## 3 Experimental Results and Discussion
### Sensor Data Analysis
#### 3.5.3 Soil Parameters  
Figure 19 shows the recorded air and soil temperature data graphs, where the green line represents the air temperature, and the blue and red lines represent the soil temperatures of Plant-1 and Plant-2, respectively. It is clear from the figure that the soil temperatures follow the air temperature. The Plant-2 soil temperature is close to the air temperature, while the soil temperature is lower for Plant-1 than Plant-2. This phenomenon can be analyzed from the fact that Plant-1 soil is in regular soil, and Plant-2 is in fertilizer soil, and fertilizer soil tends to be warmer. Figure 20 shows the recorded soil moisture data graphs, where the blue and red lines represent the soil moisture of Plant-1 and Plant-2, respectively. It is worth noting that during the experiments, both Plant-1 and Plant-2 were watered on 7 June 2023 (15:30 h), 9 June 2023 (17:11 h), and 11 June 2023 (7:33 h). Once watered, both Plant-1 and Plant-2 receive an equal water volume. The water volume on 9 June 2023 is twice that of other days. The effect of watering on the soil moisture is clearly shown in the figure, where the soil moisture increases significantly at the watering time. Further, the effect of double water volume on the watering is shown with the very high increment of the soil moisture on 9 June 2023. Further investigation of Figure 20 shows a strange phenomenon where the soil moisture peaks slightly in the morning around 09:00 h daily, even though there is no watering. Since there is no water addition, the soil moisture should follow a trend of decreasing slowly. Therefore, the increase in soil moisture at the time is caused by a sensor reading error. This can be analyzed by referring to Figure 19, where at 09:00 h, the soil temperature increases significantly, which causes aberrant reading of the soil moisture. Figure 18: A daily air and leaf temperatures data graphs. Figure 20 also shows that the Plant-2 soil moisture is lower than Plant-1. This can be understood from Figure 19, in which the soil temperature of Plant-2 is higher than of Plant-1. The higher temperature mean more water evaporation, thus lowering the soil moisture. Figures 21 and 22 show the recorded soil moistures and EC data graphs of Plant-1 and Plant-2, respectively. The blue and red lines represent the soil moisture and EC, respectively. The figures show that the EC follows the soil moisture profile, where the soil EC increases when the soil moisture increases. The aberrant reading of soil moisture is encountered, as described earlier, which also occurs in the case of the soil EC. Figure 23 shows the recorded soil EC data graphs, where the blue and red lines represent the soil EC of Plant-1 and Plant-2, respectively. The figure shows that the soil EC is higher for Plant-2 than Plant-1. It is caused by the fertilizer soil for Plant-2, which conducts more electricity than the regular soil of Plant-1. Figure 19: Recorded air and soil temperatures data graphs. Figure 20: Recorded soil moisture data graphs. Figure 24 shows the recorded soil pH data graphs, where the blue and red lines represent the soil pH of Plant-1 and Plant-2, respectively. The figure shows that the Plant-2 soil pH is acid, which is caused by the fertilizer soil of Plant-2. The figure also shows that the data reading is noisy. The noisy data is a result of the sensor accuracy of \(\pm\)0.3 pH and the effect of the soil moisture or EC error reading, as shown in the Plant-2 soil pH on 11 June 2023 (after 21:13 h). Figures 25 and 26 show the recorded soil moisture, N, P, and K data graphs of Plant-1 and Plant-2, respectively. The blue, red, green, and purple lines represent the soil moisture, N, P, and K, respectively. The figures show that the soil N, P, and K follow the soil moisture profile. However, since no other treatment exists except watering, the soil N, P, and K should not change during five days of observation. Therefore, the soil NPK measurement using the JXCT sensor highly correlates with the soil moisture measurement.