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

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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

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Changes in cation exchange capacity(ash-free; pH 7)

FAPA

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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

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Poultry

Inorganic N release – Spring and summer 2000

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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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