Digging Deeper: Can Crop Rotations Outperform Fertilizers Under Drought Conditions?

[Transcript]

Charlotte: Ugh these plants won’t grow! I keep adding fertilizer but the soil is too dry!

Leila: You can’t just keep adding fertilizer!

Charlotte: What? What else would I do?!

Leila: Did you know that fertilizers are responsible for 2% of global CO2 emissions?

Leila: Fertilizer fuels rapid algae growth in the water that produces harmful blooms and hurts wildlife!

Charlotte:  Not to mention, fertilizers can make dry soil worse by blocking nutrient absorption!

Leila: So, we decided to explore an amazing fertilizer alternative that would help with these issues!

Both: Crop rotations!

Leila: Our project’s focus was to observe how crop rotations compared to fertilizers under drought conditions.

Charlotte: We grew arugula in simulated drought and non drought conditions, in four soil variants - two of which with cover crops grown previously.

Leila: Then we sent it to the lab to test for biomass and a bunch of nutrients

Charlotte: And what we found was shocking it-

Leila: Charlotte, we forgot to introduce ourselves!

Charlotte: Oh, sorry, this is our project Digging Deeper!

Leila: I’m Leila!

Charlotte: I’m Charlotte!

Both: And we can’t wait to meet you at the Canada Wide Science Fair!

The Problem with Fertilizers

Fertilizer production contributes about 2% of CO₂ emissions globally, adding to climate change. Agriculture is the second largest source of climate change pollution.

However, fertilizers harm the environment in many ways, not just through the pollution of carbon emissions. They also harm the ecosystem by leaking nutrients into waterways, which is often termed nutrient pollution. This can cause excessive growth of harmful algae, leading to death among wildlife and causing issues in the fishing supply chain.

Fertilizers can also slow the bacteria of growth in the soil. Bacteria are vital for growth of many plants and without them the plants become more reliant on the fertilizers.

Crop Cycles

With our previous science fair project in 2024, we tested the viability of crop cycles. Our project demonstrated how plants could be healthy and strong with no fertilizer at all. So, this made us wonder if crop cycles could compete with fertilizer in encouraging successful plant growth.

Droughts

Agriculture is a tremendous part of Prince Edward Island and it is one of the leading sources of income. So, whenever we had one of the worst droughts in PEI history last summer, it affected everyone. We knew this was a huge issue, so we wanted to see if there was anything that could help in future droughts that isn't harmful to the environment.

Question

All of these areas led us to the question: Can crop cycles outperform fertilizer under drought conditions?

Experimental Design

Spinach was chosen because it produced the strongest arugula growth in our last experiment.

Soybeans were chosen because they are nitrogen fixators, which have been proven to be beneficial in plant growth.

A control group was used for comparison and to test whether untreated soil produced the best results

A fertilizer group was included to compare cover crops to a common practice in agriculture/gardening.

Each soil was tested under both simulated drought and non-drought conditions.

Materials

Plastic bins/drawers

8.8L Lambert Potting Mix

Distilled water

Watering can

Liquid measuring cup

Ruler

Miracle-Gro fertilizer

Seeds

Veseys Astro Arugula

Veseys Seaside Spinach

Veseys Karikachi Edamame Soybeans

Procedure

Planted two bins of spinach and two bins of soybeans.

Grew cover crops for one month.

Removed plants and collected soil samples.

Planted arugula in cover crop soils plus control and fertilizer watered soils.

Created drought and non drought conditions for each soil type.

Grew arugula for one month while watering according to whether it was drought or non drought.

Collected final soil samples and tested for biomass.

Controlled Variables

Same amount of soil in every bin

Distilled water used for all of the plants

Equal sunlight exposure

Same watering amounts within drought groups and non-drought groups

Same number of seeds planted for each bin

Same planting depth for each bin

Data Collection

Plant Growth Data

Plant height

Leaf width

Fresh matter

Dry matter (biomass)

Soil Data

Soil analysis test

Soil moisture measurements

Soil pH measurements

Observations

Leaf color

Plant health

Other visible growth differences

Plant Growth Performance

Plant growth data showed consistent differences between treatments across multiple measurements including biomass, height and leaf size.

