Soil properties influencing hydraulic sealing of the surface on Alfisols in the Sahel

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" Soil properties influencing hydraulic sealing of the surface on Alfisols in the Sahel "
J. W. Heil A. S. R. M. Juo, Kevin J.

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1113096
Doc. No	:	TLpq304069235
Main Entry	:	A. S. R. M. Juo, Kevin J.
	:	J. W. Heil
Title & Author	:	Soil properties influencing hydraulic sealing of the surface on Alfisols in the Sahel\ J. W. HeilA. S. R. M. Juo, Kevin J.
College	:	Texas A&M University
Date	:	1993
student score	:	1993
Degree	:	Ph.D.
Page No	:	156
Abstract	:	Surface seals reduce crop yields and increase erosion by decreasing infiltration and increasing runoff. Seals form when intense rainfall breaks aggregates into smaller particles that clog pores. The objectives of this study were to (1) identify sealing soils in selected Alfisols in West Africa and to define the processes of sealing; (2) determine the soil properties which affect sealing. Six soils at Hamdallaye, Niger, and two soils at the Cinzana Research Station, Mali were studied. Seals in fallow fields at the Cinzana Research Station were actually deeply compacted soils due to structural losses from cultivation or heavy animal traffic. The following results were obtained from the Hamdallaye soils. Infiltration measurements with a disk infiltrometer were >130 mum/s in the unsealed sites and 3 to 103 mum/s in the sealed sites. Dry unconfined strength was about 36 mg/m2 in the sealed sites and 5 mg/m2 in the unsealed sites. The seals were structural seals. Thin section analysis showed a dense 0.1 to 1 mm thick continuous plasmic layer just below a 1 mm thick layer of loose bare sand. All of the 12 sites studied with clay contents greater than five percent were sealed, and all of those below five percent were not. All of the seals were associated with erosion, where the sandy topsoil was eroded to expose an argillic horizon. Amounts of exchangeable aluminum, iron, and pH all correlated with clay content. Low pH (4.9 in sealed sites) causes the soils to flocculate, so that disaggregated clay remains flocculated in silt-size particles and clogs pores. Silt content is often an indicator of sealing in other soils, but because of low silt contents and flocculated clay in these soils, clay content is diagnostic of sealing. Seals created under artificial rainfall on the Hamdallaye soils consisted of either two- or four-layer seals, depending on clay content. The seals formed quickly and were fully developed after 30 minutes of rainfall. Dispersion of the clays with Na saturation before rainfall prevented seal formation in soils with less than 10% clay due to complete eluviation of the clay.
Subject	:	Agriculture
	:	Agriculture
	:	Agronomy
	:	Biological sciences
	:	West Africa