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This article in SSSAJ

  1. Vol. 45 No. 2, p. 391-396
    Received: Aug 11, 1980
    Accepted: Nov 5, 1980

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Nitrogen and Phosphorus Transported by Eroded Soil Aggregates1

  1. E. E. Alberts and
  2. W. C. Moldenhauer2



Most mathematical models that are being developed to predict sediment discharges from farm fields, watersheds, and basins consider the detachment, transport, and deposition of soil aggregates. This study was conducted to determine the effect of three tillage treatments and two cornstalk residue levels on the size distribution and N and P concentrations of eroded soil aggregates. Measurements were made by applying simulated rainfall to 3.7 by 10.7 m plots located on a silt loam soil in north central Indiana.

Over 60% of the sediment from moldboard-plowed and disked-only plots was composed of aggregates > 0.05 mm, whereas about 30% of the sediment from chisel-plowed plots was composed of aggregates > 0.05 mm. The addition of cornstalk residue to give 20% surface cover on the moldboard-plowed and disked-only plots decreased the percentage of >0.05-mm aggregates by about 12%.

Nitrogen and P concentrations of the 2- to 1-, 1- to 0.5-, and 0.5- to 0.21-mm aggregates were generally 10% lower than the N and P concentrations of the aggregates <0.05 mm. The highest N and P concentrations were associated with the 0.21- to 0.05-mm aggregates. However, this size fraction represented a small percentage of the eroded particles.

Nitrogen and P concentrations of aggregates eroded from the chisel-plowed plots were about 40% higher than the N and P concentrations of the aggregates eroded from the moldboard-plowed plots. Differences in N and P concentrations reflected differences in the transport capacity of the runoff. As increased residue cover reduced runoff velocity, only those aggregates of lower densities and sand contents were transported. As a result, aggregates eroded from chisel-plowed plots contained a greater proportion of silt and clay which was reflected in their higher N and P concentrations than did aggregates eroded from moldboard-plowed plots.

Nitrogen and P concentrations of uneroded aggregates separated by wet sieving were determined and compared with the N and P concentrations of the eroded aggregates. Enrichment ratios were > 1.0, which indicated that nutrient enrichment occurred for all size fractions of eroded aggregates.

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