Influence of Diet of the Red Wiggler Earthworm (Eisenia fetida) on Nitrogen, Phosphorus, and Potassium (NPK) Nutrients, Organic Matter, and Carbon: Nitrogen (C:N) Ratio within the Vermicompost Casts

By K’Lona J. Lofton

Red Wiggler Earthworm (Eisenia fetida). Photo: Rob Hille / CC BY-SA

Abstract

Earthworms are important to agricultural success, earning them the nickname of “farmer’s best friend,” by providing a dual benefit. They help lessen waste by digesting organic material and are known for turning “trash into treasure” through a process called vermicomposting (Misra, R. V. et al., 2003). Vermicomposting consists of using the epigeic, or surface dwelling, earthworm to digest organic and raw material, which results in a rich excretory end product called “casts.” These casts are filled with many microbes and nutrients, including the plant growth promoters nitrogen, phosphorus, and potassium (NPK) that aid in its action as an organic fertilizer (Wani, KA. 2013). Several studies have been performed to address vermicomposting and an earthworm’s ability to maintain soil fertility. However, it is unknown if one source of composting material is more beneficial for vermicomposting than another. In this study, I aimed to determine if one compost material resulted in higher nutrient levels of (NPK) in excretory casts from Eisenia fetida, red wiggler earthworms. The red wiggler worms were fed five different diet materials: paper waste, “worm food,” vegetables and fruit, manure, and kitchen waste (ground coffee, eggshells, and tea bags.) Daily temperature recordings were taken with weekly pH level testing. It was hypothesized that one source of composting diet would be significantly greater in NPK nutrients, organic matter, and C:N ratio. Results revealed that there was no significant difference between each worm diet. These results may provide important information that could be utilized to help preserve and naturally fertilize the soil, ultimately aiding in sustainability with the growing agricultural demand.

Introduction

Earthworms were once referred to as “unheralded soldiers of mankind” and “friends of farmers” by one of the most famous scientists in history, Charles Darwin. Darwin has shaped the world with his theory of evolution but what most do not know was his last and final work was spent studying earthworms and their potential to be an environmental revolution (Rajiv, S. et al. 2010.)

Earthworms provide many benefits to the soil ecosystem that are determined by their ecological grouping, or ecotypes. These ecotypes include the Epigeic earthworm that resides in the surface of the soil, and mainly feed on decaying organic material on the surface. Endogeic worms live deeper within the topsoil where they create horizontal burrows and eat only dead plant matter such as dead plant roots, and the anemic earthworms live in the deepest part of the soil where they create permanent burrows, and only go to the surface to drag their food, such as leaf litter, into the soil to eat. (Cluzeau, D. Balesdent, J. & TRehen, P. 2001) All of these roles combined create the benefits of increased nutrient availability, better aeration for water, and overall a more stable soil structure that inhibits plant growth.  Though these are important properties to obtain a healthy soil, what really gives them the nickname “farmers best friend’ is the valuable benefit of the excrete they leave behind. This excrete, referred to as “vermicasts,” can act as a highly nutritive organic fertilizer that is rich in humus, as well as main plant growth promoters, such as nitrogen, phosphorus, and potassium, micronutrients, and beneficial soil microbes. One way to vitalize this import end-product from earthworms is through a process called vermicomposting. Vermicomposting is a composting method that uses epigeic earthworms to digest and recycle organic material to create the “vermicasts.” This process provides a dual benefit of creating an organic fertilizer while also recycling organic waste.

The creation of agro-chemicals such as fertilizers, pesticides, and herbicides, has led farmers to stray away from organic practices in order to help meet the agricultural demand of the increasing human population. However, in a recent study it has been found that these chemicals can be detrimental to our health and environment by killing the beneficial soil organisms, destroying natural fertility in the soil, harming the biological resistance in crops making them more susceptible to pests and disease, and contributing to soil, air, and water pollution (Savci 2010). Agro-chemicals are also contributing to the world-wide issue of groundwater pollution. Ground water is responsible 51% of drinking water for the U.S. and accounts for 64% of irrigation that is used to grow our crops so once it is polluted with toxic chemicals, it may take many years for the contamination to dissipate, or clean up (US EPA 2001). These chemicals combined have contaminated almost every aspect of our environment. Therefore, there is a need for an innovative and more sustainable way to grow our food, while preserving our soil, water and air. Research on earthworms, and vermicomposting may help pave the way.

