ED-STEEP: Education Solutions to Environmental
and Economic Problems
STEEP Research Reports – Soil Organic Matter
Bezdicek, D.F., J. Hammel, M. Fauci, D. Roe and J. Mathison. 1999. Impact of long-term no till
on soil physical, chemical, and microbial properties. 1999 STEEP Research Reports.
Bezdicek, D., S. Albrecht, M. Fauci, M. Flury and J. Hammel. 2001. Impact of direct seeding on
crop water use efficiency, soil physical and microbial properties and quality of soil organic
matter, 2001 STEEP Research Reports.
Bezdicek, D., S. Albrecht, M. Fauci, M. Flury, J.P. Fuentes, and J. Hammel. 2002. Impact of
direct seeding on crop water use efficiency, soil physical and microbial properties and
quality of soil organic matter, 2002 STEEP Research Reports.
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Research Summary
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Concerns about the loss of soil organic carbon (SOC) through tillage and erosion, and
concern of global warming have stimulated interest in direct seeding in the Pacific
Northwest.
Tillage decreases soil organic matter (SOM) and soil particulate organic matter (POM).
POM is the partially decomposed sand-sized organic fraction that serves as a reservoir of soil
nutrients that are released during the growing season and replenished from seasonal surface
residue.
The increase in SOM under no-till is greatest at sites that receive higher rainfall. In lower
rainfall areas, there is little plant residue to contribute to SOM.
Highest soil organic carbon was found in 70+ year old grass-pasture in Oregon and in 25year no-till soil in Washington.
Total soil organic nitrogen was significantly greater under no-till at 3 high rainfall locations.
Under no-till, the greater surface residue and organic matter content of soil caused an
increase in the activity of microorganisms (i.e., bacteria and fungi).
Soil organic carbon and nitrogen were over 2 x higher in natural prairie soil than farmed soil.
% organic matter of surface soil was 24% greater in no-till soil compared with conventional
tilled soil.
% nitrogen of surface soil was 42% greater in no-till soil compared with conventional tilled
soil.
The lowest soil organic carbon occurred in fields after 68 years of conventional wheat-fallow
in Oregon, because fallowing and tillage encourage residue decomposition and loss of soil
organic carbon.
After only 2 years of direct seeding in Washington, the light fraction of soil organic carbon
increased by 180%, and the POM fraction increased by 29% in the upper 5 cm of soil.