Impacts of Enhanced Efficiency Nitrogen Fertilizers on Yield-scaled N2o Emissions in Illinois Maize by Rebecca Graham Thesis

Nitrous oxide (N2O) is a potent greenhouse gas (GHG) with about 300 times the global warming potential of CO2 and significant levels of this GHG come from agriculture. A two-year field experiment was conducted to assess the ability of enhanced efficiency nitrogen fertilizers (EENFs) to minimize yield-scaled N2O emissions while maintaining nutrient utilization and crop productivity of maize. In addition to an unfertilized control (zero N), N source treatments applied at 202 kg ha-1 at planting included anhydrous ammonia (AA), UAN + nitrapyrin, ESN, and SuperU. Gas samples were collected using static closed chambers. Soil inorganic N concentrations, soil temperature, and precipitation were monitored throughout the growing seasons. Crop N content, grain yield, and nitrogen recovery efficiency (NRE) were also determined each year. Over the two-year trial, we found that EENFs did not consistently reduce N2O emissions or increase grain yields relative to the conventional AA treatment. Soil N concentrations were not correlated with daily N2O flux rates. In 2015, injected UAN + nitrapyrin increased N2O and yield-scaled N2O emissions relative to the other N sources, while AA produced the highest emissions in 2016, but not the highest yield-scaled emissions. These results indicate the difficulty in identifying ways to decrease yield-scaled N2O emissions using different N sources under variable weather conditions each year that likely influenced fertilizer N transformations in soil.