composts what is compost and why use it? what organisms are involved in the composting process? ...
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Composts What is compost and why use it? What organisms are involved in the composting
process? What chemical changes occur during
composting? What are the optimal conditions for composting
Temperature Moisture Oxygen
Does composting kill harmful pathogens (plant and human), nematodes and weed seeds? Safety regulations
Compost production systems Small scale Commercial
What is compost – why use it?Composting is the decomposition of plant remains and other once-living materials to make an earthy, dark, crumbly substance that is excellent for adding to houseplants or enriching garden soil.
•compost improves soil structure, texture, aeration - increases the soil's water-holding capacity.
•Compost loosens clay soils and helps sandy soils retain water.
•improves soil fertility and stimulates healthy root development
•Organic matter provides food for microorganisms - nitrogen, potassium, and phosphorus mineralized
The Science of Composting Composting is the natural process in which living
organisms decompose organic matter into inorganic matter in the soil.
The organisms feed on the organic material and through respiration generate the energy that they use for movement, growth, reproduction or stored energy.
The organism excrete inorganic material that enriches the soil.
When the organisms die, their bodies add to the organic matter in the compost pile.
Fresh OrganicMaterials Oxygen+
Carbon Dioxide
Compost Energy+ +
Microbes,Moisture,and Time
Slide credit: Tom Richard, Penn State University
•Too little N:
•there will be few microorganisms, and decomposition will be slow.
•Too much N:
•some will turn to ammonia that will volatilize, creating an odor.
Organisms use carbon as a source of energy and nitrogen to grow and reproduce.
Experimental test - effect of C:N ratio on nitrogen retention in compost
Initial C:N ratio
Final nitroge
n%
Nitrogen conservatio
n %
1 20 1.44 61.2
2 20.5 1.04 51.9
3 22 1.63 85.2
4 30 1.21 99.5
5 35 1.32 99.9
Factors affecting the compost process
NB. Moisture level also critical
C:N ratio
Aeration
Size and texture
Moisture level is also critical
•Optimum moisture content 40-60%
•Feels moist to touch, but when squeezed only produces few drops
Ideal conditions for composting
Parameter OK IdealMoisture 40-65% 45-60%C:N ratio 20-40:1 25-35:1Oxygen >5% >10%Temperature 43-66 C 54-60 CBulk density 1000 lbs/yd 1000 lbs/ydpH 5.5-9.0 6.5-8.0
The Science of Composting
Composting goes through three distinct phases that can be characterized by temperatures.
• Mesophilic Phase (moderate temperature)• Thermophilc Phase (high temerpature)• Mesophilic Phase (moderate temperature again)
Three Phases of Thermophilic Composting
0102030405060
0 10 20 30 40
Time (days)
Tem
pera
ture
(C
)
The Science of Composting Mesophilic Phase 1 (10-40 0 C)
• Lasts only a few days• Explosive growth of bacteria and fungi• Rapid breakdown of soluble sugar and starches
Thermophilic Phase (>40 0 C)• Can last from several days to several months depending on size of
system• Mixed population of heat loving organisms• High heat helps breakdown of proteins, fats, “tough” plant material
like cellulose• High temperature (>55 0C) kill weeds and pathogen harmful to
humans• Higher temperature (>600C) kill organism needed for decomposition
Mesophilic Phase 2 (10-40 0 C) “Curing Phase”• Can last several months• Bacteria, fungi, actinomycetes( mix between bacteria and fungus,
give “earthy” smell) predominate. Invertebrates active. • Supply of organic material has decreased. Remaining organic
material is slowly broken down. • Additional chemical reactions take place to make remaining organic
material more stable
The Science of Composting:ChemistryImportant factors in compost chemistry Carbon-Nitrogen Mix (C/N Ratio)
Carbon provides energy source and building material for 50% of composting organisms’ cells
Nitrogen important in formation of proteins, nucleic acids, amino acids, enzymes etc. for organisms
30:1 Carbon to Nitrogen optimum mix (decreases in curing phase)
