Earthworm Distribution and Demographics Along a Naturally Occurring Salinity Gradient.

Over 90% of crop producers in North Dakota are affected by naturally occurring soluble salts (primarily sodium, calcium, and magnesium sulfates), which originate in the parent material and migrate to the soil surface. Salinity levels can be high enough to limit crop production and influence soil management decisions. Our objective was to examine the distribution and demographics of earthworms in an annual cropping field that is affected by surface salinity, and that is currently undergoing management to limit salt migration and improve soil health. We established a transect to capture increasing levels of soil electrical conductivity (EC), and collected intact soil cores for worm counts and soil samples for chemical analyses. With increasing salinity levels, we observed a decrease in soil organic matter content and total worm counts for all worm age classes. Worm cocoon counts were not different across salinity levels. Juvenile worms were the most abundant age class in non-saline soils, but were the most reduced by increasing salinity levels. Consistent cocoon counts and decreasing juveniles across the salinity gradient indicate that adult worms migrate into saline areas, but are not able to establish a viable population. Earthworm species present in the study were predominately Aporrectodea trapezoides and Aporrectodea tuberculata with Octolasion tyrtaeum. Worm occurrence and age classifications may be an easy indicator for producers to monitor salinity levels and soil health.