Anna Eynard

Document Type

Thesis - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School



Soil structural stability and soil organic C content usually decrease with cultivation. However no-till systems may increase soil C content and improve soil structure. This study was conducted to examine the effects of three different management systems (grassland, no-till, and conventional-till) on the structure of prairie soils in central South Dakota. Eight sites were selected as replications along the Missouri River. Six Ustolls and two Usterts were studied. Morphological descriptions were made of structure, pores, and roots. Soil bulk density, penetrability, water infiltration and retention, dry and wet aggregate sizes and stability, and soil organic C distribution in dry and wet aggregates of different size and stability were also measured. Most soil structural changes due to cultivation were observed in the top 0-0.20 m. Granular structure was dominant under grass, whereas plates, blocks and compacted layers were most common in conventional till and no-till soils. Cultivated soils were less porous (total soil porosity 50%) than soils under perennial grasses (total soil porosity 56%). Wet aggregate stability, water infiltration at 0.30 kPa tension and water retention at 10 kPa tension were higher in grass than in cultivated soils at 78 compared to 42%; 22 compared to 9 μm s- 1; 0.37 compared to 0.33 g g-1 for grass compared with cultivated respectively. Loss of aggregate stability occurred together with organic Closs. Soil organic C was not significantly increased by the no-tillage practices applied in this study (43 Mg ha-1 in no-till vs. 39 Mg ha-1 in till, for 0-0.20 m depth). No-till soils showed evidence of increased biological activity, pore formation and aggregate stabilization, but most structural characteristics developed under tilled systems persisted after 6-16 years of no-till. Changes in soil structure due to management systems were most evident in Ustolls where cultivation determined net soil C losses. Soil properties of Usterts were less affected by land use and management practices. Significant improvement of soil structure and increase in soil organic C in the top 0.20 m of soil appear to require greater than the average 10 years of no-till management represented in this sample of fields from central South Dakota.

Library of Congress Subject Headings

Soil structure -- Missouri River Watershed
Soil structure -- South Dakota
Structural stability



Number of Pages



South Dakota State University