Short communication
Temperature and soil moisture content effects on the growth of
Lumbricus
terrestris
(Oligochaeta: Lumbricidae) under laboratory conditions
E.C. Berry
a, D. Jordan
b,*
aEntomology Department, Iowa State University, Ames, IA 50011, USA
bDepartment of Soil and Atmospheric Sciences, The School of Natural Resources, University of Missouri, 302 ABNR Building, Columbia, MO 65211, USA
Accepted 6 June 2000
Abstract
The growth ofLumbricus terrestriswas determined under varying temperatures and soil moisture contents under laboratory conditions. Our objective was to identify the optimum soil moisture or temperature that would aid in the reproduction ofL. terrestrisfor inoculations in areas devoid of this species. A laboratory experiment using different growth chambers for temperature control with varying soil moisture contents was conducted at the National Soil Tilth Laboratory in Ames, IA. Five temperatures, three different soil moisture contents, and horse manure as a food source were selected and replicated 10 times. It was found that 308C were fatal toL. terrestrisafter 14 d and 258C after 182 d. Regardless of temperature, worms reared under high soil moisture content (30%) developed faster and increased in mass than those reared at 20 or 25% soil moisture content over 266 d. Optimum temperature and soil moisture content for mass rearing ofL. terrestriswas identi®ed at 208C and at 30% soil moisture content for these Iowa soils.q2001 Elsevier Science Ltd. All rights reserved.
Keywords:Lumbricus terrestris; Soil moisture; Temperature; Earthworms; Mass rearing
Lumbricus terrestris (L.) is one of the more important earthworm species that contribute to soil processes (Curry and Cotton, 1983) because they incorporate organic matter, increase soil aggregation, in¯uence soil aeration and water in®ltration, etc. (Darwin, 1881; Satchell, 1983; Edwards et al., 1990; Kladivko and Timmenga, 1990; Alban and Berry, 1994). Burrows formed by this species are permanent, usually vertically oriented and may extend to depths of 2 m or more (Ehlers, 1975). L. terrestris feeds on plant and animal litter that may be pulled down into the burrow or used in forming middens in undisturbed land (Binet and Curmi, 1992). Natural colonization byL. terrestrisis slow and thought to result from low reproductive and dispersal rates (Curry, 1988). Experimental releases ofL. terrestrisin coal mine spoils (Vimmerstedt and Finney, 1973; Hamilton and Vimmerstedt, 1980) and in reclaimed peat (Curry and Bolger, 1984) resulted in increased fertility and productiv-ity. Interest has increased for developing techniques for mass rearing and inoculating earthworms in reduced or no-tillage agricultural systems. Werner's study (1996) on inoculative release ofL. terrestris in a California orchard showed that apple leaf litter incorporation was signi®cantly increased by this earthworm in the organic plot where no
soil disturbance occurred. Currently, inoculation projects are limited because techniques for mass rearing of earth-worms are not fully developed (Curry, 1988) and because of limited information on the optimum environmental conditions for different species of earthworms.
Temperature and soil moisture are two key environmental factors that would signi®cantly in¯uence any techniques used in developing an appropriate procedure for mass rear-ing of earthworms, especially L. terrestris. In a series of studies Butt (1991) and Butt et al. (1992) investigated the effects of factors, such as soil temperature, soil moisture and food source on the production of L. terrestris. They compared the effects of temperature and nutrition on cocoon production, incubation and hatchling growth. They found cocoon development and hatchling growth were most rapid at 208C but the greatest annual production was recorded at 158C. Some of these ®ndings are also echoed in the studies by Daniels et al. (1996) who found that with an adequate food source available (e.g. dandelion leaves), L. terrestrisincreased in weight at an optimal temperature of 15±17.58C. Soil moisture obviously has an effect on the growth and activity of L. terrestris. When soil moisture is optimum, earthworms increase in mass and in their activity if food sources are available (Lee, 1985; Edwards and Bohlen, 1996). Our objective for this laboratory study was to determine optimum soil moisture and temperature forL. Soil Biology & Biochemistry 33 (2001) 133±136
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terrestrisand its potential for mass rearing and inoculation in Iowa soil using manure as a food source.
