|Huang, Chi Hua|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2008
Publication Date: 7/1/2009
Citation: Reichert, J.M., Norton, L.D., Favaretto, N., Huang, C., Blume, E. 2009. Settling Velocity, Aggregate Stability, and Interrill Erodibility of Soils Varying in Clay Mineralogy. Soil Science Society of America Journal. 73(4):1369-1377.
Interpretive Summary: The problem of soil erosion by water depends greatly upon the presence of lack of stable granules of soil called aggregates, especially, in soil with a high clay content. Generally, the more stable the aggregates are, the more water will enter the soil and less soil erosion will occur. However, even a well aggregated soil can have high erosion losses when water runs off because of the ease at which these aggregates can be transported. This movement is a result of both how large the aggregates are and how heavy they are. We conducted a study with a device that will allow us to measure not only how stable aggregates are but also how fast they fall in water which is a measure of how they may be transported. We compared both dry and moist aggregates with this method and related the results to erosion from small pans. The results show that factors other than aggregate stability can affect the amount of erosion. These include a water table or drainage, dispersion and the breakdown of aggregates by just wetting them. The impact of this research is that we can enhance erosion control on these high clay soils by preventing the dominant erosion processes from occurring in the field.
Technical Abstract: The relation of soil structural stability with soil erodibility depends on the mechanisms of aggregate disruption of different aggregate sizes and the measurement technique. In this study, we evaluated the relationship between settling velocity and stability of aggregates of different sizes, and interrill erodibility for ten clay soils, as affected by soil properties and slow wetting to reduce slaking. Soils with 4.76-8 mm diameter aggregates with greater slaking index (SIV50) when settling in water had also greater slaking under wet sieving (SIMWD for 4.76-8 mm aggregates) and slower fall velocity (V50D for 4.76-8 mm aggregates). Interrill erodibility (Ki) had greater correlation with the mean weight diameter (MWD) of stable aggregates in the 1-2 mm size class, than for the whole soil (aggregates < 8 mm), and no correlation was observed with any of the slaking indexes involving wet sieving (SIMWD) or settling in water (SIV50). Multiple regression analysis indicated that 89% of the variability in erodibility for prewetted soil (KiW) was explained by MWD of prewetted 1-2 mm stable aggregates (MWDW), available water content, and fall velocity of 1-2 mm dry aggregates (V50D), while 96% of the variability in erodibility for dry soil (KiD) was explained by MWDW for 1-2 mm prewetted aggregates, water dispersible clay, and V50D for 1-2 mm aggregates. Correlations among aggregate stability and fall velocity with soil properties suggest that physical-chemical properties of the clay play an important role in aggregate stability of these soils with higher clay content which affects interrill erodibility. A confounding effect of high water table, low drainage and slaking may explain the higher erodibility and lack of slaking reduction effect on our prewetted soil under simulated rainfall.