Influence of Earthworm Activity

On Spatial Distribution of Surface Crop Residues

Catherine A. Fox

Agriculture and Agri-Food Canada, Harrow, Ontario, Canada.    ( This email address is being protected from spam bots, you need Javascript enabled to view it )

 Lumbricus terrestris (Linnaeus 1758) or the nightcrawler has an important role in the decomposition of surface crop residues especially for minimum tillage management systems in south central Canada particularly for regions of the St. Lawrence Lowland with fine textured soils.  A characteristic behaviour of these earthworms is to come out of their burrows at night to forage for food sources.  The result is that leaves, small stems and even pebbles are pulled into the opening of the burrows creating rounded piles of debris mixed with soil material; that is, middens.  The middens are very noticeable on the soil surface and because of this can be used as a measure or indicator of the extent of activity for L. terrestris for accessing crop residue materials.

This behaviour was taken advantage of in a comparison study that examined the influence of agroforestry buffers (i.e. native vs planted hedgerows) on the adjacent cropland.  The hypothesis was that the presence of the treed hedgerows affected earthworm populations by supplying additional food resources from leaf litter and shading temperatures and as a consequence there would be increased activity whereby crop residues would be noticeably removed.  The second hypothesis was that the extent of this influence into the adjacent crop would decrease with distance from the hedgerows.

A 100 m grid with 10 m intervals was set up at 2 field sites with four transects at the 0, 30, 60 and 90 meter points along the hedgerows.  On each of these transects, earthworm activity was assessed by counting of middens at following distances into the adjacent field: close to treed buffer, at 30 , 60 and 90 meters.  At each assessment point, a 60 x 60 cm wooden frame was placed on the soil surface at positions, north, east, south and west.  The number of middens and a visual estimation of the percentage area still covered by residues was recorded.  The mean number of middens and mean per cent of residues remaining on the surface was plotted for the sampling area with contour positions determined by kriging option using Surfer7^® software.

An inverse relationship was observed between areas with increasing midden numbers and per cent residues remaining on the surface.  The implications of the spatial distribution of middens and residues will be discussed.