What happens when you dig dirt?
In Fall of 2024, right before the first frost, I took a soil probe and collected several samples of soil from across the Historical Renaissance Kitchen Garden at the Kinney Center for Interdisciplinary Renaissance Studies. During my time as a Renaissance of the Earth Fellow, I acquainted myself with the land which surrounds the Kinney Center. I surveyed, ran through the vast meadow, harvested vegetables from the garden, and pruned branches from the orchard. As a Plant and Soil Science scholar, I repeatedly found myself asking a question through my work: What happens when you dig deep? What lies beneath our feet and the plants which inhabit the garden? These questions would become the foundation of my independent research project on the Kinney Center’s soil and the blog that follows…
Hannah collecting soil samples
To start, I gathered soil samples, separating them based on the herbal/annual side of the garden and the perennial side, and mixed them. I then laid each of the samples out on a pan to dry before bringing them to a microscope. During my search for materials, I reached out to Emeritus Professor of Plant Pathology & Nematology, Robert Wick, to ask him if I could borrow his lab for my project, which I was working on as a Fellow with the Director of the Kinney Center and founder of the Renaissance of the Earth Project: Prof. Marjorie Rubright. Marjorie invited me to work in the garden as my lab and welcomed me to the Center’s library as my research hub. Professor Wick generously offered up his knowledge and Nematology Lab to welcome my samples.
To understand the teeming biology beneath our feet, I knew I would need to look at these samples under a scope. Although humans interact with the soil through a variety of activities, the absence of much macroflora and macrofauna is deceiving to our understanding of what is active beneath the surface. My mission was to uncover life that cannot be seen through the naked eye. I wanted microflora and fauna, specifically nematodes, to be the star of my very own soil show. The story that follows showcases the complexity of this life beneath our feet – sustaining the earth and sustaining all of us in the process. I hope you’ll enjoy!
What is a nematode?
A nematode is a non-segmented microscopic eel-like roundworm that can be beneficial or non-beneficial while living in soil or plant root tissues (Washington State University, 2017). Nematodes are incredibly diverse and present a variety of benefits to agricultural systems, depending on the production system and breed of nematode present. Due to the activity throughout the Kinney Center and years of varied maintenance in the garden, I wanted to pay particular attention to nematode populations to help understand the current soil conditions and health.
Bacterial (free-living) nematode
To do this, Rob and I conducted a nematode extraction to isolate the nematodes from the soil particles and plant tissues. We conducted this extraction with the soils by wet sieving and sugar flotation to be able to identify and count the number of nematodes present. We want to know this because it will tell us more about the abundance of organismic activity within the soils, and depending on the type of nematode, can inform us of parasitic activity. After properly wet-sieving 25 cc (cubic centimeters) of soil from each sample into tubes, both samples were filled with water in the tubes. The tubes were then placed in a centrifuge at about 3,400 RPM for 6 minutes. What this does is help the separation of soil organisms from particles and tissue. After it was done, the water was decanted from the tubes. Then, sugar solution was added to each tube about a cm from the top, and stirred to break up the soil pellets and bring the nematodes to the surface. The tubes were then placed back into the centrifuge at about 3,400 RPM for 1 minute. By doing this, we were forcing the soil to the bottom of the tube, while bringing the nematodes to the top. Once the second centrifuge was done, the sugar water was decanted through a 500 mesh sieve to hold the nematodes. After, the nematodes were back washed into the tubes and placed into a counting dish. Once prepped, we then placed each of the samples under a microscope to begin counting.
With Rob’s expertise, we were able to identify 6 varieties of nematodes in each sample, including: free living, lance, stunt, ring, lesion, and Tylenchus. The perennial portion of the garden had substantially more free living, stunt, and Tylenchus nematodes compared to the annual garden soil. The annual garden soil also had lance and ring nematodes, whereas the perennial garden soil had none. Nematodes are not host specific, meaning they can feed on both grasses and woody plants. With that being said, lance, ring, and stunt are typically associated with grasses in high numbers. Lesions on the other hand are not as closely associated with grasses. It is interesting to consider how the Kinney Center soils are host to these nematode numbers when the kitchen garden is made up of primarily herbaceous plants.
Nematode tables
For perspective, 100 cc of soil equates to less than a half-cup of soil. Although the number seems small in comparison to what we may be used to, this is only representing a small fraction of what is actually inhabiting and thriving within our soils. If we extrapolated these numbers to include the entire garden, we would be witnessing hundreds of thousands of nematodes. To identify an abundance of nematodes in relation to a small area of land, we are witnessing a thriving ecosystem which hosts a variety of microorganisms swarming beneath our feet.
Why do we look beyond the surface?
By conducting an extraction, we are able to uncover another world of life living beneath the surface. Although we may not see or feel these organisms, it does not mean they are not there and busy at work. In other words, we are peering into an invisible world which surrounds us. We look beyond the plants to observe the biology we may otherwise ignore because it is not easily tangible. When we take the time to notice microorganisms such as nematodes, we are investing in the health and continuity of our soils. In this action, we are moving toward a deeper understanding of how our food systems function in a cycle, and depend on the health of not only the creatures above, but also below, the surface.
References:
“Washington State University.” WSU Tree Fruit | Washington State University, treefruit.wsu.edu/web-article/nematodes/. Accessed 5 Mar. 2025.