To obtain similar earthworms, both in mass and genetic uniformity, hatchlings of L. terrestriswere obtained from colonies that had been reared for two generations at the National Soil Tilth Laboratory in Ames, IA (USA). During rearing, colonies were maintained on a mixture of two soils (a Clarion loam, ®ne-loamy, mixed, mesic Typic Hapludolls and a Webster silty clay loam, ®ne-loamy, mixed, mesic Typic Haplaquolls) and fed partially decomposed horse manure. Rearing conditions for L. terrestris consisted of containers held in continuous darkness with a constant supply of horse manure with a 30% constant soil moisture held at 208C for two generations. Cocoons were collected from the rearing containers by wet sieving the soil (2 mm). The cocoons were placed on moistened paper towels in 27 cm (dia.) plastic dishes, incubated in a growth chamber at 208C and kept in constant darkness until the hatchlings emerged from the cocoons.
The mixture of the Clarion and Webster soil was used for the test study (described under the Rearing Experiment). Each test container was prepared by weighing 750 g of air dried soil and 10 g of air-dried ground horse manure into 17£12£6 cm3plastic dishes. Three soil moisture contents were maintained gravimetrically for 266 d or until the
worms died. Selected soil moisture contents of 20, 25, or 30% were established in the dishes and allowed to equili-brate for approximately 24 h prior to introducing the worms. Temperature was maintained in separate computer controlled bioclimatic chambers at 10, 15, 20, 25 and 308C for 266 d.
L. terrestrishatchlings weighing between 60 and 80 mg were selected for test purposes. Each container was inocu-lated with a singleL. terrestrishatchling. At 14-d intervals, the worms were extracted by handsorting, weighed and examined for their general condition and sexual maturity. Development of sexual maturity was determined by obser-ving the ®rst appearance of tubercula pubertalis, glandular ridges in or near the ventral margin of the clitellum, and the presence of the clitellum, which is a ring of ¯eshy glandular tissue that is most noticeable on a mature earthworm (Fender, 1985). The earthworms were then placed into freshly prepared containers as described above. This proce-dure continued for 266 d or until the earthworms died.
The experiment was designed as a randomized complete block arranged in split plots and each treatment was repli-cated 10 times. Whole plots consisted of ®ve temperatures and subplots consisted of three soil moistures as described above. This resulted in 30 (3£10) moisture containers in each (®ve) bioclimatic chamber for a total of 150 experi-mental units. Tukey's test was used as a mean separation procedure (SAS Institute, 1989).
Soil moisture and temperature signi®cantly affected the growth in terms of live weight ofL. terrestris(Figs. 1 and 2). To obtain information on the optimal temperature and moisture ranges for this earthworm, we choose to average the data for temperature and soil moisture. If there were critical differences for these two factors, we separated this data by both temperature and soil moisture content (Fig. 3). When averaged across all temperatures, the most signi®cant increase in mass forL. terrestriswas at 208C. In about the ®rst 40 d, no difference was observed in the weight gain of the worms. Some of the worms that were exposed to
E.C. Berry, D. Jordan / Soil Biology & Biochemistry 33 (2001) 133±136 134
Fig. 1. Effect of temperature on live mass ofLumbricus terrestris. Data are means averaged across moisture. Error bars are standard error n30:
Fig. 2. Effect of moisture on live mass ofLumbricus terrestris. Data are means averaged across temperature. Error bars are standard error n50:
temperatures greater than 208C did not survive the test. Worms that were exposed to 258C survived for about 182 d and survival at 308C was reduced to 14 d (Fig. 1). When worms were held at a constant temperature of 108C they weighed less than those held at 15 or 208C. For exam-ple, on day 98 the mass of worms reared at 208C were 62.3 mg which was signi®cantly greater p,0:05 than
those held at 158C (47 mg worm21) or 108C (14 mg worm21). The effect of temperature on mean daily weight gain at 10, 15, and 208C were 32, 46, and 49 mg worm21d21, respectively.
