kwantlen farm school 2012 chris thoreau. what is composting? the rapid biological decomposition of...

Composting 101

Kwantlen Farm School 2012

Chris Thoreau

Composting 101

What is Composting?

The rapid biological decomposition of organic matter

Microorganisms turning organic matter into plant food

Rapid nutrient cycling

Breeding of microorganisms or worms

This is my approach to composting

Our goal in composting: to provide microorganisms with the food they need to thrive and thus rapidly decompose organic materials while retaining the maximum amount of nitrogen in those materials

Composting 101

Many types of composting

Anaerobic Composting/Digestion

Slow process in absence of oxygen or in low oxygen environment

Easy method for small-scale composting

Retains nitrogen very well

“Backyard” Composting

Small-scale; good for home waste diversion

Requires little management

Composting 101

Worm Composting

Can be done indoors or on large scale

Results in nutrient-rich compost or “castings”

Finished compost in 3-5 months or sooner depending on system

Relatively high management needs (harvesting)

Composting 101

“Hot” Composting

Method for large quantities of organic matter

Rapid decomposition - as little as 4-8 weeks for certain materials

Requires some management to ensure high quality

We will focus on this method

Composting 101

So let’s breed some microorganisms…

Hot Composting

Best method for rapidly making large volumes of compost

Heat can destroy weed seeds and pathogens

Good for soil fertility and structure building

Requires frequent monitoring and turning

Process of building pile is important

Composting 101: Hot Composting

Hot Composting

Often benefits from off-farm nitrogen source

Works good as soil inoculant

Quality of compost depends on:

• Quality of feedstock/composting materials

• Quality of monitoring

• Effort in preparing pile


Six key elements to good hot compost (and most other methods as well):

1. Carbon:Nitrogen (C:N) ratio

2. Air

3. Water

4. Surface Area

5. Critical Mass of Pile

6. Diversity of Materials


1. Carbon to Nitrogen Ratio

Food for the compost pile – must be balanced

Ideal ratio: 24:1

Microorganisms need 24 carbon molecules for every 1 nitrogen molecule they consume

Ratio too wide (e.g., 50:1)?

Process is slower

Ratio too Narrow (e.g., 10:1)?

Process is faster, but nitrogen lost as ammonia



How to Balance:

General rule: equal parts browns and greens

This shifts depending on how brown or green

Increased surface area in nitrogen materials:

Increases decomposition rate

Acts like higher N content, but used up quicker

Get familiar with common materials available to you



Essentially, the C:N ratio determines how hot the compost pile will get

The heat is a by-product of microbial activity

An indicator of how happy your microorganisms are

Nitrogen is often a limiting factor

Importing nitrogen is crucial for good hot compost

Too much heat = too much N = N loss to ammonia

– Also reduces diversity of microorganisms


2. Air

Your microorganisms need air to breathe

Gas exchange is crucial for life

Think of your compost pile like your soil

How much air does it need (by volume)?

About 20-25%

How do we promote good aeration?

Mix pile consistently as you build it

Use some woody and fibrous materials


2. Air

Even with good porosity air space will decline

Pile becomes more dense as it decomposes – filling pores

Passive aeration tubes can be used to maintain air flow

How do I reintroduce air into the pile?

Usually by turning the pile and mixing the contents

More nitrogen can be added at this point if needed


2. Air

Air is used to control rate of decomposition

Adding air can increase decomposition rate

Removing air slows the process

Can be used to help correct high C:N ratio

Forced air used for in-vessel systems


2. Air

Air can be added passively or actively

Passive:

Building good porosity into the pile using “twiggy” materials

Using perforated pipes horizontally layered in the pile

Active:

Physically turning or manipulating the pile

Forced air used for in-vessel systems


3. Water

Your microorganisms need water – just like you

• Water also softens materials for decomposition

Good porosity allows extra water to drain away

Makes it difficult to over water your pile

Some materials with have a higher water content

Other materials will be very dry


3. Water

Water usually needs to be added to the pile

Add water while building your pile

How much water?

