Dry aggregate stability is an important soil physical property for evaluating tillage and wind-erosion research. Research in this study was aimed at developing a model for predicting soil aggregate stability as influenced by intrinsic soil properties, with particular application to wind erosion. Aggregates from 10 Kansas soils with a wide textural range were tested periodically for stability during a 3-yr period. The logarithm of aggregate stability was regressed against the intrinsic soil properties (geometric mean diameter of primary particles, specific surface area, water content at-1500 J/kg matric potential, and clay content). Clay content and water content at-1500 J/kg were both good predictors of mean aggregate stability. A resulting empirical model estimates mean aggregate stability from either clay or water content with coefficients of determination of 0.97 and 0.96, respectively. Further testing is planned by running the model with several independent data sets to estimate the probability of aggregate stability within specified limits for particular soils. W IND-EROSION RESEARCH SCIENTISTS have been charged with developing improved wind-erosion prediction technology as a possible replacement for the wind-erosion equation (Hagen, 1991a). Improved wind-erosion prediction technology requires that we improve our ability to measure and predict, in time and space, the susceptibility of soil to wind erosion. The main properties of dry soil aggregates affecting

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.

Alternate methods of residue management for reduced tillage under irrigation and in double cropping systems are constantly being sought. One method that is becoming increasingly popular is residue burning. Knowing how to best manage crop residues to maintain desirable soil physical properties for decreasing erosion and increasing crop yields in these cropping systems is a problem. This study was conducted to determining the influence of several methods of residue management for winter wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] on physical properties of Richfield silty clay loam (fine, montmorillonitic, mesic Aridic Argiustolls). Residue management treatments were: residue removed by burning, residue removed by baling and hauling, incorporation of the residue produced during the immediate past cropping season, and incorporation of twice the amount of residue produced by the crop. Most of the soil physical properties measured were not influenced by either grain sorghum or wheat residue management treatments; however, they differed between crops. The soil aggregates from the sorghum plots were smaller, more fragile, less dense, less stable dry, and more stable wet than the aggregates from the wheat plots. The pore size distribution of the soil from the Ap horizon of the sorghum plots was more conducive to water infiltration. The saturated hydraulic conductivity was several times greater in the soil cores obtained from the sorghum plots than those obtained fro the wheat plots.

No abstract

A FTER rain showers, wind erodible-size particles on the surface dry rapidly and often begin abrading the surface aggregates and crust while the latter are still moist. The objectives of this investigation were to measure the abrasive loss rates of moist aggregates and develop prediction equations of the loss rates that would be useful in field studies as well as in development of complex wind erosion models. Accordingly, soil samples were obtained from four soils ranging from a sandy loam to a silty clay loam. Forty aggregates, 4, to 6 cm in diameter, were selected from each soil and then further subdivided by establishing four moisture levels with 10 aggregates at each level. Each aggregate was abraded in an enclosed chamber using a calibrated sandblasting nozzle. A stability test was also conducted on air-dried subsamples of each soil. In this test, 1.3 to 1.9 cm diameter aggregates were crushed to a fixed end point and the work done per unit mass (J/Kg) was measured. Test results showed that the slope of a regression line for the abrasion loss rate versus normalized moisture content varied in a systematic manner, as dry aggregate stability ranged from low to high. Thus, it was possible to develop a simple estimating equation to predict abrasion loss rate as a function of average dry aggregate crushing energy and aggregate moisture content.