Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2001
Publication Date: N/A
Interpretive Summary: Reduced tillage and even no-tillage cropping systems are being used to reduce production costs and reduce soil erosion. One of the many changes that is often measured after several years of no-till is an increase in maximum water infiltration rate. The objective of this research was to determine whether reduced tillage had produced greater infiltration rates in a long-term wheat/pea tillage study, and if increased earthworm populations might help explain why. The research found that the tillage treatment with the least soil disturbance supports more than five times the earthworm population of more aggressive tillage practices. Even so, the earthworm populations found in this semi-arid environment after 30 years of minimum tillage are very low (25 per square meter) compared to more humid environments. Where there were the highest numbers of earthworms, infiltration rates were highest. This research indicates that earthworms might be an important factor in achieving the high infiltration rates necessary to prevent erosion, even in semi-arid environments where their populations are very low.
Technical Abstract: Dryland farming 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) population was 25 per meter square. Plots subject to tillage by plow (25 cm depth) or chisel (35 cm depth) averaged less than four earthworms per meter square. The shallow tillage treatment also had the highest infiltration rate of 70 mm per hour compared to 36 for chisel, 27 for spring plow, and 19 mm per hour for fall plow treatments. The highly variable nature of earthworm counts and infiltration measurements prevented dconclusive correlation between the two, but increases in both can be attributed to minimum tillage.