Farm and Field

Study proposes circular phosphorus economy for Midwest

Posted: Jan. 5, 2020 1:50 am

The U.S. Midwest produces at least a third of the world's corn and soybean supply each year, and feeding the world requires a lot of fertilizer, mostly in the form of nitrogen and phosphorus.

While nitrogen literally can be pulled out of the air, phosphorus has to be mined from finite phosphate rock reserves, mostly in Morocco, and treated to be made available to plants.

Additionally, some phosphorus applied to agricultural fields is lost through erosion, carried away with soil particles into waterways, where it can degrade water quality and contribute to "dead zones."

A new Journal of Environmental Quality report from the University of Illinois describes the feasibility of recycling phosphorus on a regional scale in the Midwest, simultaneously solving the problem of an uncertain global supply and minimizing loss from agricultural fields.

The concept of recycling phosphorus in the Midwest isn't entirely new, but the U of I report represents the first time biogeochemists, economists and engineers have come together to consider the true feasibility of a holistic phosphorus recycling system in the Midwest.

The researchers considered all the waste sources of phosphorus in the U.S. and honed in on several overlooked in previous thought experiments, including corn ethanol and soybean processing plants.

One of the biggest roadblocks to establishing a circular phosphorus economy in the Midwest is the current cost of fertilizer. Pound for pound, phosphorus fertilizer is more expensive than nitrogen, but at the moment, it's much cheaper than the current cost of recycled phosphorus.

The researchers say phosphorus trading schemes, similar to carbon credits, could be part of the solution.

"In the article, we talk about the possibility of point sources paying farmers to take recovered phosphorus off their hands," said Andrew Margenot, assistant professor in the Department of Crop Sciences and lead author of the report. "Our job as researchers is to show farmers that these alternative phosphorus sources won't compromise crop yields and could save them money on phosphorus inputs."

Leucine in pig diets

Recent changes in corn and sorghum processing for ethanol have led to changes in the composition of grain byproducts, including distiller's dried grains with solubles, a major component of swine feed.

As a result, today's DDGS is typically higher in the amino acid leucine than is necessary to meet nutritional requirements of pigs, and according to U of I research, excess leucine in pig diets can decrease protein synthesis and reduce feed intake.

U of I professor Hans Stein and a team fed diets with varying levels of leucine to growing pigs over 15 days to see why a high amount of one amino acid leads to the issues even though proteins are made up of amino acids.

The study shows pigs fed excess leucine eat less because their brains are not making enough serotonin, the hormone that controls appetite.

The research team also determined that leucine decreased protein synthesis by breaking down related amino acids isoleucine and vanline.

"If you have excess leucine in the diet, the body makes more of the enzyme needed to break down leucine. But that enzyme also breaks down valine and isoleucine. Even if you had enough valine and isoleucine in the diet, you basically create a deficiency of those amino acids," Stein said.