United States Corn: Fertilizer Use Efficiency Doubles between 1980 and 2014

Fertilizer use efficiency has many definitions. One of the most useful is "partial factor productivity" (PFP). The following four charts show trends for PFP for nitrogen (N), phosphorus (P), and potassium (K) fertilizers applied to the United States corn crop from 1964 through 2014. They are calculated from corn yield data (USDA-NASS) and from surveys of applied rates reported by USDA-ERS. The surveys of applied rates were not conducted in the years 2004, 2006-2009, and 2011-2013. Blue dots represent results where USDA-ERS estimated the application rates, and red dots assume linear interpolation between reported rates applied for 2010 and 2014. For details on the calculations and references to data sources, see the linked spreadsheet.

Trends are similar for all three nutrients, because the main driver is the increasing trend in yields over the past 50 years. Variations in weather, however, show dramatic effects on both yield and fertilizer use efficiency from one year to another. For example, drought in 2012 likely reduced PFP well below trendline, while high yields in 2004 and 2009 may have done the opposite. The actual values for each of these three years should be treated with caution since they are based on estimated, not surveyed, application rates.