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Title: MASS-SIZE SCALING IN SOIL AGGREGATES AS AFFECTED BY AGGREGATE MOISTURE CONTENT AND SOIL COMPACTION

Author
item Pachepsky, Yakov
item GUBER, ANDREY - MOSCOW STATE UNIV.
item LEVKOVSKY, E. - MOSCOW STATE UNIV.

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2003
Publication Date: 11/1/2003
Citation: Pachepsky, Y.A., Guber, A.K., Levkovsky, E. 2003. Mass-size scaling in soil aggregates as affected by aggregate moisture content and soil compaction. Soil Science. Vol. 169:1-12.

Interpretive Summary: Soil aggregate analysis presents an important characterization of soil structural organization. Experiments with dry soil aggregates have shown that the mass of aggregates changes with their size so that the aggregates become looser as their size increases. Such dependence has been successfully explained by the fractal scaling theory that furnished two parameters to characterize mass-size relationships. One of them is the exponent that shows how pronounced is the loosening with the size increase. Another parameter is the reference mass of the unit-size aggregates. Recently this theory was extended to simulate the mass-size scaling in wet soil aggregates. Both parameters of the fractal theory were simple linear functions of aggregate water content. The objective of this work was to evaluate the sensitivity of those parameters to soil compaction caused by wheel traffic. Irrigated ad non-irrigated plots were laid out at silty clay soil under fallow, and treatments of one pass and three tractor passes were applied. The plow horizon was sampled a week after treatments. Volume of individual aggregates for four depths in the plow layer was measured with kerosene method at air-dry water content, at two intermediate water contents between saturation and air-dry, and at saturation. Both slopes and intercepts of the dependence of fractal dimension and reference aggregate mass on water content were more sensitive to compaction than traditionally used bulk density and aggregate size distributions. Those findings introduce physics-based parameters to characterize changes in soil structure caused by soil management and leading to changes in soil ability to retain and transmit water and solutes.

Technical Abstract: 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 on aggregate size. There were several reports that density-size relationships in air-dry aggregates follow predictions of a model assuming aggregates to be mass fractals. Recently it was demonstrated 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 work was to evaluate sensitivity of fractal parameters to soil compaction caused by wheel traffic. Irrigated ad non-irrigated plots were laid out at silty clay Greyzem under fallow, and treatments of one tractor pass and three tractor passes were applied. Volume of individual aggregates for four depths in the plow layer was measured with 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 R2 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 soil bulk density and aggregate size distributions. Parameters of fractal scaling showed a promise to diagnose compaction in studied soil.