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SDSU leads multistate study on the power of swine manure in growing better crops

Farmers feed their animals the crops they grow. The animals produce manure that is applied on crop fields to promote plant growth. Farmers harvest those crops and feed them back to their animals, and the cycle repeats over and over again.

Producers have been applying manure on their crop fields as fertilizer for generations. It was a practice developed to utilize a resource many farmers had ample access to — animal manure — and make it a value-added product.  
Manure contains three important nutrients that can help promote plant growth: nitrogen, phosphorous and potassium. It’s a sustainable product that farmers continue to use and have seen positive returns in the form of increased crop yields.

However, while anecdotal evidence consistently supports the claim of increased yields with the application of swine manure, there is limited data from controlled research trials investigating this topic, especially in a comprehensive study across different agroclimatic regions in the contiguous U.S. at once.

That is, until now.

In 2022, a group of faculty and staff from South Dakota State University began developing a research project to see what effect swine manure application has on crop yields and soil quality. The objectives were to determine the effect of swine manure on soil health properties (biological, physical and chemical), determine the effects of swine manure on soil nutrient levels and compare corn yield influenced by swine manure and commercial fertilizer.

To complete a project of this magnitude, there needed to be input from multiple academic areas, including animal science, agronomy and agricultural engineering. By utilizing knowledge in these areas in a collaborative effort, the researchers have been able to take this project to the next level and develop well-rounded experiments that hope to answer an important question for producers across the nation: Does swine manure increase crop yields more when compared to commercial fertilizers, and if yes, does it achieve that by improving soil health and quality?

The primary team on the project includes:

• Bob Thaler, Farm Credit Services of America Endowed Chair in Swine Production, Distinguished Professor and SDSU Extension swine specialist
• Sushant Mehan, assistant professor and SDSU Extension water resource engineer specialist
• Anthony Bly, SDSU Extension soils field specialist
• Sara Bauder, SDSU Extension forage field specialist

John McMaine was also an instrumental part of starting the project at SDSU. Now an associate extension professor in biosystems and agricultural engineering at the University of Kentucky, McMaine is still a part of the project and serves as a resource for the project and those involved.

The vision

“Nobody’s more sustainable than a farmer,” said Thaler, co-primary investigator on the project. “All they need is science to demonstrate why it has been working for generations, and to show the strong symbiotic relationship between livestock and crop production.”

Initially, researchers thought the project would be localized to South Dakota, with samples taken from a few local producers’ fields. However, while discussing the project with industry leaders, Thaler was directed to the National Pork Board. They were very interested in the project as the findings could help identify the real added value of swine manure, and its benefit to the soil.

To take the project to another level, the National Pork Board awarded SDSU a $3.5 million grant to cover testing and sampling in up to 17 states. The goal of doing experiments in multiple pork-producing states across the Midwest was to account for weather and other conditions that could impact the results. They eventually were able to get commitments from 10 states that had the proper resources to conduct the experiments: Illinois, Iowa, Michigan, Minnesota, Missouri, Nebraska, Ohio, Pennsylvania, South Dakota and Wisconsin.

The method

Analyzing the change in crop yield was top of mind, but it’s a relatively short-term effect. Soil health, on the other hand, impacts crop growth and quality in the long-term, which is why the project needed to focus on both. To ensure accurate and consistent testing, research fields at land-grant universities in each of the participating states are utilized, and all follow a strict protocol that was developed by Bly.

“We wanted to devise a methodology that we felt most could do. Really it was about the sampling and detection of any differences in soil health properties that were important,” Bly said. “Soil health encompasses chemical, physical and biological properties so we really have to measure all three of those.”

At each location, there are three test plots that have specific fertilizer treatments applied. One plot is applied with commercial fertilizer in the spring ahead of or after planting according to local land-grant university soil fertility recommendations. The second plot is applied with swine manure according to state regulations for concentrated animal feeding operations (CAFOs). The third plot is treated the same as the second except it also receives a starter fertilizer application according to local standard practices.

