## 3 Results
### Construction  
The lysimeter cultivation tank consisted of bent and welded stainless steel plates. Inside it, horizontal bars were arranged as parallel rings to increase the resistance and reduce the deformations of the plates. The internal dimensions of the cultivation tank were 1000 mm \(\times\) 600 mm, with a depth at the ends of 300 mm and in the centre of 350 mm. The lysimeter dimensions were determined to align six lettuce plants in a 60-degree staggered pattern with a 330 mm plant spacing (Figure 1). An inverted truncated pyramid shape of the cultivation tank bottom facilitates the drainage and avoids water accumulation. The drained water outlet was automatically controlled by an electrovave placed in an orifice at its deepest point.  
A support structure was placed under the cultivation tank, which transmitted the loads to the foundation base structure. In the prototype, 40 \(\times\) 40 mm and 2 mm thick profiles were welded together (Figure 2b (B)). The ends of the internal structure supports were fixed to L-shaped pieces and welded to the foundation base. This design reduces the weight during assembly and facilitates maintenance operations. Inside the main structure, the cultivation tank laid on an internal support structure where the five load cells are located: four for the cultivation tank and one for the water collector vessel drained by the cultivation tank. Under the cultivation tank was located the drainage system formed by a cylindrical stainless-steel tank with a curved bottom to facilitate water evacuation, whose function was to collect the drainage water for later measurement.  
Figure 4: Three-dimensional view of the results obtained in load combination 1 for the walls of the main structure of the removable weighing lysimeter. (**a**) Resulting displacement (mm) and (**b**) Von Mises equivalent stress (MPa).  
Figure 5: Three-dimensional view of the results obtained in load combination 1 for the walls of the base of the removable weighing lysimeter. (**a**) Resulting displacement (mm) and (**b**) Von Mises equivalent stress (MPa).  
The load cells were installed according to the manufacturer's specifications on a smooth supporting surface. The load cells were supported by a steel structure on which the stainless-steel cultivation tank is located. The load cells are screwed to steel cylinders of 30 mm diameter. The cylinders were welded to the support structure of the cultivation tank. To prevent the damage of load cells due to accidental overloads, a screw was installed under each of them. These screws provided end stops to the load cells movements.  
The main structure was a buried container in contact with the ground, with free internal dimensions of \(1030\times 630\times 660\) mm (length \(\times\) width \(\times\) depth). The cultivation tank was placed inside with a \(15\,\mathrm{mm}\) separation gap on each side (Figure 2b (C)). In order to improve the support capacity of the main structure with the ground, the structure was provided with a base as a shallow foundation. The loads were transmitted in a way that was acceptable to the ground (Figure 2b (D)). In addition, this base ensured a support surface with which the main structure could be levelled facing possible ground settlements. Heavy rains or the increase of the phreatic level could flood the main structure. To avoid that, the water was extracted by a submersible pump connected to a flexible rubber tube. This pump system was designed to conduct the drained water to the exterior and pour it off a minimum distance of 4 m from the lysimeter. This extracted water did not interfere with the growth of plants around the lysimeter.