BACKGROUND:

The Food and Agriculture Organization (FAO) of the United Nations estimates that there are more than 833 million hectares of salt-affected land around the globe. According to the FAO’s calculations, this translates to almost 8.7% of Earth’s land mass. The FAO also found that 20-50% of irrigated soil across all continents is too salty for efficient agricultural life. As a result, more than 1.5 billion people around the world experience difficulty growing food because of soil that is over-salinated (FAO, 2022).  Moreover, these challenges are further compounded by the pressing issue of climate change, which threatens to exacerbate these effects in the coming years.  

Climate change significantly harms crop growth and crop yield, and the harm it causes is projected to increase over time (Walling and Vaneeckhaute, 2020). Zhang et al. found that total arable land, which is the land used for planting crops, could decrease by 0.8-1.7% over the next 50 years as a direct result of climate change (Zhang, 2010). To mitigate these impacts, farmers have employed synthetic fertilizers to increase plant germination and growth. It is estimated that nearly 50% of the world’s population now depends on synthetic fertilizer to grow crops (Walling and Vaneeckhaute, 2020). However, as we will discuss, excess fertilizer can negatively impact soil quality by creating high concentrations of salt (Smith, 2020). When viewed in the context of an ever growing human population and the increasing impacts of climate change, it is critical to investigate ways to lessen the negative effects of soil salinization on plant germination and plant growth (FAO). 

An area worthy of investigation is whether co-planting salt-tolerant crops, such as marigolds (members of the Asteraceae plant family), together with less salt-tolerant crops enables the growth of the latter in saline soils. This process of companion planting involves planting different types of plants in close proximity to each other. Companion planting has been shown to aid pest control, increase pollination and optimize nutrient intake (Gao, 2023)  However, little is known about companion planting's effect on salt tolerance. Further, it will be critical to understand why and under what specific circumstances companion planting provides the best aid to the less salt tolerant plant.  Equipped with this knowledge, scientists will be well positioned to help farmers address new challenges with salinization and climate change around the globe.  

Soil becomes saline in a variety of ways. Dry climates and low rates of precipitation are among the most common causes of elevated soil saline levels. These factors have been exacerbated by climate change, which has caused temperatures throughout the world to rise as well as more severe and frequent storms (Center for Climate and Energy Solutions, 2023). Elevated temperatures have been shown to increase evaporation rates, which force the evaporation of moisture from soil, leaving excess amounts of salt behind (Cherlinka, 2021). Coastal surges caused by violent storms and rain have also increased soil saline levels. When ocean and sea levels rise, seawater inundates low elevation and, after ocean surges recede, the sea water evaporates. This traps salt in soil which ultimately increases soil salinity (Yu, 2021).  There are also anthropogenic, or people-based, ways in which soil becomes salinated, which include the use of salt-rich irrigation water, poor irrigation practices, or from excess amounts of synthetic fertilizer (Panagos, 2010). All of these factors have created increased salinity in soil, and their impacts are likely to add up over time.

Climate change has degraded soil throughout the world, forcing farmers to use increased amounts of synthetic fertilizer. Between 2000 and 2015, the number of people fed by crops treated with synthetic fertilizer rose from 2.7 billion to 3.5 billion (Ritchie, 2017) While synthetic fertilizer is meant to improve soil quality, leading to better crop yields, it has a negative second hand effect. Synthetic fertilizers which have high concentrations of salt, increase soil salinity wherever they are used (Ritchie, 2017). 

Salt appears naturally within soil and, at appropriate concentrations, is essential to soil quality and plant health. According to the FAO, non-saline soil has less than 3 grams of salt per liter of soil water, while highly saline soil has 12+ grams of salt per liter of soil water (FAO, 1985). In saline soil, the most common soluble salts are the chlorides and sulfates of sodium, calcium, and magnesium. At appropriate concentrations, sodium ions in saline soil can help plants absorb water and gain osmotic potential. Calcium and magnesium ions serve as essential plant nutrients. Calcium is required for structural roles in the cell walls and membranes while magnesium is required for chlorophyll production (White, 2003). Thus, if magnesium is deficient, there is a shortage of chlorophyll which results in poor and stunted plant growth. (Massoud, 1988). 

