Re-Evaluating Nitrification Inhibitors and Nitrogen Management Effects On Nitrous Oxide Emissions In Corn.

Nitrous oxide (N₂O) is a potent soil-derived greenhouse gas that significantly contributes to global warming; N₂O comprise 40-44% of the CO₂ equivalent emissions from soil under rain-fed, and 16-33% under irrigated corn in the United States.  On a global scale, agricultural N₂O emissions are projected to increase 35-60% by 2030 due to increased N fertilizer use and animal manure production (FAO, 2003).  We reviewed research conducted in the last 3 decades to determine the current state of knowledge on the effects of nitrification inhibitors and related aspects of N management on the rate of nitrification of applied nitrogen fertilizers, N₂O emissions from soil, and nitrogen use efficiency (NUE) in corn. Although scientists agree that most nitrification inhibitors delay the nitrification process, and have potential to reduce N₂O emissions from fertilized cornfields, opinion is divided whether these delays significantly lowered growing-season N₂O emissions, improved NUE and/or corn yield.  Nitrapyrin, the most commonly used nitrification inhibitor, occasionally reduced corn yield at agronomic optimum N application rates, even though significant yield increases due to nitrapyrin were observed at lower-than-optimum N fertilizer rates.  Few experiments have been conducted to address how timing of N application and placement depths (with or without inhibitors), and spread across the various N application timeframes used by corn farmers (e.g. early fall, late fall/pre-plant and spring pre-plant or sidedress applications) affect N₂O emissions.  In particular, limited data exist to assess N₂O emissions following spring sidedress-applied N, especially given the availability of reformulated nitrapyrin - Instinct™ - for application with liquid N fertilizers, and the introduction of more N efficient corn hybrids in use today.  On-going experiments across Indiana indicate that Instinct™ reduced N₂O emissions by up to 53%, across soil and tillage systems. Availability of technologies that can integrate nitrification inhibitors and N management options in time and space offers opportunity for further research in integrated nitrification inhibitors and N management that best reduce N₂O emissions in corn.