THE FINAL

 3/27/2024

Note: hyperlinked words tie to other blog posts that may provide more information/context.

Four types of fertilization methods were used for this experiment: controls of just pine bark, compost mixed with pine bark, a liquid fertilizer application on pine bark, and a compost tea application on pine bark mixed with compost. Each method was applied to a group of three plants. The compost was sourced from my grandpa who makes his own, and it is derived from table scraps and eggshells. The compost tea was made with this same compost based on NC State Extension guidelines. The purpose was to identify if organic nutrient sources were just as capable of sustaining a plant as synthetic fertilizers. 

Over the course of six weeks, I recorded for each plant the number of flowers present, the number of flowers deadheaded, the height of each plant from the tallest leaf to the base of the pot, and any visual or care notes.

The plants were stored in a portable greenhouse located in my garage. This was done in order to maintain a stable environment (especially because this experiment began in February when temperatures were still low). As time went on, I realized the greenhouse was keeping the plants too humid, which is what I believe caused the root rot of the two fertilizer plants. As the days began to get warmer in March, I started removing the cover of the greenhouse to release the humidity. The plants were still in the garage which kept the temperatures relatively stable.

Table 1: Collected Growth Data

These are the growth results from the six weeks of the experiment. 

(height was measured from the tallest leaf to the bottom of the pot)

Please note: Compost & Scraps 1+3 (later Compost & Tea) are in taller pots.

This was alright because it is the average overall 

increase/decrease in growth I'm comparing.

The group with the greatest increase in growth was the Fertilizer. A 24-8-16 fertilizer was applied twice to these plants, once initially at the beginning of the experiment and then again three weeks later. This result makes sense to me because the fertilizer is the most concentrated and/or readily available nutrient source I used. Compost may have a good amount of nutrients, but it takes a while to decompose, and the compost tea is more diluted. 

However, these results do need to be considered in the context that two of the Fertilizer plants died of root rot. One before measurements had started and the other halfway through the experiment. This is a source of error because in the end the recorded data for the Fertilizer group is based on the one remaining plant.

Plants growing out of pots Week 6

All of the plants showed a decline in height in the last two weeks of the experiment. I have a couple guesses as to what the cause of this could be (especially because plants don't typically grow backwards). My first idea is that this decline in growth is another reaction towards growing in the adverse humidity of the greenhouse. However, what makes the most sense to me is that this is the plants settling and branching out for more light. As the experiment went on, the plants did not want to stay within the confines of their pots. Several of them began to trail down the sides of their pots, which is still growth but doesn't show up in a record of height. This could be attributed to lack of light or to the pruning I had to do in order to combat the rot stimulating the plants to grow in an outward direction. 

For the first half of this experiment, several of the plants had pale or yellowing leaves towards the base of the plant. The plants were on a six-hour light timer (the options were 6, 12, 16). This was switched to 12 hours, and the plants greatly appreciated this. The amount of yellow/pale leaves also decreased. 

Controls Week 2                                    Controls Week 6

Originally, I attributed the paling of these lower leaves to not getting enough light. While I still believe this is at least the major cause of the yellowing (if not the only cause), I do want to consider what possible nutrient issue this could be.

Plant Name	Week 1	Week 2	Week 3	Week 4	Week 5	Week 6
Control 1	N	N	N	N	Y	N
Control 2	N	N	Y	S	N	Y
Control 3	N	N	S	Y	N	N
Compost 1	N	N	Y	N	Y	S
Compost 2	Y	Y	Y	N	Y	Y
Compost 3	N	S	N	N	Y	Y
Fertilizer 1	N	Y	Y	N	N	Y
Fertilizer 2	N	N	N	RIP	RIP	RIP
Fertilizer 3	RIP	RIP	RIP	RIP	RIP	RIP
Compost & Scraps 1	Y	Y	N	N	Y	Y
Compost & Scraps 2	N	N	N	N	Y	Y
Compost & Scraps 3	N	N	N	Y	Y	Y

Table 2: Compiled record of pale/yellowing mentioned. 

KEY:

Y = Yes/lots/decent amount
S = Some/not a lot/minimal
P = only pale
N = No/none recorded/insignificant amount

ab = at base/specifically mentioned lower or older leaves
RIP = Rot Is a Pain
*towards the end of this I began to be more concerned with/focused on the rot than recording the 2-3 yellowing leaves. It’s possible that the plants still had a few yellowing leaves and I didn’t record this detail along with the rotting branches. However, I do know the plants’ color looked better after the lighting was fixed.

