Earthworm population dynamics as a consequence of long-term and recently imposed tillage in a clay loam soil
Citation
Fox, C.A., Miller, J.J., Joschko, M., Drury, C.F., Reynolds, W.D. (2017). Earthworm population dynamics as a consequence of long-term and recently imposed tillage in a clay loam soil. Canadian Journal of Soil Science, [online] 97(4), 561-579. http://dx.doi.org/10.1139/cjss-2016-0092
Plain language summary
Earthworms are important for creating and maintaining the health of agricultural soils. Through their burrowing activity, they stimulate soil microbes, mix and aggregate soil, increase infiltration of rainwater, and improve the soil’s ability to store and retain the air and water necessary for crop growth. Earthworms also sequester carbon and improve soil fertility by consuming and burying large amounts of surface organic matter, such as crop residues left on the soil surface after harvest. As a result, one of the key biological indicators of soil health is the presence and abundance of earthworms.
Although it is known that soil disturbance, such as moldboard plowing and disking, can reduce earthworm numbers through fatal injury, burrow disruption and egg destruction, the degree of reduction and the associated impacts on diversity and age structure of earthworms species are still poorly understood. Hence, the main objective of this study was to characterize and compare earthworm population dynamics (i.e. abundance, species diversity and age structure) among undisturbed bluegrass sod, and a corn-soybean crop rotation using either traditional moldboard plow tillage or no-tillage. Moldboard plow tillage creates maximum soil disturbance by inverting and breaking up the top 10 to 30 cm of soil, while the only soil disturbance associated with no-tillage is cutting of a narrow seed planting slot by the corn or soybean planter.
Bluegrass sod was the best overall environment for earthworms, in that it hosted the greatest abundance and range of species, along with the best distribution of juveniles and adults. Moldboard plowing, on the other hand, had the lowest abundance and fewest juvenile earthworms. Although no-tillage had greater earthworm abundances and more juveniles than moldboard plow, these numbers were still substantially lower than those in sod – likely because of less food availability under no-till.
Knowledge gained by studies like this one will help develop “best management” tillage systems that optimize earthworm population dynamics, and thereby improve and maintain the health of our agricultural soils.
Abstract
Earthworm abundances were tracked from 1997 to 2012 in established tillages (since 1983) and recently imposed tillages (since 1997) from a Brookston clay loam soil (Orthic Humic Gleysol) at Woodslee, ON. The tillages included the following systems: long-term fall moldboard plowing (CT83) and its 1997 conversion to no tillage (NT97-CT83), long-term no tillage (NT83) and its conversion to moldboard plowing (CT97-NT83), long-term ridge tillage (RT83) and its conversion to moldboard plowing (CT97-RT83), and long-term bluegrass sod (BG83) and its conversion to moldboard plowing (CT97-BG83). Lumbricus terrestris and Aporrectodea turgida were the most abundant of six species identified. The NT83 system had the greatest earthworm numbers except for 2012 when RT83 had equal abundance because of increased Ap. turgida juveniles. Populations in NT97-CT83 increased significantly from 1997 to 2012 because of reduced mechanical disturbance and greater surface residues. During 1997, 1999, and 2003, mean abundance in CT97-BG83 was not different from that of BG83, which likely occurred because buried sod continued to provide ample food. The CT97-RT83 system showed a decline in earthworm populations relative to RT83. The CT97-NT83 treatment had the most significant earthworm decline, reflecting a substantial increase in soil disturbance. Characterizing tillage system effects on earthworm dynamics (e.g., diversity, occurrence, adult, and juvenile abundance) will provide essential data for landscape models.