Regardless of temperature, greater worm mass was seen at 25 and 30% moisture after 182 d (Fig. 2). Throughout the 266 d test, worms exposed to 20% moisture weighed signif-icantly less than 30% soil moisture content. Towards the end of the test (182±266 d), worms at 25 or 30% soil moisture content were signi®cantly greater in mass than at 20% soil moisture. The effect of soil moisture content on average daily weight gain at 20, 25, or 30% were 35, 43, and 49 mg worm21d21, respectively.
We examined the effect of each temperature at each soil moisture content onL. terrestrisgrowth. Our data consis-tently shows that at each temperature the worms mass increased over time with the greatest increase at 30% soil moisture content. Furthermore, soil moisture becomes criti-cal at higher temperatures (25 and 308C) (Fig. 3). We present data only at 258C because at 308C the worms were dead after 14 d. Signi®cant differences were observed between soil moisture contents at 30% versus 20 or 25% (Fig. 3). A decline in worm mass was seen at 126 d at 20% soil moisture and at about 182 d at 25% soil moisture content. At 258C signi®cantly greater mass was seen for the worms at 30% soil moisture.
Regardless of soil moisture content, worms exposed to low temperature (108C) took longer to develop the tubercula pubertalis and clitellum (physical observation, data not presented). The duration for these developments was differ-ent for each soil moisture contdiffer-ent. For example, worms at 108C with a soil moisture of 20%, developed tubercula pubertalis in 166 d and aclitellum in 216 d. At the same temperature when the soil moisture content was increased to 30%, tubercula pubertalis were ®rst noticed in 122 d and the worms became fully clitellated in 166 d. In contrast, tubercula pubertalis were ®rst observed and the clitellum developed in 48 and 73 d, respectively, for worms at 208C and at 30% soil moisture content.
Soil moisture content and temperature are key factors in rearingL. terrestrisfor inoculative purposes. Our study does suggest some optimal temperature and moisture conditions that should be consider for these midwestern soils. In our study, temperatures equal to or greater than 258C were detri-mental to L. terrestris which is consistent with other research. However, under controlled conditions these worms did survive for 182 d or about six months if the temperature was 258C (Fig. 3), which is considerably longer than other similar studies (Butt, 1993). In some
environmen-tal conditions 208C is the upper limit for survival of L. terrestris under controlled and ®eld conditions and most of these species seem to do better at about 158C or below (Butt et al., 1992; Daniels et al., 1996; Whalen and Parme-lee, 1999). At 30% soil moisture at 258C, worms can be reared for up to 182 d. Whalen and Parmelee (1999) observed that L. terrestris had the greatest mass in soil maintained at 108C and 20% soil moisture content under laboratory conditions. An optimal temperature of 208C with about 30% soil moisture would be recommended in a silty clay loam or loam Iowa soil. Our worms were at a comparable mass (weight gain) as other studies have shown (Butt, 1993). We were able to maintain our worms for considerably longer than other researchers with the primary difference in the studies being the food source. We fed our worms a steady supply of partially decomposed horse manure as compared to dried cattle manure in the experiment by Butt (1993). Further experiments using different food sources need to be conducted to determine more about the effect of this factor.
Acknowledgements
The authors express their sincere appreciation to Mrs Victoria C. Hubbard for preparation of the ®gures and statis-tical analyses. We also thank Dr Matthew Werner and two anonymous reviewers for their comments and suggestions.
