Improving Nitrogen Management and Corn Productivity through Enhanced Efficiency Fertilizer and Cover Crop Integration in Nebraska Cropping Systems

Authors

Madhusudhan Adhikari, University of Nebraska-LincolnFollow

First Advisor

Javed Iqbal

Committee Members

Joe Luck, Girma Birru, Guillermo Balboa

Date of this Version

5-2025

Document Type

Thesis

Citation

A thesis presented to the Faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Agronomy

Under the supervision of Professor Javed Iqbal

Lincoln, Nebraska, May 2025

Comments

Copyright 2025, Madhusudhan Adhikari. Used by permission

Abstract

Effective nitrogen (N) management is vital for sustaining corn yield and reducing environmental impacts in Nebraska cropping systems. Three field studies were conducted to evaluate the impact of 1) fertilizer type (anhydrous ammonia [AA] with nitrification inhibitor: enhanced efficiency fertilizer [EEF] or AA without EEF) and N application timing (pre-plant vs. split with side-dress UAN) on in-season soil N availability, crop response, nitrous oxide (N₂O) emissions, residual soil N and N use efficiencies (NUEs); 2) winter cover crop (CC) species and crop rotation variability on CC biomass production, N uptake, soil N dynamics, and cash crop performance in rainfed corn-soybean system; and 3) diverse summer CC species after winter wheat on CC biomass production, N uptake, soil N dynamics, and subsequent corn performance in rainfed conditions in Eastern Nebraska. Results from the first study indicated that EEF moderately improved soil NH₄-N retention, reduced soil NO₃-N concentration by 5-17% but had limited impact on corn yield, NUEs or nitrous oxide (N₂O) emissions. Similarly, split N application increased daily N₂O emissions after side-dress application, residual soil NH₄-N and NO₃-N levels under drier year but failed to improve corn yield and NUEs. The findings highlighted that in fine-textured, high-SOM soils of irrigated corn systems, the agronomic and environmental benefits of EEF and split N application are limited when N rates are at or above optimal. The second study indicated that winter cover crop (CC) establishment was constrained by below-average precipitation and short growing periods during fall each year, resulting in low biomass (< 0.2 Mg ha^-1) and N uptake (< 5 kg N ha^-1). Additionally, CC species with measurable biomass led to non-significant reductions in spring soil NO₃-N levels by approximately 15%. Neither crop rotation nor CC treatment significantly affected corn or soybean grain yield, suggesting their minimal agronomic and environmental benefit under dryland conditions. Further, the third study showed substantial variation in CC biomass production (0.74 – 8.63 Mg ha^-1) and biomass N uptake (25 – 187 kg N ha^-1) depending on species selection. Legume species such as Sunn hemp, hairy vetch, and forage peas significantly increased soil NO₃-N availability, corn N uptake, and grain yield in the subsequent corn crop. These treatments provided substantial N credits (up to 99 kg N ha^-1) and improved NUE, reducing the need for additional synthetic N inputs. Thus, integrating legume CC species following winter wheat offers a promising strategy to enhance N cycling, improve NUE, and sustain corn productivity while reducing N fertilizer inputs in temperate rainfed systems. Collectively, the findings from these three studies emphasize the importance of site-specific and system-specific nitrogen management strategies in corn-based cropping systems of eastern Nebraska.

Advisor: Javed Iqbal