B. 4. How to Tell Good Compost

Compost Standards

Use the chart below(in development) to determine whether the compost you have can successfully transfer the minimum organism biomass for each of the different groups in the soil or compost food web to the soil.

Your soil needs the right biology in order to grow the plants you want, without the use of toxic chemicals. If your soil, potting mix, hydroponics medium, or compost lacks the minimum set of organisms, steps need to be taken to re-establish the right set of organisms.

First, you need to establish what biology is present in your soil, and what biology is in the compost or compost tea you will add to the soil. The fastest way to do this is to send in a sample of both the soil and compost or compost tea to determine the biology present.

Second, you need to determine who you adding the compost or tea to the soil. Directly on the surface may mean a time period while the organisms move into the soil. Typically, bacteria and fungi need to be carried deeper into the soil by protozoa, nematodes, earthworms, and/or microarthropods. If you don’t have these larger predator organisms, then you have to physically move the organisms into the soil, by tillage (which will harm the predators an fungi), or by coring and re-filling the core holes with compost, or a mix of compost and sand.

The alternative to using microbial assays to fix your soil is use of cover crops and organic matter additions to try to move the biology in the right direction. If you have time and an observant eye, you can use plant responses as an indicator that the additions you made last year, or earlier in this year are moving the biology in the correct direction. This approach takes time and patience, and may result in the loss of a crop or two before you learn to recognize what the plants are trying to tell you about the management you perform.

The compost you use needs to have the right biology. That’s the answer, the right biology.

With the right set of organisms, disease organisms will be prevented from having unrestricted access to your plants. Nutrients will be retained in your soil, instead of ending up in your drinking water, surface waters and the ocean, killing the organisms there as the result of toxic accumulations of nutrients. Nutrients will be cycled into the proper forms at the proper pH, at the proper time, for the growth requirements of your desired plant, if the right biology is present. Soil structure will be improved, and typically, pesticide use falls to practically nil when the biology sets the conditions in your soil to select for the growth of your desired plant. Water use decreases, because you retain water in the soil instead of having it wash right through the soil. Organic matter is important, but the biology on that organic matter are the real keys. Together, the right biology and the foods to feed them will allow the plant you want to grow to the exclusion of other plants.

Desired levels of organisms (direct microscopy) in aerobic compost or vermicompost (measured in fresh weight compost, but expressed per gram dry weight of compost).

In the past, these values were considered to change slightly through the year, but as we realized that good compost has to reach temperature regardless of ambient temperatures. That means you can compost in Minnesota in the middle of the winter – you just have to have the starting materials at 60 to 65 or higher for the first three days to get things going.

Bacteria

• 15 to 25 or more µg active bacteria /g dry weight compost
• 150 µg (fungal compost) to 300 or more µg (bacterial compost) total bacteria /g dry weight compost
• 15,000 - 25,000 or more bacterial species (using molecular methods), minimum total bacterial biomass using direct methods

Fungi

• 15 to 25 µg or more active fungi /g dry weight compost
• 150 (bacterial compost) to 300 or more (fungal compost) µg total fungal biomass/g dry weight compost
• Hyphal diameters should on average be 2.5 micrometers or greater than 2.5 µm
• 5,000 to 8,000 or more fungal species (using molecular methods), minimum total fungal biomass using direct methods

Protozoa

• 50,000 or more protozoa per gram dry weight compost
  25,000 or more flagellates
  25,000 or more amoebae
  50 - 100 ciliates. Higher numbers indicate anaerobic conditions resulting from compaction, water-logging, discontinuities in soil

Nematodes

• 20 to 100 BENEFICIAL nematodes per gram dry weight of compost
  10 - 15 bacterial-feeders
  5 - 10 fungal-feeders
  1 - 5 predatory nematodes
  No root-feeding nematodes

Mature Compost

• < 10% activity of bacteria and fungi indicates a mature compost

Habitat requirements for beneficial bacteria, fungi required to obtain thermal death of pests and pathogens

Thermal Compost

• Maintain 5.5 ppm O2 (dissolved gases) or higher during compost cycle
• Pleasant Smell
• Moisture 45 to 75%
• For thermal compost: Temperature of 55 C or higher for at least 3 days in all parts of the compost: No greater than 70 C. Compost must be turned to achieve adequate temperature throughout pile. Turn compost every time compost approaches 68 to 70 C to maintain adequate air throughout pile.

Vermi-compost

• For vermicompost: At least 75 to 80% of the material in the worm bin must actually pass through the worm digestive system. No weed seed can be added or materials must be pre-composted

Testing Requirements

• Starting materials used must be stated
• Chemistry and Pathogen Testing must meet local standards (city, county, state, Federal).
• Test each batch for organisms for the first three months or until tests show three consistent sets of compost produced at or above levels given above
• Once initial testing passed, test each 3 months, or each set of different starting materials.

Thermal compost

• For thermal compost: Turning times, daily temperature, end moisture, and daily CO2 or O2 data must be submitted for each batch of compost

Vermi-compost

• For vermicompost: Number of worms per unit volume must be assessed, temperature, and oxygen data must be submitted

Sampling requirements for healthy foodweb assessment

Thermal compost

• At 5 feet height above ground, dig directly toward the hottest center of the compost (measure temperature and CO2 or O2), remove sample 2 feet into the pile. Place in clean container.
• Repeat 5 to 10 times at equidistant spacings on both sides of the compost pile
• Mix with clean utensil.
• Remove approximately 500 g of compost, place in clean plastic, sealable bag and send overnight to SFI lab. Send with completely filled out sample submission form
• Match the fungal:bacterial ratio to the requirements of the plant; give a clear indication of intended use requirements
• Date to be used by, and required storage conditions to assure maintenance of beneficial organisms must be on the bagging materials.

Vermi-compost

• Mix material removed from worm bin in clean container.
• Remove approximately 500 g of compost, place in clean plastic, sealable bag and send overnight to SFI lab. Send with completely filled out sample submission form
• Match the fungal:bacterial ratio to the requirements of the plant; give a clear indication of intended use requirements
• Date to be used by, and required storage conditions to assure maintenance of beneficial organisms must be on the bagging materials

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