# Smart Hydroponic Cultivation System for Lettuce
## 2 Materials and Methods
### Monitoring and Control System
The three remaining lettuces from each treatment were used to determine the proximal composition of the moisture percentage, protein content, fat, fiber, ash and carbohydrate levels. For the analysis, samples were collected from the upper, middle and lower sections of each plant. Moisture content was determined by drying the sample at 70 \({}^{\circ}\)C in a vacuum oven until it reached constant weight. Protein content was calculated using the Kjeldahl method [41], employing a micro digester (model MDK-6, Novatech Equipos Cientificos S.A. de C.V., Naucalpan, Mexico) and a nitrogen to protein conversion factor of 6.25 to estimate crude protein. The ash content was determined through calcination in a muffle furnace (model 273, Indef S.R.L., Buenos Aires, Argentina) at an air temperature of 550 \({}^{\circ}\)C for 24 h. Total fat content was determined using the Soxlet method [42], with n-hexane as the extraction solvent. Finally, carbohydrate content was calculated by difference. For statistical analysis of the collected data, normality was first verified using the Shapiro-Wilk test. Subsequently, an analysis of variance (ANOVA) was performed to identify significant differences among the treatments used. Mean comparisons were conducted using [PERSON]'s test at a 5% significance level. Statistical procedures were performed using Microsoft Excel (version 2021), with its built-in data processing tools. ## 3 Results

### NFT Hydroponic System

The proposed hydroponic system is presented in Figure 8, where two hydroponic channels (Figure 8,A) are shown, each capable of housing up to five plants. The hydraulic pump (Figure 8,B) is responsible for delivering the nutrient solution from the tank through the hoses (Figure 8,C), while the return pipe (Figure 8,D) facilitates the recirculation of the remaining nutrient solution. Additionally, the CPVC frame (Figure 8,E) provides the necessary inclination for the system to function properly. ### Plant Growth Chamber

Figure 9 shows the plant growth chamber, where smart monitoring and control system is employed (Figure 9,A). The chamber includes a \(CO_{2}\) parts-per-million sensor (Figure 9,B), a PPF sensor (Figure 9,C), an air temperature and RH sensor (Figure 9,D), an inverter-type air conditioning system (Figure 9,E), full-spectrum LED lamps (Figure 9,F) and the developed NFT hydroponic systems: T100 (Figure 9,G), T75 (Figure 9,H) and T50 (Figure 9,I). Figure 8: Photograph of the developed NFT hydroponic system. The system consists of two hydroponic channels (A), each capable of holding up to five plants. The hydraulic pump (B) is used to drive the nutrient solution through 10 mm diameter hoses (C). The return pipe (D) allows the recirculation of the unabsorbed solution. The entire setup is supported by a CPVC structure (E). Figure 9: Developed plant growth chamber. The chamber includes: the smart monitoring and control system (A), \(CO_{2}\) sensor (B), photosynthetically active radiation sensor (C), air temperature and RH sensor (D), inverter-type air conditioner (E) and full-spectrum LED lamps (F). Also shown are the three NFT hydroponic systems used: T100 (G), T75 (H) and T50 (I). The system's operation was verified through a 26-day case study. Data for environmental variables were recorded at 5 min synchronization intervals, resulting in 29,980 entries per variable, allowing real-time tracking of their behavior. As shown in Figure 10, a responsive web application (Figure 10a) was developed to visualize environmental variables in real time through graphical representations. Likewise, an Android mobile application (Figure 10b) was designed for the same purpose. A failure alert system was implemented which sends email notifications if data transfer to the server is interrupted for more than 30 min. It is important to note that both applications allow users to modify the setpoints for environmental variables via text input fields and export historical data for further analysis and decision-making.