Enhanced efficiency fertilizers: a multi-site comparison of the effects on nitrous oxide emissions and agronomic performance

The need to understand the effects of enhanced efficiency fertilizers (EEF) for their effect on nitrous oxide emissions and agronomic performance was the motivation underpinning this multi-location study across North America. Research locations participating in this study included Ames, IA; Auburn, AL; Bowling Green, KY; Fort Collins, CO; St. Paul, MN; Pullman, WA; University Park, PA; and Winnipeg, Manitoba, Canada. All of these sites collected observations on various forms of enhanced efficiency fertilizers for their effect on nitrous oxide emissions throughout the year and agronomic performance of corn (Zea mays L.), cotton (Gossypium hirsutum L.), and wheat (Triticum aestivum L.). The agronomic impact of these materials shows there is an inconsistent effect on crop production which has been noted in previous studies comparing EEF to non-EEF materials. In cotton production in the southeast, there was no effect of EEF materials on yield or fiber quality. The majority of the studies evaluated the effect of EEF materials on corn yield and showed inconsistent effects on grain yield. The use of EEF materials caused an increased greenness in corn canopies in Iowa and increased grain yield because of the delayed senescence of the plant canopy. The use of a chlorophyll index or the plant senescence index revealed that the increase in grain yield could be attributed to an increased duration of green leaf area of the corn crop during the grain-filling stage. In all crops the use of EEF materials increased the nitrogen use efficiency of the crop which demonstrates that EEF materials will have both positive environmental and agronomic responses. Enhanced efficiency fertilizers exhibit mixed results for their combined impact on N2O emissions and crop production. The primary factor limiting a consistent response among locations is the variation in the seasonal weather during the growing season. In general, the effect of EEF materials on N2O emissions is positive during the period immediately following application compared to non-EEF materials; however, the rainfall pattern during the remainder of the growing season determines the overall efficacy of these materials. Overall, the materials evaluated in this study across multiple locations revealed that these fertilizer materials function as enhanced efficiency fertilizers.