# HydroLab: A Module for the Investigation of Fertigation Strategies in Hydroponics
## 2 State-of-the-Art  
In the literature, several studies can be found that focus on test benches for investigating technological recommendations related to irrigation and fertigation strategies. In this section, these approaches are illustrated, outlining how they differ from the one proposed in this work. [PERSON] et al. [16] constructed an A-frame hydroponic structure to conduct their experiment, which included five distinct treatments replicated four times. The main focus of the study was to assess the impacts of different substrates on the physiological growth of lettuce plants. However, it is worth mentioning that the test bench was not located inside a _greenhouse_, which means that the microclimate surrounding the plants could not be controlled. As a consequence, the obtained results were highly influenced by the external environment, limiting the development of technological recommendations. Therefore, only studies conducted in greenhouses are considered. Next, various works related to the proposal of test benches for investigating _irrigation strategies_ are presented. [PERSON] et al. [17] conducted an experiment to assess the yield, width, and length of lettuce leaves under different irrigation configurations. Specifically, irrigation tape was installed at various depths: on the surface and at subsurface depths of 10, 15, and 20 cm. Lettuce plants were cultivated in plastic containers filled with sandy clay loam soil. The same time-based irrigation (i.e., periodic irrigation) was applied across all four depths, ensuring a controlled environment for the experiment. It is important to note that the proposed test bench allows for the investigation of irrigation tape installed at different depths. However, it does not facilitate the exploration of various irrigation strategies based on different scheduling events. [PERSON] and [PERSON] [18] propose an automated irrigation system capable of maintaining a desired level of volumetric water content (VWC) in the substrate of potted plants. Dielectric moisture sensors were employed to measure VWC every 20 min. When the measured VWC felt below the set point, the controller activated a solenoid valve to initiate irrigation. The effectiveness of the proposed irrigation system was evaluated through the cultivation of 16 independent groups of plants, each with a unique set point value. However, the authors did not utilize it as a test bench to provide technological recommendations. [PERSON] et al. [19] conducted a study to examine the effects of time-based irrigation compared to dielectric sensor-based irrigation. The experiment involved placing pots on 1% sloped PVC troughs, with each trough dedicated to a specific treatment. The cultivation of green beans was used to compare three treatments with different set points of VWC, along with a treatment involving time-based irrigation. It is important to note that in contrast to the approach proposed in our work, authors incorporated fertilizers directly into the substrate rather than injecting them into the irrigation system for fertigation purposes. Although [PERSON] and [PERSON] [18] and [PERSON] et al. [19] proposed versatile test benches, their focus remained on the investigation of irrigation strategies. Consequently, we will next analyze works that specifically address _fertigation_. [PERSON] et al. [20] carried out an experiment to compare the effects of two substrates on tomato cultivation: (i) texzontle and (ii) a mixture of texzontle with vermicompost. The irrigation volume and frequency were determined based on the water retention capacity of texzontle, and an automated system was used to deliver the nutrient solution to the plants. Each treatment, including a control group, consisted of 12 plants, resulting in a total of 36 plants for the experiment. It is important to note that while the experiment focused on comparing two substrates, the fertigation strategy remained consistent across all treatments. [PERSON] et al.