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Research Highlights

Research Highlights
Assessing the Benefits of Manure Applications and Cover Crops on Soybean Yield

Photo: United Soybean Board

By Barb Baylor Anderson

Global meat consumption has increased 58 percent over the past 20 years, according to USDA. And egg production in the United States alone rose by 17 percent between 2008 and 2017. 

With those increases in demand come more manure production, which can be managed as either a waste product or as a valuable resource to enhance crop production and build soil health. 

Michelle Soupir, Iowa State University professor in ag and biosystems engineering, is hoping for the latter. As principal investigator of research funded by the Iowa Soybean Association, she is leading integrated study of manure management, tillage and cover crops in corn-soybean systems for long-term yield, soil health and environmental resilience results.

“If agriculture is to contribute to fewer impaired waters, help protect public health and promote more sustainable systems, farmers need to better understand manure and cover crop management to optimize crop yield and environmental benefits,” says Soupir. “Producers will obtain valuable information to help guide management options to minimize contaminants from drainage water.”

Soupir says a 20-year study on poultry manure’s impact on crop yield, soil and water quality and farm economics in a corn-soybean rotation and continuous corn has been completed. Results showed improved soybean yields when manure was applied during the previous corn year compared to urea ammonium nitrate (UAN) application. Poultry manure-amended fields had increased particulate matter levels, indicating potential for greater infiltration and water-holding capacity. Manure-amended plots had lower or similar nitrate levels in drainage compared to UAN-treated plots.

“The goal now is to assess the benefits of manure application and cover crops on soybean yields, water quality and soil health,” she explains. “A new field site has been designed for comparison of manure and land management practices, with immediate and ongoing goals of evaluating crop yield response to manure application timing and cover crops and water quality impacts with conservation tillage practices. This will lead to multi-year studies with environmental datasets.” 

Table 1. The Iowa State research covers a variety of common nitrogen sources and management practices to evaluate the impact on soybean yield, soil health and water quality.

Soupir has designed a new field site and is collecting baseline soil data. Shallow soil samples will be collected from all plots in the fall, while deep core soil samples were already collected at the start of the project in fall 2020. They will be analyzed for crop-available nitrate nitrogen. Additional measurements include other nutrients, soil pH and organic matter. 

“This project has a range of scenarios that will be applicable to much of the Midwestern U.S. It was designed to provide relevant soil health, yield and water quality information for a range of practical scenarios (see the table below),” she says. “We plan to use poultry manure because of our past work showing benefits of fall poultry manure application.”

Soupir says while the study is a long-term project, she hopes to have useful information for farmers regarding water quality impacts and yield within the first three years. 

“We are also exploring options for additional funding to evaluate novel soil health indicators that will provide early information to farmers, such as best management practices like cover crops, to encourage a long-term commitment to sustainable systems,” she adds.  

To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.