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March 17, 2023
By John LovettUniversity of Arkansas System Division of AgricultureArkansas Agricultural Experiment Station
Download a photo of struvite
FAYETTEVILLE, Ark. — Struvite, the same substance that makes up kidney stones and
irritates sewage plant operators, could be an effective alternative to using a limited
supply of mined phosphate for crop fertilizer.
According to the U.S. Department of Agriculture,19 percent of the 22.02 billion tons of fertilizer used in the United States in 2015,
the most recent data available, was phosphate based.
Struvite is the common name for magnesium ammonium phosphate, a crystal-like substance
that often coats the inside of sewage pipes and causes blockages. Struvite can, however,
be created by chemical engineers from solid wastes or wastewater as a fertilizer with
slow-release potential because most of it is not water soluble.
The substance is taken up by plants as magnesium, nitrogen and phosphorus as the roots
acidify the soil around it, so excess nutrient runoff is limited.
There are two ways to precipitate struvite from a solution. The “electrochemical method”
involves using an electrical current through a magnesium electrode, putting magnesium
atoms into the solution that react with ammonium and phosphate in the solution. The
“chemical method” usually includes adding magnesium salts to a solution, which results
in a chemical reaction with the ammonium and phosphate. Using either method, struvite
Two-year field studies by the Arkansas Agricultural Experiment Station showed that
struvite produced by electrochemical means performs as well as the common sources
of phosphate fertilizer, and the chemically created struvite, on yields in corn, rice
and soybeans in east Arkansas soils.
“The results of our study demonstrate that electrochemically precipitated struvite
has potential as an alternative fertilizer source for upland and lowland row crops
in eastern Arkansas, where there is a documented nutrient deficiency,” said Kristofor
Brye, University Professor of applied soil physics and pedology with the experiment
station, the research arm of the University of Arkansas System Division of Agriculture.
The field study’s results are the culmination of research done with chemical engineers
and agricultural economists supported by the National Science Foundation.
Recovering nutrients from wastewaters could have a positive impact on the environment
and create an additional revenue stream for wastewater treatment facilities, Brye
A previous experiment station study indicated flood-irrigated rice grown with electrochemically
precipitated struvite produced less methane, a greenhouse gas, than other phosphate
fertilizers, including a chemically precipitated struvite.
A confirmation study is ongoing.
“A fertilizer-phosphorus source that is environmentally friendly, as the product of
recovered nutrients from wastewater, would be a substantial benefit for Arkansas row-crop
producers, provided electrochemically precipitated struvite is economically cost-effective,”
Research by the University of Arkansas chemical engineering department has been supported by the National Science Foundation to develop innovative methods of creating electrochemically precipitated struvite.
Testing the options
Prior to the two-year field studies on each crop, Brye said no field research had
been conducted using electrochemically precipitated struvite in the highly agriculturally
productive soils of the Mid-South and southern United States. Lauren Greenlee, former
associate professor in chemical engineering for the University of Arkansas, had the
idea for an electrochemical approach to making struvite from wastewaters, Brye said.
She decided to prove the concept of making the material and Brye followed up with
agronomic testing. Greenlee is now at Penn State University. The studies were conducted
from 2018 to 2020.
Previous research leading up the field trials for each crop included lab and greenhouse
studies, including a study by Niyi Omidire, now a postdoctoral fellow in crop, soil and environmental sciences
at the University of Arkansas, comparing a chemically precipitated struvite to triple
super phosphate on both irrigated and non-irrigated land in a wheat-soybean double
crop system in east Arkansas. The results upheld the use of chemically precipitated
struvite as a potential alternative fertilizer-phosphorus and magnesium source on
a silt-loam soil for crop production.
Brye also served as adviser to crop, soil and environmental sciences graduate student
Ryder Anderson’s struvite in moist-soil incubation study. Ryder’s study showed phosphorus concentrations differed among soil textures and
previous management histories, indicating struvite’s “slow-release” characteristic
is more dependent on soil type.
