Introduction
Agriculture is an extremely valuable and common practice around the entire world. Without agriculture, we would not have the convenience of selecting the foods we want or producing said foods at a quantity that is feasible for the current population. Its importance is reflected in the United States 2019 GDP of 1.109 trillion dollars (Indiana State Department of Agriculture, 2019). Agriculture is responsible for 10.9% of employment or 22.2 million jobs (Economics Research Services, 2021). In addition to the economic benefits, agriculture permits not only large quantities of foods, but nutrient dense food, to varying regions around the world thus allowing a healthy diet which is directly correlated to human health.
Indiana is one of the foremost agricultural dense areas in the United States. Approximately fifteen of the twenty-three million acres, or 65%, in Indiana are used for agricultural purposes (Indiana State Department of Agriculture, 2019). In addition, Indiana exported 4.6 billion agricultural goods as of 2017, and with the growing population this is only expected to increase (Indiana State Department of Agriculture, 2019).
Agriculture, however, is not without its faults. A major consequence of agriculture is the effect is has on soil fertility and soil biodiversity. Over half of the topsoil layer has been degraded, known as soil erosion, due to farming (WWF, 2021). This is significant because this layer of the soil helps maintain its structure which in turn allows for the proper flow of water and other nutrients (WWF, 2021). Additionally, the topsoil is where the plants receive all of their nutrients and where the organic matter and soil biodiversity is contained (MCSWCD). If the microorganisms in the soil are not able to receive the nutrients they need, or their habitat is destroyed, they will likely not be able to adapt and plant growth will suffer due to inactivity in microorganismal function. Even worse, various microorganism biodiversity could be lost forever. The full extent of microbial diversity in the soil is extremely difficult to know as there is about one billion bacteria per gram of soil and placing that in a lab setting is not always feasible (Patra, 2021). However, organisms have their own niches that make up a larger web of the ecosystem. Disturbing that niche could certainly impact another seemingly distant corner of that world which will create a rippling effect.
Background
Biodiversity is a critical component to the survival of humans. Without biodiversity and the copious niches that are present due to it, we will inevitably struggle with resources we often take for granted. One important sector of biodiversity that is overlooked is soil biodiversity, more specifically microorganisms and insects.
Microorganisms in the soil are known to have many benefits for both plants and animals. Soil bacteria are known to have several vital roles in maintaining soil fertility and recycling nutrients for plant use (Johns, 2017). These functions include conversion of nitrogen to an up-takeable form for plants, conversion of ammonium to nitrite, nitrate to nitrogen, to name a few (Johns, 2017). Despite their importance, many microorganisms in soil have never been categorized and thus the extent of their ecological services cannot be fully understood (Almond et al., 2020). Plants require certain elements to grow including nitrogen, phosphorus, and potassium (Van Der Heijden et al., 2008). Microorganisms are needed because plants cannot directly absorb these nutrients, nitrogen specifically, from the atmosphere (Van Der Heijden et al., 2008). The bacteria control the cycles of nitrification making the soil well balanced (Ochoa-Hueso et al., 2016; Van Der Heijden et al., 2008). Microorganisms are not just limited to bacteria though. Certain species of fungi are able to increase plant diversity and form a symbiotic relationship by supplying nutrients (Van Der Heijden et al., 2008). What’s even more interesting about soil microorganisms is the balance between “good” pathogens and “bad” pathogens. While helpful bacteria facilitate the distribution of nutrients, harmful bacteria can negatively impact plants. However, they are kept at bay by the ability of plants to evolve and move to regions where they are desensitized to the effects of these microbes (Van Der Heijden et al., 2008). Fertilized soil leads to more plant growth and the ability for different plants to be sustained in one area, due to the abundance of nutrients within the soil. As you can imagine, disrupting this biodiversity can upset the balance of minerals in soil and thus affect plant growth.
