Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Plant Science

First Advisor

Paul E. Fixen


Two field experiments were established in 1983 to evaluate the effect of nitrogen (N) on corn, oats and soybeans grown under various tillage sytems [sic] in east central South Dakota. A corn-oats rotation was grown under moldboard plow (MP), chisel plow (CH), and no-till (NT) tillage systems in a Poinsett silty clay loam soil (Udic Haplaboroll, fine-silty, mixed). In southeast South Dakota a corn-soybean rotation and a continous [sic] corn rotation were grown under MP NT and till plant (TP) and MP CH and NT systems, respectively on an Egan silty clay loam soil (Udic Haplustoll fine silty mixed). Nitrogen was applied at 4 rates (including a check) as either topdressed ammonium nitrate or injected urea-ammonium nitrate. Denitrification at the east central site in 1984 measured 11, 16, and 25 kg N ha-1 in MP, CH, and NT systems in which 112 kg N ha-1 was topdressed, respectively. Rates of denitrification in the NT system were significantly reduced by injecting 112 kg N ha-1. However, missing data prevented the difference from being accurately estimated. Nitrogen mineralization rates appeared to be higher under MP tillage than under reduced tillage in both years at both locations. This difference was estimated to be 24 kg N ha-1 at the east central site (ave of oats and corn) in 1983. Leaching prevented accurate N mineralization rate calculations [sic] at the other sites/years. At the Poinsett site, total N requirement of corn at optimum yield was the same for different tillage systems. However, N required per Mg of grain was slightly lower for the MP system because of the slightly higher optimal yield compared to the reduced tillage systems. Oat yield under reduced tillage resulted in a slightly lower yield potential and slightly higher N requiremnt [sic] than under MP tillage. Two unusually wet springs occurred at the southeast site which delayed the planting of corn. This coupled with very dry summers resulted in low yields in both years. The CH system yielded significantly less corn grain and silage in 1983 and significantly more silage in 1984 than other sytems [sic] in the continuous [sic] corn rotation. Tillage method did not affect yield of corn in the corn-soybean rotation in either year. Soybean yield was significantly higher in the TP system than the MP and NT systems in 1983, but significantly lower than in to [sic] the MP system in 1984.

Library of Congress Subject Headings

Corn -- Soils -- Nitrogen content
Oats -- Soils -- Nitrogen content
Soybean -- Soils -- Nitrogen content




South Dakota State University