Composting Flashcards
What is Composting?
A biological process in which microorganisms convert organic materials into a soil-like material called compost
In Composting we are controlling…..
conditions so that materials decompose faster
Why bother composting on the farm?
Two functions:
- Turns waste products into an easily handled material
- creates a valuable commodity
Why bother composting on the farm? Negatives
- Major undertaking
- Deserves the same commitment given to other farm tasks
Benefits of Composting
- Soil Conditioning
- Sell-able product
- Improved manure handling
- improved land application
- Lower risk of pollution or nuisance complaints
- Pathogen Destruction
- Bedding Substitute
- Disease suppression
Drawbacks to Composting
- Time and Money
- Land
- Odor
- Weather
- Potential Loss of N
- Diversion of Manure and crop residues from cropland
- Slow release of nutrition
Benefit: Soil Conditioning
- Excellent Soil Conditioner
- Adds Organic matter
- Improves soil structure
- Reduces fertilizer requirements
- Reduces potential for erosion
Benefit: Sell-able Product
Price of compost
Bulk average is $10 per cubic yard
Benefit: Improved manure handling
- Reduces weight, moisture content, and activity of manure
- can be applied during times of years when manure cannot
- minimizes runoff and N loss
Benefit: Improved land application
- Composting convert N in manure into a more stable organic form
- Manure can have a high C:N ratio
Why is applying manure directly bad?
Causes N immobilization if manure is applied directly
What does composting do to manure?
lowers C:N ratio to acceptable levels
needed ration of C:N
CHECK THIS RATIO
25-30:1
Benefit: Lower risk of pollution or nuisance complaints
- Manure can be considered a nuisance in livestock operations
- Odor complaints
Every state has a “_______” law
right to farm: protects farmers from odor complaints during normal farming operations
Benefit: Pathogen destruction
- Outbreaks of Giardia and other protozoans can cause human and animal health issues
- Protozoa are killed by exposure to 140 F for 30 min
- Proper composting can eliminate certain pathogens
Benefit: Bedding Substitute
- Some poultry and livestock operations are using compost as a bedding
- safe and effective
Benefit: Disease Suppression
Reduces soilbourne plant diseases
What temperature can compost piles reach?
170-180 F
Drawbacks: Time and Money
- Requires equipment, labor, management
- May be necessary to purchase special composting equipment (upwards of ~$100,000)
Drawbacks: Land
-Can occupy considerable land area
Drawbacks: Odor
- Composting can smell depending on raw materials used
- End product is not odorous
Drawbacks: Weather
- Composting slows or halts with cold weather
- ~55 F
Drawbacks: Potential loss of N
composted manure often contains less N than raw manure
Drawbacks: Slow release of nutrition
- Nutrients in compost are complex
- Must be mineralized in the soils before they become available to plants
The composting process
Aerobic or oxygen requiring breakdown of organic materials by microorganisms under controlled conditions
The composting process
- Microorganisms consume oxygen
- Generates considerable heat and CO2
- Water losses can amount to half the weight of initial materials
- reduces volume
The composting process is most rapid when:
-C:N ratio is balanced appropriately
-Oxygen is adequate
-Moisture is limiting
Temperature is such that thermophilic microorganisms are encouraged
Compost is….
inexact
What happens during composting?
- Begins as soon as materials are piled together
- Introduce oxygen through mixing
- Almost immediately microorganisms began consuming oxygen
- Supply decreases
- Aerobic decomp slows and will eventually cease
Aeration 2 types
- Passive (natural convection or diffusion)
- Forced aeration (blowers/fans)
Mechanical agitation or turning….
- supplies limited amounts of oxygen
- when turning we create pore space which allows for diffusion to occur
What happens during composting?
Release of heat:
- Directly related to activity of microorganisms
- Thus temperature is a good indicator of composting process
- After hours, heat release is noticeable as microorganisms start consuming easily degradable compounds (soluble sugars)
- Temperatures rapidly increase to 120-140 F
- Maintained for several weeks and temperatures gradually drop back to ambient air temperature
- Reflects the rate and type of decomposition
What happens during composting? caution
- if oxygen is readily available and microbial activity is intense piles or windrows can easily heat to over 140 F
- above 140 microbes begin to die
- composting process ceases
Compost Curing
- Curing follows the active stage
- While Curing, materials continue to decompose but much more slowly
- rate of oxygen consumption is so low that pile can withstand no aeration
- composting does not stop….material continues to decompose until the last remaining nutrients are consumed
When is compost “done”?
