Relationships of Nitrous Oxide Emissions to Fertilizer Nitrogen Recovery Efficiencies in Rain-fed and Irrigated Corn Production Systems: Data Review

Project Summary

Nitrous oxide (N₂O) emissions from corn production systems are a large societal concern because so much of the N fertilizer applied to crop production in the United States is applied to corn, and because agriculture alone accounts for the majority of N₂O emissions from all sources. The IPCC (2006) has estimated that an average of approximately 1.0% of the N fertilizer applied is lost as N₂O, but we know from our own studies in rain-fed corn production that estimated emissions can sometimes exceed the equivalent of 5% of the N in the N fertilizers applied.

Over the years of scientific monitoring of N₂O emissions, the predominant reporting method has been to quantify episodic and/or cumulative growing season N₂O emissions per unit land area. Later refereed publications included acknowledgement of the importance of reporting yield scaled N₂O emissions, but not until relatively recently has there been a plea to focus on emissions within the context of actual N use efficiencies. The recent meta-analysis by Decock (2014) highlighted the low proportion of past N₂O emission studies that included critical information on treatment effects on crop N export (let alone any mention of crop N uptake).

The central hypothesis of this proposal is that increased corn plant N uptake (as a fraction of the fertilizer N applied) will be associated with reduced N₂O emissions on area-scaled, yield-scaled, and NRE-scaled (i.e. plant N uptake per unit of N fertilizer initially applied) methods of interpreting relative N₂O emissions from different management systems for corn production.