The goal of the two-year confirmation field study was to evaluate the potential effectiveness
of struvite for use in corn, rice and soybeans. Electrochemically precipitated struvite
from real wastewater is now being used in a field study to test greenhouse gas emission
differences in flood-irrigated rice. Researchers are also looking at rain runoff levels
of each phosphorus source.
How the test was done
A uniform application rate of phosphorus was used for each fertilizer source in the field study. The chemically precipitated
struvite was Crystal Green® by Ostara.
Generally, struvite contains between 11 and 26 percent total phosphorus depending
on the initial source and production method. Because of the small amount of electrochemically
precipitated struvite that could be created in the lab, the field test areas in the
two-year study were equally small, 5-by-5 feet.
Brye said there were no major differences in yield performance between the electrochemically
precipitated struvite and all the other mined phosphate sources used in the various
studies for rice, corn, and soybeans.
While the researcher’s struvite appeared to be more effective on corn and soybeans
than rice, Brye said there are contributing factors that would lead him to believe
there is more to the story.
When rice is flood-irrigated, the plants can tap into a greater pool of phosphorus
released by the water, but the fertilizer is less efficiently used than in corn. Also,
corn has a different root structure that allows it to explore the ground better and
the slow-release characteristic of struvite better matches the physiological growth
of corn and soybeans, he said. Corn also has a higher phosphorus demand than the other
Economics of recycling
“By all accounts we’ve concluded this electrochemically precipitated struvite can
be more than a viable alternative fertilizer phosphorus source,” Brye said. “While
there is no large-scale production of electrochemically precipitated struvite, there
is large-scale production of chemically precipitated struvite.”
Studies show that recovery of struvite from wastewater treatment plants is possible
and would be a relief in the wastewater treatment industry, Brye said.
“Struvite works as a fertilizer, but it is only a rational choice if the benefits
of using it outweigh the costs,” said Jennie Popp, professor of agricultural economics
and agribusiness and associate dean of the University of Arkansas Honors College.
Popp noted more research is needed to determine the economic feasibility of electrochemically
precipitated struvite in row-crop agriculture. However, their economic analysis of
the experiment station’s field study data shows electrochemically precipitated struvite
showed “real promise” on corn when they price similar products, like the chemically
precipitated struvite Crystal Green, to estimate a price. The results were mixed on
the other crops, Popp said.
In addition to Brye, Greenlee, Omidire, Anderson and Popp, co-authors of the related
struvite studies included Leah English, research program associate in agricultural
economics and agribusiness; Laszlo Kekedy-Nagy, now a postdoctoral fellow at Concordia
University in Montreal, Canada; Edward E. Gbur, retired director of the experiment
station’s Agricultural Statistics Laboratory; Leandro Mozzoni, former soybean breeding
and genetics associate professor for the experiment station; and Trenton Roberts,
associate professor and Endowed Chair in Soil Fertility Research for the experiment
Use of product and brand names in this release does not imply endorsement by the University
of Arkansas System Division of Agriculture.
To learn more about Division of Agriculture research, visit the Arkansas Agricultural
Experiment Station website: https://aaes.uada.edu. Follow on Twitter at @ArkAgResearch. To learn more about the Division of Agriculture,
visit https://uada.edu/. Follow us on Twitter at @AgInArk. To learn about extension programs in Arkansas,
contact your local Cooperative Extension Service agent or visit www.uaex.uada.edu.
The University of Arkansas System Division of Agriculture’s mission is to strengthen
agriculture, communities, and families by connecting trusted research to the adoption
of best practices. Through the Agricultural Experiment Station and the Cooperative
Extension Service, the Division of Agriculture conducts research and extension work
within the nation’s historic land grant education system.
The Division of Agriculture is one of 20 entities within the University of Arkansas
System. It has offices in all 75 counties in Arkansas and faculty on five system campuses.
The University of Arkansas System Division of Agriculture offers all its Extension
and Research programs and services without regard to race, color, sex, gender identity,
sexual orientation, national origin, religion, age, disability, marital or veteran
status, genetic information, or any other legally protected status, and is an Affirmative
Action/Equal Opportunity Employer.
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Media Contact: John LovettU of A System Division of AgricultureArkansas Agricultural Experiment Station(479) email@example.com