Nitrates are also found in saline soil, but far less frequently (Jacobsen, 2014). However, because of the increased use of synthetic fertilizer due to climate change, nitrate ion concentrations have been increasing. While low soil nitrate levels are necessary for plant growth, high levels are dangerous to plants. Between 2000 and 2015, the amount of people fed by foods treated with synthetic fertilizer rose from 2.7 billion to 3.5 billion (Ritchie, 2017). Hanson et al. found that excess levels of nitrates prevent plant roots from absorbing adequate amounts of water (Hanson, 2013). Chen et al. found that when nitrate supply in soil reached 0.45N/kg there was a steep decrease in plant growth (Chen, 2004). Notably, there is a lack of research on how increased amounts of nitrates in saline soil will affect plant growth in the Asteraceae plant family.

Saline soil affects plant growth and plant germination in a multitude of ways. High levels of salt in soil cause plants to become dehydrated. When plants are dehydrated, they experience osmotic stress which is an imbalance of water and electrolytes. Because water comprises approximately 70% of plants’ cell content, osmotic stress can cause critical cell damage (Southern, 2020). Osmotic stress can also affect the ability of a plant to absorb water. Kaiwen et al. found that when exposed to a ~10% Na salt concentration, Alfalfa (Medicago sativa) absorbs a significantly smaller amount of water than it would if it were exposed to normal soil (less than 4.0 Electrical Conductivity). When plants are under stress from salt, excess amounts of Na+ ions disrupt the balance of the plant’s metabolism. Salt stress affects metabolism by disrupting water balance, causing ion imbalances, inducing oxidative stress and altering hormonal regulation.  These disruptions lead to lowered metabolism, which can be characterized as weakening of the photosynthesis and respiratory processes, inhibition of the plant’s growth, and in some cases plant death (Kaiwen, 2020). 

With the ever increasing amount of synthetic fertilizer being used to treat soil around the globe (Ritchie 2017), identifying a salt-tolerant plant that can be successfully planted with other less tolerant crops in saline soil could ultimately prove to be valuable to the agriculture industry. 

Marigolds, in particular, are a reliable model organism that has similar growth processes to over 27,000 plants in the Asteraceae (Aster) plant family, including lettuce plants, daisies and dandelions (Rolnik, 2016). Marigolds are also known to be good testing plants, as they can grow in most types of soil and climates. They are also an important aromatic species with a high industrial value in their essential oil (Kumar, 2020). Last year, I studied marigold salt tolerance to assess whether marigolds are a salt tolerant crop. The purpose of studying the salt tolerance of marigolds is to advance our understanding of the salt tolerance of the many different types of Asteraceae plants (Featherstone, 2020). In their study, Comparative Study of the Effects of Different Soluble Salts on Seed Germination of Wild Marigold, Kumar et al. tested how Na2SO4 and NaCl salts affect marigold germination (Kumar, 2020). Germination, the process by which an organism grows from a seed or spore, generally takes two to six weeks (Wolny, 2018). Abiotic factors that affect germination include droughts, excess light, salinity, seed burial depth, and soil pH. (Humphries, 2018).  For the negative control, marigold seeds were placed into a petri dish of distilled water in order to establish a baseline germination percentage. For both the positive and experimental controls, marigolds were placed into 50 millimolar concentrations of their respective salts. Sodium chloride (NaCl) was chosen to establish a positive control as it is the most commonly found salt in soil. Sodium sulfate was used for the experimental arm because it was predicted to have stronger negative effects on germination percentage (Hongqiao, 2021). It was hypothesized that marigold’s high germination success rate in saline soil could correlate with future effective crop growth and development (Kumar, 2020). The goal of the experiment was to obtain the percentage of marigolds that germinated in both the 50 mM sodium chloride and sodium sulfate soluble salt solutions to determine if marigolds are a salt tolerant plant. 

