Abstract
Graphical Abstract
STEM is taught by Dr. Crowthers (Dr. C), and STEM 1 focuses on scientific writing and our independent research projects. We use this class to hone our skills for writing scientific papers, which includes developing abstracts, research backgrounds, methods, results and analysis, and conclusions. As a part of our STEM 1 class, we develop our own independent research project, and we apply these technical writing skills as we move through the project. STEM 1 culminates in a presentation of this project, which is representative of all the work we have accomplished so far in STEM class.
High tunnel water usage is inefficient due to the rainwater that is underutilized because of the impermeable covers and because of the severe dependence of high tunnels on underground nonrenewable sources of water. With severe fluctuations in weather patterns caused by climate change, the presence of droughts makes the inefficiency of high tunnel water usage all the more prevalent and impactful. In this project, I aimed to develop a method for collecting more rainwater off of a high tunnel by looking at different materials for a high tunnel cover.
High tunnel water usage is inefficient because of rainwater waste, and the dependence on other, usually underground, water sources.
The aim of this project is to develop a method for collecting rainwater from high tunnels.
High tunnels, which are used to extend a farmer’s growing season
(Gu, 2021), are inefficient in terms of their water usage. High
tunnels are impermeable, which results in a need for irrigation (Gu,
2021). The water for irrigating plants underneath high tunnels comes
from unsustainable underground water resources (James, 2023). In
California, along with many other places around the world, better
water resource management is needed, as aquifers have been depleted
so severely that hundreds of wells have dried up or are in danger of
drying up (James, 2023). Rainwater is underutilized as an irrigation
source because of the impermeability of high tunnels, which has
contributed to water waste and the depletion of underground water
resources.
Impact of Severe Climatic Conditions on Agriculture:
With the continual rise in carbon dioxide levels in the atmosphere around the globe, the average surface temperature of the Earth has also risen (Lindsey & Dahlman, 2023). This has paved the way for more intense and frequent climatic events (Li et al., 2021; Climate Change Is Causing Global Hunger, n.d.). These intense climatic conditions have repercussions on crop yields and the greater agricultural industry, which is further predicted to lead to economic downturns (De Winne & Peersman, 2021).
One type of the aforementioned intense disasters is droughts.
Droughts have led to economic repercussions across Russia and
Ukraine, where the reoccurring droughts have led to fluctuations in
the prices of wheat and corn all over the globe (Banerjee et al.,
2018). Another type of intense disaster that is impactful on the
agricultural industry is tropical storms. High amounts of rainfall,
caused by tropical storms, can lead to plants and soil washing away,
decreasing the crop yield for the areas where these storms hit
(Fletcher et al., 2018). Tropical storms and hurricanes can also
contribute to storm surge and the contamination of freshwater
resources with saltwater, impacting both humans and agriculture
(Fletcher et al., 2018). The impacts of intense disasters on
agriculture have an even greater effect on the world due to rising
global populations, and the need for better food resource
management.
Population Food Needs:
Around the world there is a need for better food resource
management, and more readily available healthy food options (World
Health Organization, 2019), and the agriculture industry will be one
of the factors needing to adapt to meet this need. This need for
better food resource management will continue to grow as the global
population increases towards a projected global population of 9.8
billion people in 2050 (United Nations, n.d.). Though growing food
has been made more difficult due to increased climatic disasters
(Climate Change Is Causing Global Hunger, n.d.), more food will need
to be made available in the future. Currently, there are farming
practices, including the usage of high tunnels, that allows for more
food to be produced, however, these farming practices are not always
efficient in resource usage, highlighting an area for improvement.
High Tunnels:
High tunnels, or hoop houses, are used to extend the yearly growing season for at least 4-6 weeks (Gu, 2021), allowing for a greater amount of food to be produced. They are comprised of steel or plastic structures, on which a plastic covering lies (Gu, 2021). High tunnels provide protection to plants against UV radiation and cold and frost at a relatively low cost (Gu, 2021). The tunnels are impermeable and require other forms of irrigation besides rain (Gu, 2021). Usually, plants grown within high tunnels are watered through drip irrigation systems, small sprinkler systems, or hand watering (Majumdar, 2018), with water often sourced from underground water resources. The impermeability of the plastic covering leads to issues with water waste, as any rainwater that would generally soak into soil is unable to and just washes away.
Some crops typically grown under high tunnels include tomatoes,
cucumbers, and strawberries (Supriya, 2021; JSS Advantage - February
2010, 2010; RFAgriculture, 2020; Gu, 2021), which all require large
amounts of water for proper growth. Tomatoes and strawberries are
most commonly grown in California (Guan et al., 2018; USDA, 2020),
and both require about 1-2 inches of water per week to grow properly
(Cohrs, 2023; Lobo, 2023; Rhoades, 2021; Growing Berries, n.d.). Due
to these plants being grown underneath high tunnels, even if
California got enough water during the year, which this year it did
at an average of 1.85 inches (California Water Watch, 2023), the
plants would not receive any of it. The inability of water to pass
through the high tunnels to assist in the irrigation of plants
highlights an issue revolving around water waste and agricultural
irrigation practices.
Aquifers:
In many agricultural areas, water is drawn from aquifers for irrigation purposes, and this can also lead to a multitude of problems with water resource sustainability (James, 2023). For example, in California, water has been pumped out of aquifers to irrigate agricultural land for at least 20 years, and this has caused the subsequent depletion of waters within the aquifers (James, 2023). In dry years, reliance on these aquifers for irrigation purposes is higher, and when this reliance stays high for a long time, the aquifers are eventually depleted of water and can collapse (James, 2023; Desert Research Institute, 2023). Aquifer depletion can also lead to subsidization, which is the gradual sinking of land, which can be a major problem for agriculture, infrastructure, and coastal areas that are at risk from flooding (Desert Research Institute, 2023). This presents a need for a water management system that does not rely on aquifers to water crops.
