WASHINGTON, Aug. 3, 2016 - A new model that estimates the age of inorganic nitrogen in the soil could lead to big reductions in the amount of fertilizer applied across the Midwest.

Praveen Kumar, Lovell Professor of Civil and Environmental Engineering at the University of Illinois, Urbana-Champaign, said that understanding how long – and why – nitrogen remains in the soil can ultimately help farmers determine where and when they should apply it.

“We may be able to apply fertilizer specifically in areas that are deficient in nitrogen, in precisely the amount that the plants need to uptake, rather than just applying it uniformly,” said Kumar. “Potentially, we could see a significant reduction in fertilizer amounts."

Kumar and graduate student Dong Kook Woo, also at U-Illinois, published their results in the American Geophysical Union’s Water Resources Research. The National Science Foundation (NSF) supported the research through its Critical Zone Observatory (CZO) for Intensively Managed Landscapes, one of 10 NSF CZOs; others are in Arizona, Delaware/Pennsylvania, California, Colorado and South Carolina.

“Knowing how long nitrate resides in the soil will lead to more efficient agriculture that maximizes plant health without overdosing the environment,” said Richard Yuretich, program director in the NSF’s Division of Earth Sciences.

Woo said the most surprising conclusion was that “we found a lower average age of nitrogen in soybean fields,” even though nitrogen is not applied to soybeans. “We found that is mainly because soybeans uptake the old nitrogen, so the average age is reduced."

In addition, Kumar and Woo discovered that contrary to what they assumed – that, like water, they would find “younger” nitrogen on the top level of soil and “older” nitrogen lower in the soil column – they instead found the opposite.

One of the forms of nitrogen, ammonium, accumulated in the topsoil. Explained Woo:

“Ammonium has a positive charge, which adheres to the soil particles and prevents it from leaching to the deeper layers. Because of that, we observe relatively higher nitrogen age in the upper layers, compared with the age of the nitrate that dissolves in water, which doesn't have that barrier and can migrate down through the soil.”

The model is not quite ready for prime time, but “we are reasonably close,” Kumar told Agri-Pulse, predicting that “in terms of having a reasonably good technological product, (it’s) probably within reach within a year.”


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