In the context of saline soil, companion planting emerges as a critical strategy for sustainable agriculture. Co-planting, or intercropping, involves the simultaneous cultivation of different plants in close proximity to each other. This strategy has proven essential in tackling saline soil problems. Karakas, et al., planted strawberries, a plant known to be adversely affected by slightly or moderately saline conditions, in companion with a common purslane (Portulaca oleracea L.), a plant known to be salt tolerant, like marigolds. Karakas studied the co-planting of strawberries and purslane to see how their companionship would affect growth and overall yield. They found the companionship of strawberries with purslane increased fresh weight, dry weight, fruit average weight and the total fruit yield of strawberry plants. When strawberries were planted alone in a 60 millimolar (mM) saline soil concentration of sodium chloride (NaCl), they had an average weight of 9.8 grams at maturity. However, when they were planted in companion with purslane, their average weight was 15.74g, an increase of 5.94g. At a 90mM concentration of NaCl the coplanted strawberries had an average fruit weight of 12.65g, 7.05g higher than the strawberries planted on their own (Karakas, 2021). Karakas et al. also hypothesized that this approach optimized resource utilization, ensuring efficient absorption of water and nutrients and that co planting improves soil structure and biodiversity, further bolstering the land’s resilience against salinity.

The salt sensitivity of lettuce is a significant concern in agriculture due to its widespread cultivation and dietary importance. As a salt sensitive plant, lettuce is highly vulnerable to the adverse effects of soil salinity. Excessive salt levels in soil can disrupt lettuce’s ability to regulate water and nutrient uptake, leading to stunted growth, wilted leaves and reduced overall quality (Adhikari, 2019). This makes understanding and addressing the salt tolerance of lettuce an important consideration for both growers and consumers. 

Here in, I will present the findings of a research project where co-planting marigolds, a salt tolerant plant, with lettuce, a salt sensitive plant, will be investigated for agricultural applications.  Based on prior co planting research, we hypothesize that co planting these crops in saline soil will result in improved lettuce growth and health compared to lettuce grown in saline soil without marigolds. These results will help demonstrate the extent to which the presence of salt tolerant marigolds helps to reduce soil salinity levels, making the soil more conducive to lettuce growth. This will provide valuable information on how companion planting can lessen the effects of soil salinity.

METHODS:

Study Overview: 

The present study primarily expands on three studies. First, Kumar et al.’s report investigated the effects of saline soil on marigold germination percentage. Germinating marigolds in varying salt solutions, Kumar’s study found that marigold’s can be appraised as salt tolerant plants (Kumar, 2020). On the other hand, one crop that is very salt intolerant, or salt sensitive, is lettuce. Adhikari et. al., found that lettuce is sensitive to salinity, and that saline soil can reduce lettuce’s biomass, and overall growth (Adhikari, 2019). Lastly, Karakas et al. planted strawberry seeds, a salt sensitive plant, in companion with purslane, a salt tolerant plant (2021). Their work found that when the two were planted in companion, the strawberries' fresh weight, dry weight, fruit average weight and the total fruit yield increased (Karakas, 2021).

Originally, wild marigold seeds and butter crunch lettuce seeds were acquired and germinated in 50 millimolar (mM) sodium sulfate (Na2SO4). After germination, three of each seed type were selected and sown into nursery pots full of Miracle Grow soil. Four weeks after the seeds were planted, plant height was measured to determine whether or not marigolds were an effective companion plant for lettuce in saline soil. Preliminary studies completed on butter crunch lettuce seeds indicated that they were overly tolerant to saline soil, so the study was switched to focus on strawberries which in past studies, were shown to have very low salt tolerance (Karakas, 2021). 

Wild marigold seeds and strawberry seeds were acquired and germinated in both 50mM sodium sulfate and in tap water. First, strawberry seeds were germinated on their own in tap water, then in either normal or saline soil, to establish baseline growth for strawberries in each condition. This represented the two negative controls for the experiment because a negative control is a control group that is not exposed to the experimental treatment. Strawberries and marigolds were also germinated in tap water and then planted together in non-saline soil, to establish a baseline for their growth. This represents the positive control in this experiment because a positive control is a group in an experiment that receives a treatment with a known result and therefore should show a particular change during the experiment.   Finally, strawberries and marigolds were germinated in tap water and then planted together in saline soil to examine the effects of companion planting on the growth of strawberries in saline soil. However, due to Fast Plants seeds' extreme sensitivity to saline soil, no tangible data was collected. Because of this, the study’s focus was shifted away from strawberries and towards Fast Plants (Brassica rapa). Fast plants have shown to be sensitive to salt, while not overly sensitive to the point that they wouldn’t grow. 

