Evaluation of Nitrogen Fertilizer Additives for Enhanced Efficiency in Corn on Iowa Soils

Abstract

Core Ideas Landscape position was selected and N fertilizer treatments were designed to promote significant denitrification and enhanced potential volatilization. No agronomic benefit was found using urea with nitrification and urease inhibitors or urea with a polymer coating. Lack of response to inhibitor products and coated urea were likely due to rainfall timing and amount shortly after application, reduced volatilization due to high soil retention of NH4, and slowed nitrification rates from cool soil temperatures after application. Recent years of high rainfall and prolonged wet soil conditions in Iowa have renewed interest to protect losses of fertilizer nitrogen (N) in corn (Zea mays L.). This study evaluated effect of N additives and a slow‐release urea product on the soil NO3–N fraction of total inorganic N, mid–vegetative growth N stress, grain yield, and corn nitrogen use efficiency (NUE). Field trials were conducted at two Iowa State University Research Farms in 2013 and 2014. Sites were selected for probable response to applied N with different nitrification product treatments and coated urea (fine‐textured soils that were poorly drained with high organic matter) and urease inhibitor products (incorporated vs. unincorporated). Urea and treated urea were applied at 120 lb N/acre and incorporated and left on the surface. Overall, there was no agronomic benefit from using urea with nitrification inhibitors (Instinct and SuperU), urea with urease inhibitors (Agrotain, SuperU, and Factor), or urea with a polymer coating (Environmentally Smart Nitrogen). Lack of response to nitrification and urease products was potentially due to climatic conditions during the study. Significant rainfall shortly after N application moved urea into the soil profile (minimizing NH3 volatilization) and slowed nitrification rates from cool temperatures early in the season.