FRACTAL DESCRIPTION OF SOIL FRAGMENTATION FOR VARIOUS TILLAGE METHODSAND CROP SEQUENCES

Soil structure has been difficult to quantify and, at best, has been s tudied semiquantitatively. Fractal representation of soil fragmentatio n can provide an indication of soil structure. The purpose of our stud y was to use fractal analysis to quantify soil fragmentation under var ious tillage and crop sequence treatments at different times during th e growing season. We collected soil samples from four tillage treatmen ts (established 10 yr earlier) of chisel, disk, no-till, and moldboard . plow in factorial arrangement with two crop sequences of corn (Zea m ay L.)-soybean [Glycine mar (L.) Merr.]-corn (C-S-C), and soy-bean-cor n-soybean, (S-C-S) on a Sharpsburg (fine, montmorillonitic, mesic Typi c Argiudoll) soil. Aggregate-size distribution was used to calculate f ractal dimension (D) for each treatment. Higher D values indicate grea ter soil fragmentation and a soil dominated by smaller aggregates. The opposite is true for lower D values. Differences in soil fragmentatio n observed for tillage treatments after autumn tillage became even gre ater over winter. Soil fragmentation increased over autumn and winter, with D increasing in the order of plow > chisel > disk > no-till. For mation of larger soil aggregates increased during tbe growing season f or all tillage systems. The D values for C-S-C were smaller than S-C-S in the no-till, indicating that the previous year's corn in C-S-C pro vided more large aggregates. Soybean appears to have negative effects on large-aggregate formation in no-till Aggregate densities, averaged across tillage and crop sequence, increased from 1.25 to 1.77 Mg m(-3) as the aggregate diameter decreased from 6.38 to 0.162 mm. Fractal an alysis was found to be useful in determining soil fragmentation differ ences due to different tillage methods and crop sequences.