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

Abstract

The Horse Heaven Hills (HHH) is the world's driest rainfed wheat (Triticum aestivum L.) region where soils are highly susceptible to wind erosion due to use of tillage during the fallow phase of the winter wheat–summer fallow (WW-SF) cropping system. Wheat straw residue biomass 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 of 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. Random roughness was typically lower for NTF as compared with UTF in spring and late summer at both sites. Summer fallow treatments influenced soil aggregation whereby 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 HHH.