It was hypothesized that the overall crop yield of Fast Plants. in saline soil will increase when planted in companion with marigolds. 

In summary, the present study aims to build upon the work of Kumar et al., and Karakas et al., while considering the results of of Adhikari et al’s study (2020; 2021; 2019). The summary plans to answer the question of how companion planting marigolds and Fast Plants in saline soil will affect the overall crop yield of Fast Plants . 

Safety Protocol:

When in the lab, a lab coat, disposable gloves, and goggles were worn at all times, to protect skin and eyes from potential injury, especially if glass were to break. Furthermore, hydrogen peroxide (MSDS), and Sodium Sulfate (Na2SO4) (MSDS), were used during the procedure that required exposed skin and eyes to be covered at all times. In all sections of the procedure where these chemicals were used, protective eyewear was worn, so as to protect eyes from potential irritation. 

Seed Care and Storage:

Marigold seeds, (The Old Farmers Almanac, B08YY4PZJL) and Fast Plants seeds ( FYZTCOCPT, B097JWM4CJ) were stored in a cool (20°C (68°F)), dark location protected from moisture. Seed packages remained sealed until use. After some seeds were used, the seed packets were properly resealed by firmly closing each bag, not allowing any air in, and placing them back into the same location (Kumar, 2020). 

Creation of 50 mM Sodium Sulfate Solution (Na2SO4)

A 50mM sodium sulfate solution was chosen because it had shown to have the most manageable effect on plant growth (Kumar, 2020). In previous studies, 25mM had been tested, however the effects of that solution had not been adverse on plant growth. Other solutions that were tested ranged from 75mM to 200mM. It was seen in all of the concentrations in that range that the effects on germination and plant growth were far too adverse. 

Anhydrous sodium sulfate (Flinn Scientific, 7757-82-6) was acquired and 1.78 g was measured in a weigh boat on a scale (Flinn Scientific, OB2143) (Kumar, 2020). The 1.78 g of Sodium Sulfate was gently poured into a 250 mL volumetric flask (Flinn Scientific, GP4035).The flask was filled with distilled tap water till the base of the flask was approximately half full and the solution was swirled by hand until all visible chunks of sodium sulfate had dissolved. After that, the volumetric flask was filled to the 250 mL mark with distilled water, covered with two pieces of parafilm, and inverted gently for 10 minutes to mix it thoroughly. This process was repeated whenever new sodium sulfate solution was needed. 

Seed Germination

Before seed germination began, to remove the risk of mold, 3 9 cm petri dishes were sterilized by measuring approximately 3 mL of of 3% hydrogen peroxide into a 3mL plastic pipette, that was then released onto a paper towel (Amazon Basics, B09HHDW53K), which was used to wipe the inside of the petri dishes thoroughly (Kumar, 2020). Marigold and Fast Plants seeds were sterilized with 3% hydrogen peroxide by soaking in the solution for 5 minutes (Kumar, 2020). 10 marigold seeds and 10 Fast Plants seeds were then placed into each of the three petri dishes. 3 250 mL beakers were filled with approximately x mL of tap water. The seeds soaked in their respective beakers for 10 minutes, as to remove any exterior bacteria or substances from the outside of the seeds (Kumar, 2020). After 10 minutes, the seeds were removed from the beakers and placed into 3 more 250 mL beakers that were filled with approximately x mL of  50 mM Na2SO4 solution. This time, the seeds were placed by a window that gets unrestricted sunlight, and were left to soak for 24 hours. This allows the seeds to sufficiently soak in the solution, furthering the adverse effects of the salt solution on the seeds growth (Kumar, 2020). 

After 24 hours of soaking, the seeds were placed directly back into their respective petri dishes. Before being placed into their petri dishes, 2 9cm Whatman’s filter paper (Carolina, 712800) were placed into each petri dish. Seeds were removed from their beakers, by pouring the salt solution over a 9 inch fine mesh sift (Webake, B07ZRJFYH1) which caught all of the seeds. Before placing the seeds into the petri dishes.  Using tweezers, seeds were carefully removed from the sift, and placed into their petri dishes. Immediately after that, in their petri dishes, the seeds were dosed with 3mL of 50 mM Na2SO4. This process was repeated once a day for seven days (Kumar, 2020). 