Compost is considered finished when:
- C:N ratio is low enough to not immobilize N when applied to fields
- Oxygen demand has decrease substantially
- Temperature has returned to ambient air temperature
- Odor is that of earth
Factors affecting process
- Oxygen and aeration
- Nutrients (C:N)
- Moisture
- Porosity
- Structure
- Texture
- Particle size
- pH
- Temperature
- Time
Factors: Oxygen and aeration
- Need for oxygen is greatest at early stages
- Minimum concentration of 5% within pore spaces is necessary (air contains ~21% oxygen)
- Aeration removes heat, water vapor and other gases
- Without sufficient oxygen process becomes anaerobic
Factors: Anaerobic decomposition
- involves a different set of microorganisms
- slower and less efficient
- little heat is generated (thus not as much water loss)
- Develop intermediate compounds (methane, hydrogen sulfide, organic acids, etc)
- During anaerobic decomp intermediate compounds accumulate
- Anaerobic decomposition is very odorous
Factor: C:N ratio
- Carbon (c), Nitrogen (N), phosphorus (P) and potassium (K) are the primary nutrients used by microorganisms
- NPK are also the primary plant nutrients
- Concentrations of these three nutrients determine the “value” of the compost
Factor: C:N ratio continued
- Some organic materials contain sufficient nutrition (manures, plant residues and food waste)
- C (too much or too little) is the largest “problem” in composting
- Microorganisms use carbon for both energy and growth (Use N for protein and reproduction)
in general organisms need about ___ times more C then N
25
- thus our C:N ratio needs to be balanced such
- Balanced C:N ratio usually ensures that other nutrients aren’t lacking
C:N ratios
25-30:1 are desirable
20-40 and even 50:1 can provide good results (the higher the ratio, the longer the process takes)
below 20:1 available C is fully utilized without stabilizing all N
Excess N is then lost as ammonia or NO2
Factor: Moisture
- Necessary to support microbe metabolism
- medium for chemical reactions
- transport nutrients
- allows microorganisms to move
- Biological activity ceases at moisture levels below 15%
- Moisture levels should be maintained at 40-65%
- Below 40% moisture activity slows
- Above 65% moisture fills pore space limiting oxygen (can lead to anaerobic conditions)
Rule of thumb for moisture
materials are too wet if water can be squeezed from them….. too dry if they do not feel moist to the touch
Factor: Porosity, structure, texture and size
- Porosity, structure, and texture refer to physical properties of materials (size, shape, consistency)
- can have a large influence on air diffusion
- these physical properties are adjusted by grinding or mixing
- materials can be added to adjust these properties and are called bulking agents
Porosity
- Same as porosity in soil
- measure of air space within the particles
- determined by particle size, continuity of air space
- Larger particles (uniform) creates higher porosity
Structure
- refers to rigidity of particles
- how much do they resist compaction and settling?
- good structure helps with porosity
Texture
- Describes the available surface area for microbe activity (decomposition occurs on surface of particles)
- aerobic microbes buildup in the liquid layer surrounding particles
- the particles shrink and decompose as the microbes work from surface to interior of a particle
Texture surface area of particles…
- increase as particle size decreases (aerobic decomp increases as particle size decreases
- but porosity declines
Rule of thumb texture
particle size should be 1/8-2 inches average diameter
pH
- relatively insensitive to -starting pH of raw materials
- preferred pH range is 6.5-8.0 (buffering makes wider pH range possible)
- pH matters in materials with excessive N (pH above 8.5 encourages conversion to ammonia (N loss))
- changes throughout the process (production of organic acids)
- regardless of pH of materials end product will be near neutral
Temperature
- Temperature ranges for microorganisms
- Mesophilic (50-105 F)
- Thermophilic (over 105F) kills more pathogens, weed seeds, and fly larvae
-it is suggested to maintain temp between 110-150F
- human pathogens are killed at 131 F
- Destruction of weed seeds happens at or above 145F
Most heat occurs through water evaporation
- materials should not be allowed to dry below 40%
- low moisture increases possibility of high temps and spontaneous combustion
Time
Length of process depends on:
- materials used
- temperature
- moisture
- frequency of aeration
- user requirements
Proper moisture, C:N ratio and aeration mgmt ensure shortest time frame
OM sources
-Cover crops, green manures
-Crop residue
-Compost
-Livestock manure
-Sewage sludge
-Processing wastes
(Vegetable processing plants, wood processing plants, breweries, etc.
How do I choose a source?
- Are you organic or conventional?
- What is the nutrient content?
- What is the C:N ratio?
- In what form is the material?
- Does it contain harmful components such as weed seeds, heavy metals or chemicals which will inhibit crop growth?
- Will growth inhibitors produced affect crop?
- What is required for transportation and application?
Cover crop:
a crop planted between periods of regular crop production to provide other benefits besides foot production.
Cover crops can also be planted….
between or among production crops for purposes of weed suppression and other benefits
Cover crops include….
