Vermicompost: The Solution for the Use of Inorganic Substances in our Food Systems
Abstract
Investigating replacements for inorganic chemical controls of pests and pathogens is essential to preserve the productivity and longevity of our agricultural lands. This literature review examines the effects that vermicompost and vermicompost teas have on harmful accumulations of pests, pathogens, and toxins found within our agricultural systems. The studies discussed provide strong evidence that vermicompost can improve soil health, reduce pests, decrease accumulation of toxic substances, and suppress soil-borne and foliar pathogens in plants. Vermicompost contains high populations of beneficial microbes that assist plants in their defense against infection. These microbes suppress pathogens via nutrient competition, antibiosis, hyper-parasitism/predation, and systemic-induced resistance. The use of vermicompost and vermicompost tea in integrated pest management strategies can significantly reduce the use of synthetic pesticides and promote more regenerative practices within our agriculture systems.
Introduction
As the human population continues to grow, there is an ever-increasing demand on the agricultural systems of our world. Food scarcity has led to many innovations within the field of agriculture, but at what cost? In our quest for growing more crops more efficiently, we have created systems that are completely dependent on synthetic chemicals, such as inorganic fertilizers and pesticides. Monocultures, especially when treated by synthetic means, are biologically barren wastelands for all levels of the trophic chain— from pollinators and predatory insects down to the beneficial bacteria and fungi that live beneath the soil’s surface. These microbes play a crucial role in the overall health and longevity of agricultural soils.
When high populations of beneficial microbes are present, organic matter that is contained within the soil like root mass and crop residues are quickly broken down into nutrients that facilitate the growth and survival of the plants above. Through the loss of this easily overlooked microbial diversity, our cropping systems have become less resilient and more susceptible to invasion from pests or pathogens that can spread quickly and cause growers to lose entire fields of crop. Microbial diversity acts as a multifaceted defense mechanism against pest and pathogen invasion through competitive exclusion, direct antagonism, enhancing host resistance, and altering environmental conditions to favor beneficial organisms over harmful ones. The application of vermicompost (VC) or vermicompost teas (VTC) can restore microbial diversity and be used to effectively combat harmful pests and pathogens within cropping systems.
Vermicomposting is a safe, scalable, and regenerative method of managing organic waste that involves the use of worms to convert organic matter into compost. This compost can then be brewed into a foliar spray (tea) or be used directly as a nutrient-rich organic fertilizer. The process of brewing vermicompost tea is similar to brewing tea at home. Worm compost is placed into a mesh bag, then suspended in a tank of water and left to brew for a number of days. Typically an aeration pump is added into the water tank to increase the levels of oxygen, creating an ideal environment for the beneficial microbes contained within the compost to flourish. In addition to being a beneficial organic fertilizer, worm castings (excrement) have been shown to have numerous benefits for soil health, which include improved soil structure, water-holding capacity, nutrient availability, and microbial activity [1]. The studies that will be discussed in this paper have found VC and VTC to be effective in suppressing various pathogens and pollutants found within our agricultural fields.
Microbial Activity
Vermicompost has been shown to positively alter the physiochemical characteristics of soil and improve overall health through the addition of macro and micro-nutrients, vitamins, enzymes, and hormones, which are essential to the overall health of a plant [1]. Research done on VC and its ability to outcompete harmful pathogens often reported an added bonus associated with its application— a positive correlation between vermicompost and overall plant biomass [2]. This can be attributed to the diverse quantity of beneficial bacteria and fungi that reside in the vermicompost. These beneficial microbes work hard breaking down dead organic matter into its trace elements, making nutrients more readily available to be taken up by plants. In turn, the plants create stable habitats for the microbial communities within their rooting zones. Vermicompost stands out as a powerful soil amendment, enriching soil with vital nutrients and fostering mutually beneficial relationships between plants and diverse microbial communities. This synergy promotes nutrient availability and overall plant biomass, highlighting the diverse benefits of vermicompost and its effect on enhancing microbial activity within soil systems.
Effects on Plant Pathogens and Pests
Just like humans, plants are susceptible to contracting diseases that may hinder their ability to grow, and in the worst cases even bring about their demise. Commercial cropping systems are especially vulnerable to disease outbreaks due to a lack of care for biodiversity in most of our standard industry-growing practices. These harmful practices can include: monocultures, lack of crop rotations, inefficient irrigation systems and the overuse of synthetic pesticides and fertilizers. As an epidemic strikes in a field, it is typical procedure to control the outbreak through the employment of chemical sprays, crop burning, and soil fumigation. While these practices may be effective at eliminating harmful pathogens, they are also very efficient at killing off any beneficial bacteria and fungi that reside in the soil. When fields lose these beneficial microbes, their soils lose the ability to maintain structure, retain water, cycle nutrients, and ultimately the ability to facilitate plant growth without the help of inorganic fertilizers. Once a system has reached this point of dependance on synthetic fertilizers and pesticides, plants become increasingly more susceptible to biotic and abiotic stressors. Continuous reliance on synthetic means to mitigate pests and pathogens can lead to significant impacts on plant communities, including reducing plant defense mechanisms, disruption of natural pest protection and in some cases lead to the development of pesticide resistance in target pests and pathogens. Chemical control can be used as a short-term mitigation, but the long-term effects that it has on plant health and soil diversity render this an unsustainable option.
