incubations, the soil was air-dried for 5 weeks and sieved through a 2 mm screen. After air-drying and sieving, the collected soil was pre-incubated at 35% water-filled pore space (WFPS) for a week. Following existing procedures [16; 17], 271 g of pre-incubated soil was mixed with AS, LFD, or KC, and calcium ammonium nitrate (CAN; 30%) that was used as a reference for the experiment. Additionally, unfertilised soil was used as a control for all treatments. After mixing the soil and respective fertiliser thoroughly, the mixture was filled in cylindrical tubes (dimensions: 18 cm height, 3.6 cm diameter) and compacted to the bulk density of 1.4 Mg m\({}^{-3}\) (10 cm compacted height). Subsequently, the WFPS of the mixture was increased to 50% using distilled water. A total of 120 tubes (4 replicates \(\times\) 5 treatments \(\times\) 6 sampling moments) were incubated for 120 days. The fertilisers were added at the dose corresponding to 170 kg total N ha\({}^{-1}\) yr\({}^{-1}\), which is the maximum permissible limit of livestock manure in the nitrate vulnerable zones [18]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Soil Characteristics**} & \multicolumn{4}{c}{**Fertiliser Recommendation**} \\ \hline  & **Potato Field** & \multirow{2}{*}{**K-Poor Soil**} & **Potato Field** & \multirow{2}{*}{**K-Poor Soil**} \\  & **Soil** & & & **Soil** & \\ \hline N total stock (kg ha\({}^{-1}\)) & 4030 & 3930 & & \\ N-supply capacity (kg ha\({}^{-1}\)) & 60 & 45 & N kg ha\({}^{-1}\) yr\({}^{-1}\) & 310 & 310 \\ C/N-ratio & 13 & 17 & & \\ Plant available S (kg ha\({}^{-1}\)) & 4 & 161 & SO\({}_{3}\) kg ha\({}^{-1}\) yr\({}^{-1}\) & 23 & 23 \\ Plant available P (kg ha\({}^{-1}\)) & 6.5 & 5.4 & P\({}_{2}\)O\({}_{5}\) kg ha\({}^{-1}\) yr\({}^{-1}\) & 0 & 60 \\ Plant available K (kg ha\({}^{-1}\)) & 500 & 115 & K\({}_{2}\)O kg ha\({}^{-1}\) yr\({}^{-1}\) & 70 & 265 \\ Plant available Ca (kg ha\({}^{-1}\)) & 190 & 55 & CaO kg ha\({}^{-1}\) yr\({}^{-1}\) & 75 & 75 \\ Plant available Mg (kg ha\({}^{-1}\)) & 300 & 115 & MgO kg ha\({}^{-1}\) yr\({}^{-1}\) & 0 & 21 \\ Plant available Na (kg ha\({}^{-1}\)) & \textless{}20 & \textless{}20 & & & \\ pH & 5.8 & 6 & & & \\ C-organic (\%) & 1.5 & 2 & & & \\ OM (\%) & 3.1 & 3.6 & Effective OM kg & & \\ Clay (\%) & 2 & 2 & & & \\ Silt (\%) & 12 & 6 & & & \\ Sand (\%) & 83 & 88 & & & \\ \hline \end{tabular}
\end{table} 
Table 2: Initial characteristics of the two soils that were used for this study and the fertiliser recommendations for growing consumption potatoes. At every 20 day interval, destructive sampling was done during which 10 g of soil per tube was mixed with 50 mL of 1M KCl, and the suspension was shaken end-over-end for 30 min, and subsequently filtered. The filtrate was measured colourimetrically by a continuous flow auto-analyser (Chemlab System 4, Skalar, the Netherlands) for the determination of ammonium (NH\({}_{4}\)+-N) and nitrate (NO\({}_{3}\)\({}^{-}\)-N). For the N incubations, the net N-release (Nrel,net, Equation (1)) and N-mineralisation rate (Nmin,net, Equation(2)) were calculated. The net N release is the difference between mineral-N available in the fertilized soil and mineral-N available in the control (Ncontrol) divided over the total N applied in the fertilised treatment (Equation (1)) [19]. \[\mathrm{N_{rel,net}(\%)}=\frac{\left(\left[\mathrm{NO_{3}^{-}-N,treatment} \right]-\left[\mathrm{NO_{3}^{-}-N,control}\right]\right)+\left(\left[\mathrm{ NH_{4}^{+}-N,treatment}\right]-\left[\mathrm{NH_{4}^{+}-N,control}\right]\right)}{ \mathrm{N_{total}}\ \mathrm{applied}}\times 100 \tag{1}\]  
The calculation of Nmin,net was carried out via subtracting net N release rate at a particular time (Nrel,net(t)) with the amount of mineral N already present in the products at the start of the experiment ((Nrel,net(t = 0)) [20] (Equation (2)).