When the amount of fertilizer exceeds crop needs, emissions of nitrous oxide—a greenhouse gas produced in the soil following nitrogen addition—rises faster than expected.
Nitrous oxide is the third most important greenhouse gas, behind only carbon dioxide and methane, and destroys stratospheric ozone. Agriculture accounts for around 80 percent of human-caused nitrous oxide emissions worldwide, which have increased substantially in recent years, primarily due to increased nitrogen fertilizer use.
New research suggests farmers could cut emissions if they matched the amount of fertilizer applied to how much the plants actually needed—not too little and not too much.
“Our specific motivation is to learn where to best target agricultural efforts to slow global warming,” says Phil Robertson, director of the Kellogg Biological Station Long-term Ecological Research Program at Michigan State University and senior author of the paper published in the Proceedings of the National Academy of Sciences.
“Agriculture accounts for 8 to 14 percent of all greenhouse gas production globally. We’re showing how farmers can help to reduce this number by applying nitrogen fertilizer more precisely.”
The production of nitrous oxide can be greatly reduced if the amount of fertilizer crops need is exactly the amount that is applied to farmers’ fields. Simply put, when plant nitrogen needs are matched with the nitrogen that’s supplied, fertilizer has substantially less effect on greenhouse gas emission, Robertson says.
The research also informs fertilizer practices in underfertilized areas such as sub-Saharan Africa, says researcher Iurii Shcherbak, lead author of the paper.
“Because nitrous oxide emissions won’t be accelerated by fertilizers until crop nitrogen needs are met, more nitrogen fertilizer can be added to underfertilized crops with little impact on emissions,” she says.
Adding less nitrogen to overfertilized crops elsewhere, however, would deliver major reductions to greenhouse gas emissions in those regions.
The study provides support for expanding the use of carbon credits to pay farmers for better fertilizer management. Carbon credits for fertilizer management are now available to US corn farmers. This paper provides a framework for using this system around the world.
The National Science Foundation, the Department of Energy’s Great Lakes Bioenergy Research Center, and the Electric Power Research Institute funded the study. MSU AgBioresearch also contributed to Robertson’s work.
<Global metaanalysis of the nonlinear response of soil nitrous oxide (N2O) emissions to fertilizer nitrogen >, Published on Journal <PNAS> in June 2014