If you think applying extra nitrogen (N) to fields will bank it for future crops, or build organic matter, Richard Mulvaney begs to differ.

After several years poring over data from decades-long farm plots across the U.S. and Europe, the University of Illinois fertility specialist and fellow researchers Saeed Khan and Tim Ellsworth believe excessive N applications are “browning the green revolution” by burning up soil carbon and reducing soil N levels.

In case after case, they found that for farm ground fertilized with N-P-K, or unfertilized as a check, there was a loss, over time, in the amount of soil carbon and N. This contradicts what many growers have been taught — that N fertilizer is an important building block for increasing organic matter.

Soil is the Source

A 5-year moving average of corn yields in Illinois shows yields have improved from about 60 bushels in 1960 to nearly 180 bushels as of 2010. While many feel this is a great example of how American agriculture has succeeded, Mulvaney says there’s more to it than that.

Mulvaney has data that show N application rates began to level off around 1980, but yields have continued to march northward, so it’s hard to say how N fertilizer is the driving force for higher yields. If it’s not the fertilizer helping yields, what is it? Where is the N coming from? 

“There is another source, and it’s a four-letter word called ‘soil,’” Mulvaney says.

To prove his point, Mulvaney shared yield data…