Lighting Setup

A 40 watt bulb was screwed into a 8.5 inch aluminum clamp lamp (VIVOSUN, B07H8G6PKX). While the seeds were germinating, the lamp was placed directly above the seeds, approximately 6 inches away from the petri dishes. Using an outlet timer (BM-Link, B00MWHQZX0), the lamp was set to 16 hours on and 8 hours off. This was done so the seeds would be subject to a normal daily light cycle (Kumar, 2020). 

The same process was repeated for the lighting of the seeds sown in soil, except that the light was placed approximately 1 foot above the top of the soil. 

Seed Germination Data Collection

Once a day, for the first seven days of growth, germination percentage was recorded into data tables. This was done by counting how many seeds had germinated and dividing it by the total number of seeds in the petri dish, then calculating the percent germination based on that. Germination percentage was tracked in Fast Plants seeds germinated per petri dish, marigold seeds germinated per petri dish, total Fast Plants seeds germinated, total marigold seeds germinated and total seeds germinated, all daily. 

Potting Setup

To set up the potting soil and containers in which the Fast Plants and marigolds grew, nursery pots (UPMCT, B08TWBZX4H) were acquired. These nursery pots have an opening diameter of five inches, a height of 4.7 inches and a bottom diameter of 3.5 inches. To create the potting mix, each nursery pot was filled with Miracle Grow soil mix to the pre-marked line near the top of the pot. Then, the soil was dumped into a plastic bin (Akro-Mils, 30224YELLO) that is 6 inches wide and 2 feet long. In this bin, all of the soil was evenly spread out and 200 mL of tap water was poured over the soil, to evenly wet it ​​(Kumar, 2020). The soil was thoroughly mixed by hand until it was evenly damp. The wetted soil was then placed back into the same nursery pot, ready to have seeds sowed into it. This process is repeated for both the negative and positive control pots.

Seed Sowing

3 germinated marigold seeds and 3 germinated Fast Plants seeds were placed into each pot, in an evenly spaced pattern, approximately ½ inch into the soil, according to package instructions. Working from left to right, one marigold seed was placed then one lettuce seed. these seeds would be placed approximately one inch apart and were placed in 2 rows of three. Adhikari et al. found that this distance was optimal for co-planting by trying different companion planting distances and seeing that there was the best growth when the seeds were one inch apart (Adhikari, 2019). Seeds were placed in rows of three, and note cards were placed directly in front of each pot, that clearly represented where each seed was placed in its pot.  The notecards indicated the general location of each Fast Plants (S) and marigold (M) seed and were marked with an S or and M. This process was repeated for all controls that had both marigolds and strawberries in them. For the pots that just had Fast Plants in them, the seeds were still sowed in 2 rows of three. 

Watering

Once a day, at approximately 9AM, both the marigold and lettuce seeds were watered. It is important that the plants get watered at a similar time each day.  A 3 mL plastic pipette was dipped into a beaker of 50 mM Na2SO4 and filled to the mark on the side of the pipette which indicated 3 mL of solution was in the pipette. Then the solution was squirted directly onto each seed in the pots. This process was repeated twice for each seed, so every day each seed was watered with 6 mL of 50 mM Na2SO4 (Kumar, 2020). For the negative control pots where Fast Plants are being treated with salt, this same process was repeated. For the other negative control pots, where Fast Plants are being treated with normal water, and the positive control, where marigolds and Fast Plants are being treated with tap water, the seeds were watered with 6mL of tap water a day. 

Plant Growth Data Collection

Once every 3 days, for four weeks after sowing the seeds, plant height was measured in centimeters. Using a ruler, the stalks of both of the marigold and lettuce plants were individually and gently pushed up against the side of a ruler, and the measurement of height in centimeters was taken. The base of the stalk can be found by tracing the plant to where it comes out of the soil. Photos were also taken to qualitatively document the plant's growth every 3 days. This data served as valuable qualitative data when analyzing growth over time. Photos were organized into digital albums, labeled by the name of the pot. For example, an album labeled “MSP1 + Na2SO4,” represents marigold and Fast Plants seeds germinated in saline soil. Photos for that pot were organized in chronological order based on pot naming.  

