# Controlled Drainage Effectiveness in Reducing Nutrient Outflow in Light of Climate Changes
## 3 Results
### Effect of CD on Quality Drainage Outflow  
The results of the analysis of the NO\({}_{3}\)-N loads carried out indicate a significant reduction in the amount of carried loads when CD began on 1 March in all scenarios for the three climate models (Table 6). This confirms the classification of this date into two homogeneous groups a and b with a range from 0.11 to 0.51 kg ha\({}^{-1}\). Also, the lowest values of loads were shown for the 15 March date for the MPI model, with a range from 0.42 to 5.58 kg ha\({}^{-1}\). The CD technique that started on 1 March reduced load leaching by an average of 24.34, 22.79, and 19.06 kg ha\({}^{-1}\) compared to FD in wet years for the GFDL, MPI, and UKESM models, respectively. In contrast, in normal years, the average load was 14.33, 19.74, and 21.93 kg ha\({}^{-1}\), and, in dry years, it was 13.36, 17.25, and 14.36 kg ha\({}^{-1}\) for the GFDL, MPI, and UKESM models, respectively. The start of withholding outflow after the 1 April and 15 April dates did not reduce the amount of NO\({}_{3}\)-N loads leached. Figure 8: Reduction in drainage outflow for different variants of CD practice under wet (**A**), normal (**B**), and dry (**C**) years for GFDL, MPI, and UKESM climate change models (bar charts show the average values and SD; different letters indicate significant differences (\(p\leq 0.05\)) between variants of drainage according to the Tukey test). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{\
\begin{tabular}{c} **Drainage** \\ **Variants** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Initial GWT** \\ **(cm b.s.l.)** \\ \end{tabular} } & \multicolumn{4}{c}{**Head NO\({}_{3}\)-N (kg ha\({}^{-1}\))**} \\ \cline{3-6}  & & \multicolumn{2}{c}{**Wet**} & \multicolumn{2}{c}{**Normal**} & \multicolumn{2}{c}{**Dry**} \\ \hline \multicolumn{6}{c}{GFDL} \\ \cline{3-6} \multirow{3}{*}{FD} & 40 & 31.93 & l & 21.64 & g, h, i, j & 20.59 & j, k, l, m \\  & 60 & 24.90 & h, i, j, k, l & 14.70 & e, f, g, h & 13.72 & e, f, g, h, i, j, k, l \\  & 80 & 17.35 & e, f, g, h, i & 7.45 & a, b, c, d, e, f & 6.61 & a, b, c, d, e, f, g \\ \hline \multirow{6}{*}{CD} & 40 & 0.46 & a & 0.40 & a, b & 0.41 & a \\  & 60 & 0.39 & a & 0.27 & a, b & 0.27 & a \\  & 80 & 0.30 & a & 0.15 & a & 0.14 & a \\ \cline{2-6}  & 40 & 24.45 & h, i, j, k, l & 17.82 & f, g, h, i & 17.66 & h, i, j, k, l, m \\  & 15.03 & 60 & 17.69 & e, f, g, h, i & 11.17 & a, b, c, d, e, f & 11.01 & d, e, f, g, h, i, j, k, l \\  & 80 & 10.59 & a, b, c, d, e, f & 4.35 & a, b, c, d, e & 4.23 & a, b, c, d, e \\ \cline{2-6}  & 40 & 31.32 & l & 20.78 & g, h, i, j & 20.52 & i, j, k, l, m \\  & 1.04 & 60 & 24.29 & h, i, j, k, l & 13.86 & d, e, f, g & 13.66 & e, f, g, h, i, j, k, l \\  & 80 & 16.76 & d, e, f, g, h, i & 6.65 & a, b, c, d, e, f & 6.56 & a, b, c, d, e, f \\ \hline \multirow{6}{*}{CD} & 40 & 31.63 & l & 21.64 & g, h, i, j & 20.59 & j, k, l, m \\  & 60 & 24.61 & h, i, j, k, l & 14.70 & e, f, g, h & 13.72 & e, f, g, h, i, j, k, l \\  & 80 & 17.06 & e, f, g, h, i & 7.45 & a, b, c, d, e, f & 6.61 & a, b, c, d, e, f \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Average NO\({}_{3}\)–N (kg ha\({}^{-1}\)) loads for wet, normal, and dry years for GFDL, MPI, and UKESM climate change models. Figure 9: Surface runoff for FD and different variants of CD practice and GFDL, MPI, and UKESM climate change models under wet (**A**), normal (**B**), and dry (**C**) years (bar charts show the average values and SD; different letters indicate significant differences (\(p\leq 0.05\)) between variants of drainage according to the Tukey test). Holding the outflow on the date of 1 March significantly reduced the amount of PO4-load lifted from the site compared to FD. Two homogeneous groups, a and b (Table 7), were determined for each scenario, considering this date for all climate models. For the MPI model, significantly lower loads were also obtained on the 15 March date.