Fertilizer runoff isn’t the only thing that is polluting fresh water. That’s just the quickly and easily detected source of nitrate contamination from residential and agricultural synthetic fertilizer use . Recently it became known that this is only part of the nitrate issue. The big picture? It ain’t pretty. That bible verse about the sins of the fathers affecting the third and fourth generation comes to mind.

In 1982 two different sets of researchers – at the Université Pierre et Marie Currie in France and the University of Calgary had the foresight to start a study on what really happens to 100% of synthetic nitrogen applied to cropland. Their project has been running for 30 years, but it didn’t begin until about 40 years after chemically created nitrogen started being used to grow food, fiber, and flowers. Their paper, “Long-term fate of nitrate fertilizer in agricultural soils,” which was published late in October of 2013 in the Proceedings of the National Academy of Sciences of the United States of America.

A Lot of Surprised Experts

What they’ve found is that 10% of that single application of manufactured nitrogen remains unused and has traveled in the form of nitrate to a depth of about 6 feet (2 meters) since the measuring began in 1983. Now 30 years later, they can see that it really increases to 15% of the total applied as organic matter releases it’s residual into the soil. Six feet doesn’t sound like much, but water table comes into play. They now conclude in the two test plots it will take at least another 50 years to reach the groundwater. Bernhard Mayer in the University of Calgary’s Department of Geoscience realizes that this nitrate leaking will take a lot longer to finish it’s travels in a drier climate. Precipitation is the cause of the residual nitrate moving further and further below the surface.

Synthetic nitrogen has been applied to farmland all over the world since after World War II on an annual basis. And each year’s fertilization leaves it’s own 10% as a residual entity that over time becomes 15% of water-borne nitrate. If no further applications of synthetic nitrogen were applied anywhere on the globe again, it could take 4-5 generations before the full impact of residual damages to appear.

How Bad Can It Be?

In 2010 over 21 million tons of synthetic fertilizer spread on cropland alone. That computes to at least 300,000 tons of nitrate that will leach into groundwater in approximately the year 2090.  Notice that no figures for all the millions of tons of lawn fertilizer, Miracle Gro and other non-organic nitrogen applied every year to yards and gardens has been added. The realistic amount of future deep soil nitrate leaching is much greater. Agriculture does not dwarf residential fertilizer use.

The certified organic farming industry in the USA is contributing to the problem. They can use animal manure from non-organic feed lots to fertilize their crops, which contains synthetic nitrogen from the grain the animals were consuming. When it comes to water quality, if we’re going to be organic, then organic fertilizer needs to be totally organic. This means using only organically raised animal manure for fertilizers.

Want More Info?

  • Residual nitrate info and numbers — Science Direct.
  • A look at how partially organic fertilizer is adding to the issue here.
  • Synthetic fertilizers and nitrogen primer — Organic Valley.

Tammy Clayton

Content crafter and Senior Editor at Garden Culture Magazine
Tammy has been immersed in the world of plants and growing since her first job as an assistant weeder at the tender age of 8. Heavily influenced by a former life as a landscape designer and nursery owner, she swears good looking plants follow her home. (Some feel she's got a perennial obsession, others say the problem is tomato plants.)

If you don't find her at the desk - check the gardens. When not writing and weeding, she enjoys a good book, painting junk furniture, and blending the harvest of heirloom tomatoes and chiles into salsas.