Compost handling in agriculture systems: Disease-suppressing and growth-promoting composts

Part two of a six-part series on compost utilization and management on farms.

hands holding black compost
Compost made from dairy manure and straw. | Photo credit: Charles Gould

Compost contains a full spectrum of essential plant nutrients, but the real value of compost lies in its ability to improve soil health and provide plant protection. Part one of this series by Michigan State University Extension educators focused on how compost is made and how farmers are often motivated to purchase compost for its nutrient content.

A 2021 long-term study conducted by researchers at the University of California-Davis looked at the impact of different management practices on soils and crops, including utilization of compost. The researchers found two things:

  1. Only when you add compost do you get carbon storage in soils. Practices utilizing cover crops alone and fertilizer alone actually showed reduced carbon storage in soils.
  2. When compost and cover crop soils are infected with Salmonella and Listeria, the good microorganisms found in compost were able to outcompete the ones that make humans sick. Soils without compost had 4 to 5 times as many disease-causing pathogens at day ten in comparison to the soils with the compost.

Another study found that young composts ranging between 35–106 days which had a relatively short curing time and low nitrogen content resulted in the most plant disease suppression. Compost is not a fungicide, however, these findings do provide a compelling argument for making compost a central component of regenerative agriculture and standard operation procedures.

Compost components and management vary widely, which means not all composts provide the same level of soil health improvements and plant protection. The feedstocks used to make the compost and how the compost was managed all impact the microbial diversity of the compost and the nutrients that are available for crop uptake. That is why understanding the composting process is so important, as covered in part 1 of this series.

Understanding how the composting process works helps farmers ask the compost manufacturer detailed questions to help select the best compost for their specific cropping system. It’s also important to understand the soil food web and soil health because compost and the soil must work together to maximize the value of the compost in a cropping system.

Compost builds soil by feeding microbes which produce glues that hold soil particles together, acids that release mineral components into the soil, and compounds that stimulate plant growth. One of the best resources available to help understand the relationship between compost and the soil is the Soil Biology Primer.

While compost contains nutrients essential to plant growth, the real value of compost lies in its ability to improve soil health and provide plant protection. Not all composts are created equal, so it is important for farmers to know how the compost was managed to ensure it performs correctly in their individual cropping systems.

Part three in this series addresses compost storage considerations.

Other articles in this series:

Part 1: Compost handling in agriculture systems: How is compost made?

Part 3: Compost handling in agriculture systems: Appropriate storage options

Part 4: Compost handling in agriculture systems: compost transfer and equipment calibration

Part 5: Compost handling in agriculture systems: Land application

Part 6: Compost handling in agriculture systems: Right-to-Farm coverage of on-farm compost production

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