Data Processing

To see if there was an adverse effect on Fast Plants grown in normal soil vs saline soil, the germination percentage between the two sets of control pots was compared. An independent two tailed T-test was conducted between comparing each treatment to determine if there was a statistical difference in the Fast Plants’ growth. Lastly, germination percentage was compared between marigolds and Fast Plants grown together in normal soil or saline soil.. An independent two tailed T-test was once again conducted to examine whether or not there was a statistical difference between the total crop growth and yield. 

RESULTS AND DISCUSSION:

Figure 1: Marigolds treated in water germinated at the highest rate, a rate of 80% after day 5. Marigolds that were treated with sodium chloride (NaCl) germinated at the next highest rate, 73% of those seeds had germinated after 5 days. The seeds treated with Sodium Sulfate (Na2SO4) had the lowest germination rate, with a rate of 70%. 

Marigolds (Tagetes minuta) seeds were subjected to varying salt treatments in a germination experiment, with a negative control (marigold seeds treated with water), a positive control (marigold seeds treated in a 50 mM concentration of Sodium Chloride), and an experimental control (marigold seeds treated in a 50 mM concentration of Sodium Sulfate).

Each condition had three petri dishes. In each petri dish there were 20 seeds. 

As anticipated, the negative control exhibited strong germination, showing the highest overall germination rate and highest germination on day 1 (66.67% +/- 5.06% of seeds germinated, n = 60). In contrast, the positive control demonstrated higher initial germination (38.33% +/- 14.24%, n = 60) than the experimental group on day 1 (33% +/- 15.42%, n = 60), but lower than the negative control, consistent with established expectations by Kumar, who published that Sodium Sulfate would have the most inhibitory effects on marigold germination (2020). 

By day 5, no significant changes in germination were observed, as non-germinated seeds were removed to restore osmotic potential. Statistical analysis (independent, two tailed t-test) revealed significant differences in germination rates between the experimental group and both the negative control (p = 0.032, p<0.05) and the positive control (p = 0.036, p<0.05) by day 7, confirming the impact of salt treatment on marigold seed germination. Notably, none of the seeds removed from any treatment arm that underwent osmotic potential restoration germinated during the experiment. No outliers or sources of error were detected. 

These results suggest that marigolds possess a degree of salt tolerance, as shown by their ability to germinate under saline conditions. Overall, in line with what Kumar studies found, marigolds can be appraised as a salt tolerant crop.  Because marigolds can be appraised as salt tolerant crops, they may be able to help the growth of salt sensitive crops in saline soil. Fast plants, a salt sensitive crop, could potentially benefit from companion planting with marigolds. If marigolds can prove to be an effective companion plant in saline soil, they could potentially be used as companion plants for other crops in the future. 

Figure 2: Fast Plants germinated at a rate of 73% after 3 days. It is important to note that there was new observed germination in Fast Plants after day 3. The marigolds germinated at a rate of 66.67% after 5 days. There was new germination each day for the marigolds 

Both marigolds and Brassica Rapa (Fast Plants) saw significant germination over the course of days when treated with water. There was no observed increase in germination after day 3 in fast plants, as they reached a total germination percentage of 73% (+/- 4.97%). The marigolds experienced new germination throughout each of the 5 days, reaching a total germination percent of 66.67% (+/- 7.23%) by day #. This data reveals that marigolds and fast plants both experience strong germination in water, and sets a baseline for what healthy germination percentages look like. 

Figure 3: Fast Plants germinated at a rate of 46.67%. There was no observed germination after day 3. The marigolds germinated at a rate of 60%, with new germination each day.

When fast plants and marigolds were germinated together on filter paper in a 50 mM concentration of sodium sulfate, the germination percentages were as expected. The marigolds did not have a positive effect on the germination of Fast Plants in saline conditions.  The fast plants had a germination percentage of 23.33% (+/- 4.93%) after day 1, compared to a germination percentage of 26.67% (+/- 5.2%) in fast plants when they germinated in sodium sulfate without marigolds. The marigolds seeds also experienced similar germination percentages when compared with previous data on germination percentage without fast plants. With fast plants, they had a percentage of 23.33% (+/- 4.93%)  after day 1, and without, they had a percentage of 33% (+/- 4.32%)  after day 1. There were 2 biological replicates in this experiment.  

