B. 2. The Compost Food Web

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Compost organisms perform a number of important processes during composting. But their importance doesn’t stop there – those organisms survive and live in soil, on leaf surfaces, and around roots, leaves, stems, blossoms, etc. They can create a protective layer on leaves, stems, blossoms, fruit and any above-ground as well as below ground surface.

Bacteria and fungi – the WHOLE diversity of these organisms, not just one or five or 20 species, but the whole 25,000 or more that could potentially be present in good compost - retain nutrients in the compost, and ultimately, in your soil too. Or on your leaf surfaces, if you could somehow get compost to stick to leaves. Except, that is possible, if you turn the compost into compost tea – see the sections on compost tea!

Protozoa and nematodes – the good guy nematodes only please! – then mineralize nutrients from the retained nutrients held by the bacteria and fungi. In compost, these mineralized nutrients serve to help other organisms grow and utilize the carbons sources in the organic matter put in to the compost pile.

Bacteria and fungi build micro- and macro-aggregates in the compost as well, and the protozoa and nematodes help build the larger pores in compost, so within a week or so, if you have the right biology in the compost, air passageways and water-infiltration-hallways have been built by the organisms. Turning becomes less and less critical as the biology grows and forms structure for you.

If the compost pile can be left alone, and you have a good set of local microarthropods or earthworms that can move into the pile, then they will move into the pile and set up housekeeping too, stimulating the growth of the fungi, and building structure, improving aeration, aggregation, and taking care of any pathogens in the pile.

Vermicompost, or composting using worms instead of heat, shifts the species of bacteria, fungi, protozoa and nematodes as compared to thermal composting, and generally, worm-compost contains some extremely beneficial bacterial and fungal species that are in lower densities in thermal compost. The worms quite clearly enhance certain beneficial bacterial and fungal species. Worm compost is also generally much higher in protozoa, and often have quite complex aggregation patterns that result in a great range of food resources for the beneficial species in the compost.

The dynamic, living system in compost is very influenced by the foods you choose to put into the compost pile, by the biology on the organic matter going into your pile, and by rain, wind, heat, sunlight, and pollution that occurs while you are composting. Only if some disturbance harms the community of beneficial organisms in compost will disease be able to get foothold in the pile.

Understanding compost health requires knowing:

1. what organisms should be present (community analysis),
2. how many are present (total biomass of each group), and
3. how many should be functioning (active biomass).

If anything has been harmed or reduced, or put out-of-balance during the composting process, you either have to start over again, or use a good compost tea to replenish the lost organisms.

Plants depend on beneficial microorganisms in the following ways:

1. to protect them from pathogens,
2. to retain nutrients in the soil so they do not leach from the root zone,
3. to cycle nutrients into plant available forms (both predator-prey and mycorrhizal fungi function to these ends),
4. to improve uptake of soil or foliar nutrients,
5. to break down pollutants in the soil, on on aboveground plant surfaces or around the roots, and
6. to build the air passageways, hallways, lving rooms, dining rooms, kitcnes, and swimming pools that allow air and water to move into the soil, and to be retained so roots can grow as deep into the soil as physiologically possible, and obtain water and nutrients all year long, regardless of drought.

If the organisms that perform these benefits are missing, they need to be replaced.

The food web in compost will not contain many of the higher level predators if the compost is turned often. But as time from last turn increases, and there is a source of the beneficial organisms to colonize the pile, the higher trophic level, predator organisms will colonize, survie and grow in the compost pile.

Pests in the compost pile need to be discouraged by the habitat built by the biology in the pile. A good compost should be resistant to any diseases moving into the pile, because the beneficials have fully occupied the pile. If something happens to favor the growth of pests, however, then diseases or pests may be selected, and take over the pile. Biology is always a process, never totally stable, never something you can just ignore.

Factors important in making compost:

• The starting materials
• Commercial composting
• i. Quality
• ii. Quantity
• Back-yard composting
• i. Quality
• ii. Quantity
• Moisture
• Aeration – chunkiness and aggregation
• Mixing/Turning
• Commercial composting
• Back-yard composting

The Starting Materials

Do you want the final compost to be bacterial, or fungal? Are you making thermal compost, or worm compost? Do you want to be finished in 6 weeks, or can you take more time?

You have to know these answers in order to select for the right kinds of starting materials. We can reach the same end-point – from the plant’s point of view – with any composting approach you want to take. From the point-of-view of the microbiology of the compost, each stick of wood, each leaf of each plant, each different kind of material you add in will change the species composition of the compost pile.

Diversity

From a human point of view, what level of resolution do we need to know?

We don’t need to know the precise names of all the organisms in the compost pile. Just like a human city, we don’t need to know the first and last names of each human in the city in order to be able to know if that city is a good place to live. Is it functioning properly?

We need to know if the diversity of bacteria is adequate, if there is enough bacterial activity so the functions of nutrient retention, disease-competition and microaggregate building are going to be performed adequately. Fungal diversity needs to be adequate too, so the functions of the fungi are carried out properly. So, we need to know active bacterial biomass, total bacterial biomass, active fungal biomass, and total fungal biomass in order to know if the compost is good for the plant we want to grow.

Activity

There are minimal levels of activity and total bacterial biomass, active and total fungal biomass that are needed regardless of plant type, and then we can change whether the compost will be more fungal or more bacterial, by adding in foods that shift fungal or bacterial growth, just as you put the compost out on the soil, or use it to make compost tea.

To heat or not-to-heat?

Heat in a thermal pile is the result of the growth of bacteria and fungi. The more rapidly bacteria and fungi grow, the faster the pile will generate heat. You have to have the right ratios of carbon and nitrogen, but all the rest of the nutrients must be adequate so these other nutrients are not limiting either. But generally, in plant material, all the other nutrients are in good amount, it is the C:N ratio that will determine how hot the pile will get.

These ratios, the proper way to alter the relative amounts of high nitrogen plant material to not-high nitrogen plant material to low nitrogen plant material is explained in the compost book.

The compost biology book also explains why with back-yard composting, the ratio of high N to not-high N to low N has to be different. With back-yard composting, we only have to turn once after the pile has gotten started, but with commercial composting, we have to turn more often.

The need for proper “chunky” material is also explained, as well as how to aerate the pile. Again, back-yard is quite different from commercial conditions.

There are any factors that can be worked with to make compost be what your plants need, and that will help you reduce, and most likely end entirely, your reliance on toxic chemicals in order to raise high yields of fruits and vegetables. Let us help you do that. Check out the Compost Biology book available June 2004.

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