Field Rainfall Simulator Studies on two Clay Soils of the Darling Downs, Queensland. 11* Aggregate Breakdown, Sediment Properties and Soil Erodibility

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Loch R.J
Dabbollan T.E
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Size distributions of the solids in runoff water were measured for two clay soils subjected to simulated rain under a range of plot lengths and two tillage orientations. Selective transport did not appear to have affected the sediment size distributions. Therefore these could be used as a measure of soil structure and aggregate breakdown by rainfall and runoff. There was little dispersed clay, most of the sediment remaining aggregated. For each soil, sediment size distributions were bimodal, peaks in sediment size being related to orders of aggregation in each soil. Concentrations of dispersed clay provide evidence that stresses on aggregates moved by rain impact on flowing water were greater than on those moved in rills by flowing water alone. Consistent with this, sediment size distributions showed much less breakdown to sizes < 0 '125 mm in rills. Suspended load (sediment < 20 JIm) showed little temporal t1uctuation. and little or no decrease with time, suggesting that for these soils, aggregate disruption by raindrops and overland flow provides a continuous source of suspendable material. Bed-Ioad was more variable and saltating and contact load appeared to be complementary to some extent.
Soil Science, 21, p. 47-58