# HYDRUS-1D Simulation of Nitrogen Dynamics in Rainfed Sweet Corn Production
## 2 Material and Methods
### Field Experiments and Measurements
#### 2.1.3 Measurements  
In the experimental field, rain-gauge, 5 TE sensors with EM 50 data logger, ET-gauge, observation well, Parshall Flume RBC and soil water samplers were installed as shown in Figures 1 and 2. Data-logging rain-gauge and ET-gauge were used to record rainfall and evapotranspiration. The water drainage as a result of runoff was rescored using Parshall Flume RBC with CR200X logger (SZ-CR200X/7070). The 5 TE sensors along with EM 50 data logger were installed at 20, 40, 60, 80, and 140 cm depths to monitor soil water content. The climate data (i.e., temperature, humidity, and wind speed) were obtained from the adjacent meteorological station. The reference evapotranspiration (\(ET_{0}\)) was computed through the Penman-Monteith equation [24] using available soil, crop, and climate data. Then, the crop evapotranspiration (\(ET_{c}\)) was calculated as a product of the reference evapotranspiration (\(ET_{0}\)) and the crop coefficient (\(K_{c}\)) under normal conditions [24]. The Kc values for the early, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Depth (cm)** & **Clay \%** & **Silt \%** & **Sand \%** & **Textural Class** & **Bulk Density** & **Conductivity** \\
0–20 & 65.36 & 9.79 & 24.84 & Clay & 1.36 & 12.86 \\
20–40 & 53.28 & 15.24 & 31.45 & Clay & 1.39 & 12.43 \\
40–60 & 58.66 & 13.12 & 28.23 & Clay & 1.31 & 12.78 \\
60–80 & 70.20 & 20.22 & 09.58 & Clay & 1.22 & 18.11 \\
80–140 & 71.74 & 18.03 & 10.23 & Clay & 1.24 & 17.56 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical properties of the soil in the experimental field at Malaysian Agricultural Research and Development Institute (MARDI). \begin{table}
\begin{tabular}{c c c} \hline \hline
**First Season (2018)** & **Second Season (2018)** & **Agricultural Activities** \\ \hline \multirow{4}{*}{16 February} & \multirow{4}{*}{5 September} & \multicolumn{2}{c}{Basal fertilizer application} \\  & & (60 kg N\(\cdot\)ha–1) NPK 15:15:5; Sowing of sweet corn (10 kg of seed\(\cdot\)ha–1) \\ \cline{3-3}  & & & Second fertilizer application (25 kg N\(\cdot\)ha–1) \\ \cline{3-3}  & & & Third fertilizer application (24 March 10 October (25 kg N\(\cdot\)ha–1) \\ \cline{3-3}
5 April & 21 October & Fourth fertilizer application (10 kg N\(\cdot\)ha–1) \\ \cline{3-3}
3 May & 15 November & Harvesting \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Details of agricultural activities in the experimental field at MARDI during two sweet corn growing seasons. development, mid and late stages of sweet corn were taken as 0.4, 0.8, 1.15 and 1, respectively [25]. Observation wells were installed to monitor the groundwater table. The water table fluctuated around 150 cm during rainfall as shown in Figure 3.  
Figure 1: Field layout of equipment installed for investigation of water and Nitrogen (N) balance components. Figure 2: A view of the installation of different equipment in the field. During the crop growing season, water samples of surface runoff were collected when rainfall events occur to predict the nutrient losses from the field. Nutrients loss due to runoff was calculated by multiplying the values of NH4+-N and NO3--N with water flux. Soil water samplers (SWS) that consist of porous ceramic cups, were used to collect soil solutions every week throughout the growing season. The SWS were installed at 20, 40, 60, 80 140 cm depths in plant rows (Figure 4) and evacuated to about 80 kPa with the help of a vacuum pump with a tensiometer to get a sample every time. Finally, the concentration of NH4+-N and NO3-N were analyzed following Standard and Industrial Research Institute of Malaysia (SIRIM) procedure at United Plantations Laboratory, Teluk Intan, Perak. The cumulative N leaching at 60 cm depth was calculated by multiplying N concentration with corresponding water fluxes at 60 cm depth and integrated to the entire growing period. The nutrient losses were calculated from the equation given as [26].