Key Takeaways
Benefits Depend on Weather: Dual-inhibitor (DI) fertilizers worked best in wet spring conditions. They improved nitrogen retention and increased yields in 2024, but didn’t help in the drier years (2022 and 2023).
Better Nitrogen Holding: In wet conditions, DI fertilizer significantly boosted soil ammonium and improved crop health.
Lower Risk to Water: After harvest, leftover nitrate in the soil stayed below risk levels. More ammonium remained in dry years, likely because dry conditions slowed nitrogen changes in the soil.
More N Didn’t Mean More Uptake: Plants didn’t take up more nitrogen just because more was applied. Total nitrogen in the plants and grain didn’t change much by fertilizer type or rate.
Best Strategy: Combine moderate nitrogen rates, DI fertilizers and in-season tools (like soil tests and canopy sensors) to get the best crop response and protect water quality.
As groundwater nitrate contamination remains a concern across Nebraska, many producers are exploring the potential of enhanced efficiency fertilizers (EEFs) to improve nitrogen use efficiency (NUE) and reduce environmental losses. In a recent three-year field study, we evaluated the performance of a dual-inhibitor (DI) fertilizer (combination of urease and nitrification inhibitors) compared to conventional urea at the Eastern Nebraska Research and Extension Center (ENREEC). Urease inhibitors temporarily slow the conversion of urea to ammonium, reducing ammonia volatilization, while nitrification inhibitors delay the microbial conversion of ammonium to nitrate, thereby reducing nitrate leaching and nitrous oxide emissions. The research focused on how variable early-season precipitation influenced nitrogen availability, crop response, and NUE in irrigated corn production systems.
Study Design and Conditions
The study, conducted from 2022 to 2024, included three nitrogen application rates: suboptimal (105 lb/A), optimal (135 lb/A), and excessive (165 lb/A) based on the University of Nebraska-Lincoln (UNL) recommendation. Treatments were applied to corn in a no-till, corn–soybean rotation under linear sprinkler irrigation. Each of the three years represented distinct early season rainfall conditions, with April–May precipitation 34% below normal in 2022 (dry), 79% below normal in 2023 (very dry), and 19% above normal in 2024 (wet). These contrasting moisture patterns provided a unique opportunity to assess the performance of EEFs under different weather regimes.
Nitrogen Availability and Crop Response
Results indicated that nitrogen availability and crop response were strongly influenced by weather, particularly early season moisture. In 2024, when spring conditions were wetter, the DI fertilizer significantly increased soil ammonium (NH₄⁺) concentrations by 47% compared to conventional urea, suggesting reduced nitrification and ammonia volatilization. However, nitrate (NO₃⁻) levels were also elevated under excessive N rates with the dual inhibitor, likely due to the eventual nitrification of remaining ammonium under high N loading.
Importantly, in 2024 only, DI-treated plots produced a 9% higher grain yield than urea. In contrast, no yield advantage was observed in the drier years of 2022 and 2023.
Improving Nitrogen Use Efficiency
Across all years, suboptimal nitrogen rates improved NUE metrics — including partial factor productivity, nitrogen recovery efficiency (NRE), nitrogen utilization efficiency (NUtE), and agronomic efficiency (AE) — regardless of fertilizer source. These results reinforce the value of matching N supply to crop demand, especially when using EEFs.
Grain nitrogen content and total N uptake did not differ significantly by N rate or source, indicating that additional nitrogen did not always translate into greater plant N assimilation.
Furthermore, in-season canopy reflectance measurements (Normalized Difference Red Edge Index, NDRE) from 2024 revealed 3%-8% higher values in DI-treated plots compared to urea, suggesting enhanced crop vigor during wetter growing conditions.
Residual Nitrogen and Environmental Risk
Post-harvest soil sampling showed that residual nitrate-N concentrations in the 0- to 4-feet profile averaged 16.5 lb/A — below Nebraska’s leaching risk threshold. Residual ammonium-N concentrations, however, were greater in the drier years, possibly due to lower microbial activity and limited conversion of ammonium to nitrate. These findings highlight the need to align nitrogen source and application timing with weather and soil conditions to minimize off-season nitrogen losses.
Practical Implications for Farmers
This study provides several important takeaways for Nebraska producers.
First, dual-inhibitor fertilizers can improve nitrogen retention and yield, but primarily in wet springs when loss risks are high. In drier years, the yield advantage of such products may be negligible.
Second, using suboptimal N rates (10%–20% below UNL recommendations) in combination with split applications or EEFs offers a practical strategy to improve NUE without compromising yield.
Lastly, weather-based adaptive management — using soil nitrate testing, canopy sensing tools and in-season adjustments — is essential to optimize nitrogen efficiency and reduce environmental losses.
Conclusion
As Nebraska continues to experience year-to-year variability in spring rainfall, this study highlights that the benefits of nitrogen stabilizers are context-dependent. Enhanced efficiency fertilizers, particularly those with dual inhibitors, tend to be most beneficial when applied at moderate nitrogen rates under wetter-than-normal conditions. In contrast, during dry years, urease inhibitors can still play a valuable role in reducing ammonia volatilization losses.
To maximize the agronomic and environmental benefits of these tools, it is essential to integrate them with site-specific management strategies and precision technologies. Doing so will support sustained high yields while helping to protect water quality in Nebraska’s irrigated corn systems.
