Effects of Enhanced Efficiency Nitrogen Fertilizers on Agronomic Parameters and Loss Pathways in the Subtropical Mississippi Delta Region

Minimizing nitrogen (N) loss is critical for improving N use efficiency (NUE) in crop production and reducing its effects on the environment. Management practices such as seasonal application timing of N fertilizers and the addition of enhanced efficiency N fertilizers (EENFs) were investigated for the high N requirement of the two most common cereal crops globally, corn (Zea mays L.) and wheat (Triticum aestivum L.), in the subtropical climate of Louisiana. Field research was established during the 2016 and 2017 seasons at the LSU Agricultural Center’s Dean Lee and Central research stations to examine the effect of different EENFs and the effect of application timing on agronomic parameters and loss pathways. Treatments included UAN stabilized with dicyandiamide (DCD), 3,4dimethyl pyrazole phosphate (DMPP), and N-(n-butyl)thiophosphoric triamide (NBPT) in the corn trial. In the wheat trial, urea with the same stabilizers and coated urea (CU) at varying ratios with urea was examined. Earlier application of N fertilizers increased corn grain yields (GY) at vegetative growth stage 3 (V3) by 9% and 24% higher yields compared to V6 and V8 applications, respectively. The CU treatments at early application increased GY for the wheat crop, while later season N application demonstrated higher wheat yields. The trend for NUE was correlated to GY for both crops. Fertilizer stabilized with both NBPT and DCD demonstrated the greatest residual soil total N. This was confirmed by the lowest N2O emission factor (EF) of 0.51% for UAN stabilized with NBPT and DCD in the corn field. Overall runoff losses of NO3- were minimal and constituted only 1-3% of total applied 15N. Inorganic soil N contents were similar among treatments after 60 days. A separate incubation study showed that the CU treatment maintained a steady release that had greater NH4+ and NO3- levels at day 40 of the incubation. Overall the EENFs decreased N losses but did not increase agronomic parameters for corn and wheat