The sample locations are determined by each on-site sampling team and represent similar soil types. For consistency, the plots are planted with corn every year. The project will continue and the experiments will be replicated for five years. Soil samples were taken prior to manure application and will be taken every year after harvest. The project has almost reached the halfway mark, as the experiments will be complete by 2029.

Like any project, there were bound to be challenges, especially for a project of this size, taking place in many locations. One challenge has been that not all sites have the same equipment and resources, and some even have differing state recommendations and protocols.

“Other states have different types of manure management systems,” Bly said. “They apply their manure at different timings. Some states have different soil testing recommendations, so that has been a challenge to bring all those together.”

This led to a unique challenge for Bly as he worked to create the protocol that must be followed at every location. After many rounds of revisions, they eventually landed on a protocol they believed every state could follow.

“We can’t go around and do all of the work ourselves, so we have to trust that the other institutions are following the protocol and doing the job as best they can,” Bly said.

Since there are so many people involved in the project, it was important to establish a communication plan. Along with assisting on the agronomy side of the project, Bauder has acted as the communication liaison to assist other states with any issues they run into or direct questions they have to specific members of the research team.

After the samples are collected at the research plots, they are sent out for testing. To ensure consistency, soil samples from every plot are sent to Ward Laboratories Inc. in Kearney, Nebraska. There, a comprehensive analysis of the soil is completed, focusing on the chemical and biological properties including nutrient analysis and soil health indicators.

Beyond analyzing the characteristics of the soil itself, the team has placed high importance on analyzing how the soil interacts with water. To do so, a portion of each sample is sent to SDSU’s Soil Health and Water Quality – HydroSolve Lab in Brookings. Graduate and undergraduate researchers focus on testing the soil’s physical properties to estimate parameters that impact water movement in the soil. These tests allow the team to make even more discoveries about the impact of these soil treatments.

“It is super important to maintain soil health, so you need to keep the right nutrients in their right place so that it’s not impacting the water quality downstream,” Mehan said. “The overall goal is for the plants to absorb the right type and amount of nutrients and water, especially at the time when they need it the most, so that farmers have better crop yields.”

The future

So far, the team has already tested 400-500 samples that were collected during the 2023 season in all 10 states. With this data, the team has been able to utilize the results for various conference presentations. SDSU serves as the repository for all data and will be the institution that publishes the findings on the overall study. However, each state is allowed to use its own data however it wants to. For example, the University of Missouri has already published a web article after analyzing the data its team collected in year one.

SDSU Extension has also published educational materials related to the impacts of swine manure on soil properties and best practices for swine manure application. While the project is ongoing, these fact sheets are important educational materials that can be utilized by producers. The team hopes to soon have a dedicated webpage where materials can be housed on the SDSU Extension website.

Once the project is complete and all the data has been analyzed, they plan to host a symposium where other researchers, producers and policymakers can hear and better understand the results.

“We want to have such solid science that nobody’s going to be able to disagree with it,” Thaler said. “You want good science for people to be able to use it for production, for people to be able to make sound policy and to understand the true value and impact of manure.”

Beyond the science, a big takeaway from this project will be the importance of collaboration. Not only did it require collaboration with other institutions, but it also required collaboration and understanding from a variety of disciplines.

The agronomists are interested in learning about the effect of various fertilizers on plant growth. The engineers are interested in learning about the effect on water holding capacity. And the animal scientists are interested in learning about the overall impact and value of swine manure. Through collaboration, they can dive deeper into all these things with just one project.

Thaler, who has served SDSU for more than 38 years, recently announced that he will retire next fall. He will continue to consult and advise on the project, and another animal scientist is expected to join the team to support the work moving forward.

“SDSU is really fortunate to have the leadership of Dr. Thaler,” Mehan said. “Without him, this project would not be possible. It’s bringing together aspects of the environment, livestock and engineering together which is very rare for these types of projects.”