# HYDRUS-1D Simulation of Soil Water Dynamics for Sweet Corn under Tropical Rainfed Condition
## 2 Material and Methods
### Field Experiments and Measurements
#### 2.1.2 Experimental Design and Measurements  
The research work was designed based on an intensive field experiment in real field conditions. The experiment was carried out in a 770 m\({}^{2}\) (35 m \(\times\) 22 m) field. Sweet corn 'Hibridmas' was planted during both seasons at 10 kg/ha where plant-plant (P \(\times\) P) and row-row (R \(\times\) R) space were maintained as 20 cm and 75 cm respectively. Harvesting dates were on 3 rd May and 15 th November for the first and second season 2018 respectively. The growing period for the first season (February-May 2018) was 76 days whereas for the second season (September-November 2018) it was 71 days. The total rainfall recorded during the first and second season is 75.8 cm and 79.7 cm, respectively. In the experimental field, rain-gauge, RBC Parshall Flume, evapotranspiration (ET)-gauge, and 5 TE sensors with EM 50 data logger were installed as shown in Figure 1; Figure 2. The sprinkler irrigation system was installed in the field for supplement irrigation. The amount of precipitation was measured using a data-logging rain-gauge. The amount of water drained from the field was measured by using Parshall Flume RBC with CR200X logger (SZ-CR200X/7070) whenever the runoff event occurs at the outlet point. ET gauge was used for evapotranspiration (ET) measurements. However, the evapotranspiration (ET) calculations were also made using the Penman-Monteith equation. The daily climate data required for ET calculations, i.e., temperature, humidity, radiation, and wind speed were obtained from the adjacent meteorological station. Soil moisture measuring sensors (5 TE) with EM 50 data logger was installed at 20, 40, 60, 80, and 140 cm depths. TDR-300 was used for monitoring soil moisture of topsoil. For a few samples, soil moisture measurement was done through the oven dry method in the laboratory. Laboratory and TDR-300 measurements also helped in calibrating sensor measurements. Two observation wells were installed to monitor groundwater table daily. The water fluctuated with rainfall occurring, otherwise, it remained around 150 cm. Three tensiometers were also installed at depths 20, 40, and 60 cm to observe pressure head within the root zone. Soil samples were collected from the field at different depths of 0-20, 20-40, 40-60, 60-80, and 80-140 cm to determine the physical and chemical properties of the soil. The standard pipette method was used for soil texture analysis, which is considered as a reference method to classify soil texture. Table 1 presents the percentages of sand, silt, and clay of soil. The textural analysis was performed at Soil Physics Laboratory, Faculty of Agriculture, UPM. For the chemical properties, soil samples were tested at United Plantations Laboratory, Teluk Intan, Perak. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Depth (cm)** & **Clay \%** & **Silt \%** & **Sand \%** & **Textural Class** & **Bulk Density (g cm\({}^{-3}\))** & **Conductivity Ks (cm d\({}^{-1}\))** \\ \hline
0–20 & 65.36 & 09.79 & 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 c c c c} \hline \hline
**Depth (cm)** & **pH (Airdry)** & **EC umoh/cm** & **CEC cmol (+)/kg** & **Organic Matter \%N** & **P mg/Kg** & **K mg/Kg** \\ \hline
0–20 & 6.87 & 62.80 & 5.88 & 0.14 & 55 & 74.1 \\
20–40 & 5.95 & 64.90 & 5.68 & 0.12 & 26 & 74.1 \\
40–60 & 6.20 & 45.75 & 6.49 & 0.12 & 39 & 19.5 \\
60–80 & 5.80 & 41.47 & 7.47 & 0.11 & 30 & 42.9 \\
80–1 The subsurface water collection system was designed and installed to collect water percolated below the root zone (Figure 3). The concrete block of 1 m\({}^{3}\) was buried in soil for this purpose.