Despite the depleting nature of farming, sometimes the act of tilling itself is not the only risk. Pesticides, an accessory to farming, have many deleterious effects that go beyond the soil. The chemicals that are present in pesticides are useful to prevent any unwanted pests from eating away at the crop or causing disease to it. Essentially, pesticides are used to save crops and therefore eliminate profit loss for the farmers. In the United States, about one billion pounds of pesticides are released each year (Alavanja, 2009). According to the National Institutes of Health (2009), these chemicals are mostly non-carcinogenic to humans but have no regulations in terms of protecting soil biodiversity. However, research found that soil organisms are drastically affected by the use of pesticides. Invertebrates in the study showed increase in mortality, inhibited reproduction and overall biological processes (Schulz et al., 2021). What is more is that pesticides can reside in the ground for many years after they are released, which inevitably causes harm long-term (Schulz et al., 2021). Pesticides coupled with the physical erosion that agriculture causes are harming soil biodiversity at alarming rates.
Isolating plots of land from other plants and limiting the space to only soybeans and corn can also have an impact on soil biodiversity. One study suggested that when isolating an ecosystem, species richness drastically declines which supports that agriculture could have already had major impact on the soil biodiversity’s disintegration (Peay et al., 2015). In areas that had been converted for agriculture usage, microorganisms did not function as efficiently as they had before in a diverse ecosystem, leading researcher’s to believe plant diversity directly impacts soil microorganism biodiversity as well (Eisenhauer et al., 2017).
Additionally, as climate change progresses and global warming occurs, there has been a direct correlation to nutrient availability, microorganism, and temperature. Warming has been linked to an increase in microbial biomass which could lead to a new infectious disease emergence if microbial organisms are not balanced (Haugwitz et al., 2014). Furthermore, warmer temperatures within the soil demonstrated microorganisms working harder to rectify the imbalance so plant fitness would not suffer (Lau & Lennon, 2012).
For my research, I want to narrow this perspective to Bloomington, Indiana. As aforementioned, Indiana is an extremely agriculture dependent state. Many individuals rely on agriculture as a way of life and income.
With this knowledge, I wanted to know how drastically Indiana’s soil biodiversity has been impacted and what future implications this would have on human health, given our reliance on agriculture. To do this, I plan to go to plots of land that have been exposed to agriculture practices throughout the years and take soil samples and quantitatively measure the organic matter, phosphorus, potassium, calcium, magnesium, and pH levels. I chose these levels to measure because they are indirect indicators of the soil biodiversity due to their function in the soil. The levels of these minerals and the pH can show us if the microorganisms are successful at their niches of converting, recycling, and storing nutrients. In contrast, I plan to go to plots of land that have not been touched by agriculture and compare the levels measured in these samples to the samples from the other plots. I anticipate seeing a change in the mineral soil composition levels due to the harmful effects of agriculture on soil biodiversity. However, this could be contingent upon the practices of the farmer. Farmers who participate in conservation tillage, crop rotation, decreased pesticide use, and crop covers will likely have more soil biodiversity because they are actively trying to reduce soil erosion and maintain soil structure (Power, 2010). Through this research, I hope to better understand how Bloomington contributes to conserving soil biodiversity and what the long-term impacts on human health will be.
Materials and Methods
To analyze the soil biodiversity present, I will use indirect indicators in the form of soil nutrients. The nutrients present in soil are often recycled by the microorganisms and other small creatures that reside there, making the presence (or lack thereof) of nutrients a sound indicator of biodiversity (Stark et al., 2014). In order to answer the research question of how agriculture impacts soil biodiversity it’s important to know which nutrients to look, what plots of land should be tested, and what materials are needed to obtain to most accurate results for comparison. Lastly, I’ll also be delving into volunteer work with the Monroe County Soil and Water Conservation District (MCSWCD) to better understand how agriculture, soil biodiversity, and the Bloomington community impact one another and where the future directions lie.
To begin my journey in answering these questions, I first contacted the MCSWCD to gather insight from those who regularly see the impacts of agriculture on the environment. From there, I interviewed Martha Miller—the director, to understand her perspective. After inquiring about her work, I also took on a volunteer position for the department to understand my research better and have a hands on approach within the community.
