Dryland fanning in the Mediterranean climate of the Pacific Northwest, USA supports extremely low earthworm populations under conventional tillage. Increases in earthworm populations are being observed in fields under no-till cropping systems. A 30+ year experiment with four tillage levels in a pea (Pisum sativum L.)-winter wheat (Triticum aestivum L.) rotation was evaluated for earthworm populations and ponded infiltration rates. Where tillage has been limited to 2.5 cm depth, Apporectodea trapezoides (Duges) mean population was 25 m(-2). Plots subject to tillage by plow (25 cm depth) or chisel (35 cm depth) averaged less than 4 earthworms m-2. The shallow tillage treatment also had the highest average infiltration rate of 70 mm h(-1) compared to 36 for chisel, 27 for spring plow, and 19 mm h(-1) for fall plow treatments. The highly variable nature of earthworm counts and infiltration measurements prevented conclusive correlation between the two, but increases in both can be attributed to minimum tillage.
