## 2 Materials and Methods
### Irrigation Scheduling Management
#### 2.2.3 Irrigation Scheduling Based on the Monitoring of Plant and Soil Water Content (PlaSoMan)  
A smart irrigation water system was utilized based on the monitoring of plant water status and moisture soil level, as shown in Figure 2. The first step involves the evaluation of the water status of the plant through the determination of the CWSI (Crop Water Stress Index). To this end, three infrared temperature sensors (Melexis Technologies NV, Belgium) were used to detect the canopy temperature and placed in three representative areas of the field. Each infrared temperature sensor was positioned parallel to the plant rows 0.5 m above the canopy, pointed at 45\({}^{\circ}\) toward the tomato rows, and the canopy temperature was recorded every 15 min. The weather station placed next to the experimental field measured relative humidity, air temperature, solar radiation, wind speed, and precipitation every 15 min. All variables were measured at 2 m height. Crop temperature, together with the air temperature and humidity values, were used by the system to calculate CWSI as follows [15]:  
\[\text{CWSI}=\frac{\left(\text{T}_{\text{c}}-\text{T}_{\text{a}}\right)-\left( \text{T}_{\text{c}}-\text{T}_{\text{a}}\right)_{\text{LB}}}{\left(\text{T}_{ \text{c}}-\text{T}_{\text{a}}\right)_{\text{UB}}-\left(\text{T}_{\text{c}}- \text{T}_{\text{a}}\right)_{\text{LB}}}\]  
where T\({}_{\text{c}}\) is the canopy temperature (\({}^{\circ}\)C); T\({}_{\text{a}}\) is the air temperature (\({}^{\circ}\)C); (T\({}_{\text{c}}-\text{T}_{\text{a}}\))\({}_{\text{LB}}\) term corresponds to non-water-stressed baseline (lower baseline), and (T\({}_{\text{c}}-\text{T}_{\text{a}}\))\({}_{\text{UB}}\) term corresponds to stressed crop condition (upper baseline). Both lower baseline and upper baseline were estimated using the following two empirical equations [15]:  
\[\left(\text{T}_{\text{c}}-\text{T}_{\text{a}}\right)_{\text{LB}}=\text{A}+ \text{B}\;\times\;\text{VPD}\;(\text{lower baseline})\]  
\[\left(\text{T}_{\text{c}}-\text{T}_{\text{a}}\right)_{\text{UB}}=\text{A}+ \text{B}\;\times\;\text{VPG}\;(\text{upper baseline})\]  
where VPD (kPa) is the vapor pressure deficit assuming leaf temperature equal to air temperature; A is the intercept and B is the slope of the linear regression ofagainst VPD. In our experimental conditions, A was equal to 1.54 \({}^{\circ}\)C and B was equal to \(-\)1.95 \({}^{\circ}\)C kPa\({}^{-1}\). VPG (kPa) is the difference between the saturation vapor pressure evaluated at Ta and air temperature plus the intercept (Ta + A). VPD and VPG were calculated using Ta and RH [16]. The CWSI values range between 0 (optimal crop water status) and 1 (high crop water stress). The CWSI threshold to start irrigation has been fixed at a value equal to or higher than 0.3 [17]. At this threshold, the system evaluates the soil water content to calculate the irrigation volume to apply to the crop. To make this, frequency domain reflectometry (FDR) sensors were placed at four soil depths (0.15, 0.3, 0.45 and 0.6 m) in the same three representative areas used for leaf temperature monitoring. The soil moisture data were stored and processed by the software. The software also considers the soil hydrological value of field capacity (Table 1) and it can calculate the required irrigation volume to bring the soil to its field capacity value. The new system conducts a soil water content check even when the CWSI is below 0.3 (good plant water status). If the soil moisture value falls below the fixed threshold of 40% of the available water depletion, the necessary irrigation volume is calculated to bring the soil to its field capacity value. Thus, irrigation started every time the CWSI was equal to or higher than 0.3, or whenever the soil moisture was equal or lower than the fixed threshold. This double-checking of plant water status and soil moisture level represents the innovativeness of the system as it allows irrigation to start even in situations of crop water stress regardless of the soil water conditions.