Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

P. Mark Walthall

Abstract

Crust formation in three soils from Mexico (Nadurargid, Durustoll and Calciorthid) and three soils from Louisiana (two Fragiudalfs, and a Hapludalf) was investigated. The objectives were: (1) to characterize crust morphology; (2) to quantify type, distribution, and geochemistry of cementing agents; and (3) to evaluate the effect of management practices on infiltration, erosion, crust strength, and corn and soybean emergence. Three management practices, bare, protected, and gypsum-amended were evaluated. Crust morphology in the soils of Louisiana indicated the development of a compacted layer in the upper 0.1 mm of the bare and gypsum-amended soils. Aggregation was improved with the gypsum amendment. The soil surface was sealed by clay-size particles in the protected soil. In the Mexican soils, fine particles were dispersed, sealing the soil surface. Calcite, free iron oxides, amorphous Si, and gypsum, were identified as cementing agents by SEM/XRF analysis. There was no accumulation of free Fe oxides or amorphous Si and Al in the crusts, relative to the subsurface zones. As a soil amendment, gypsum induced precipitation of calcite in cases where calcite was not detected in the soil initially. Infiltration rate and ponding time were improved in all six soils by gypsum amendment. Erosion was decreased in the gypsum-amended soils by 54% and 98% in the protected soils, compared to that in the bare soils. Crust strength increased by 90% in the soils of Mexico and by 25% in the soils of Louisiana as rainfall duration increased from 30 to 60 min. The higher values of crust strength in the soils of Mexico were related to higher water-dispersible clay indices and higher amorphous Si contents in these soils. Corn emergence was reduced by 75% in the soils of Mexico and 13% in the soils of Louisiana when rainfall intensity was increased from 30 to 60 min. Soybean emergence was decreased by 77% in the soils of Louisiana. No soybean emergence was observed in the soils of Mexico when rainfall increased from 30 to 60 min.

Pages

184

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