BENEFITS OF LIQUID COMPOST AMENDMENTS

A vibrant microbial ecosystem plays a critical role in agricultural soil. In healthy soil, microbes:

• Promote soil aggregation, improving water infiltration and retention
• Increase root development and carbon sequestration
• Expand plant nutrient uptake, resulting in more nutritious crops
• Improve plant health, promoting resistance to pests and disease

Where this ecosystem is inadequately developed, microbial populations can be extracted from biologically rich compost and applied to the soil as a liquid compost extract. One pound of compost can produce 4-10 gallons of extract, making it far more efficient than solid application of compost. Microbial populations in the extract can be multiplied further by adding nutrients and aerating the mixture for a set time to create compost tea.

Compost extract produced by water jet separation of microbes from compost material can be stored for 2-3 weeks before use. Microbial foods can be added at time of application for consumption within the soil. The relative concentration of bacteria, fungi and protozoa in the extract closely reflects that of the original compost. This makes it ideal for in-soil applications, as it allows farmers to inoculate their soil with the full spectrum of beneficial microbes at once. 

COMMON COMPOST EXTRACT APPLICATIONS:

• Fertigation, including pivot irrigation systems
• Foliar sprays
• In-furrow applications when planting seed
• Seed coating prior to planting
• Root drenching prior to bareroot/plug planting
• Biochar inoculation

COMMON MICROBIAL FOODS ADDED PRIOR TO APPLICATION:

• Blackstrap molasses – feeds bacteria
• Fish hydrolysate – feeds fungi
• Kelp powder – feeds fungi
• Chitin powder – feeds microbes, adds calcium to soil 

Extract vs. Tea

Compost tea production employs a “brewing” process designed to expand the population of certain microbes by adding microbial foods and aerating the liquid for 12-48 hours. The tea must be applied immediately, or harmful anaerobic microbes will take over. The biological makeup is far less diverse than extract, as a few bacterial strains will tend to dominate the mixture, and fungi and protozoa do not increase significantly in the brewing process. Compost tea is an effective foliar application, as the large number of beneficial bacteria will out-compete pathogenic strains and prevent disease. 

The diagrams below illustrate the difference in microbial diversity between extract and tea. (DNA sequencing by Zack Jones, images courtesy of Aggregodata. Read Zack's full blog post here.)

The DNA profile of the bacterial population present in a vermicompost sample. Plant growth promoting strains are outlined in green.

The DNA profile of extract made from that compost shows similar bacterial makeup to the source compost.

The DNA profile of compost tea made from the same compost is dominated by a few bacterial strains.