Although nitrogen fertilisers are critical for growing crops to feed the world, when used in excess they can pollute our water long term, researchers say. 

A study entitled ‘Managing nitrogen legacies to accelerate water quality improvement’ provides six steps to address nitrogen pollution and improve water quality. The work carried out by the University of Waterloo in Canada provides a roadmap for scientists, policymakers and the public to overcome the challenges associated.

“We have to think about the [nitrogen] legacy [ie, nitrogen that has accumulated over decades] we leave for the future in a strategic way from both the scientific and socio-economic angles,” said Nandita Basu, a professor of Earth and Environmental Sciences and Civil and Environmental Engineering at the University of Waterloo and the study’s lead author. “This is a call to action for us to accept that these legacies exist and figure out how to use them to our advantage”.

The study recommends the following six steps:

1. Focus research to quantify the length of time the nitrogen stays in our ecosystems to adjust our expectations for conservation timelines
2. Find ways to use the legacy nitrogen as a resource for growing crops instead of adding new nitrogen fertilisers to our ecosystems
3. Target conservation strategies to get the maximum water quality improvement instead of a widespread blanket approach
4. Combine conservation methods that reduce the amount of nitrogen that has already left the farm fields with methods that harvest nitrogen from past legacies accumulated in the soil
5. Monitor water quality at both large and small scales so that short-term results can be seen at scales like a farm field and long-term results downstream at river basins can also be tracked
6. When assessing the economic impacts of conservation strategies, incorporate cost-benefit analyses

The study also notes that nitrogen legacies are different around the world depending on the climate and historical land use, as well as land management patterns.

“It’s time we stop treating nitrogen legacies as the elephant in the room and design watershed management strategies that can address these past legacies,” said Basu. “We need to ask ourselves how we can do better for the future”.