Owens second hypothesis [1] states that the surface shear stress induced by the fluid on the stationary sediment on the ground in a particle saltation layer equals the threshold for particle entrainment. Despite the fact that most numerical models describing sediment entrainment and particle mass fluxes in turbulent boundary layer flows make use of Owens second hypothesis, no direct experimental validation of this assumption has been presented to date. We present direct measurements of the fluid shear stress on the ground in sand saltation layers to validate this hypothesis. The shear stress was measured for different wind velocities with various particle concentrations in the saltation layer using Irwin sensors. Additionally, particle concentrations in the saltation layers were estimated from shadowgraphic images taken with a high speed camera.