50% water by weight!

Pile should be quite wet

“As damp as a wrung out sponge”

Organic matter will absorb water and allow pore space to remain for air flow


4. Surface Area

Microorganisms are small – their food should be too!

Increased surface area = easier and faster dining

Chopping up materials greatly increases decomposition rate – especially high C materials

Materials can be screened after composting to reduce large pieces before adding to soil

Large pieces of OM in soil can tie up nitrogen – especially high carbon materials


Area of activity

5. Critical Mass of Pile

Microorganisms create heat when eating and they like to stay warm

Larger pile = increased insulation

1 metre cube pile is sufficient for good insulation

Larger piles insulate well

Bottom of pile may be anaerobic



Your microorganisms like a diverse diet

Also results in more diverse microorganisms

Diversity of materials = diversity of nutrients

Also makes it easier to balance C:N ratio

Dynamic accumulators can be grown specifically to be added to pile to improve quality and N content

Use large, fast-growing plants that re-grow after cutting

Comfrey; Angelica



Diversity of materials is not essential to make compost

But it is essential to make good compost

Compare the following compost piles

Horse manure and leaves

Horse manure, chicken manure garden waste, comfrey, okara, grass clippings, leaves, sawdust, willow branches


Other things to consider:

The seasonality of composting materials

Carbon materials are prevalent in the fall

Nitrogen materials are prevalent in the growing season

What off-farm materials are easily available?

Manures; leaves or other carbon materials



Composting of weed seeds, rhizomes and diseased plants

Is it safe? How to do so safely?

Where and how will you compost?

Do you have a staging area?

Do you have a tractor?

Using a bin or windrows?



Protect the pile from the weather

To control water level in pile

Knowing the C:N ratio of the most common materials is important in making a good pile

Learn how to judge C:N ratio of new materials

Very active soil food web in compost pile

Many trophic (feeding) levels

Different organisms digest different materials at different times


Soil Food Web

Bacteria are primary decomposers of OM

Work quickly on diversity of materials

Generate heat in compost pile

Fungi also important

Only organism that breaks down lignin (found in wood)

Thrive in acidic environments

Active in latter parts of decomposition


Soil Food Web

Arthropods

Consume OM and each other

Work on outside of pile when hot

Worms

Consume their weight each day in OM

Help aerate compost pile


The Evolution of a Hot Compost Pile:

Our goal:

To build a compost pile, taking into consideration the six principles of hot composting, that will heat up to a temperature of 55ºC and maintain that heat for up to several weeks


1. Stockpile materials on farm

Materials will start to decompose

2. Import nitrogen (if required) and build the pile

3. Monitor pile temperature

4. Turn or aerate pile when temperature has dropped by 8 - 10ºC

Add N if required when turning for first time

Turn pile 3-5 times upon cooling

5. Let pile cure


1. Stock pile materials from on farm

These are organic materials generated on the farm

Weeds

Leaves

Harvest trimmings

When pile is of sufficient size bring in manure source for hot compost


Composting 101: Hot Composting2. Import Nitrogen

Nitrogen is limiting factor for rapid decomposition

Manure

Okara

Grass Clippings

3. Build Pile

Start with rough materials on the bottom

Layer carbon and nitrogen materials

Mix every 3-4 layers

Water pile while building

Add aeration pipe while building

Top with carbon materials; cover with tarp


4. Monitor Pile

Use thermometer to check temperature

If T too low

– Too dry? Too wet? Not enough N?

Watch for falling temperature

– Signal to turn pile


5. Turn Pile

Use machine or fork depending on size

Mix materials well when turning

Add N if desired

Add water if needed


6. Let Pile Cure

Larger organisms finish off decomposition

Bacteria and fungi continue to work


kwantlen farm school 2012 chris thoreau. what is composting? the rapid biological decomposition of...

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