Mass-size scaling in soil aggregates as affected by aggregate water content and soil compaction

摘要

Determining aggregate size distribution is a common way of characterizing soil structure. Information about soil structure can also be derived from examining the aggregate mass or density of aggregate size. There have been several reports indicating that the density-size relationships in air-dry aggregates follow predictions of a model assuming aggregates to be mass fractals. It was demonstrated recently that such model is applicable to wet aggregates if parameters of this model are assumed to be linear functions of gravimetric water contents. The objective of this study was to evaluate sensitivity of fractal parameters to soil compaction caused by wheel traffic. Irrigated and nonirrigated plots were laid out at silty clay Greyzem under fallow, and treatments of one tractor pass and three tractor passes were applied. The volume of individual aggregates for four depths in the plow layer was measured by kerosene method at air-dry water content, at two intermediate water contents between saturation and air-dry, and at saturation. The mass fractal model fitted data in a satisfactory manner within the range of water contents from air-dry to saturation with a R-2 of 0.999. Both the slope and the intercept of the dependence of fractal dimension and reference aggregate mass on water content were more sensitive to compaction than to soil bulk density and aggregate size distributions. Parameters of fractal scaling showed promise for diagnosing compaction in studied soil.