When considering greenhouse gas (GHG) emissions from fertilizer use, the focus should be on nitrous oxide (N2O) emissions from fertilizer applied to cropland and grassland.
Nutrient use efficiency, the proportion of nutrients applied from all sources that are taken up by the crop, is a useful indicator of fertilizer management performance. Low output/input ratios often reflect risks of nutrient losses to the environment, while high ratios, above 100 percent, reflect soil nutrient mining practices that reduce soil fertility if practiced over several consecutive years. Both cases are unsustainable.
The fertilizer industry promotes 4R Nutrient Stewardship (applying the Right Nutrient Source, at the Right Rate, at the Right Time, in the Right Place) as the main intervention to improve nitrogen use efficiency and minimize N2O emissions from fertilizer use.