References
Alban, D.H., Berry, E.C., 1994. Effects of earthworm invasion on morphol-ogy, carbon, and nitrogen of forest soil. Appl. Soil Ecol. 1, 243±249. Binet, F., Curmi, P., 1992. Structural effects of Lumbricus terrrestris
(Oligochaeta: Lumbricidae) on the soil±organic matter system: Micro-morphological observations and autoradiographs. Soil Biol. Biochem. 24, 1519±1523.
Butt, K.R., 1991. The effects of temperature on the intensive production of Lumbricus terrestris (Oligochaeta: Lumbricidae). Pedobiologia 35, 257±264.
Butt, K.R., Frederickson, J., Morris, R.M., 1992. The intensive production ofLumbricus terrestrisL. for soil amelioration. Soil Biol. Biochem. 24, 1321±1325.
Butt, K.R., 1993. Reproduction and growth of three deep-burrowing earth-worms (Lumbricidae) in laboratory culture in order to assess production for soil restoration. Biol. Fertil. Soils 16, 135±138.
Curry, J.P., 1988. The ecology of earthworms in reclaimed soils and their in¯uence on soil fertility. In: Edwards, C.A., Neuhauser, E.F. (Eds.). Earthworms in Waste and Environmental Management, Academic Publishing, The Hague, pp. 251±261.
Curry, J.P., Bolger, T., 1984. Growth, reproduction and litter and soil consumption byLumbricus terrestrisL in reclaimed peat. Soil Biol. Biochem. 16, 253±257.
Curry, J.P., Cotton, D.C.F., 1983. In: Satchell, J.E. (Ed.). Earthworms and Land Reclamation, Chapman and Hall, London, pp. 215±228. Daniels, O., Kohli, L., Bieri, M., 1996. Weight gain and weight loss of the
earthwormLumbricus terrestrisL. at different temperatures and body weights. Soil Biol. Biochem. 28, 1235±1240.
Edwards, C.A., Bohlen, P., 1996. Biology and Ecology of Earthworms, Chapman and Hall, New York.
Edwards, W.M., Shipitalo, M.J., Owens, L.B., Norton, L.D., 1990. Effect of Lumbricus terrestrisL. burrows on hydrology of continuous no-till corn ®elds. Geoderma 46, 73±84.
Ehlers, W., 1975. Observations on earthworm channels and in®ltration on tilled and untilled loess soil. Soil Sci. 119, 242±249.
Fender, W.M., 1985. Earthworms of the western United States. Part 1. Lumbricidae. Megadrilogica 4, 93±129.
Hamilton, W.E., Vimmerstedt, J.P., 1980. Earthworms on forested spoil banks. In: Dindal, D.L. (Ed.), Soil biology as related to land use practices, Proceedings of the Seventh International Soil Zoology Colloquium, Environmental Protection Agency, Washing-ton, pp. 409±417.
Kladivko, E.J., Timmenga, H.J., 1990. Earthworms and agricultural management. In: Box, J.E., Hammond, L.C. (Eds.), Rhizosphere
dynamics, American Association for the Advancement of Science, Washington, DC, pp. 192±216.
Lee, K.E., 1985. Earthworms: Their Ecology and Relationship with Soils and Land Use, Academic Press, Orlando.
Satchell, J.E., 1983. Earthworm Ecology: from Darwin to Vermiculture, Chapman and Hall, London.
SAS Institute, 1989. SAS/STAT User's Guide, Version 6, vols. 1 and 2, 4th ed. SAS Institute Inc., Cary.
Vimmerstedt, J.P., Finney, J.H., 1973. Impact of earthworm introduction on litter burial and nutrient distribution in Ohio strip-mine spoil banks, Proceedings of Soil Science Society of America 37, pp. 388±391. Werner, M.R., 1996. Inoculative release of anecic earthworms in a
Cali-fornia orchard. Am. J. Alternat. Agric. 11, 176±181.
Whalen, J.K., Parmelee, R.W., 1999. Growth ofAporrectodea tuberculata (Eisen) andLumbricus terrestrisL. under laboratory and ®eld condi-tions. Pedobiologia 43, 1±10.
