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Iowa Soybean Research Center

in collaboration with the Iowa Soybean Association

Soil Amendment with Biofuel Industry Co-products (Biochar and Digestate) for Improving Soybean Disease Management and Enhancing Soil Health

By Leonor Leandro, Professor Plant Pathology, Entomology and Microbiology, ISU

Co-Project Investigators: 

  • Santanu Bakshi, Bioeconomy Institute
  • Lisa Schulte Moore, Bioeconomy Institute, Natural Resource Ecology and Management


Project Summary

In this project, we are proposing to determine if soil amended with coproducts from the biofuel industry, namely biochar and digestate, can suppress soybean diseases caused by soilborne pathogens. We will focus our research on the pathogens that cause soybean sudden death syndrome (SDS) and soybean root rot (SRR) due to their economic importance and their soilborne nature. 

Biochar produced from woody biomass (pine) and agricultural residue (corn stover) under autothermal (air-blown) pyrolysis condition, will be obtained from Dr. Bakshi’s program. Biochars for this study are selected to represent contrasting pH, total carbon and ash diversity. Solid digestate batches will be obtained from the C-Change Grass2Gas project, directed by Dr. Schulte Moore. 

We will conduct greenhouse studies where soybeans will be grown in soil amended with biochar and digestate at different rates, in the presence and absence of the pathogens. Unamended soil will be used as controls. Plants will be assessed for growth and disease severity 4-6 weeks after planting. The initial experiments will use pasteurized soil to allow for more control of the interaction of the coproducts with the pathogens. Experiments will then progress to using natural field soil to more closely resemble the interactions that occur on farmer fields. 

We will also leverage an existing field trial with digestate applications (Dr. Schulte-Moore’s program) to collect observational data on the impact of these soil amendments in naturally occurring soybean diseases. We will visit the fields during the cropping season to rate foliar and stem diseases and we will collect plant samples to assess root disease. Field data on the effect of biochar on soybean diseases will be collected from a field trial newly established in Fall 2023 under Dr. Leandro’s or Dr. Bakshi’s program.

Additional Information

Increasing interest in biofuel production from agricultural residue results in increased amounts of coproducts, such as biochar and digestate that can be used as soil amendments in farmers’ fields. Biochar is a carbon-rich coproduct of biofuel production by pyrolysis, the burning of wastes at high temperatures in anaerobic or low oxygen conditions. Digestate is produced by microbial digestion of organic materials under anaerobic conditions. Liquid and solid digestate coproducts are formed. Here we are focused on the solid digestate, a high-fiber, nutrient-rich product.

Benefits of soil amendments with biofuel coproducts include carbon sequestration, improved soil characteristics and reduced nutrient leaching from soil. In addition, the return of agriculturally-derived carbon and nutrients to soil in the form of biofuel coproducts contributes to farm circularity, which minimizes the need for chemical inputs, can help stabilize soil nutrients, and improve soil health. However, there is minimal information on how these amendments will affect important soybean diseases, such as SDS and SRR. In order to optimize the effectiveness of circular farming systems, it is important to understand how these systems affect crop diseases and their impact on crop productivity.

We expect to learn if soil amendments with biochar or digestate have the potential to create a suppressive environment for soybean soilborne pathogens. This would be an added benefit to the use of these coproducts in agricultural fields. 

The greenhouse experiments with pasteurized soil will allow us to test how the soil amendments affect disease development in more controlled conditions and to start gaining insights on how those effects vary with the rate and the physical/chemical characteristics of the amendments. The progression to greenhouse trials with natural field soil will determine if the effects on plant disease persists in soil with a complex microbiome and other interacting soil factors. 

Finally, assessments of disease development in field trials with digestate and biochar amendments will provide insights into the potential impact of these amendments on farmer fields. 

The pressing need for biofuels will generate large amounts of valuable coproducts that are likely to be amended into agricultural fields. It is critical to soybean farmers and the soybean industry to understand how these amendments will affect soybean health and productivity. This study will provide initial insights into the potential for biochar and digestate amendments to improve management of soybean diseases. 

The data generated in this project can be used to leverage funding from federal funding agencies, such as USDA-NIFA and the EPA, for larger scale, on-farm studies. In addition, this work will build on currently funded USB projects where PI Leandro is conducting small-scale greenhouse experiments to determine if biochar soil amendments can suppress seedling disease caused by Fusarium graminearum and Pythium sylvaticum and SDS. In this project, Dr. Bakshi’s research will provide a more in-depth understanding of how the differing characteristics of biochar types affect their suppressiveness to diseases. 

The work also complements research by Dr. Ajay Nair, ISU Horticulture Dept., testing the benefits of biochar on vegetable crop production. Future collaborations with Dr. Nair would be mutually beneficial. 


(2-year project funded fall 2023)