Winter-Associated Changes in Dry-Soil Aggregation as Influenced by Management

Changes in surface soil structure during winter can increase soil erodibility. This study was conducted to examine winter-associated changes in dry-soil aggregation as influenced by crop, residue, and tillage system. These changes were studied at Hays, KS, on a Harney silt loam (fine, montmorillonitic, mesic Typic Argiustoll) in a winter wheat (Triticum aestivum L.)-grain sorghum [Sorghum bicolor (L.) Moench]-fallow rotation. Three tillage systems were used — clean tillage with residue buried, stubble-mulch tillage, and zero tillage. Residue and crop cover present during the winter was wheat residue, sorghum residue, and winter wheat. Measurements of dry aggregate stability, aggregate-size distribution as geometric mean diameter, and aggregate density were made before and after the winters of 1988–1989 and 1989–1990. Little difference occurred between clean and stubble-mulch tillage systems, which were usually different from the zero-tillage system. Greater changes in aggregation occurred during the 1989–1990 winter when precipitation was greater. Residue maintained higher surface water contents, decreased freeze-thaw cycling and drying by sublimination, and decreased fluctuations in water content. Aggregates from plots with low residue cover decreased in stability more than aggregates from high residue treatments. Generally, differences in aggregation between tillage systems were maintained during the drier winter and minimized during the wetter winter. Soil aggregates were smaller, less dense, and less stable on the zero-tillage plots in March 1989. Therefore, insufficient residue production for wind erosion control in a zero-tillage system could lead to more erodible conditions than in a conventional tillage system. Contribution no. 93-45-J from the Kansas Agric. Exp. Stn.