# Impact of Subsurface Drainage System Design on Nitrate Loss and Crop Production
## 3 Results and Discussion
### Weather, Evaportanspiration, and Subsurface Drainage Flow
This trend is further supported by the data in Figure S3, which show that the nitrogen effluent concentrations from each plot in Year 3 were lower compared to the years with corn cultivation. Thus, when exclusively considering the variables of rainfall and corn cultivation, it becomes evident that the nitrogen loss during Year 4, which had the least amount of rainfall, was actually the lowest among the corn cultivation years. We extended the approach to calculating the cumulative NO\({}_{3}\)-N loads for each plot (Figure 5). Over the study period, we observed total NO\({}_{3}\)-N losses ranging from 116.0 to 278.3 kg N h\({}^{-1}\) for all plots (CS-1: 164.3, CS-2: 127.0, CS-3: 278.3, CS-4: 242.9, CS-5: 204.6, and CS-6: 116.0 kg N h\({}^{-1}\)). We found that plots with wider drain spacing of 18.3 m and 24.4 m (except CS-4) had fewer NO\({}_{3}\)-N losses (range 116.0 to 204.6 kg N ha\({}^{-1}\)) compared to plots with 12.2 m drain spacing (164.3 and 278.3 kg N ha\({}^{-1}\)). The plots with wider drain spacing had less drain flow, due to which soil retained more NO\({}_{3}\)-N.  
\begin{table}
\begin{tabular}{p{12.3 pt} p{12.3 pt} p{12.3 pt} p{12.3 pt} p{12.3 pt} p{12.3 pt} p{12.3 pt} p{12.3 pt}} \hline \hline Year & **CS-1 (12.2 m)** & **CS-2 (24.4 m \(\times\) 1.1 m)** & **CS-2 (24.4 m \(\times\) 1.1 m)** & **CS-3 (12.2 m \(\times\) 1.1 m)** & **CS-5 (24.4 m \(\times\) 1.1 m)** & **CS-5 (18.3 m \(\times\) 0.8 m)** & **CS-6 (18.3 m \(\times\) 0.8 m)** & **Av  
In plot CS-4, we observed relatively higher NO\({}_{3}\)-N losses compared to CS-2 and CS-5, which are set up with the same drainage coefficient, despite showing similar total cumulative tile flow. This is due to the consistently higher nitrate concentrations in CS-4, while CS-2 showed lower concentrations at the beginning of the monitoring years (Figure S3). These differences may be attributed to the complex interaction of nitrate loss with factors such as temperature, soil moisture, soil microbial activity, snowmelt, soil types, etc. The observation also showed that the NO\({}_{3}\)-N load was higher in drainage water during the non-growing season compared to the growing season. This is apparently because most tile flow occurs during the non-growing season. The average load during the non-growing season ranged from 16.5 kg N ha\({}^{-1}\) to 42.3 kg N ha\({}^{-1}\), whereas during the growing season, the average load ranged from 4.8 kg N ha\({}^{-1}\) to 20.7 kg N ha\({}^{-1}\) (Table 4). \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Seasons**} & **CS-1** & **CS-2** & **CS-3** & **CS-4** & **CS-5** & **CS-6** & \\  & **(12.2 m** & **(24.4 m** & **(12.2 m** & **(24.4 m** & **(18.3 m** & **(18.3 m** & **Ave.** \\  & \(\times\) **1.1 m)** & \(\times\) **1.1 m)** & \(\times\) **1.1 m)** & \(\times\) **1.1 m)** & \(\times\) **0.8 m)** & \(\times\) **0.8 m)** & \\ \hline N-G Season 1 & 45.4 & 26.5 & 71.1 & 73.3 & 44.2 & 31.5 & 292.0 \\ \hline G Season 1 & 21.8 & 4.9 & 14.3 & 9.4 & 3.1 & 0.5 & 54.0 \\ \hline N-G Season 2 & 33.4 & 27.9 & 48.7 & 51.6 & 33.6 & 35.6 & 230.8 \\ \hline G Season 2 & 43.3 & 34.7 & 49.5 & 27.4 & 43.2 & 10.2 & 208.3 \\ \hline N-G Season 3 & 21.5 & 4.9 & 18.9 & 0.0 & 28.0 & 13.4 & 86.8 \\ \hline G Season 3 & 17.2 & 10.3 & 10.1 & 13.6 & 10.4 & 7.6 & 69.2 \\ \hline N-G Season 4 & 48.7 & 16.8 & 59.3 & 63.5 & 35.9 & 16.1 & 240.3 \\ \hline G Season 4 & 0.3 & 0.8 & 6.4 & 4.0 & 6.1 & 1.0 & 18.6 \\ \hline N-G Season Ave. & 34.5 & 16.5 & 42.3 & 38.4 & 32.5 & 21.7 & 186.0 \\ \hline G Season Ave. & 20.7 & 12.7 & 20.1 & 13.6 & 15.7 & 4.8 & 87.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Nitrate-N (kg/ha) load in drain flow during growing and non-growing seasons (2018–2022). Figure 5: Cumulative daily nitrate-N loss at each site from 2018 to 2022. We also performed [PERSON]'s test to identify whether the plots' mean NO\({}_{3}\)-N load in drainage water differs and if the spacing and depth influence the NO\({}_{3}\)-N load.