Surface Soil Physical Properties after 36 Years of Cropping to Winter Wheat1
- Paul W. Unger2
A dryland tillage and cropping system study for winter wheat (Triticum aestivum L.) was conducted on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll) from 1941 to 1977, a period much longer than most field studies. In 1977, soil samples were collected from the surface layer to evaluate effects of the long-term tillage and cropping practices on dry and water-stable aggregate distribution, organic matter (OM) concentration, modulus of rupture, penetrometer resistance, and bulk density of clods. Oneway disk tillage resulted in significantly fewer small dry aggregates than sweep tillage in the wheat-fallow system, but had no significant effect in the continuous wheat system. Mean weight diameters (MWD) were similar for all tillage methods. Oneway tillage resulted in more < 0.25-mm diameter water-stable aggregates than sweep tillage in both cropping systems, resulting in lower MWD for oneway than for sweep tillage. Organic matter concentration was lower for oneway than for sweep tillage in both systems, while continuous wheat resulted in higher OM concentration than wheat-fallow for comparable tillage methods. Slight changes from 1966 to 1977 indicated that soil OM concentration was at or nearly in equilibrium with prevailing management and climatic conditions. Modulus of rupture of briquettes and resistance of briquette fragments to fracture with a penetrometer were inversely related to OM concentration, but no tillage method or cropping system had an overriding influence on soil physical properties. Dry aggregate analyses indicated that the soil did not contain enough coarse aggregates to control wind erosion, indicating the need to maintain residues on the soil surface to aid wind erosion control.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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