| Abstrakt: |
The percentages of eroded soil aggregates over 10 size classes ranging from 0.002 to 2.0 mm in diameter as affected by crop residue cover, tillage‐induced roughness, and water flow velocity were investigated under field conditions using simulated rainfall. The soils used were a 4.5% slope Russell silt loam and a 6.5% slope Martinsville loam. With no vegetation present, the smallest eroded aggregates came from a chisel‐plowed surface while the largest came from chisel‐ and moldboard‐plowed surfaces which had been disked. A no‐till treatment gave intermediate values. The D50size (the aggregate size which 50% of the aggregates exceed) in the absence of soil cover was 0.033, 0.032, 0.020, and 0.011 mm for chisel plow plus disk, moldboard plow plus disk, no‐till and chisel plow, respectively. When soil was covered by residue, the size distribution of the eroded aggregates was not greatly different among the tillage treatments. The D50size was reduced in this case to about 0.012 mm for all tillage systems. For no‐till, the percentage of the eroded aggregates > 0.05 mm decreased exponentially (r2= 0.85) with an increase in residue cover. Under chisel plowing residue was not effective in reducing the quantity of larger aggregates in the runoff. An increase in flow rate caused an increase in water flow velocity which, in turn, caused a linear (r2= 0.94) increase in the percentage of the eroded aggregates > 0.05 mm, for chisel plowing. The results from this study were explained in terms of sediment trapping capacity of the soil surface, as well as runoff transport capacity. |
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