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Field Wind Tunnel Testing of Two Silt Loam Soils on the North American Central High Plains
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.orgCitation: International Symposium on Erosion and Landscape Evolution (ISELE), 18-21 September 2011, Anchorage, Alaska 711P0311cd Paper #11103.
Authors: Robert Scott Van Pelt, Matthew C Baddock, Ted M Zobeck, Veronica Acosta-Martinez, Alan J Schlegel, Merle F Vigil
Keywords: Wind erosion, Silty soils, Erodibility, Dust emissions
Wind erosion is a natural process of sediment redistribution resulting from the shear force of the wind interacting with unprotected soil surfaces. Globally, wind erosion accounts for nearly half of all soil loss. Breaking of the prairie sod and mechanical tillage of agricultural soils on the semi-arid North American Central High Plains resulted in massive wind erosion and dust emissions in the early half of the 20th Century. The recent change from conventional tillage to no-till cropping systems and the emergence of cropping systems with fewer and shorter fallow periods has resulted in reduced wind erosion on the North American Central High Plains. This reduction has been attributed primarily to increased surface coverage by crop residues, but commonly documented changes to soil physical and chemical properties resulting from changes of crop rotations and tillage management may also affect soil loss due to wind erosion. Little is known about how cropping system-induced changes in soil physical and chemical properties affect the intrinsic wind erodibility of the soil. Intrinsic erodibility is the susceptibility of a bare, flat soil surface to entrainment by wind. We tested the intrinsic erodibilities and dust emission potentials of soils under long term studies of tillage management and crop rotations in-situ at locations near Tribune, KS and Akron, CO. The studies at both sites had been in existence for greater than 15 years at the time of testing and were established on very similar silt loam soils. All plots were in the fallow period of rotation prior to testing. At the Tribune, KS location, the plots had been under a uniform rotation of wheat-sorghum-fallow and included conventionally tilled, reduced tillage, and no-till management systems. The Akron, CO location had a combination of conventionally tilled and no-till plots with a wheat-fallow rotation, no-till plots with a wheat-corn-fallow rotation and no-till plots with a wheat-corn-millet-fallow rotation. The surfaces were cleared of remaining crop residue, tilled with a power tiller, raked, and rolled with a lawn roller, resulting in uniform, smooth surfaces with minimal surface roughness. A 6 m long wind tunnel test section 0.5 m wide was placed on the prepared surface and then attached to the fan and flow conditioning section of the wind tunnel. Tests at each plot consisted of an initial 5 minute test of erodibility conducted at 12 ms-1 wind speed without introduced silica abrader followed by a 30 minute test and a subsequent 10 minute test, both conducted at the same wind speed and with introduced silica abrader. Saltation and suspended dust emissions were measured using an isokinetic vertically integrating slot sampler that deposited saltation material in a pan and aspirated suspended dust emissions through glass fiber filters. Suspended dust emissions were also sampled using a laser particle size analyzer that records integrated measurements at six second intervals. Sediment in the pan was collected and the filters changed at the end of each of the tests detailed above. Additional samples were collected for chemical and biological analysis using an aspirated sampler with an 85 cm2 opening. No significant differences were noted in the intrinsic erodibilities or dust emissions potentials of the cropping systems. There was no clear pattern of rotation effects on erodibilities or dust emission potentials at the Akron, CO location.