## 2 Materials and Methods
### Data Input of AquaCrop Model and Analysis
#### 2.4.3 Crop Data  
Local crop characteristics such as planting schedule, soursing density, effective rooting depth, flowering and crop germination were collected for model calibration.  
To obtain the CC for the input for AquaCrop, we converted the measured LAI to CC because it is the only possible method to obtain CC values during the canopy senescence phase of the crop [53]. During the canopy senescence phase, there is no simple method to measure CC directly, because green and yellow leaves are intermingled and some leaves are partly green and partly yellow.  
LAI is one of the most important biophysical parameters characterizing a canopy [60; 61; 62]. It is a key constraint for carbon assimilation and transpiration rates, which together drive the accumulation  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Horizon**} & \multirow{2}{*}{**Description**} & **Thickness** & **PWP** & **FC** & **SAT** & **TAW** & **Ksat** & \\  & & **(m)** & **(vol \%)** & **(vol \%)** & **(vol \%)** & **(mm/m)** & **(mm/Day)** & **Tau** \\ \hline
1 & Silty clay & 0.16 & 32.0 & 50.0 & 54.0 & 180 & 15.0 & 0.22 \\
2 & Silty clay & 0.14 & 32.0 & 50.0 & 54.0 & 180 & 15.0 & 0.22 \\
3 & Clay & 0.30 & 39.0 & 54.0 & 55.0 & 150 & 2.0 & 0.11 \\
4 & Clay & 0.40 & 39.0 & 54.0 & 55.0 & 150 & 2.0 & 0.11 \\
5 & Clay & 0.65 & 39.0 & 54.0 & 55.0 & 150 & 2.0 & 0.11 \\ \hline \hline \end{tabular}  
* PWP is the permanent wilting point, FC is the field capacity, TAW is the total available soil water in the root zone (mm), Ksat is the saturated hydraulic conductivity (Ksat) and Tau is the dimension drainage characteristic [31]. All values were calculated by the AquaCrop model.  
\end{table}
Table 1: Soil horizon profile characteristics.  
of primary crop productivity. Therefore, LAI is commonly used to estimate photosynthesis, evapotranspiration, crop yield and many other physiological processes in agroecosystem studies [63].  
The LAI was estimated using the LAI-2000 Plant Canopy Analyzer (LI-COR Inc., Lincoln, NE, USA). LAI measurement began for 9 training sample points (at least 2 times measurement for each point) in both training rice plots of Group A and B for calibration during the tillering stage, when the rice in Groups A and B was 19 and 12 days old, respectively. (Figure 3). The grain yield and rooting depth were determined by removing a 1 m \(\times\) 1 m frame from each plot. Before the plants were cut, the height of the plants at ground level, the time to emergence, the first day of senescence and the maturity were recorded. The rice plants were randomly measured from 9 points within the plot. The parameters contributing to plant yield were plant height, plant density and the number of rows and lines per square meter.  
The AquaCrop model uses a canopy cover (_CC_) value instead of LAI [6] to calculate the _CC_ during the growing season, the following equation was applied [32]:  
\[\text{CC}=1-\exp^{\left(-\text{K}\times\text{ LAI}\right)} \tag{3}\]  
where CC is the canopy cover, K is the extinction coefficient and LAI is the leaf area index. The values of the extinction coefficient for rice were between 0.4 and 0.7 [32]. As the K value has a rather wide range of many rice varieties, one of the purposes of this study was to find an optimal K value for the local rice in the study area. In this experiment, rice extinction coefficients of 0.4, 0.45, 0.5, 0.55, 0.6, 0.65 and 0.7 were investigated before selecting the optimum K value for the transplanted rice parameter calibration.