Sunday, August 29, 2010

Earthworms: the most important soil and ecosystem engineers


Earthworms are thought to be the most ancient soil animals having started colonizing terrestrial environments about 600 million years ago (Spain and Lavelle 2001). They are the most predominant soil fauna except in dry and cold climates. Earthworms are semiaquatic animals which extract water continuously from the surrounding soil inorder to maintain their cuticle in a moist state to facilitate gas exchange. Thus moisture status is a major limitation to earthworm activities and distribution.
Spain and Lavelle (2001) reported that since earthworms live in direct and continuous contact with the soil matrix and the soil solution, their presistence, propagation and activity are greatly affected by the chemical (pH, dissolved ions) characteristics of the soil. Based on their sensitivity to soil pH, earthworms are grouped into acidophilic species (able to thrive below pH 6 such as in organic forest litter), neutrophilic species (they prefer soil pH 6 to 7) and basophilic species (prefer basic soils).

Three ecological types of earthworms (Spain and Lavelle, 2001)
a) Epigeics. Earthworm of this type live in the litter layers and thus are effective compost-makers. However, they have no or little effects on soil structure.
b) Anecics. These are earthworms that feed on the surface littler that they mixe with soil but spend most of the time in galleries they create within the soil. They are
also able to translocate considerable amount of leaf-litter into the soil.
c) Endogeics. Earthworms of this type live and feed within the soil. Among the earthworm types, the endogeics are the major agent of soil aggregation.
Effects of earthworms on soil properties
Earthworm burrows are known to have high continuity in both horizontal and vertical directions and thus greatly influences water and air movement in the soil. Earthworms influence the physical and chemical soil properties in many ways by burrowing, casting, feeding and propagating. According to Emmerling et al. (2002) earthworms are the most important ecosystem engineers (organisms that may modify or create their habitat and thus influence availability of resources to other species and soil properties) in arable soil due to their lasting effects on soil physical and biochemical properties.
In an interesting laboratory study to assess the impact of ecologically different earthworm species on soil water characteristics, such as soil tension, water content, and water infiltration rate, Ernst et al. (2009) exposed three earthworm species (Lumbricus rubellus, Aporrectodea caliginosa, Lumbricus terrestris) in soil columns (diameter 30 cm, height 50 cm) for 100 days with a total fresh earthworm biomass of 22.7 ± 0.4 g per column, each in duplicate. Each column was added with 30 g of sieved and rewetted horse manure placed on the soil surface as a food source. Precipitation events (10 mm) were simulated at day 28 and day 64.
Results revealed that ecologically different earthworms modify soil water characteristics in different ways. The anecic L. terrestris and the endogeic A. caliginosa showed the tendency to enhance the drying of the topsoil and subsoil. Their intensive and deep burrowing activity seemed to enhance the exchange of water vapor due to a better aeration in the soil. In contrast, the epigeic L. rubellus tended to enhance the storage of soil moisture in the topsoil, which might be linked to lower rates of litter loss from soil surface and thus a thicker litter layer remaining. A. caliginosa led to considerable higher water infiltration rates and faster water discharges in the subsoil, relative to the other species, probably due to a high soil dwelling activity.
Vermiculture
The term "vermiculture" refers to the cultivation of epigeic earthworms grown in an organic matter substrate with no soil. Rearing soil dwelling earthworms undercontrolled conditions requires an understanding of their needs. Many earthworm species can exhibit a degree of plasticity in behavior, so general maintenance does not necessarily require extremely large containers. L. terrestris for example does not need access to a vertical borrow and can be bred in pots which may be only a few cm in depth (Butt, 2009).
References
Butt, KR. 2009. Collection and rearing of earthworms. Workshop Kommission III der DBG, 20-21.03.2009, Trier, Germany
Emmerling, C, M Schlotter, A. Hartmann, and E. Kandeler. 2002. Functional diversity of soil organisms- a review of recent research activities in Germany. JPNSS 165:
408-420.
Ernst G, D Felten, M Vohland, and C Emmerling. 2009. European Journal of Soil Biology 45: 207-213.
Lavelle, P. and A.V. Spain. 2001. Soil Ecology. Kluwer Academic Publishers. Dordrecht, 654p
Photo source:


9 comments:

Anonymous said...

I am working with an NGO here in Davao and I have heard a lot about vermiculture and the "great things" about vermicast as soil fertilizer but I have doubts. What is your opinion about it? Do you believe in what some sustainable agriculture advocates are saying about IMO that it is the future of sustainable agriculture? I hope for your scientific opinion. Many thanks. By the way, I find your blog excellent. It is a source of many important and many interesting ideas for me kasi malayo ako sa library. Keep it up.

Victor B. Asio said...

Thanks for your comments. Vermicast is an organic material and thus it can improve soil quality and enhance crop performance. The only problem is that the amount that should be applied varies with soil type, crop, and climatic conditions. And very little scientific studies have been done on this aspect. For example, most of the trials conducted by students in the department revealed no increase in rice and corn yields upon application of vermicast. I think the rates used were low to cause any improvement in crop performance. Concerning indigenous microorganism (IMO)and other bio-organic preparations which are claimed to be effective biofertilizers, I think that some of them maybe effective at high rates (in several tons)but rigid scientific testing is urgently needed. To cite an example, in all natural soils, the activity of native microorganisms which are important for nutrient transformations and decomposition process can be enhanced by simple addition of organic materials. You do not need the tedious process of preparing IMO fertilizer using all sorts of food materials, sugars, etc. The important questions are: do these materials really improve soil quality and crop yield? If so what are the specific soil parameters and microorganism populations that are enahnced? At what rates of application can this be attained? Under what soil conditions are they effective? What crops are responsive?

Ronnie L said...

Isang estudyante po ako. sa field trip po namin, we visited an LGU na nag produce ng vermicast from their solid waste noon. wala na daw ngayon dahil mahirap mag maintain ng vermiculture. madali daw mamatay ang earthworms.

Anonymous said...

earthworms have died maybe because of heavy metal pollution since solid waste was used to produce vermicast...just maybe...

Anonymous said...

namatay siguro and earthworms because of heavy metal pollution since solid waste was used to produce vermicast...

irish geneston said...

namatay siguro ang earthworms maybe because of heavy metal pollution since solid waste was used to produce vermicast...

gwen ortiz said...

Hello sir, I'm Gwen Ortiz a BS Biology student currently studying the impact of heavy metals to earthworms from coal fired power plant here in Davao City. Sir i would like to ask some of your articles and if you have some research paper about this topic sir. thank you.

Samadhan Agrotech said...

Good work ! good continuation :)
Purchase Organic Fertilizers

Samadhan Agrotech said...

Good work ! good continuation :)
Purchase Organic Fertilizers