Earthworms are everywhere but, in some places, more so than others

          Out of sight out of mind, right? That seems to explain why earthworms never get the attention they truly deserve. Even though we may rarely see them, earthworms have become a necessary staple in many ecosystems due to their ability to improve soil structure and nutrient cycling (Edwards & Bohlen, 1996). For humans, these benefits have the potential to improve the efficiency of agricultural fields. Therefore, it is important to manage these plots of land such that they maintain soil characteristics that are well suited for the survival of earthworms (Chan, 2001). Previous research has sought out to study this relationship between earthworm abundance and soil properties (Chan & Barchia, 2007). 

Earthworms can help improve the soils in which we grow our food (Picture from https://www.veggiegardener.com/earthworms-the-unseen-worker-of-garden-soil/)

Chan and Barchia investigated the effects of soil properties on the distribution and abundance of earthworms in agricultural soils on a single dairy farm in New South Wales, Australia. They excavated worms from various fields on the farm by digging up soil blocks and counting how many worms were found in each one. They then collected the soil adjacent to each excavated block so that its properties could be measured. They found that earthworm abundance varied significantly across the sampled fields, with soil compaction being the main driver of this difference. These results go against previous research that found differing soil properties to have no significant effect on earthworm abundance (Mele & Carter, 1999). However, unlike Chan and Barchia, this study used multiple farms with different site histories and did not measure soil compaction as a soil characteristic, which has been supported to affect earthworm abundance (Söchtig & Larink, 1992). Chan and Barchia’s research indicates the importance of identifying soil properties that are known to affect the presence of earthworms, as well as past management practices, in order to more effectively introduce or sustain desirable earthworm species to improve the soil within agricultural fields (Chan & Barchia, 2007).

          Where there’s soil, there tends to be earthworms. This means that they’re not only present in natural or rural areas, but within our urban landscapes as well. In their paper, Chan and Barchia discuss the importance of considering past management practices and site histories when evaluating how agricultural soil affects earthworm abundance, which is a concept we can also apply to the Grinnell College campus. Because it is important for the campus to appear aesthetically pleasing to appeal to students and faculty, our campus contains many well-maintained plant beds. My lab partner, Jasper, and I sought out to determine whether the earthworm abundance in the soil of these maintained plant beds differs from their abundance in the soil of nearby unmaintained beds. In our case, the presence or absence of maintenance at our sites would represent differences in management practices. Because the maintenance of a plant bed can encompass many different factors that could affect its soil characteristics, such as the use of herbicides and mulch or stepping on the soil, a difference in abundance wouldn’t be able to be pinpointed to a specific factor. However, a difference in abundance would then warrant for future studies to further investigate these specific factors to determine if all of them or only certain ones have an affect on earthworm abundance.

Example of a maintained site.

Example of an unmaintained site.

References

Chan, K. Y. (2001). An overview of some tillage impacts on earthworm population abundance

and diversity—implications for functioning in soils. Soil and tillage research, 57(4), 179-

191.

Chan, K. Y., & Barchia, I. (2007). Soil compaction controls the abundance, biomass and

distribution of earthworms in a single dairy farm in south-eastern Australia. Soil and

Tillage Research, 94(1), 75-82.

Edwards, C. A., & Bohlen, P. J. (1996). Biology and ecology of earthworms (Vol. 3). Springer

Science & Business Media.

Mele, P. M., & Carter, M. R. (1999). Species abundance of earthworms in arable and pasture

soils in south-eastern Australia. Applied Soil Ecology, 12(2), 129-137.

Söchtig, W., & Larink, O. (1992). Effect of soil compaction on activity and biomass of endogeic

lumbricids in arable soils. Soil Biology and Biochemistry, 24(12), 1595-1599.