A physically based wind-erosion climatic factor has been derived: CE = pf [,~2 _ (~. + .H/pa2)]3/2/(,,)d,~where p is the air density, a is a constant made up of other constants (von Karman, height of wind speed observation, roughness parameter), u is the horizontal wind speed, uT is threshold wind speed, f(u) is a wind speed probability density function, and .~1 is the cohesive resistance caused by water on the soil particles. Cohesive resistance is proportional to the square of water content relative to water content at -1500 J kg-1. Relative water content is approximated from the Budyko dryness ratio and the Thornthwaite PE index with similar results. CE is calculable from wind speed and other generally available meteorological data, and is usable in the wind erosion equation without some of the limitations of a previously used wind erosion climatic factor.

Most methods used to estimate aggregate stability apply an unmeasured force, or a measured force without knowledge of transfer, to a single or a group of aggregates. A technique is needed to estimate aggregate stability based on quantitative transfer of energy. This paper presents an energy-based procedure for evaluating dry-aggregate stability. Soil aggregates were crushed by diametrically loading them between parallel plates. The energy of crushing was determined by integrating the area under the force against distance curve. The aggregate-surface area after comminution was calculated from aggregate-size distribution and aggregate density; the aggregates were assumed to be spherical. The results are expressed as energy per unit of surface area, joules per meter squared (J/nr). Example values obtained from field-sampled aggregates for several soil series ranged from 3.7 ± 0.7 for Hotlake silt loam (coarse-silty, mixed, mesic Aquic Haploxerolls) to 43.9 ± 7.5 for Bearden silt loam (fine-silty. frigid Aerie Calciaquolls). The wide range of aggregate stabilities among different soils made it possible to distinguish among them even though variability among aggregates of the same soil was relatively large. The results were relatively insensitive to initial aggregate size but sensitive to crushing end point.

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

No abstract

No abstract