Vermicomposting is the process of turning organic debris into worm castings. Although worm castings have been found to improve the condition of the soil and the growth of plants, there has not been much research done on this subject. The objectives of this project were: 1) To determine the optimal vermicompost/soil admixture for growth of Pelargonium hortorum; and 2) To compare the growth of geraniums in the optimal vermicompost/soil admixtures to those grown in standard potting soil supplemented with chemical fertilizer. Each of the vermicompost/soil admixture setups—control, 5%, 15%, 30%, and chemical fertilizer—were tested using a Hach Soil Test Kit before plant growth to find the soil pH and amounts of phosphorus, nitrate-nitrogen, and potassium in the soil. Ten plants in each setup were observed and measured weekly for five weeks. Results of this study showed that after applying the vermicompost to the soil, the amounts of phosphorus, nitrate-nitrogen, and potassium rose, which helped the plants grow better. Analyses of variance were done to compare the growth rates of the compost admixture plants with those in the control group. The difference in the plant height was significant at the p>.05 significance level. The difference in the plant width and leaf midrib length was significant at the p>.2 level of significance. F-Ratio tests were done to compare the growth rates of the 15% vermicompost/soil admixture and the chemical fertilizer groups. The difference in the plant height, plant width, and leaf midrib length were not significant.
Earthworms have been on the Earth for over 20 million years. In this time they have faithfully done their part to keep the cycle of life continuously moving. Their purpose is simple but very important. They are nature’s way of recycling organic nutrients from dead tissues back to living organisms. Many have recognized the value of these worms. Ancient civilizations, including Greece and Egypt valued the role earthworms played in soil. The Egyptian Pharaoh, Cleopatra said, “Earthworms are sacred.” She recognized the important role the worms played in fertilizing the Nile Valley croplands after annual floods. Charles Darwin was intrigued by the worms and studied them for 39 years. Referring to an earthworm, Darwin said, “It may be doubted whether there are many other animals in the world which have played so important a part in the history of the world.” The earthworm is a natural resource of fertility and life. (1)
Earthworms live in the soil and feed on decaying organic material. After digestion, the undigested material moves through the alimentary canal of the earthworm, a thin layer of oil is deposited on the castings. This layer erodes over a period of 2 months. So although the plant nutrients are immediately available, they are slowly released to last longer. The process in the alimentary canal of the earthworm transforms organic waste to natural fertilizer. The chemical changes that organic wastes undergo include deodorizing and neutralizing. This means that the pH of the castings is 7 (neutral) and the castings are odorless. The worm castings also contain bacteria, so the process is continued in the soil, and microbiological activity is promoted. (2)
Vermicomposting is the process of turning organic debris into worm castings. (3) The worm castings are very important to the fertility of the soil. The castings contain high amounts of nitrogen, potassium, phosphorus, calcium, and magnesium. (1) Castings contain: 5 times the available nitrogen, 7 times the available potash, and 1 ½ times more calcium than found in good topsoil. (4) Several researchers have demonstrated that earthworm castings have excellent aeration, porosity, structure, drainage, and moisture-holding capacity. (5) The content of the earthworm castings, along with the natural tillage by the worms burrowing action, enhances the permeability of water in the soil. Worm castings can hold close to nine times their weight in water. (1) “Vermiconversion,” or using earthworms to convert waste into soil additives, has been done on a relatively small scale for some time. (4) A recommended rate of vermicompost application is 15-20 percent.
Vermicomposting is done on small and large scales. In the 1996 Summer Olympics in Sydney, Australia, the Australians used worms to take care of their tons and tons of waste. They then found that waste produced by the worms was could be very beneficial to their plants and soil. (6) People in the U.S. have commercial vermicomposting facilities, where they raise worms and sell the castings that the worms produce. Then there are just people who own farms or even small gardens, and they may put earthworms into their compost heap, and then use that for fertilizer.
The objectives of this project were: 1) To determine the optimal vermicompost/soil admixture for growth of Pelargonium hortorum; and 2) To compare the growth of geraniums in the optimal vermicompost/soil admixture to those grown in standard potting soil supplemented with chemical fertilizer. After library research, it was believed that geranium growth would vary among different vermicompost/soil admixtures, and that optimal vermicompost/soil admixture would produce better plant growth than chemical fertilizer. Therefore, the null hypotheses were: 1) There would be no significant differences among geranium growth in different vermicompost/soil admixtures; And 2) There would be no significant differences in geranium growth between the optimal vermicompost/soil admixture and those supplemented with chemical fertilizer.
