# Sustainable Management of Water Resources in Supplementary Irrigation Management
## 3 Results
Further, there was a strong relationship between TDR and VWC (r = 0.94, \(p\) < 0.05). In the 28 to 32 cm soil layer (Figure 5c), VWC ranged from 10.1 to 35.6% (23.8% on average). As previously mentioned for the 28 to 32 cm soil layer, TDR 30 cm-long rods were excluded from the analysis since there was a difficulty with properly inserting rods into dry soil despite preparing holes. As a result, the TDR showed unreasonable measurements. In this layer, Watermark followed the trend in SWC up to the point when  
Figure 6: (**a**) Watermark vs. Soil Water Content (SWC) 10 cm, (**b**) Watermark vs. SWC 20 cm, (**c**) Watermark vs. SWC 30 cm, (**d**) Watermark vs. SWC 45 cm, (**e**) Tensiometer vs. VWC 20 cm, (**f**) Tensiometer vs. VWC 30 cm, (**g**) Tensiometer vs. VWC 45 cm, (**h**) Time Domain Reflectometry (TDR) vs. VWC 10 cm, (**i**) TDR vs. SWC 20 cm. SWC was out of range of readily available water. At that time, the sensor readings showed 199 cbar until the first rainfall event (June 23, 6 L), when the sensor reading was reduced to 118 cbar and afterward to 21 cbar after the rainfall event on June 27, 16.6 L. Furthermore, with the drying of the soil, the sensor readings were increasing, which confirms that [PERSON] recorded the changes in SWC. Here, the best fitting relationship was described with a polynomial line (Figure 6c), and a strong negative correlation was established between Watermark and SWC at this soil depth (r = \(-0.93\), \(p<0.05\)). As for tensiometer, similar to Watermark, the sensor captured changes in SWC up to 83 cbar (readily available water) at the beginning of the study. Afterward, the SWC was below the measuring capability of the tensiometer. After the measuring scale dropped to 0 cbar, sensor service was required since the soil had become too dry and the tensiometer had lost suction. The tensiometer generally overestimated SWC (Figure 6f) and performed worse than in the 10 to 20 cm soil layer (r = \(-0.76\), \(p<0.05\)). Similar results were obtained in 30 to 45 cm soil layer (Figure 5d), where VWC ranged from 11.2 to 28.7% (28.7% on average). Watermark showed a strong negative correlation (r = \(-0.93\), \(p<0.05\)) with VWC, and in the previous soil layer, Watermark captured the changes in SWC at the beginning of the study when the SWC was high, but at this depth, SWC was not influenced by later rainfall events (2 June, 24.3 L). As a result, the Watermark readings were 199 cbar until the rainfall event on 27 June (16.6 L). Good Watermark performance in high SWC was described with a polynomial line (Figure 6d, R\({}^{2}\) = 0.93). On the other hand, the tensiometer captured the rainfall on 27 June, but immediately after that, the measuring scale dropped to 0 cbar and service was again required (r = 0.003, Figure 6g). As for the laboratory calibration, Watermark and tensiometer are best described by a linear relationship, while TDR was best described by polynomial (Figure 7). It is obvious for Watermark and TDR that the calibration is less scattered regarding field calibration. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Watermark**} & \multicolumn{4}{c}{**Tensiometer**} & \multicolumn{4}{c}{**TDR**} \\  & \multicolumn{4}{c}{**Field Calibration**} & \multirow{2}{*}{**Lab. **} & \multicolumn{4}{c}{**Field Calibration**} & \multirow{2}{*}{**Lab. **} & \multicolumn{4}{c}{**Field**} \\ \cline{2-2} \cline{6-11}
**cm** & **10** & **20** & **30** & **45** & & **20** & **30** & **45** & & **10** & **20** & \\ \hline RMSE & 3.1 & 1.7 & 2.7 & 2.8 & 1.2 & 3.2 & 4.9 & 5.0 & 2.6 & 2.1 & 2.2 &