The use of N additives and slow release materials with ammoniacal fertilizer varies throughout the U.S. Corn Belt due to differing N loss potentials across climate, soils, and production systems. In Iowa, recent years of high rainfall events and prolonged wet soil conditions has renewed interest to protect fertilizer N loss from denitrification, leaching, and greenhouse gas emission with use of nitrification inhibitors. These loss processes can be significant in Iowa soils that are poorly drained and have high organic matter, high pH, and high populations of denitrifying bacteria. Subsurface tile drainage is also prevalent in farmer fields throughout the state, a contributing pathway for nitrate leaching. Leaching loss is the major contributor to N in surfaces waters reaching the Gulf of Mexico. Farmers who utilize minimum or no-tillage systems can benefit from urease inhibitors to minimize volatilization from surface applied urea or urea containing fertilizers. Evaluation of urease and nitrification inhibitors, and slow release fertilizer products, is needed to best provide advice to farmers on appropriate use with urea fertilizers for agronomic performance, as well as potential to aid in reducing loss that affects water and air quality. Urea is an important N fertilizer source across the Corn Belt, with consumption in Iowa at approximately 180,500 U.S. tons (2010-2011 fertilizer year). Proper and improved use efficiency options are important for farmers.

The objective of the study was to determine the effect of urease inhibitors, nitrification inhibitors, and slow release urea products on soil inorganic-N, N use efficiency and yield in corn biomass and grain, and nitrous oxide (N2O) emission from soil.