Brown and woody carbon Green and moist nitrogen
The Science of Composting:ChemistryImportant factors in compost chemistry Oxygen
Needed to oxidize carbon for energy Without oxygen will produce rotten egg smell
pH Level Acids form as organisms digest organic material and
lowers pH Lower pH encourages fungi and the break down of
“tough” matter If pH too low (<4.5) limits microorganisms’ activity
Changes in Ammonium-N distillation method; fresh sample
Changes in Carbon to Nitrogen Ratio
Dan Sullivan and Linda Brewer
Composting time (days)0 20 40 60 80 100 120 140
CE
C
(cm
ol k
g-1co
mpo
st-C
)
0
100
200
300
400
500
Changes in cation exchange capacity(ash-free; pH 7)
FAPA
Temperature
Fatty acids
NH3 emitted
pH
days
Compost chemistry - pH
The Science of Composting:Physics
Important factors for compost physics: Temperature
3 Phases Want to maintain temperature between 55-600C Temperature impacted
Heat generated by organism Heat lost to environment through conduction, convection
and radiation shape and size of pile Moisture content (specific heat and heat capacity of
water)
The Science of Composting:Physics
Important factors for compost physics: Particle size
Microorganism activity occurs on surface of organic material
The more surface area for organisms to attack, the quicker the decomposition want smaller particles
Flip-side: The smaller the particles, the more dense and compact the material resulting in poor oxygen circulation
The main players1. Bacteria:
major decomposers, breakdown simpler forms of organic material
2. Actinomycetes:degrade complex organics such as cellulose, lignin, chitin, and proteins –earthy” smell, long “spider webs” filaments
3. Fungi:Break down tough debris, too dry, too acidic or too low in nitrogen for bacteria to eat
What do microbes in compost do? Consume organic matter to grow
Stabilize organic matter Aerobic oxidation produces CO2
Anaerobic produces reduced compounds organic acids, alcohols
Mineralize nutrients Organic to inorganic forms (protein to NH4)
Transform nutrients Nitrification – pH and temperature sensitive
NOTE: invertebrates not important in high temperature composting, only in cold
Compost Quality
Compost Maturity and Nitrogen Release Characteristics in Central Coast Vegetable
ProductionJuly 2002
CA Integrated Waste Management Board
Marc Buchanan, PhD
Compost Maturity
Defined as various levels of maturity based upon:
C:N ration of 25 or less, plus at least one from each of the following:
Group A (tests to determine compost stability)
CO2 evolution or respiration
Oxygen demand
Dewar self-heating test
Group B (tests to further determine maturity in reference to potentially phytotoxic compounds)
NH4-NO3 ratio
NH3 concentration
Plant test (seed germination and growth)
Volatile organic acids concentration
Compost Maturity
Very Immature
C/N ratio greater than 25, and/or stability test is greater than 12, and/or NH4 is greater than 500 and no nitrate present.
Immature Unstable compost Odors likely High toxicity potential Immobilization (tie-up) of available nitrogen
Moderately Mature
Stability test greater than 6 and less than 8 and/or when nitrate is detected and is greater than 25 ppm N.
Mature
Cured compost Odor production not likely Limited toxicity potential Positive impact on available soil nitrogen
Very Mature Well-cured compost No continued decomposition No odors
Compost Quality MeasuresTest Rating
VM M IM
CO2 Test Stability 1 (respiration rate)
C / unit organic matter/ day < 2 2 – 8 > 8
BIO-C CO2 Stability 2
C / unit organic matter / day < 2 2 – 8 > 8
NH4-/NO3-N Ratio < 0.5 0.5 – 3 > 3
Seed Germination
% of control > 90 80 – 90 < 80
Plant Vigor Tests
% of control
> 90 80 – 90 < 80
C:N below 25
C:N
Stability1
Stability
2
% germination
% vigor
Ammonium -N ppm
Nitrate -N
ppm
ratio
Compost
Green Waste
average 14 92 90 244 287 13.6 range 7-29 VUS -VS US - VS 85-100 75-
100 22-579 0-784 0.03 - 122
Blend
average 12.7 59 38 745 155 14.9 range 8-18 VUS - VS VUS -
VS 20-95 0-94 0-2477 0-485 0 -130
Poultry
7 S S 0 0 5578 0.0 nd
COMPOST QUALITY INDEX for Commercial ProductsBased on 13 monthly samples for green waste, 11 for blend, and
1 poultry manure compost.
