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United States Department of Agriculture

Agricultural Research Service

Title: Slaking in Fragipan and Argillic Horizons

Authors
item Lindbo, David - NORTH CAROLINA STATE UNIV
item Rhoton, Fred

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 4, 1995
Publication Date: N/A

Interpretive Summary: The ability of soil material to slake (disintegrate) when immersed in water is one of seven field clues used to confirm the presence of a fragipan horizon. Since soils without fragipan horizons are assessed at a higher value for taxation purposes, positive identification of these soil layers is important to the landowner as well as researchers. Some soil materials from non-fragipan horizons also exhibit slaking which creates identification problems since these measurements are not quantitative. We developed a quantitative method to measure the rate of slaking that permits the separation of fragipan and non-fragipan horizons based on this property. In addition to aiding in the identification of fragipan horizons, this method can be used to assess the susceptibility of these soil materials to erosion once exposed at the surface

Technical Abstract: Fragipan horizon identification is based on seven field clues, none of which are quantitative in nature. The ability of uncemented horizons (including fragipans) to slake or fracture when immersed in water is the basis for the last of these clues. The objectives of this study are to determine if slaking is unique to fragipan horizons and to quantify slaking in selected horizons from soils of the southern Mississippi Valley Silty Uplands, designated as Major Land Resource Area (MLRA) 134. Clods from the Btx1 horizons of the Loring and Grenada soils (fine-silty, mixed, thermic Typic Fragiudalfs, and fine-silty, mixed, thermic Glossic Fragiudalfs, respectively) and Bt horizons of a Memphis soil (fine-silty, mixed, thermic Typic Hapludalfs) were used for comparisons. Slaking was quantified by weighing the air-dried clods and measuring the length of time required for the clod to completely slake after being immersed in water. All of the horizons investigated slaked in water. Although slaking rates varied from site to site, both Loring and Grenada Btx1 slaking rates (2.3 and 1.7 g min**-1, respectively) were significantly lower than Memphis Bt slaking rate (4.6 g min**-1). Regression analysis suggests weak to no relationship of slaking rates to sand content (r**2 = 0.24) and no relationship of slaking rates to silt or clay content, or to extractable Fe or Si. The data presented suggest that quantified slaking rates may be useful in differentiating fragipans, but the data set needs to be expanded to include other parent materials and soils from other MLRAs.

Last Modified: 12/20/2014
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