Vermicompost has been looked at as a possible solution for mitigating harmful plant pathogens and the vectors that transmit them. Root-knot is a disease that can affect a wide range of crop plants and is induced by parasitic nematodes. Root-knot nematodes secrete enzymes into roots that cause the plant’s cells to swell and form nodules that the nematodes then use for food, shelter, and as a nursery to lay up to 1000 eggs. Not only do these nodules hinder a plant's ability to properly uptake nutrients, but they also reduce the marketability of the crop. A study conducted by Shova Mishra (2017) at the University of Hawaii looked at the effects that different ages of vermicompost tea had on the penetration, reproduction, and hatching of the nematodes. The results showed that VTC significantly decreased the nematode's capability to penetrate plant roots and hatch from their eggs with minimal effect on their reproduction. Reduction in penetration and hatching abilities was theorized to be the result of one or the combination of the following: host plant resistance caused by beneficial rhizobacteria, secretion of enzymes that cause the hydrolysis, or destruction, of eggshells, and an influx of beneficial microbes that exert competitive exclusion on the nematodes [3]. These beneficial microbes are able to outcompete the nematodes for resources leading to a decline in the parasitic nematode populations.
Similarly, Istifadah et al. (2020) found that an increase in beneficial microbes inhibited the growth of the pathogen Alternaria solani, an oomycete that causes early blight in tomato plants [4]. Oomycetes are fungus-like organisms that reproduce via spores that can overwinter in soil for up to 4 years. Istifadah’s team treated inoculated tomato plants with microbial-rich compost and monitored them for multiple weeks to test the pathogen suppression capabilities. The microbial-rich compost showed up to 47% disease suppression compared to that of non-enriched compost. In this study, they also tested the use of fungicide on the infected plants which yielded a 70% suppression of early blight. While the fungicide tested better, it is important to note that this treatment also removed any form of beneficial fungi that may be present in the soil. Fungi play an important role in the ecology of plant communities— creating subterranean mycelial networks, they form symbiotic relationships with plant roots to exchange water and nutrients for sugars that plants excrete in return. Preserving these microbes has also been shown to be successful at reducing pollutants and pathogens that can cause harm to humans.
Effects on Human Pathogens and Toxins
Due to large supply chains, infected produce can be transported and distributed before contamination is known—resulting in quick spread and high infection rates within the population. In 2019, an E. coli outbreak was traced back to romaine lettuce that was harvested from the Salinas Valley in central California. The CDC reported a total of 167 people infected with E. coli. Of that total, 85 were hospitalized and 15 developed hemolytic uremic syndrome, a type of kidney failure [5]. It was theorized that E. coli. was introduced to agricultural fields through cow manure. Due to the widespread use of manure as a popular organic fertilizer in crop production, it is important to assess the capability of VC systems to decompose organic wastes and decrease pathogen populations. A study conducted by Hossein Karimi and a team in 2017 examined the changes in microbial pathogen dynamics after mixing vermicompost with both cow manure and sewer sludge. The team found that VC was a sufficient way to transform organic waste into a class A compost while also reducing the number of pathogens[6]. Singh et al. (2018) detail similar findings when determining the rate of decomposition of manure via VC systems. It was reported that in 172 days, the total biomass of manure was reduced from 45.9% to 3.5%, and the application of VC led to a decline in the number of harmful pathogens in the system [1].
Both studies also assessed VC’s ability to reduce the accumulation of toxins like heavy metals in soils. While VC's ability to regulate contaminants varies depending on a pollutant’s mobility, through proper steps of remediation VC was able to reduce substances like arsenic, mercury, and selenium [1]. VC performs a series of functions to remedy soil contaminants that include: immobilization, reduction, volitation, and modification. First, VC is used to immobilize pollutants by its ability to retain ionic compounds. The VC then induces a chemical reduction process through the provision of electrons and carbon substrate for microorganisms. The microbes are then able to volatilize harmful elements such as As, Hg, and Se through the process of methylation. Lastly, VC releases weak acids into the soil that aid in the transformation of the soil’s physiochemistry providing a favorable environment for these processes to take place [1]. It was also found that the composting worms themselves possess the ability to bioaccumulate these toxins within their bodies during the composting process [6].