Spinach soil produced the strongest overall growth

Highest biomass

Tallest plants

Largest leaf width

Healthiest leaf colour and appearance

Soybean soil produced moderate-high growth

Good biomass

Second tallest plant

Good leaf width

Healthy but slightly less vigorous than spinach

Control soil showed less than optimal performance

Lower biomass compared to cover crop soils

Moderate height and leaf size

Fertilizer soil performed the weakest

Lowest biomass

Shortest plants

Smallest leaves

Leaves appeared unhealthy

These results suggest that crop rotation soils supported stronger plant development than fertilizer treated soil in this experiment.

Drought vs Non-Drought Results

There wasn't a major difference between drought and non-drought conditions across most soil types. While drought conditions reduced growth in some cases, the overall ranking of the soils remained the same.

Spinach soil performed best in both drought and non-drought conditions

Soybean soil consistently remained second

Control soil consistently remained third

Fertilizer soil remained the weakest in both conditions

This suggest that the benefits of cover crop soils were strong enough to support arugula growth even under simulated drought conditions. Spinach soil, in particular, maintained high performance regardless of water availability.

Key Observations and Interpretation

Cover crop soils outperformed fertilizer soil in both categories.

Spinach had the most positive impact on arugula growth.

Soybeans performed well but may have been limited by early removal, which may have prevented full nitrogen fixation nodule development.

Fertilizer may have negatively impacted soil conditions because of salt buildup.

We noticed a white fluff growing on the plants, especially the ones that did well, and after some research we think this may be saprophytic mold (Slide 5).

Overall, the results show that the cover crop soils, especially spinach, provided better soil benefits than fertilizer. The crop rotations supported plant growth under both drought and normal conditions.

Crop cycles are better in drought conditions than fertilizer. Our arugula that was in the fertilizer soil was sad and droopy, whereas when it was planted in spinach soil it was tall and full. If a plant has grown previously in the soil it can help hold water better, which can then be absorbed by the next plant. Some plants can also help add nutrients to the soil, or transform nutrients into forms easier consumed by the plants (ex. nitrogen fixing bacteria). Furthermore we learned that fertilizers can sometimes negatively impact plants during a drought, due to salt buildup. Crop cycles are the best option overall that can improve plant growth, no

matter the condition!

Why Did Arugula in Spinach Soil Perform the Best?

Microorganisms and Bacteria:

Spinach may not be a nitrogen fixator, but it can still promote nitrogen fixing bacteria such as rhizobium and Actinomycetota phyla.

Spinach could have added lots of other helpful bacteria which helped plant growth.

Papiliotrema, Pseudomonadota, and Bacillota are all known to promote plant growth and decompose organic matter.

Further Research

Test for soluble salts, ammonia, and nitrates to better understand soil nutrients

Examine bacteria and mold growth to assess overall soil health

Future Improvements

Use a wider variety of soils, not just potting soil (we would try PEI soil)

Try different types of fertilizers to compare effectiveness

Next Steps

Run multiple planting cycles (ex. grow a new crop after arugula)

Experiment with different plants to see how results vary

What We’d Do Differently

Include more tests and variables from the start

Increase the number of trials to improve accuracy

We couldn’t have completed this project without the support of several amazing people.

First, thank you to PEI Analytical Labs who allowed us to utilize their facilities and equipment for our nutrient testing. Their guidance and willingness to help us with questions we had helped us tremendously.

Secondly, thank you to our families for their constant support. From driving us to different locations to encouraging us through the process, we are extremely grateful. A huge thank you to Trevor Campbell for recording and editing our video, we appreciate it enormously!

Finally, we thank Mme. Lise Deveau for her encouragement and guidance. She always helped us find a way to clarify concepts and supported us through the whole process.

Their contributions helped make our project possible.

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