Nitrogen Fertilization Strategies for Corn in Southern Illinois: Effects of Application Timing, Starter Fertilizer, and Cereal Rye on Yield and Nutrient Balance

Author

Osman Guzel, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2025

Degree Name

Doctor of Philosophy

Department

Agricultural Sciences

First Advisor

Brevik, Eric

Second Advisor

Sadeghpour, Amir

Abstract

Effective nitrogen management is crucial for both maximizing yields and minimizing nitrogen residues, particularly in poorly drained clay soils common in southern Illinois. The studies in this thesis evaluated multiple site-year field studies addressing nitrogen rate, nitrogen timing, and cover crop management to minimize environmental impacts and maximize economic benefits. In the first study, eight different pre-plant nitrogen rates (0-394 kg N per ha) were evaluated in 12 site-year studies. The economic optimum nitrogen rate, EONR, was found to range from 167 to 361 across different years and field conditions. The Maximum Return to Nitrogen (MRTN) determined for Southern Illinois was only 17%, and N leaching was found to be greater than EONR for all site-years. In the second study, two different nitrogen applications were compared in a 10-site-year corn trial: pre-planting and sidedress. The results showed that the EONR of sidedress nitrogen application was 8% lower than that of pre-planting nitrogen. It was concluded that N-based leaching losses were reduced by 30 kg N per hectare without any yield loss. The third study examined the impact of integrating cereal rye as a cover crop into corn production on yield. In the study areas where cover crops were used, although higher EONR values were found due to N immobilization, no statistically significant loss was observed. This thesis study found that N timing and the integration of cover crops into corn production reduced losses from environmentally harmful nitrogen and increased effective fertilizer efficiency. These findings highlight the need for the development of MRTN-based tools that integrate factors such as timing, weather, and soil variability in Southern Illinois.