- Grasses
- Legumes
- Non-legume broadleaves
Grasses
- Fine fibrous root system
- Well suited to holding soil in place
- Improve soil structure
- Must be fast growing and relatively easy to kill (can be chemically or mechanically or winter killed)
- Do not fix N
- Can accumulate large quantities of N from the soil
Commonly used grasses for cover crops
- Rye
- Winter wheat
- Oats
- barley
- Sorghum sudan
- ryegrass
- corn
- pearl millet
Legumes
- Fix N from the atmosphere
- Supply N to succeeding crop
- Protect the soil from erosion
- Add organic matter
- Fixed N varies between species (in general more shoot growth= more fixed N)
- Aggressive tap roots
Commonly used legumes for cover crops
- Hairy vetch
- crimson clover
- Austrian winter pea
- peas
Non-legume broadleaves
- May have a role as green manure crops
- Cannot fix N
- Absorb large quantities of N (and other nutrients) from soil
- Not winter hardy
Commonly used Non-legume broadleaves for cover crops
- buckwheat
- oil seed or tillage radish
- marigolds
- canola
Why choose grasses?
- Generally improves soil coverage over winter
- Increases the root mass to stabilize topsoil
- Other crops (viny cover crops) will climb grasses
- Serves as a nurse crop for slower growing species
- Covers ground quickly
Grass disadvantages
- Winter survival
- can end up with more fresh residue that equipment can handle
Why choose legumes?
- Legume cover crops contribute up to 300 kg N per ha per year (depending on species, climate, mgmt and soil physical properties)
- OM increases result from legume cover crops (largely due to root system)
Why choose legumes
N accumulation and release in legume in controlled by:
- rate of biological N fixation
- Growth stage at which crop is killed
- Residue biochemistry
- Association with decomposing microorganisms
- Climatic conditions (i.e. temperature and moisture)
So how do we decided on a cover crop rotation?
-Is the main purpose to add N, or to scavenge nutrients?
-Do you want the cover crop to provide large amounts of residue to build soil C?
-Does the soil have a compaction problem?
-Will the climate and water holding capacities of your soil influence water uptake by cover crop and “steal” water from main crop?
-Is erosion control in fall or spring a primary objective?
-Are root diseases or plants parasitic nematodes a problem?
Is weed suppression your main goal?
-What species is best for you climate (i.e. winter)?
How so we kill cover crops?
- Winter Kill
- Herbicides
- Tillage or discing
- Roller crimper
Cover crops allowing no-till
Weed control can be almost 100%
What are green manures?
- crops which are tilled back into the soil while they are still green
- the proactive of growing lush plants on the site into which you want to incorporate organic matter, then turning the soil while it is still fresh
Green manures
fast growing plants sown to cover bare soil. often used in the vegetable garden, their foliage smothers weeds and their roots prevent soil erosion. when dug into the ground while still green, they return valuable nutrients to the soil and improve soil
Two types of green manure
- In-situ green manuring
- Green leaf manuring
In-situ green manuring
- Short duration legume crops are grown and buried ~60-80 days after sowing
- On site nutrient resource generation
Green leaf manuring
green leaves and tender plant parts are collected, added to soil and turned under 15-30 days prior to the sowing of crops
Composing Methods
- determine the rapidity of the process
- Chosen methods affects temperature control, materials movement and odor control
4 general groups of composting methods
- Passive composting
- Windrow composting
- Aerated piles
- In-vessel composting
Passive composting
Involves stacking materials in a pile to decompose over a long period
-Passive composting of manure
Passive: stacking materials in a pile
little agitation or management
Passive: Passive composting of manure
- Typically anaerobic in nature
- little if any air diffusion
- Produces leachate containing partially degraded organic compounds
Passive composting issues
- Main issue is porosity (creates lack of oxygen)
- But can add bulking agent to aid with porosity and structure
-Is slow (low aeration rate and odor may be a potential problem)
Windrow Composting
- Places materials in long narrow piles (windrows)
- Agitate or turned on a regular basis
- Typically 3 ft high for dense materials (12 ft. for fluffy materials, leaves)
- Width varies 10-20 ft
- utilized for very specific operations
Windrow Agitation Equipment
- Bucket loader
- Rotary drum with flails
- Tow behind rotary drum
- Elevated face conveyor
Aerated Static pile
Uses a blower to supply air
- allows larger piles
- no turning or agitation of materials
- active stage completed in 3-5 weeks
- 5-8ft high
- cover layer of finished compost
Cover layer of aerated piles
the cover layer we are putting on is our source of microbes and affect air flow
Passively aerated windrows/piles
A piece of pipe that diffuses air to bottom but air is not forced
much slower, compaction
In-vessel composting
-Group of methods which confine materials within a building, container or vessel
ex. bin composting
Rotating drums
Silos (auger system, bottom unloading)