Materials and Methods

Five small scale, 15″ x 15″ x 22″, indoor composting bins will hold 2,000 red wiggler worms (unclejimswormfarm.com). These bins will be monitored in a classroom at the United Tribes Technical College. Bins labeled according to each of the 5-worm diets: (A) paper waste, (B) worm food (unclejimswormfarm.com), (C) decayed vegetable and fruit scraps, (D) aged buffalo manure (Roybal Buffalo Ranch located in South Eagle Butte, SD), (E) kitchen waste (pulverized egg shells, tea bags and ground coffee). Daily temperatures will be recorded using a pen-type pocket thermometer (Comark KM400 Digital Pen-Type Pocket Thermometer w/ 3″ Stem, Black) along with weekly pH testing using LaMotte Garden Kit (Carolina Biological Supply Company).

The bedding of each bin will contain half a block of coconut husk (unclejimswormfarm.com), and roughly one handful of shredded newspaper. Moisture is essential for worm survival and productivity; therefore, all organic waste will be soaked in water (Selden et al. 2005). Prior to the first feed, the worms will be free of disturbance for approximately one week to adjust to the new environment. Once the worms have acclimated to the bedding, they will be fed once a week for the next 6 weeks by the surface-feeding method.  The food of each diet will be spread across the surface roughly ½ in thick.

The composting bins consist of layered chambers. Once the feed is composted in bottom layer, new food will be added to the top layer, which will allow the worms to migrate further up leaving the vermicompost ready to harvest. To begin separating the vermicompost from the bedding, a 3 layered sieve colander, and 300 mm sieve stainless cloth (both ordered from amazon) will be used. Once all 5 bins are separated, 1 quart of the vermicompost will be placed into a zip lock bag with correct labels.  These vermicompost samples will be sent to Pennsylvania State University: Agricultural Analytical Services Laboratory for testing of the nitrogen, phosphorus, and potassium (NPK) nutrients, organic matter percentage, and carbon:nitrogen (C:N) ratio in the vermicompost. The results will be analyzed by using an ANOVA test either rejecting, or accepting the hypothesis. 

Results

Daily temperature results and weekly pH levels that were analyzed with an ANOVA test showed no significant difference between each 5 worm diets. (See Figures 1.1 & 1.2)

Results from the Penn State laboratory show that the organic matter levels are consistent with all bins except bin C (fruit and veggies) which shows a lower percentage level. Results also show that bin B (worm food) and bin E (kitchen waste) have slightly higher nitrogen levels, bins B (worm food) and bin D (buffalo manure) show higher phosphorus levels, and bin C (fruits and veggies) has the highest amount of potassium. (Figures 2.2)

A desired range for carbon:nitrogen ratio is 25:1:1. Results shown in table 1.1 reveal that bin A (paper waste) has the highest carbon level when compared to the rest of the bins. Bins B (wormfood), C ( fruit and veggies), D (buffalo manure), and E (kitchen waste) are in the desired range for a comfortable (C:N) ratio. (table 1.1)

Discussion

Data from Penn State has shown that there were no significant differences with each five compost diets for the red wiggler earthworm (Esienia fetida.)  Based on observations, bin A (paper waste) had no obvious problems, bin B (worm food) that has shown higher levels of nutrients, also had the highest rates of worm deaths and shown to be the least productive bin. pH levels of this bin has also been acidic throughout the 6 weeks of composting, starting after the first feed of the worm food (contains saw dust, cornmeal, wheat) that was given the first week, suggesting an unfavorable diet. Bin C (fruits and veggies) have shown the most productive activity of the red wiggler and produced greater amounts of worm casts compared to other bins. Bin D (buffalo manure) took awhile for the worms to start composting. This may be due to the fact that the manure had not been pre-processed, dried out or weathered down, because of the smell of ammonia or salt.  Bin E (kitchen waste) was the second bin that had more acidic pH levels, as well as more worm deaths.

Despite the results, observations through six weeks of vermicomposting has provided great information on how to effectively manage a worm bin.  Temperature range from 70 degrees fare height to 80 degrees fare height seem to be a desired range, along with a pH level that is more alkaline than acidic. Bedding with each bin is an essential part of a healthy bin. It has shown to act as a  “safe zone” for the worms when the food was unfavorable.  There are many different ways to feed worms while vermicomposting, but with the small-scale bins, surface feeding method seemed to work well (spreading the food 1 in. thick over the bedding.) 

Further research is necessary to understand the nutrient levels of each compost diet and its influence on the earthworm castings. Future directions for this research will be to replicate the study for an extended period to get a clearer understanding of vermicomposting. With new information regarding the earthworm casts filled with nutrients, may provide many benefits to sustaining, or re-generating the soil.

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About the Author
K’Lona Lofton, a Lakota from the Cheyenne River Sioux Tribe, is currently enrolled into the Environmental Science and Research bachelor’s degree program at United Tribes Technical College in Bismarck, ND, where she is completing her senior research project on vermicomposting. She plans to pursue a master’s degree in soil science, focusing on edaphology and the soil’s ecological relationship with land cultivation, practices, and plants.

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