Once I had become a volunteer and learned a bit more about soil conservation in Bloomington, I decided on data collection techniques for the soil samples. Based on the resources available, it’s not exactly possible to isolate microorganisms from the soil and do a quantitative count and identify each species. Through the advice of the MCSWCD, we collected samples and tested them for respective nutrients levels. The diversity within the microbial communities has been shown to be influenced by the soil composition (and vice versa) towards the topsoil, where plants mostly derived their nutrients, hence affecting plant productivity (Delgado-Baquerizo et al., 2017). Because agriculture contributes strongly to topsoil erosion, gathering soil quality data from this part of the soil will provide insight to soil biodiversity and how it may be lacking (World Wildlife Fund, 2021). Knowing this, we will be collecting samples and testing for the following: potassium, sulfur, calcium, magnesium, nitrogen, organic matter, phosphorus, and pH levels.
Inorganic nutrients such as nitrogen, phosphorus, sulfur and many more are typically in forms that are not able to be taken up by plants immediately (Schmidt et al., 2002). Therefore, plants are reliant on microbes within the soil to convert these minerals into usable forms, making their bioavailability limited depending on the region or the number of microbes’ present (Jacoby et al., 2017). Microorganisms convert these inorganic elements into soluble forms that plants are able to absorb (Cao et al., 2015) Thus, measuring the levels of these nutrients is an indicator to the soil biodiversity and the capability for plants to grow in a particular area. In order to obtain accurate samples, we must use several materials.
Organic matter is usually a good indicator of healthy soil due to the vastness of nutrients and microorganisms recycling those nutrients (USDA, n.d.). Generally, soils should be composed of 5-6% of organic matter, however, lands exposed to agriculture typically have organic matter of 3% (USDA, n.d.).
Phosphorus is a nutrient that is quite limited in soils. In fact, it is often limiting factor to a plants growth (Cao et al., 2015). In fact, because phosphorus is limited and vital for plant growth, many farmers will use synthetic fertilizers that contain the element (Cao et al., 2015). However, an imbalance in the environment can cause organisms to be unable to adapt leading to less biodiversity. This imbalance, like with other nutrients or biomass, is influenced by temperature, water content, carbon availability within the soil (Richardson et al., 2017). It will be important to analyze this nutrient, given its limited quantity and gradual soil heating due to climate change.
Calcium, magnesium, and other inorganic nutrients are converted to useable forms based on the environment around them (converting anions or neutral compounds to cations). This phenomenon, known as the cation exchange capacity (CEC) takes place primarily in the organic matter and allows for the soil to retain micronutrients (Cation Exchange Capacity, 2021). This component is important to soil health as the CEC directly influences soil pH, which must be between six and seven (USDA, 1998)
The method for this experiment, as counseled by the MCSWCD, will revolve around four plots of land. Site 1 will be an agriculture plot that has constant cover crops and no tillage in over thirty years. Site 2 will be an agricultural plot where the farmer does not use soil conservation methods and a significant amount of synthetic pesticides and fertilizers. Site 3 will be a greenhouse where constant crop rotation occurs. Site 4 will be a pasture with livestock grazing. The landowners’ identities will remain anonymous to protect their livelihood and locations. Due to approval restrictions, we were not able to obtain a nature plot. However, we are hopeful to see the comparison in soil biodiversity indicators between plots of land that use sustainable agricultural practices and those that do not.
All plots of land (where samples are collected) will be similar in size. Utilizing smaller plots will reduce the need for more samples as there will be less variation in nutrient quality due to the size. We tested four different plots of land (Site 1, Site 2, Site 3, and Site 4) that have unique characteristics about them and thus can provide insight as to how agriculture effects soil nutrient distribution and in turn, soil biodiversity.