Fast plants reached a peak germination percentage of 46.67% (+/- 17.23%)  with marigolds, and 50% (+/- 15.04%)  germination without. Marigolds reached a peak germination of 70% (+/- 8.34%) without fast plants, and a percentage of 60% (+/- 9.19%)  with fast plants. 

This data reveals that the germination of fast plants and marigolds together have no effect on overall germination percentage, as expected. The effectiveness of the co-planting of fast plants and marigolds will be revealed in overall height, and dry mass. 

Figure 4: Fast Plants co-planted with marigolds in water exhibited an average growth of 2.4 centimeters (cm), with a standard deviation (STDEV) of 1.92 cm. Fast plants that were co-planted with marigolds in Sodium Sulfate had an average growth of 2.3 cm, with a STDEV of 1.4 cm, proving once again that there was a lot of variation in the Fast Plants growth. Marigolds that were co-planted with Fast Plants exhibited an average growth of 4.7 cm in water, with a STDEV of 2.32 cm. When marigolds were planted in saline soil with Fast Plants they exhibited an average growth of 3.4 cm, with a STDEV of 2 cm. 

In summary, co-planted Fast Plants with marigolds exhibited similar growth when grown in saline soil, or non saline soil. This shows that saline soil did not necessarily have an adverse effect on the growth of Fast Plants when they were planted with marigolds. Statistical analysis (independent, two tailed t-test) revealed that the growth difference between these two groups was insignificant (p= 0.8, p<0.8). This finding suggests that the presence of marigolds in saline soil alongside Fast Plants could potentially mitigate the negative impacts of salinity on Fast Plant growth. Marigolds are known to possess certain properties that may help improve soil quality or reduce the harmful effect of saline conditions. Further research could be used to explore whether marigolds could be utilized as a natural solution for improving other crops' resilience in saline environments. 

Marigolds that were co-planted with Fast Plants in water exhibited much stronger growth then marigolds in saline soil. This reaffirms the significant impact of soil salinity on the growth of marigolds when co-planted with Fast Plants. Although marigolds can be appraised as salt tolerant crops, saline soil still has an adverse affect on their growth, regardless of the crop they are co-planted with.

Figure 5: Fast Plants planted in water exhibited an average growth of 2.52 centimeters (cm) with a Standard Deviation (Stdev) of 0.3cm. Fast Plants planted in water and marigolds had an average growth of 2.43cm with a Stdev of 1.92cm. Fast Plants planted in saline soil grew an average of 1.11cm with a Stdev of 1.56cm. Lastly, Fast Plants planted in saline soil with marigolds exhibited an average growth of 2.26cm with a Stdev of 1.4cm.

When Fast Plants were planted in a sodium sulfate saline solution they exhibited stronger growth when they were planted in companion with marigolds, then when they were planted on their own. This confirms the hypothesis that marigolds would have a positive effect on the growth of Fast Plants in saline soil. However, statistical analysis (independent, two tailed t-test) revealed that the difference in their growth was ultimately insignificant (p = 0.07, p>0.05). 

This experiment hoped to reveal that marigolds would increase the growth of Fast Plants in saline soil. This would be because marigolds are salt tolerant plants, and when they are planted in companion with salt sensitive plants, they can help the salt sensitive plants grow. However, because of the T-test revealing the insignificance between the two’s growth, it is fair to say that more trials need to be performed to thoroughly determine whether or not marigolds truly help the growth of Fast Plants in saline soil. 

It is important to note that the Fast Plants value is so low because many of the seeds died before they could grow. 9 out of the 18 total seeds did not grow at all. This contributes significantly to the low value of the Fast Plants growth without marigolds. It could be inferred that marigolds help Fast Plants stay alive, along with growth when planted in Saline Soil. Once again, more trials would need to be conducted to thoroughly determine the effects of marigolds. 

In summary, Marigolds could prove to be effective companion plants in saline soil, however this data does not thoroughly determine whether or not marigolds are effective companion plants.

Lab Notebooks

Lab Notebook #1

Lab Notebook #2

Lab Notebook #3

WORKS CITED:

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