Document Type

Thesis - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Robert L. Todd


Denitrification is an important process involving the loss of nitrogen from agricultural soils. This study investigates denitrification on a Beadle clay loam and a Worthing silty clay loam in a landscape in Eastern South Dakota. Comparisons were made in 1986 and 1987 of these soils under four different tillage systems: Moldboard plowed, chisel plowed and disked, ridge tillage, and no tillage systems. Soil core samples (0 to 5 cm) from continuous corn plots were utilized to determine nitrogen loss by denitrification and volumetric moisture biweekly through the growing seasons. In addition, organic matter residue amount, bulk density, and precipitation were also reported. In the laboratory, glucose and nitrate additions were related to denitrification in the Worthing soil of different aggregate sizes. Glucose and nitrate additions stimulated denitrification when added at 625-ug glucose g-1 soil. However, amounts in excess of this failed to stimulate activity. Five sizes of Worthing soil aggregates (<1, 1 to 2, 2 to 4.8, 4.8 to 6.4, and 6.4 to 9.5 mm) were maintained at 45% volumetric moisture on a sand tension table and subsequent denitrification rates were measured. No differences were seen. Tillage practices were found to relate to denitrification rates. No differences were observed between the other three tillage treatments, however the Worthing lowland soil better potential to denitrify than the Beadle upland soils relating to the higher volumetric moisture on the Worthing soil. Estimated denitrification for the two years varied between 3- and 36-kg nitrogen loss ha-1 yr-1 on the Beadle soil, and 17- to 36-kg nitrogen loss ha-1 yr-1 on the Worthing soil. A computer model was developed to predict denitrification rates as a function of volumetric moisture. A volumetric moisture value of 22.3% or less would completely inhibit denitrification. Soil volumetric moistures found in this study varied between 15 and 55%. Of the parameters measured in this study, volumetric moisture appears to be the most significant factor. However, potential losses of nitrogen by denitrification should be considered in designing soil management schemes since tillage methods can greatly control soil moisture.

Library of Congress Subject Headings


Tillage -- South Dakota

Soils -- South Dakota -- Nitrogen content



Number of Pages



South Dakota State University