An effective microorganism (EM) refers to any of the predominantly anaerobic organisms blended in commercial agricultural amendments. Effective microorganisms are produced by Em Research Organization, Inc., among others. In commercial agricultural amendments or for environmental applications such as for septic tanks, EM is purported to support sustainable practices in farming, improve composting operations, and to reduce environmental pollution, with "the problem of reproducibility and lack of consistent results."
Many of the so-called "pit additives" used for improving the performance of sanitation systems, namely pit latrines, septic tanks and wastewater treatment plants, are also based on effective microorganisms. Despite the claims made by manufacturers, available studies which have used scientific methods to investigate these additives have come to the conclusion that long-term beneficial effects are not proven.
Effective microorganisms (EM-A, EM-Bokashi) show no effect on yield and soil microbiology in field experiments as bio-fertilizer in organic farming. Observed effects relate to the effect of the nutrition rich carrier substrate of the EM preparation.
- Lactic acid bacteria: Lactobacillus casei
- Photosynthetic bacteria: Rhodopseudomonas palustris
- Yeast: Saccharomyces cerevisiae
- Others: beneficial microorganisms that exist naturally in the environment may thrive in the mixture.
The concept of "friendly microorganisms" was developed by Professor Teruo Higa, from the University of the Ryukyus in Okinawa, Japan. He reported in the 1980s that a combination of approximately 80 different microorganisms is capable of positively influencing decomposing organic matter such that it reverts into a "life promoting" process. Higa invoked a "dominance principle" to explain the effects of his "Effective Microorganisms". He claimed that three groups of microorganisms exist: "positive microorganisms" (regeneration), "negative microorganisms" (decomposition, degeneration), "opportunist microorganisms". In every medium (soil, water, air, the human intestine), the ratio of "positive" and "negative" microorganisms is critical, since the opportunist microorganisms follow the trend to regeneration or degeneration. Therefore, Higa claimed that it is possible to positively influence the given media by supplementing with "positive" microorganisms.
The concept has been challenged and no scientific studies support all of its claims. This was acknowledged by Higa in a 1994 paper co-authored by Higa and soil microbiologist James F Parr. They conclude "the main limitation...is the problem of reproducibility and lack of consistent results.".
Parr and Higa mention soil pH, shading, soil temperature and flooding as factors affecting the interaction of EM with local microorganisms and with each other. The approach that Higa and Parr recommend is maintaining pH and soil temperature within conditions known to be detrimental to negative microorganisms as well as the addition of EM to tip the balance of positive and negative microorganisms in favor of the former.
They dismiss inoculants that include only a single microorganism as generally ineffective due to the uncertainty about the conditions in which a single microorganism would be effective. They cite the acknowledgment by the scientific community that multiple microorganisms in coordination with good soil management practices positively influence plant growth and yield.
Various researchers have examined the use of EM in making organic fertilizers and investigated the effects of the fermented organic fertilizer on soil fertility and crop growth. The resulting effects on crop growth depend upon the organic fraction, direct effects of the introduced microorganisms, and indirect effects of microbially-synthesized metabolites (e.g., phytohormones and growth regulators).
Due to the fact that only very few studies exist which have used scientific methods to investigate additives based on EM, any claims made by manufacturers regarding long-term beneficial effects need to be treated with care.
In a community course of the Christchurch city council, New Zealand, 4-13 year old students can "learn the science behind reducing and utilising organic waste as a resource by turning it into natural fertilisers".
- Higa, Dr. Teruo; Dr. James Parr (1994). Beneficial and Effective Microorganisms for a Sustainable Agriculture and Environment (PDF). Atami, Japan: International Nature Farming Research Center. p. 7. Retrieved 14 August 2016.
- Foxon, K; Still, D (2012). Do pit additives work?. Water Research Commission, University of Kwazulu-Natal, Partners in Development (PiD), South Africa.
- Mayer, J.; Scheid, S.; Widmer, F.; Fließbach, A.; Oberholzer, H.-R. (2003–2006). "Effects of ‚Effective Microorganisms EM' on plant and microbiological parameters in a field experiment, Zürich, Switzerland" (PDF). orgprints.org. http://orgprints.org/9691/. Retrieved 21 August 2016.
- Mayer, J., Scheid, S., Widmer, F., Fließbach, A. & Oberholzer, H.-R.: How effective are “Effective microorganisms (EM)”? Results from a field study in temperate climate. Applied Soil Ecology 46, 230–239(2010) doi:10.1016/j.apsoil.2010.08.007
- "Trademark Guidelines". emrojapan.com. 2011. Retrieved 13 November 2011.
- Szymanski, N.; Patterson, R.A. (2003). "Effective Microorganisms (EM) and Wastewater Systems in Future Directions for On-site Systems: Best Management Practice." (PDF). In R.A. and Jones, M.J. (Eds). Proceedings of On-site '03 Conference. Armidale, NSW, Australia: Lanfax Laboratories. pp. 347–354. ISBN 0-9579438-1-4. Retrieved 2006-11-14.
- Yamada, K.; Xu, H. L. (2001). "Properties and Applications of an Organic Fertilizer Inoculated with Effective Microorganisms". Journal of Crop Production. 3: 255. doi:10.1300/J144v03n01_21.
- Pei-Sheng, Y.; Hui-Lian, X. (2002). "Influence of EM Bokashi on Nodulation, Physiological Characters and Yield of Peanut in Nature Farming Fields". Journal of Sustainable Agriculture. 19 (4): 105. doi:10.1300/J064v19n04_10.
- Xu, H. L. (2001). "Effects of a Microbial Inoculant and Organic Fertilizers on the Growth, Photosynthesis and Yield of Sweet Corn". Journal of Crop Production. 3: 183. doi:10.1300/J144v03n01_16.
- Xu, H. L.; Wang, R.; Mridha, M. A. U. (2001). "Effects of Organic Fertilizers and a Microbial Inoculant on Leaf Photosynthesis and Fruit Yield and Quality of Tomato Plants". Journal of Crop Production. 3: 173. doi:10.1300/J144v03n01_15.
- Daiss, N.; Lobo, M. G.; Socorro, A. R.; Brückner, U.; Heller, J.; Gonzalez, M. (2007). "The effect of three organic pre-harvest treatments on Swiss chard (Beta vulgaris L. Var. Cycla L.) quality". European Food Research and Technology. 226 (3): 345. doi:10.1007/s00217-006-0543-2.
- Daiss, N; Lobo, M. G.; Gonzalez, M (2008). "Changes in postharvest quality of Swiss chard grown using 3 organic preharvest treatments". Journal of food science. 73 (6): S314–20. doi:10.1111/j.1750-3841.2008.00842.x. PMID 19241576.
- "Fertilising for the Future". ccc.govt.nz. Christchurch City Council. Retrieved 27 November 2015.
- Mohit M Rao. "Micro bugs may help in restoring our embattled water bodies". The Hindu.
- "EM balls produced by royal project". The Nation. 2 November 2011.