Earthworm Populations and Soil Carbon Following Seven Years of No-Till Management in the Palouse Region of Northern Idaho.

Little is known about how earthworm population density and soil carbon concentrations change after adoption of no-till (NT) practices within the Palouse region of northern Idaho. The objective of this study was to determine changes in and controls over earthworm population density and soil carbon over time once tillage is eliminated.  Tillage treatments [conventional till (CT) and no-till] were established in 2000. Soils and earthworms were sampled once a year for a seven-year-period. Earthworms responded quickly with significantly larger densities in NT after three years. Earthworm density in NT plots ranged from a high of 227 individuals m^-2 in 2006 to a low of 42 individuals m^-2 in 2005.  Density in CT plots was lower than in NT plots and ranged from 52 individuals m^-2 in 2006 to a low of 15.3 individuals m^-2 in 2007. Spring earthworm density appears to be most strongly correlated to winter precipitation under NT (R=0.78) and CT (R=0.60) treatments. Total soil C concentrations appear to be increasing in the top 5 cm of soil in NT plots. Within the 0-to 2.5-cm depth, mean total C increased from a mean of 1.8% in 2001 (one year after the tillage treatments were established) to a mean of 2.3% in 2006. A smaller increase was found in the 2.5-to 5-cm depth. Together the data suggest that adoption of NT enhances earthworm density in a relatively short period of time. Increased earthworm density should improve key soil properties such as water retention, infiltration and soil organic matter over time in these systems. Total soil carbon does appear to increase slowly under NT but this change was limited to the first 5 cm of soil after 7 years.