Physical and Chemical Properties of Eroded Soil Aggregates

RAINFALL simulation was used to evaluate the characteristics of aggregates eroded from erosion plots on two loess soils in southwestern Iowa. The mean aggregate diameters (D50) for interrill erosion were 44 and 34 ^m for soils with 26% clay and 1.9% carbon and 22% clay and 0.8% carbon in their matrix, respectively. The D50 size increased as rilling occurred, but the percentage of increase was quite different for the soils. The D50 size increased by 91% for the soil with higher clay, whereas it increased by only 15% for the other soil. The eroded aggregates >50 ^m in diameter contained more clay and total nitrogen than did the aggregates <50 >im, when analyzed as a single fraction. The >50-/im aggregates were also enriched in clay and nitrogen when their contents were compared to those of the matrix soil. Enrichment was greater for interrill than for interrill plus rill erosion because of greater particle selectivity during the transport process. Equilibrium phosphorus concentration curves varied with aggregate size, suggesting that 250 to 50-jum aggregates are of greater importance in buffering soluble P levels and transporting labile P than larger aggregates...