Site-Specific Evaluation of Nitrogen Inhibitors on Yield, Nitrogen Use Efficiency, Profit, and Soil Nitrogen Dynamics in On-Farm Experiments

Authors

• Christian Uwineza, University of Nebraska-LincolnFollow

First Advisor

Laila A. Puntel

Date of this Version

6-2023

Document Type

Article

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 Laila A. Puntel

Lincoln, Nebraska, June 2023

Comments

Copyright © 2023, Christian Uwineza

Abstract

Nitrogen inhibitors (N-in) are often used by farmers to reduce nitrogen (N) losses from fertilizer applications, improving nitrogen use efficiency (NUE) and mitigating environmental impact. However, there is limited understanding of the site-specific effectiveness of inhibitors and their effect on crop yield and profitability. This study aimed to (1) measure the site-specific performance of N-in using on-farm strip trials in Nebraska, (2) quantify the effects of N-in on yield, profitability, and NUE, and (3) determine if lysimeter water nitrate-N (NO₃^--N) and soil nitrate (NO₃^--N) and ammonium (NH₄⁺-N) concentrations could help quantify the benefits of N-in. Eleven experiments were established between 2021 and 2022, including nine Nebraska On-Farm Research Network (NOFRN) and one long-term N study located at South Central Ag Lab (SCAL). Randomized strip trials were established in commercial fields, the selection of inhibitor type and N application timing was determined by the growers. Yield data was collected using yield monitors. Lysimeter water samples and soil samples were collected during the first six weeks after N-in application. Whole field results indicated no significant differences in yield, partial profit, or NUE among all study sites, regardless of the use of N-in. However, site-specific analysis at a smaller scale (~ 177 m²) where lysimeter and soil samples were collected, showed significant difference for N-in compared to the control at 2 out of 5 sites. At a site characterized with a loam soil type

with 7 to 11% slope, N-in yielded 1832 kg ha^-1 more than the control (p < 0.1). Similarly, N-in outperformed N control at a silty clay loam and a fine sandy loam soil type with yield differences of 680 kg ha-¹ and 950 kg ha^-1, respectively (p < 0.1). Lysimeter water NO₃^--N, soil NO₃^--N and NH₄⁺-N concentrations did not yield conclusive evidence regarding the benefits of N-in. These findings highlight the potential variability of N-in effectiveness depending on specific soil conditions. Future studies should consider the specific field characteristics and management practices employed by growers to determine the optimal utilization of N-in products in agriculture.

Advisor: Laila A. Puntel