In order to obtain the soil samples, we will need the following supplies: soil probe, soil sample collection tubes, bucket (for soil removal), measurer, and a marker (MCSWCD). For each sample collection, we will use a measurer to ensure that the depth is consistent for each plot. We will be using a soil probe and going down to a depth of 0.2 m to consistently measure the topsoil nutrients across all plots of land, limited to Bloomington, IN (Delgado-Baquerizo et al., 2017). In order to obtain an accurate sample, we will pull soil from at least five different areas on the plot of land at a diameter of five feet from each other. Because we are measuring within the same region where temperature and weather are consistent, this eliminates the need to do multiple lab samples of each plot and at different depths (Schmidt et al., 2002).
After collecting the samples, we will package them up and send them to A&L Great Lakes Laboratories where they will store the samples cold temperatures to prevent the decomposition of the minerals or prevent pH change (Sylvian et al., 2011). Sample result time can vary, especially due to COVID-19 but results arrived within a week. Depending on the compound being tested, most minerals are in parts per million (ppm) or percentages. Since nutrient distribution varies depending on the region and the crops that are grown there, the lab will send the results as low/high for each nutrient depending on the locations where the samples came from.
While the samples are being collected, I also plan to learn more about the plots of land itself. I want to do this for a couple reasons. One, it will be important for result interpretation to know when/how much fertilizer and pesticides have been used. Second, I want to understand more about why they choose the agricultural practices they do. For one plot of land that we will be testing, the farmer uses cover cropping—a technique that can minimize soil erosion thus improving soil biodiversity and fertility. This can lead to better crop yields in the future as soil fertility and biodiversity positively correlate with that (16). I’m also interested to know more about what other soil conservation methods farmers are using and if they plan to expand on that in the future.
In addition to interviewing farmers, I am volunteering with the MCSWCD this semester to learn more about their role in the community and how they are actively working to protect soil. So far, I’ve interviewed the chair of the MCSWCD, Martha Miller and she will also be accompanying me to collect samples and answering questions that I will include in my presentation. Martha Miller has also directed me towards others in the community who are passionate about teaching soil conservation and farmers across Indiana who use these practices. All in all, the methods and materials of my project will extend beyond just data collection to better understand soil biodiversity and agriculture within the Bloomington community.
Results
The results of the experiment can be seen below in Figure 7. A&L Great Lakes Laboratories tested for organic matter, phosphorus, magnesium, calcium, potassium, pH, cation exchange capacity, and percent cation saturation.
Organic matter is where microorganisms reside as of most nutrients available to crops (Soil Biological Fertility, 2021).As previously mentioned, these microorganisms regulate micronutrient availability to the plants, as these materials are usually not immediately able to be absorbed via the root system (Cao et al., 2015). Figure 7 shows the values of each sites micronutrient stores, soil pH, and organic matter percentage.
Site 1 had an organic matter percentage of 2.3%. Phosphorus, potassium, magnesium, and calcium had mineral composition levels of 45 ppm, 169 ppm, 70 ppm, 1050 ppm respectively. Soil pH for Site 1 was 6.0 with a cation exchange capacity (CEC) of 7.5 meq/100g.
Site 2 had an organic matter percentage of 3.4%. Phosphorus, potassium, magnesium, and calcium mineral composition levels were 15ppm, 106ppm, 85ppm, and 3050ppm. Soil pH for Site 2 was 7.3 with a CEC of 16.2 meq/100g.
Site 3 had an organic matter percentage of 5.3%. Phosphorus, potassium, magnesium, and calcium levels were 106ppm, 119ppm, 165ppm, and 3000ppm. Soil pH for Site 3 was 7.1 with a CEC of 16.7 meq/100g.
Site 4 had an organic matter percentage of 6.9%. Phosphorus, potassium, magnesium, and calcium levels were 189ppm, 583ppm, 275ppm, and 3150ppm. Soil pH for Site 4 was 7.4 with a CEC of 19.5 meq/100g.
Figure 1: Soil Test Results
Analysis
Based on what is known about organic matter, phosphorus, potassium, and the other nutrients in the soil, we are able to discern what the biodiversity looks like for each plot of land and infer This indicates that because Site 1 and Site 2 have lower organic matter percentage, they likely have less biodiversity and as a result, less nutrient availability to the crops. This can be supported by the visual assessment of the soil gradients and rivets present at Site 2 and the smaller soybean growth at Site 1. Site 3 and Site 4 have standard organic matter percentages, indicating that there is enough soil biodiversity present.
