Laila A. Puntel
Date of this Version
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
Under the supervision of Professor Laila A. Puntel
Lincoln, Nebraska, June 2023
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