What is Compost? Composting Biology and Core Principals

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What is Compost?Composting Biology and Core
Principals

• David M. CrohnDepartment of Soil and
  Environmental SciencesUniversity of California,
  Riverside

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Compost definition

• An accumulation of decaying or decayed organic
  matter, as from leaves and manure, used to
  improve soil structure and to provide nutrients.
• Decay is a biological process (not a chemical
  process)
• Properties determine what is a compost (not the
  production method)

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Not all composts are created equal.

• Backyard Composting
• Vermicomposting
• Lasagna Composting
• Thermophilic Composting

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Thermophilic composting
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Compost microorganisms
Illustrations www.Digitalseed.com
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Aerobic processes
Microbes, Carbon, Oxygen
Carbon Dioxide, Water, Compost, Heat
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Thermophilic composting

• Microbes tend to specialize in the temperatures
  they prefer.
• In California soils and in our bodies mesophiles
  are most abundant. Pathogens are mesophiles.
• Between 110F and 155F, thermophiles dominate.
• Above about 160F dieoff begins.
• Reliable pathogen kill occurs above 131F.
• Heat greatly accelerates microbial efficiency.

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Thermophilic composting

• Microbial efficiency approximately doubles for
  every 18F increase in temperature
• So how much faster will organic matter decompose
  if it heats from a shady 72F to a toasty 150F ?

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Why compost?
Active Composting

• To eliminate disease organisms
• Animal ? Plant ? Human
• To produce a stable and safe soil amendment
• Nutrients ? Odors ? Phytotoxins

Curing
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Carbon

• Source of energy for microbes
• Not all forms are equally available
• lignin (less available)
• cellulose
• fats, waxes, proteins
• sugars (more available)

C
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C
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Nitrogen

• Vital nutrient for microbes
• Needed for protein synthesis
• Excess may volatilize as ammonia (NH3)
• Other nitrogenous compounds can be odiferous
• Also important for plants
• CN ratio
• initially about 351
• about 101 to 201 in cured product

N
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N
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Oxygen

• Acts as an electron acceptor
• Permits efficient liberation of energy from
  carbon
• Energy is used by microbes to grow and reproduce

O2
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Oxygen turned windrow
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Composting alternatives
Turned Windrow
In-vessel
Static pile
Illustration Rynk et al. 1992
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Water

• Clings to compost particles
• The bath within which microbes grow
• Too much fills pores
• Oxygen moves slowly into water

H2O
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Compost particle environment
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Management parameters

• Particle Size
• Porosity
• CN ratio

• H2O
• O2

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Conclusions

• The composters success in managing the process
  will determine
• Product quality
• Product consistency
• Consistent quality increases demand for composts
• Increased demand increases product value

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Questions?
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Mulches, Soil Amendments and Organic Fertilizers

• David M. CrohnDepartment of Soil and
  Environmental SciencesUniversity of California,
  Riverside

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Mulches cover the soil

• Protect soils against erosion
• Conserve water by slowing evaporation
• Control weeds
• Control certain plant diseases
• Decorate landscapes

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Soil amendments modify soil properties

• Improve tilth
• Improve water holding capacity
• Improve aeration
• Improve infiltration capacity
• Adjust pH
• Promote microbial activity and diversity

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Organic fertilizers slow release sources of

• Nitrogen
• Phosphorus
• Potassium
• Micronutrients

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Conclusions

• Mulches, soil amendments and organic fertilizers
  are uses, not products.
• Composts may serve any of these.
• Different composts have different properties, and
  some will therefore be more suitable for certain
  uses than for others.