4.1 Key findings
The flow rate of the water was relatively fast, achieving a timing of 2.8 seconds when it travelled from the top of the vertical farm to the bottom. This means that the sponges can be soaked with nutrient-infused water within seconds.
Sponges are also capable of holding and preventing water from evaporating at a faster rate, as compared to water which is uncovered. This ensures that retention of water is made better and the plants have more time to absorb the water.
Plants growing upwards is an indicator that it is taking in water, meaning that the sponges are a suitable medium for cultivating the plants.
We have found that the plants are surviving in our system. However, there are plants that are withering. We have also found that the soil constant has a better growth rate than the plants cultivated in the vertical garden. The plants on the uppermost row of the setup have also varying heights, meaning that negative phototropism does not directly affect the growth of our plants.
4.2 Explanation of key findings
This could be so due to the fact that the vertical garden is upright, hence the water is pulled down with the highest gravitational pull possible. This allows an average flow rate of 0.159m/s, which allow the soaking of the sponges to occur at a faster rate. Furthermore, the pump is turned on for 30 minutes each time, hence the time given for the absorption of water by the sponges in sufficient and that the plants will efficiently absorb the nutrient-infused water.
Since sponges are able to retain water for a longer period by preventing faster evaporation, as compared to open water, sponges are an optimal medium in substitution of soil for our vertical garden. The results shown mean that the plants would have sufficient time to absorb the water, allowing them to take in what is required. The results also meant that the sponges were capable of holding the water until the next time the pump is automatically turned on by a timer.
Over a period of 4 days, we have found out that majority of the plants in the vertical garden are growing, with the exception of two plants that are wilting. This could be caused by a lack of oxygen to the roots or overcrowding of a single sponge. Nutrients absorbed by a single stalk would then be not as abundant as compared to other sponges with fewer stalks. The soil constant also has a better growth rate than the vertical garden. This may be caused by the easily available nutrients present in the soil, whereas our system has nutrients that have to be replenished daily and that the amount of nutrients present in the water may be rather inaccurately added. This would then cause stunted growth, as seen when comparing the vertical garden and the soil constant. The plants on the uppermost row are seen to be growing, with some growing better than those found in the middle or the bottom. Negative phototropism does not seem to have any adverse effects on the growth and other factors such as the amount of oxygen circulating around the roots and the number of stalks per sponge play a role too.
4.3 Evaluation of engineering goals
We are able to construct a vertical garden with minimal and conveniently available resources, such as acrylic, sponges, plastic and equipment such as saws and drills. It also incorporates automation of lighting and watering through the use of timers which function to the preset interval. Wastage of water is negligible as all the water is reused due to it being collected in a container holding the system. It is also mixed with nutrient solution and recycled with the help of a pump. The current design takes up an area of only 759cm2. The plants are also growing similarly to those growing within soil, as seen with the soil constant. It can be placed indoors, with protection from the elements. It can fit on a tabletop, testimony that it takes up little space and land compared to conventional methods such as horizontal farming.
4.4 Areas for improvement
Our system has a flaw which may affect the growth of our plants. The lighting system is unable to spread out equally, especially when reaching out to the uppermost layer. This would cause an uneven distribution of light to the plants, resulting in non-uniform growth. Our alternative would be to acquire another similar LED lamp and position the lamps at the top and bottom of the vertical garden. Precautions have to be taken to ensure that they remain out of contact with water, possibly by covering them with waterproof materials.
We are currently keeping the acrylic box in place via wood planks, this is highly unstable because the wood we are using is not laminated, the acrylic is also connected to the wood via hot glue. Being in contact with water, the wood may start to rot or the glue may wear out and give way, causing the the structure to fall and fail. We can instead choose other materials that are waterproof and better ways of adhesion (nails and screws).
We are unable to measure the water in the tank currently, and we are only using an estimate to refill the amount of water. We could improve the system by placing a sensor/detector to monitor the water level of the tank, to keep a constant amount of water at a time. This also allows us to add an exact amount of nutrient solution into the water to ensure there is no excess or lack of nutrients which may potentially stunt the growth of the plants.
We are currently using a pump that occasionally does not keep a constant flow through the pipes. We could improve on this by purchasing a better pump that will help to ensure that each outlet will receive a constant/steady and equal flow of water. Problems we face now include excessive bubbles in the water and irregular flow.