Long-term tillage and crop rotation effect on soil aggregation
Tillage and cropping sequences play a key role in controlling soil aggregation. We measured water-stable aggregate (WSA), wind erodible fraction (WEF), and geometric mean diameter (GMD) for six mid to longterm (8 to 25 years) experiments comparing tillage and cropping sequences in the Brown, Dark Brown, and Black Chernozemic soils of Saskatchewan. In the coarse-textured soil, no-tillage (NT) had a higher value of WSA by 49% more than in the wheat-phase of fallow-wheat (F-W), and had a lower value of WEF by 27% less than in the fallow-phase of F-W compared with minimum tillage (MT). In the medium-textured soils, NT had a higher WAS, ranged from 17 to 38%, and a lower WEF, ranged from 37 to 64% compared with conventional tillage (CT), depending on crop rotation systems. The reduced WEF under NT in the medium-textured soils was due mainly to increased GMD. In the fine-textured soils, NT had a higher WSA, ranged from 10 to 19% compared with MT or CT, and a lower WEF by 47% compared with MT only in the heavy clay soil. Change in GMD was not detectable in the light- and fine-textured soils. Continuous cropping compared with rotations containing fallow improved soil physical properties by increasing WSA, reducing WEF in the medium and fine-textured soils, and increasing GMD only in the medium-textured soils. Of the three soil physical properties determined in this study, WSA was the most sensitive to changes in tillage and crop rotations, then WEF and the least GMD.
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