Mechanisms of control
Through the employment of various mechanisms, the microbes contained within VC bolster rooting zones, helping plants defend against invasion from pests and pathogens. Yatoo et al. (2021) compiled research on this topic and highlighted 4 general mechanisms that give VC its power to regulate harmful pathogens. The mechanisms include nutrient competition, antibiosis, predation, and systemic-induced resistance. In healthy environments, where microbial activity is nurtured through application of VC, beneficial populations are allowed to flourish and often outcompete harmful pathogens for nutrients contained within soils. Antibiotic producing organisms play a crucial role in soil ecosystems by shaping microbial communities, and controlling pathogen population sizes through the production of secondary metabolites that inhibit the growth or activity of competing organisms, also known as antibiosis. Control via predation has been observed in certain species of fungi who trap and consume nematodes using a noose-like structure that is constructed from hyphal strands. Finally, VC contains various bioactive compounds, including plant hormones, enzymes and secondary metabolites that can induce systemic resistance, a state of enhanced defensive capacity throughout a plant that provides broad-spectrum resistance against a wide range of pathogens [2].
Conclusion
The studies presented in this review strongly suggest that vermicompost can be an effective and low-cost way to mitigate the dependence on inorganic chemicals and facilitate the health of agricultural soils. The research highlights the importance of microbial activity and the influence that it has on soil health and plant defenses. Though there is substantial evidence for the use of vermicompost and vermicompost teas to reduce the number of toxins, pests, and pathogens, it is still not widely used today. The most likely reasons are the lack of education and understanding of our lands. Today's agricultural practices completely disrupt soil biomes that are critical for the health of plants, and create a dependence on harmful inorganic solutions. In the quest to produce more crops more efficiently, we are irreversibly dooming the productivity of soils for future generations.
About the Author: Max Luepke
Max Luepke is an class of 2024 environmental horticulture and urban forestry major with a deep-seated passion for growing food. His interest in horticulture took root at Santa Barbara City College, which advocates for an interconnected, holistic approach to plant care. The department head, Michael Gonella, frequently emphasized the principle of "feeding the soil, not the plants", a mantra that has significantly influenced Max’s perception of plant care, particularly in the realm of food cultivation. By promoting soil health, one can have a profound impact on the quality and success of crop plants. Max has conducted an analysis on vermicompost to disseminate alternative methods for the use of synthetic fertilizers and pesticides within cropping systems. From Max's perspective, the dialogue surrounding alternatives like vermicompost is somewhat absent within the undergraduate education at UC Davis. Through this research compilation, he aspires to enhance readers' exposure to more sustainable methods of managing the food that we consume.
Author's Note
This literary review, initially composed for my University Writing Program class, explores the many applications of vermicompost and vermicompost teas. My personal experience with utilizing vermicompost in my garden fostered a curiosity and a need for a more profound comprehension of the topic. The analysis I conducted reveals alternative approaches to managing pests and pathogens, diverging from conventional synthetic methods, and simultaneously enhancing soil fertility. While these strategies remain relatively under-researched, their potential impact on soil health and the nutritional value of our food warrants further scientific investigation. Encouraged by my professor's positive feedback, I am now presenting this work for consideration in the Aggie Transcript, hoping to contribute to the expanding discourse in sustainable agriculture practices.
References
Singh, Archana, and Gopal Shankar Singh. 2017. Vermicomposting: A Sustainable Tool for Environmental Equilibria. Environmental Quality Management, vol. 27, no. 1, pp. 23–40.
Yatoo, Ali Mohd, et al. 2021. Sustainable Management of Diseases and Pests in Crops by Vermicompost and Vermicompost Tea. A Review.” Agronomy for Sustainable Development, vol. 41, no. 1.
Mishra, Shova, et al. 2017. Suppression of Root-Knot Nematode by Vermicompost Tea Prepared from Different Curing Ages of Vermicompost. Plant Disease, vol. 101, no. 5, pp. 734–737.
Istifadah, N., et al. 2020. Effectiveness of Compost and Microbial-Enriched Compost to Suppress Powdery Mildew and Early Blight Diseases in Tomato. The Journal of Animal and Plant Sciences vol. 30, no. 2
Outbreak of E. Coli Infections Linked to Romaine Lettuce. Centers for Disease Control and Prevention, Centers for Disease Control and Prevention. Accessed 15 Jan. 2020, Available from: https://www.cdc.gov/ecoli/2019/o157h7-11-19/index.html.
- Karimi, Hossein, et al. 2017.Changes in Microbial Pathogen Dynamics during Vermicomposting Mixture of Cow Manure–Organic Solid Waste and Cow Manure–Sewage Sludge. International Journal of Recycling of Organic Waste in Agriculture, vol. 6, no. 1, 2017, pp. 57–61.