# Impact of Subsurface Drainage System Design on Nitrate Loss and Crop Production
## 4 Conclusions
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & \multirow{2}{*}{**Crop**} & **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** & **(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
2018 & \multirow{2}{*}{Corn} & 10,139 & 10,660 & 10,825 & 10,962 & 10,686 & 10,892 & 10,694 \\  & \(\pm\) 2565 & \(\pm\) 2900 & \(\pm\) 1394 & \(\pm\) 2020 & \(\pm\) 2662 & \(\pm\) 2978 & \(\pm\) 130 \\ \hline
2020 & \multirow{2}{*}{Corn} & 7904 & 11,335 & 10,646 & 10,492 & 9282 & 10,816 & 10,079 \\  & & \(\pm\) 3466 & \(\pm\) 3354 & \(\pm\) 898 & \(\pm\) 1305 & \(\pm\) 3200 & \(\pm\) 2970 & \(\pm\) 758 \\ \hline
2021 & \multirow{2}{*}{Soybean} & 4649 & 5432 & 4895 & 4754 & 4831 & 4886 & 4908 \\  & & \(\pm\) 2114 & \(\pm\) 1302 & \(\pm\) 1419 & \(\pm\) 1181 & \(\pm\) 1628 & \(\pm\) 1275 & \(\pm\) 270 \\ \hline
2022 & \multirow{2}{*}{Corn} & 11,885 & 12,001 & 12,416 & 11,643 & 11,836 & 11,903 & 11,947 \\  & & \(\pm\) 2657 & \(\pm\) 2233 & \(\pm\) 1930 & \(\pm\) 1653 & \(\pm\) 2024 & \(\pm\) 1902 & \(\pm\) 287 \\ \hline
3 years & \multirow{2}{*}{Corn} & 9976 & 11,332 & 11,296 & 11,032 & 10,601 & 11,204 & 10,907 \\  & & \(\pm\) 1995 & \(\pm\) 671 & \(\pm\) 974 & \(\pm\) 579 & \(\pm\) 1279 & \(\pm\) 607 & \(\pm\) 952 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Crop yield (wet weight, kg/ha) in plots CS-1 to CS-6 (2018, 2020, 2021 and 2022). losses of the crop-growing season across all plots. On average, for each plot, 4-year NO\({}_{3}\)-N losses during the non-growing season were 30% (CS-2) to 352% (CS-6) higher than those during the crop-growing season. Corn yield data from 2018, 2020, and 2022 showed higher yields in plot CS-2, followed by CS-3, CS-6, CS-4, CS-5, and CS-1. CS-2 showed relatively less NO\({}_{3}\)-N loss with higher tile flow compared to CS-6, resulting in higher productivity than the other fields. Consequently, the comprehensive analysis suggests that a wider drainage system could potentially reduce nitrate losses and promote sustainability for both the environment and agricultural productivity. However, in fields with wider subsurface drainage, there is a risk of temporarily discharging nitrate nitrogen at high concentrations during drainage events due to the accumulation of nitrate nitrogen in the soil that cannot be drained. Therefore, to mitigate the limitations associated with subsurface drainage design, agricultural engineering measures such as actively controlling the subsurface water table or implementing additional facilities (e.g., bioreactors) seem necessary. This study highlights the substantial influence of subsurface drainage design on drain flow, nutrient losses, and crop yield, with potential for optimization to enhance crop productivity and reduce nutrient losses. However, it is clear that measures to address the inherent field uncertainty in the current research should also be considered. Specifically, further research and extended field observations--such as soil profiling, hydraulic conductivity, soil water retention curves, infiltration rates, water table fluctuations, and changes in soil moisture over time--will provide deeper insights into the outcomes of this field study. We will also consider a modeling study on how the drainage design influences hydrology and crop yield to reach a comprehensive conclusion based on various scenarios using this valuable monitoring study. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app142210180/s1](https://www.mdpi.com/article/10.3390/app142210180/s1)]([https://www.mdpi.com/article/10.3390/app142210180/s1](https://www.mdpi.com/article/10.3390/app142210180/s1)), Figure S1: 8-day evapotranspiration from 2018 to 2022 (MOIDS16A2). Figure S2: Daily drainage discharge and daily precipitation at each site from 2018 to 2022.