Tuesday, 7 October 2008
George R. Brown Convention Center, Exhibit Hall E
Jodi Johnson-Maynard, Karl Umiker and Stephen Guy, University of Idaho, PSES Ag. Sci. Bldg. Rm. 242, University of Idaho, Moscow, ID 83844-2339
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.