For the week 1 results, these were recorded right after the plants had been potted, so this information is likely more indicative of the nutrient concentration/availability of the nursery media than mine. It seems overall these plants started out slightly stressed and/or with some slight nutrition error. This makes sense as they had just been repotted and placed in a new environment. 

Yellowing photographed in Week 1

The amount of paling at the base would lead me to believe that if this is a nutrient deficiency, a mobile nutrient was not as available as the plants would like. My guess would be an N deficiency because the discoloration was fairly uniform and occurred in the lower leaves. It's possible some of this nutrient was also washed from the soil by watering. However, no plant group obviously stood out as the most potentially deficient, so this doesn't seem to be an issue that directly tied to one particular nutrient management technique. 

Table 3: Total degree of paling

Numbers calculated based on information in Table 2

N=0, S=1, P=1, Y=2

The plant group with the most amount of yellowing was the Control + Tea, however, the amount of yellowing decreased as the experiment went on, as it did for the other groups as well. It's possible this could be a toxicity (as this plant was applied with an extra dose of compost in the form of tea), but if the fertilizer didn't show toxicity, I'm not sure why the less-concentrated compost + tea would. 

The plant with the least yellowing overall was the fertilizer group. This information paired with the growth information can lead one to conclude that the fertilizer group performed best nutrition-wise out of the four groups. This makes sense as the fertilizer was high in N.

However, there is one area I still would like to address. Because root rot claimed so many of my plants, I wanted to add a section on the effects of nutrition on root rot susceptibility. 

Root rot in my plants.

An in-depth discussion of the effects of nutrition management on disease resistance is found in "Plant Mineral Nutrition and Disease Resistance: A Significant Linkage for Sustainable Crop Protection." This article states, "A healthy plant will certainly have high vigor and improved resistance and hereby mineral nutrients show their capabilities in disease management (Ojha and Jha, 2021). Mineral Nutrients, such as the primary nutrients... the three secondary macronutrients, and the micronutrients... are significant in imparting disease resistance and healthy growth to the plant (Datnoff et al., 2007; Gupta et al., 2017)" (Tripathi et al. 2). In other words, good nutrition management should lead to less disease problems.

Article link:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9631425/#:~:text=The%20importance%20of%20mineral%20nutrition%20on%20plant%20disease,eventually%20affect%20the%20outcomes%20%28Meena%20et%20al.%2C%202015%29.

Table 4: Rot Comparisons

(numbers calculated based on every time rot was mentioned in my notes)

none = 0, some (including leaves) = 1, at least a branch = 2, RIP = 4

Based on this information, it's obvious the fertilizer group fared the worst since this was the only group to have plants die (see Week 1 and Week 4). Ironically, the controls with no nutrient management fared the best, which is contradictory to the article. Perhaps the nutrient applications hadn't had time to be taken up by the plant before the rot set in.

In conclusion:

Did the organic nutrient sources fare as well as the synthetic?

The Fertilizer group certainly had the greatest overall increase in growth. It also had the least amount of paling and the quickest recovery. However, the Fertilizer group fared worst against the rot. This leads me to conclude that, based on the information gathered in this experiment, under ideal greenhouse conditions, the synthetic fertilizer will fare best. 

However, because this was my first time using a greenhouse and the conditions were not consistently ideal, there were too many additional factors for me to conclude that this would always be true. The experiment would have to be replicated under more ideal conditions for the information to be credible.

Things to change if the experiment were to be replicated:

• Better humidity management. Rot was the primary issue faced by the plants, and the high humidity caused them to be under stress (indicated by the disease and the lack of flowering). Managing the humidity well from the beginning (perhaps by adding a fan or leaving the greenhouse open during the day) would likely have saved some of the plants.
• Making sure the lighting was ideal from the beginning.
• More time to give the organic nutrient sources time to be broken down.

To see the full development of my experiment, view the other posts in this blog.

These have more in-depth details on my care and methods for these plants.

Note: Over the course of this experiment, I kept an Excel document that recorded # of flowers, # of flowers deadheaded, height of plant from the tallest leaf to the base of the pot, and any visual or care notes. This is where the data and tables for this experiment are sourced.

Exam Review Questions

1. What are two examples of a form/method of supplying organic nutrients? 
2. What impact does good nutrient management have on disease susceptibility (in general)?
3. What are the symptoms of nitrogen deficiency as seen in this experiment?

 

Thank you for reading, and good luck on the exam!