Soil properties influenced by summer fallow management in the Horse Heaven Hills of Southcentral Washington

Authors: Sharratt, Brenton; SCHILLINGER, WILLIAM - Washington State University

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2017
Publication Date: 7/12/2018
Citation: Sharratt, B.S., Schillinger, W. 2018. Soil properties influenced by summer fallow management in the Horse Heaven Hills of Southcentral Washington. Journal of Soil and Water Conservation. 73:452-460. https://doi:10.2489/jswc.73.4.452.
DOI: https://doi.org/10.2489/jswc.73.4.452

Interpretive Summary: The Horse Heaven Hills of southcentral Washington is the driest rainfed wheat producing region in the world. Tillage practices performed during the fallow phase of winter wheat – summer fallow rotations are critical to conserving the soil resource and improving air quality because soils in the region are highly susceptible to wind erosion. An ARS scientist in Pullman, Washington, in collaboration with a scientist at Washington State University, found that no-tillage retained at least twice the amount of residue on the soil surface and resulted in larger aggregates as compared with traditional-tillage practices. Based upon differences in soil characteristics among tillage practices, the Revised Wind Erosion Equation predicts wind erosion to be lowest for no-tillage and 70% lower for undercutter-tillage compared to traditional-tillage practices. Land managers, wheat growers, and National Resources Conservation Service (NRCS) representatives are encouraged to use reduced tillage practices in winter wheat – summer fallow rotations in the Horse Heaven Hills for reducing wind erosion and improving air quality throughout eastern Washington and northcentral Idaho.

Technical Abstract: The Horse Heaven Hills (HHH) is the world’s driest rainfed wheat region and is highly susceptible to wind erosion due to use of tillage during the fallow phase of winter wheat – summer fallow (WW-SF) cropping systems. Wheat straw residue and cover, surface roughness, soil water content and strength, and aggregate size distribution of no-tillage fallow (NTF), undercutter-tillage fallow (UTF), and traditional-tillage fallow (TTF) were measured after primary tillage of UTF and TTF in late April and after sowing winter wheat in late August 2007 at two sites in the HHH. Residue cover and silhouette area index were at least two times greater and penetration resistance and shear stress were at least five times greater for NTF than TTF in spring and late summer at both sites. No differences were found to suggest that tillage treatments influenced near-surface soil water content or potential. Random roughness was typically lower for NTF as compared with UTF in spring and late summer at both sites. Tillage treatments influenced soil aggregation, but only in spring at one site and in late summer at the other site. Geometric mean diameter was greater and erodible fraction was lower for NTF than TTF. Based upon the Revised Wind Erosion Equation (RWEQ), sediment flux was lowest for NTF and at least 70% lower for UTF as compared with TTF. Thus, soil loss due to wind erosion can be reduced by using NTF and UTF rather than TTF for WW-SF rotations in the world’s driest rainfed wheat region.