MITIGATING AGRICULTURAL SOURCES OF PARTICULATE MATTER AND GREENHOUSE GAS EMISSIONS IN THE PACIFIC NORTHWEST
Location: Land Management and Water Conservation Research
Title: Surface characteristics of a windblown soil altered by tillage intensity during summer fallow
Submitted to: Aeolian Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 20, 2012
Publication Date: March 28, 2012
Citation: Sharratt, B.S., Wendling, L., Feng, G. 2012. Surface characteristics of a windblown soil altered by tillage intensity during summer fallow. Aeolian Research. Volume 5, Pages 1–7.
Interpretive Summary: In the wheat-fallow region of the Pacific Northwest where wheat is grown every other year, wheat growers cultivate the soil multiple times during the fallow phase of the rotation to conserve soil water for the next wheat crop. This intensive tillage practice causes extensive wind erosion of the land. Less intensive tillage practices are sought that will reduce wind erosion. Crop residue cover increased as tillage intensity decreased during the fallow period. As a result of increasing residue cover, soil erosion was estimated to be 50% lower for minimum tillage as compared with conventional tillage. A viable option for wheat growers to reduce wind erosion in the region is to use reduced or minimum tillage.
Winter wheat – summer fallow is the conventional crop rotation used on more than 1.5 million ha in the Pacific Northwest United States. Land maintained using conventional summer fallow is very susceptible to wind erosion because multiple tillage operations during the fallow period degrade and expose the soil to high winds. Alternative management strategies are needed that modify surface characteristics and protect the soil surface from erosion during summer fallow. Surface characteristics of a loessial soil were examined after subjecting the soil to seven (conventional), five (reduced), three (minimum), and zero (no) tillage operations between wheat harvest in July 2004 and sowing in August 2005. Surface biomass and roughness and soil crust, aggregation, strength, and water content were measured after tillage and sowing operations. No tillage had a more persistent and thicker soil crust and greater residue cover, silhouette area index (SAI), and penetration resistance than conventional and reduced tillage throughout the fallow period. Although these characteristics are desirable for reducing erosion, no tillage is not yet economically viable in the summer fallow region of the Pacific Northwest. For those treatments subject to tillage, minimum tillage resulted in a thicker soil crust and greater residue cover, SAI, ridge roughness, mean aggregate diameter, and penetration resistance as compared to conventional or reduced tillage following primary tillage in August 2004. Prior to and after sowing wheat in August 2005, minimum tillage resulted in 15% greater residue cover than conventional tillage. Based upon these differences in residue cover, soil loss from minimum tillage is expected to be 50% that of conventional tillage. This study suggests that minimum tillage is an effective practice to enhance residue cover and other soil characteristics for reducing wind erosion in the wheat-fallow region of the Pacific Northwest.