A comparison of turfgrass plots with no fertilizer applied (left) and a soy-based fertilizer (right). The plots with the soy-based fertilizer applied are noticeably greener.
A comparison of turfgrass plots with no fertilizer applied (left) and a soy-based fertilizer (right). The plots with the soy-based fertilizer applied are noticeably greener. Larger image

Iowa State University Researchers Develop Soy-based Fertilizer for Improved Sustainability

Members from David Grewell's research team extrude soy flour and PLA using CCUR's pilot-scale extruder. Matt Blom, a student in industrial technology, (right) sets the extruder's controls as James Burkholder, a student in materials engineering, feeds the soy-PLA mixture into the hopper.
Members from David Grewell's research team extrude soy flour and PLA using CCUR's pilot-scale extruder. Matt Blom, a student in industrial technology, (right) sets the extruder's controls as James Burkholder, a student in materials engineering, feeds the soy-PLA mixture into the hopper. Larger image

AMES, Iowa — Growing a lush and environmentally friendly lawn might be easier thanks in part to some soybeans and some innovative research from Iowa State University.

David Grewell, professor of agricultural and biosystems engineering, and James Schrader, associate scientist in horticulture, lead a team investigating the use of soy-based materials as a source of nitrogen in a fully biorenewable, slow-release fertilizer. Their goal was to develop a biobased turfgrass fertilizer that could perform as well as traditional synthetic fertilizers, while improving environmental sustainability.

Grewell said they wanted to design a fertilizer for residential and commercial use that also would minimize the effects of nitrogen run-off in waterways.

“The problem with most synthetic fertilizers is that they are water soluble and easily breakdown after a heavy rainfall, washing nitrogen downstream,” he said. “Excess nitrogen in the waterways can cause negative environmental impacts including hypoxia and algae blooms.”

A close-up view of the soy-PLA fertilizer.
A close-up view of the soy-PLA fertilizer. Larger image

The fertilizers that Grewell and Schrader have developed are considered to be “slow released.” The nitrogen that is found in the soy breaks down slowly, providing the lawn with nutrients for a longer period of time compared to typical water-soluble products.

The first stages of this research actually began much earlier while Grewell and Schrader were developing biobased horticulture pots made with a blend of soy, PLA (a polymer made from cornstarch) and other fillers. They found that during crop production in the greenhouse, nitrogen and other nutrients were slowly released, and nourished the plants growing in the containers. Grewell and Schrader took those findings and applied them to develop a bioplolymer-based turfgrass fertilizer.

Grewell’s team, led by Jake Behrens, a graduate student in agricultural and biosystems engineering, began developing various formulations using a mixture of soy flour or soy protein isolate with a PLA matrix and other filler materials. They used the equipment at the Iowa State University’s Center for Crops Utilization Research to compound the formulations and extrude and pelletize them into one-eighth-inch pieces. The pellets, also known as prills in the horticulture industry, were designed so they could be applied to turfgrass using standard fertilizer broadcast applicators or by hand.

“We developed 14 different soy-based formulations to be evaluated in turfgrass and greenhouse trials along with a synthetic fertilizer and a commercially available biobased fertilizer,” said Grewell.

Matt Blom, a student in industrial technology and a member of David Grewell's research team, feeds the extruded soy-PLA mixture into the pellet mill.
Matt Blom, a student in industrial technology and a member of David Grewell's research team, feeds the extruded soy-PLA mixture into the pellet mill. Larger image

Testing was completed in two phases led by Schrader and Kenneth McCabe, a research associate in horticulture. Phase one was conducted at Iowa State University’s Turf Grass Research Center, and was used to narrow down the number of soy-based formulations.

The fertilizers tested included the 14 soy-based formulations, one synthetic fertilizer and one commercial biobased fertilizer. They were applied to over 80 turfgrass plots, each measuring 5 feet by 5 feet. Three control replicates received no fertilizer. The team collected visual data based on the greenness of the turfgrass.

“We were able to narrow down the formulations to eight that were performing similarly to synthetic fertilizer and better than a biobased fertilizer that is already on the market,” said Schrader.

The second phase of testing was completed in the Department of Horticulture greenhouses. Over 200 marigolds were planted in 4.5-inch containers, and fertilizers were applied to them.

In the Department of Horticulture's greenhouse, over 200 marigolds were planted in 4.5-inch containers, and fertilizers were applied to them.
In the Department of Horticulture's greenhouse, over 200 marigolds were planted in 4.5-inch containers, and fertilizers were applied to them. Larger image

“Our goal with the greenhouse trials was to collect quantifiable numerical data including plant yield, nutrient analysis and water sampling,” said Schrader. “At this stage in technology development, our soy-based fertilizers are performing very well on turfgrass, and they show strong potential for use with garden crops and containerized horticulture crops. Continuing research should provide formulations optimized for these applications.”

Grewell is very optimistic with their initial findings and is looking forward to finding a market for the soy-based fertilizers.

“We have already received positive feedback from interested companies. Although we have more analytical work to complete, we are certain these fertilizers will be a viable product for the lawn care and horticulture industries and will be another value-added product for soybean producers.”

The Minnesota Corn Growers Association, the United Soybean Board and the U.S. Department of Agriculture provided funding for this project.