Phosphorus levels were all within the appropriate range apart from Site 2’s samples. Site 2 had low levels of phosphorus that is more than likely due to biodiversity loss as a result of harsh agriculture practices and the use of synthetic fertilizers and pesticides–hence not enough soil organisms present to partake in the P cycle. This trend is consistent with the magnesium and potassium as well.
In general, the findings from the soil samples indicate that agriculture does have an effect on soil biodiversity and thus plant nutrition availability. Harsher agriculture techniques with the use of the synthetic fertilizers and pesticides, harm soil organisms that play an active role in balancing soil nutrients. Without these nutrients, plants will not grow as well and will be overall less nutrient dense. The data from this experiment suggests that using sustainable agriculture techniques such a minimal disturbance, cover crops, and crop rotation, can help mitigate the impact that agriculture has on soil biodiversity.
The next step in this experiment would to be begin categorizing and analyzing soil microbiota itself. Answering questions like how many bacteria, fungi, earthworms per area of each site could reinforce these findings from the indirect indicators. Taxonomizing and identifying the microorganisms that participate in the N,P, and S cycle and help maintain the soil structure needed for proper cation conversion would help us understand what we can do to increase our crop yields, crop nutrient density, and protect soil biodiversity at the same time.
Discussion
Looking at biodiversity on a micro scale sometimes makes us forget the bigger picture. The reason we should care about soil biodiversity is that it directly impacts us. Food is not optional, and we heavily rely on agriculture to meet both of our macro and micronutrient needs. Although we do not know the extent of soil biodiversity, just like anything else, once it’s gone—it’s gone.
Soil microorganisms play a pivotal role in regulating nutrients for plant uptake. Without them, plants would either not grow or have diminished nutrient quality. Human health would suffer because we require a certain amount of nutrients per day to live healthy lives. If nutrient quality in foods decline, people will need to consume more to meet their nutrient needs which could generate more waste and greenhouse gases. It could lead to further deforestation to make more room for crops due to the increasing demand.
Apart from nutrients and crop growth, soil microorganisms regulate pathogens in the soil. Disturbance to the ecosystem could unleash the newest infectious disease. This infectious disease could significantly impact human health and also have a high mortality rate.
All in all, the lesson here is if it’s not broke—don’t fix it, or at least if you cannot protect all soil biodiversity, do your best to minimize your impact on it. It’s imperative right now that we start tackling these issues and helping the environment. It’s time to save the soils.
Future Research and Limitations
The next step in this experiment would to be begin categorizing and analyzing soil microbiota itself. Answering questions like how many bacteria, fungi, earthworms per area of each site could reinforce these findings from the indirect indicators. Taxonomizing and identifying the microorganisms that participate in the N,P, and S cycle and help maintain the soil structure needed for proper cation conversion would help us understand what we can do to increase our crop yields, crop nutrient density, and protect soil biodiversity at the same time.
In addition to testing nutrient density, it would be interesting to see people’s perception of their diet. A significant percentage of people around the world are deficient in some micronutrient or are malnourished. Assessing the current state about human health and our perception of food and how often people in Bloomington waste food would be an interesting topic for discussion.
One limitation is accessibility to resources. Based on the time constraints and nature of this class, we are not able to identify every microorganism to ensure biodiversity, or lack thereof. Instead, using indirect indicators is a great step in assessing the possibility and probability of microorganism diversity, but it is not surefire. In order to accurately depict and quantify soil biodiversity and the effect agriculture has on it, would be to take two samples—one before planting season and one after to see if there is a difference. In fact, it would be better to do this over the course of a decade to get an accurate depiction.
Another limitation is opportunities as a result of COVID-19. While I did become a volunteer at the Monroe County Soil and Water Conservation District, I was not able to attend as many events because most of the district office was closed due to the virus. However, I was still able to learn a lot and be a part of the community, but it would have been a more well-rounded experiment if there were not limitations due to COVID.
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