Admixture, Plant Growth, and Measurement Procedure
Vermicompost was obtained from a commercial vermicomposting facility, which composts mostly paper products. The geranium seeds were obtained from a plant nursery. Calculations were done to determine 5%, 15%, and 30% vermicompost/soil admixture masses and an electronic balance was used to measure the soil and compost for mixing. For each admixture ten pots were filled; the control group contained only soil, and ten pots were filled with soil mixed with chemical fertilizer. Small amounts of the planting medium from each group was set aside for testing. Geranium seeds were planted and allowed to grow for three weeks before transplanting. One geranium plant was planted in each pot. The plants were watered daily and observed for five weeks. Plant height and width were measured each week. Measurements were made on three leaf midribs on every plant weekly, and the average of the three was recorded. When the growing term was ended, the geraniums were pulled from the soil. The above-ground shoots were separated from the below-ground roots and allowed to dry for one day. An electronic balance was used to find the mass in grams of the shoot and root sections of each plant.
Each of the vermicompost/soil admixture setups—control, 5%, 15%, 30%, and chemical fertilizer added—were tested using a Hach Soil Test Kit before plant growth. Determination of soil pH was done using the aqueous soil extraction method and a Pocket Pal pH electrode. Filtered extract from a Mehlich 2 Extraction for soil was used for phosphorus analysis (PhosVer 3 Method) and potassium analysis (Turbidimetric Tetrophenylborate Method). A calcium sulfate extraction for soil provided filtered extract for determination of nitrate-nitrogen by the Cadmium Reduction Method.
Graph 1 compares mean changes in foliage height. The rate of growth for the control and 5% vermicompost was faster than other groups after two weeks of growth and continued to increase for one more week. At week four, the rate of growth for the 15% admixture group was much higher than the others. The fertilizer group grew slower than the vermicompost until week four when it exceeded the control. By week five, the growth rate of all groups was slowing, but the 15% was still faster than the others. Analysis of variance for replicated treatments showed significant differences (p>.05) between the growth rates of the different groups.
Graph 2 compares the mean changes in foliage width for the different growth media. The plants in the 30% admixture had the greatest change in width after 2 weeks. The width of the plants grew faster in all groups until week three when the rate of the width growth began to slow; however, the plants in the 15% admixture began growing faster again in width at week 4, while the others leveled off or declined. Analysis of variance for replicated treatments showed significant difference (p>.2) between the changes in width of the different groups.
Graph 3 compares the mean changes in leaf midrib length. After two weeks, the midribs were growing the fastest within the 30% compost group, but the rate declined every week thereafter. The rate of the control was the highest after three weeks followed by the 15% vermicompost. Leaf growth declined for all groups in the following weeks. Analysis of Variance for replicated treatments showed a significant difference (p>.2) in the mean changes in leaf midrib length.
Table 4 shows the average dry biomass for the different groups. The plants grown in the soil supplemented with chemical fertilizer had the highest shoot to root ratio at 14.7 to 1. The chemical fertilizer seemed to promote growth of the shoots more than the growth of the roots more than the control and vermicompost mixtures. The admixture with the greatest proportion of the vermicompost (30%) resulted in the best root development in relation to shoot growth with a shoot to root ration of 12.7 to 1 ( See Table 5). The 30% Admixture had the highest amounts of phosphorus, potassium and nitrate-nitrogen in comparison with all other vermicompost mixtures and the chemical fertilizer. The soil pH was about the same for all with a range of 6.2 – 6.5. Although the 30% admixture group gained the most nutrients, the plants might not have grown as well because the worm castings are able to hold so much water that it could almost have a drowning effect on the plants; and this group had the greatest percentage of castings.
The results of this study seem to indicate that an optimal vermicompost/soil admixture is 15% earthworm castings. The null hypothesis that there would be no significant difference in vermicompost/soil admixtures was rejected. The results also indicate that the growth of the geraniums in the optimal vermicompost/soil admixtures did not differ significantly from the growth of the geraniums in the soil that was supplemented with chemical fertilizer. The null hypothesis that there would be no significant differences in geranium growth between the optimal vermicompost/soil admixture and those supplemented with chemical fertilizer was accepted. It was also concluded that although there was no difference in the optimal vermicompost/ soil admixture group and the group supplemented with chemical fertilizer, it would still be better to use the worm castings instead of the chemical fertilizer. Worms not only improve the soil, but when worms are used to compost, they also recycle waste products that could otherwise go to a land fill or harm the environment. Further study of this project could include using different species of plants in the vermicompost admixtures and/or putting larger percentages of the vermicompost into the soil.
1. http://www.wormfarm.com/discuss.html. “Earthworms as a Natural Resource.” Chapman,
2. http://members.tripod.com/~wormigrow/. “If You Are Looking For Worms, You Are at the
3. http://www.bae.ncsu.edu/people/faculty/sherman/vermiculture/markets.html. “Potential Markets
For Vermiculture and Vermicomposting Operations.” Sherman-Huntoon, Rhonda.
4. http://www.happydranch.com/articles/reference.html. “Reference Information.”
Castings as Plant Growth Media.” Sherman-Huntoon, Rhonda.
6. http://www.gnv.fdt.net/~windle/refrence/july98.htm. “Comparing Vermicomposts and
Composts.” Subler, Scott, Clive Edwards, and James Metzger.
7. “`Ring’ Worms Cleaning Up.” The Daily Oklahoman. Anthony, Ted. 19 September