In this project, different materials that could be used on a high tunnel were tested. This testing was done to try and find a material that would reduce splashing, which would then allow the researcher to develop a material that would reduce rainwater loss off of a high tunnel. Three rounds of testing were conducted on different materials.
In the first round of testing, 5 materials representing commercially used covers were tested. 500 mL of water were dropped from a height of 67.5 inches, and a 14 by 13 by 2 inch plastic container was used to collect water. The coverings were placed on a wooden structure that was in the form of a pentagonal prism.
In the second round of testing, 3 materials considered to have characteristics similar to those seen in nature were tested. These materials were compared against the most successful material from the first experiment, which was also tested. 6.05 L of water were dropped onto each of the materials 5 separate times. The materials were placed onto a scaled high tunnel structure that was 29 inches long by 24 inches wide by 24.5 inches tall and clamped down. Water was dropped from a height of 65 inches.
It was found that one of the materials in the previous test
performed well, but was too heavy; therefore, in the final round of
testing, a piece of the same material with a half-thickness was
tested. The material was placed on the scaled high tunnel structure,
and 6.05 L of water were dropped on the cover. Using the data
gathered from the different tests, a proposal for reducing rainwater
loss off of high tunnels was developed.
Figure 1: Graph of the average water collected per material type for materials inspired by nature. 6.05 L of water was dispensed onto a scaled high tunnel model 5 times for each material, and the amount of water collected for each material was measured. The data points for each of the individual materials were averaged together. The PVC loofah mat allowed for the collection of the most amount of water on average.
Figure 2: Graph of the distribution of water saved per cover type. 6.05 L of water was dispensed onto a scaled high tunnel model 5 times for each material, and the amount of water collected for each material was measured.
Figure 3: Bar graph showing the average water collected for the different thickness PVC loofah mat. 6.05 L of water was dispensed onto a scaled high tunnel model 5 times for each material, and the amount of water collected for each material was measured. A Mann-Whitney U test was conducted (U = 10), and the U value was above the critical U value of 2.
Figure 4: Graph of the distribution of water saved for the different thickness PVC loofah materials. 6.05 L of water was dispensed onto a scaled high tunnel model 5 times for each material, and the amount of water collected for each material was measured.
Four different materials were tested, these being 3 mm polyethylene, a clear plastic mat with conical spikes, a PVC loofah mat, and a clear plastic mat with grass-like protrusions (N=5). Figure 1 shows the average water collected by each of the different materials. The 3 mm polyethylene cover had the lowest average amount of water collected, at 5.05 L out of 6.05 L on average. The PVC loofah mat had the highest amount of water collected at 5.97 L out of 6.05 L on average. Compared to the 3 mm polyethylene material, the average amount of water that the PVC loofah mat collected was statistically different (*p<0.05), meaning that the PVC loofah mat would be viable to use in the next section of the project.
Within the same data set, figure 2 shows the distribution of data for each of the materials tested. As seen in figure 2, the 3 mm Polyethylene had the biggest distribution in the data. The median of the PVC loofah mat box plot was located closer to the lower half. This may indicate the presence of an outlier. The ranges for all the materials besides the 3mm polyethylene were more consistent in terms of water collection.
Due to the weight of the PVC loofah mat, which was considered to be un-ideally heavy for high tunnel usage, a PVC loofah mat with half of the thickness was tested (N=5). As seen in figure 3, the average amount of water collected by the half-thickness PVC loofah mat was 5.90 L out of 6.05 L. This average was less than the average amount of water collected for the normal thickness PVC loofah mat but was similar enough that a statistical test was conducted. After conducting a Mann-Whittney U test, there was not convincing evidence at the α=0.05 level that the regular thickness PVC loofah mat was statistically different from the half thickness PVC loofah mat.
The objective of this project was to develop a method for reducing rainwater waste off of high tunnel structures and improve rainwater collection abilities off a high tunnel. To do this a scaled high tunnel structure was created, and different materials were tested. These materials were tested to find a material that would reduce the amount of water lost due to splashing, as this would assist in reducing water loss off high tunnels. Materials similar to commercially available high tunnel covers were first tested, and then materials similar to natural phenomena were tested. After the testing of the materials similar to natural phenomena was completed, the PVC loofah mat was found to reduce water loss the most compared to the 3 mm polyethylene cover type (*p<0.05). These results suggest that a flexible or soft material may be able to reduce water loss through reducing the impact force of the water droplets. The results also suggest that a material with an uneven surface could reduce the amount of water lost, as all three of the materials had uneven surfaces and were statistically different from the 3 mm polyethylene material (*p<0.05, **p<0.05, ***p<0.05). The PVC loofah mat was determined to be too heavy for high tunnel usage, so a half-thickness PVC loofah mat was then tested. After using a Mann-Whitney U-test because of the small sample size and irregular distribution of the data, it was found that there was not convincing evidence at the α=0.05 level that the amount of water collected for the two materials was not the same. Because of these results, a proposal for a material that would reduce rainwater loss off of high tunnels was developed. This material would be similar to the half-thickness PVC loofah mat; however, the material would be transparent or semi-transparent to allow for light to pass through to the plants. The material would be laid on top of the normal high tunnel cover, and gutters would be attached to the sides of the high tunnel to collect the rainwater and bring it to a storage container. In the future, the material could be improved because water can get stuck within it. It might also be worthwhile to consider testing the material on different styles of high tunnels in the future, to see if the material works similarly. As it is, the material proposed is designed to be used for high tunnel agriculture, but it could be applied to other areas where water is lost due to splashing, such as in an arid area where water conservation is needed and collecting as much rainwater as possible is important.