Compost Type Maturity Crop Yield
Sandy Soil Class (Coarse Sandy Loam and Fine Sandy Loam Textures)
Blend VM Baby Lettuce o VM Baby Lettuce - VM Baby Spinach + VM Baby Spinach o M Frisse ? IM Baby Spinach o IM Baby Spinach + IM Baby Chard o MM Baby Mustard + Green Waste MM Baby Lettuce + IM Baby Lettuce - IM Baby Lettuce - MM Baby Spinach + IM Baby Spinach o MM Baby Spinach o IM Baby Spinach - MM Baby Spinach - M Baby Chard o M Frisse ? VIM Baby Mustard -
Loamy Soil Class (Sandy Clay Loam Texture)
Blend M Lettuce + MM Lettuce + MM Celery + Green Waste M Lettuce o IM Lettuce o M Celery +
+ = Increased yield O = No difference vs check - = Decreased yield ? = no-compost treatment not included
0
100
200
300
400
0 50 100 150 200 250
Ino
rga
nic
N R
ele
as
ed
(lb
N/a
cre
)
Days After Incorporation
Check
Green [M-1]
Blend [M-18]
Poultry
Inorganic N release – Spring and summer 2000
-20
-10
0
10
20
30
40
50
60
VIM MM MM M M M VM VIM VIM MM M M VM
% N
itro
gen
Rel
ease
d
Compost Maturity
Blend Green
Conclusions The maturity index appears to be a useful tool to assess compost quality.
Mature composts most consistently result in positive crop yield response
Chicken manure and green waste blends provide more available N than pure green-waste composts.
Immature and very mature composts may reduce inorganic soil N sufficient to have negative impact on production in conventionally farmed soils.
High NH4-N levels associated with immature manure-based composts can reduce seed germination and crop productivity.
Mature composts can provide significant N dependent on timing of applications.
Maturity status of compost is a significant predictor of compost quality for vegetable production.
Growing Issue How effective is composting at killing
pathogens? Weeds, plant disease organisms Human pathogens!!!!
U.S.A. Composting Regulations
Biosolids, Class A compost (U.S. EPA 40 CFR Part 503) Time-temperature relationship (PFRP)
Static aerated pile, 3 days > 55 C Turned windrow, 15 days > 55 C, turned at least 5 times
Vector Attraction Reduction 14 days, 40 C minimum, 45 C average temperature
Pathogen testing criteria Fecal Coliforms < 1000 MPN/g TS or Salmonella < 3 MPN/4g TS
USDA National Organic Program §205.203 (c) Time –temperature 55 C – 70 C (CFR Part 503)
Turned windrow 15 days with at least 5 turns In-vessel or static aerated system 55 C – 70 C for 3 days
C:N ratio 25:1 – 40:1 (NRCS code 317 composting facility)
Done properly it works, but can less intensive regimes work too?
> 55 C
Why turn windrows at least 5 times in 15 days?
Prevent regrowth of Salmonella Non-uniform heating Turn cooler material into insulated center
NOSB Compost Task Force
Composting regulations too prescriptive
Manage compost to reach 55 C for 3 days
Vermicompost Aerobicity maintained by adding thin layers every 1-3 days 70-90% moisture 12 months for outdoor windrows, 4 months for wedge systems
or indoor containers, 2 months for vertical flow reactors Processed manure
Heat to 65 C for 1 hour Dry to < 12% moisture Negative for Salmonella and fecal coliforms
Animal pathogen destruction Meet current time-temperature standards
Will not eliminate all weed seeds or all plant pathogens
Attain sanitation target for particular end-use, quality assurance testing
Use technology that is financially attainable
Composting process Contain and treat leachate Exclude vectors Avoid pathogen regrowth conditions Avoid recontamination of product
Compost production systems Small scale
Compost piles need to be at least one cubic to hold the heat from decomposition
Passive composting
Commercial composting Large scale Passive aeration with turning or actively
aerated systems
Feedstock conditioning - grinding
Moisture management - most important factor to stabilize biological and chemical properties
Processing – turned windrows
www.vanierselcompost.com/. ../productie.htm
Compost blankets to moderate moisture
Composting - windrow
CO2
O2Cool
Hot
Graphic credit: Tom Richard, Penn State University
Turning helps aeration and to move material from edge into hot center region
Composting – Static forced air
Cool
Hot
CO2
O2
Graphic credit: Tom Richard, Penn State University
•Air forces heat outwards
•Some systems can switch direction to keep base core at high enough temperature
•Also helps control odor
Processing - forced aeration
Hot ammonia kills!!!
Contain, treat leachate
www.vanierselcompost.com/. ../productie.htm
Compost blankets – beware moving from fresh to curing
Cure compost with 40-50% moistureto promote competitive microorganisms and
avoid salmonella regrowth
CASFS Farm compost piles 2008
Compost Temperatures
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C #1 (* C)#2 (* C)#3 (* C)#4 (* C)