List four benefits of aerobic, high temperature, composting
1) Stabilizes volatile nitrogen. Composted organic matter cpntains nitrogen in a more stable form that is more usuable by plants.
2) Kills most pathogen and weed seeds (if piles are above 131 degrees for 15 days)
3) introduces a wider population of microbes than found in the raw ingrediants
4) Reduces volume of waste by 50%
5) Allows for use of raw materials that shouldn't be directly put in soil (eg sawdust, manure)
6) Degrades contaminates since most since most pesticides are petroleum (carbon) based and thus digestible. Organic materials also has a high capacity to bind heavy metals
7) Guarantees that the most of the end product be humus and slowly decomposing material that will become humus in the soil
8) Recycles organic matter on the farm and reduces off-farm inputs
List four improvements to soil quality that might result from the regukar incorportaion of compost into the soil
1) Improves soil structure and soil aggregate stability resulting in better drainage, aeration/gas exchange, erosion resistance, workability (tilth). Microbes secrete glue-like compounds that help bind soil particles together.
2) Increases moisture retention (100 lbs. of humus can 195 lbs. of water)
3) Slow release of nutrients and increased availability of others. Cation Exchange Capacity (CEC) is increased thus increasing availability of Ca, Mg, and K. (Also humic acids help dissolve minerals in the soil, making more minerals available to plants.)
4) Increases the population and diversity of microbes in soil that continually make nutrients available to plants. Provides food for microbes.
5) Helps buffer soil pH (compost pH is optimal 6.5-8)
7) Plays key role in soil fertility management in organic systems. Along with soil organic matter and cover crops, compost is a major source of plant available N, P, and K.
Name the key decomposer organism and describe their role at the various composting stages/temperatures.
Aerobic bacteria are the primary decomposers in the first stages of decompositio, feeding first on the most readily-available food sources like plant sugars. Their role is to do most of the primary consumption of simple carbon compounds, resulting in the liberation of heat and the warming of the compost pile and creating the environmental conditions of the subsequent colonization of microorganisms
Fungi decomposes complex carbon compounds like chitin and cellulose
Actinomycetes decompose complex carbon, like chitin and cellulose
Earthworms and other later mmigrants such as nematodes , mold mites, springtails, wolf spiders, centipedes, sow bugs, earthworms, ground beetles continue to break down organic matter after the pile has cooled.
What temperature rance is considered best for composting and why? What is too hot?
1) Between 131-150F for a minimum of 15-21 days. This should kill potential pathogenic organisms and weed seeds and prevent the volatilization of nitrogen containing compounds (eg ammonia) at higher temperatures.
2) Maximum temperatures of the compost pile should not exceed 150 F
List the key conditions necessary for aerobic, high temperature composting
1) Proper carbon to nitrogen ratio of materials: 25:1-40:1
2) Moisture: 50%-60% by weight or "moist as a wrung-out sponge"
3) Aeration: Periodic re-aeration through turning
4) Surface area of compost materials: samll particle size will result in more rapid decomposition
5) Volume of compost pile: A minimum of 5x5x5 is recommended
6) Turning and trouble-shooting: Compost piles should be turned when temperature exceeds 150F and when the temperature of the pile has began to decline. National organic standards require 5 turnings within a 15-day period with a sustained temperature of 131-170F
Why consider the carbon-to-nitrogen ratio of the various compost materials? What is considered the ideal C;N range for composting and why?
C:N ratio affects the rate of decomposition. A low C:N ratio (below 25:1) may result in too rapid decomposition and the loss of nitrogen in the form of ammonia. A C:N ratio that is too high may result in a too long a decomposition process and a low quality end product
Ideal C:N ratio range is 25:1-40:1
What factors can influence the C:N ratio of a material?
C:N ratio of a material can change due to many factors: plant growth, storage, how fertilized, and what an animal was fed
What happens when the pile is too wet?
It may not heat up, turn anaerobic, forming compounds that may stink and be detrimental to plant growth if not aerated prior to application
What happens if the compost pile is too dry?
May not heat up or sustain heat long enough to degrade the organic materals into a finished and useable product. Will often require reassembling the materials and moistening.
Why is aeration important?
To assure adequate amounts of oxygen for aerobic decomposition
What are some advantages to turning a pile?
The greater number of turnings, the faster the material will break down
How often should the compost pile be turned?
National organic standards require 5 turnings in a 15-day period with a sustained temperature of 131-170F
When should a compost pile be turned?
When temperatures exceed 150F or when the temperature of the pile has peaked, plateaued, and begun to decline.
Describe 5 qualitative indicators of compost maturity
1) Parent material should be largely indistinguishable
2) texture should be crumbly
3) Very small particle size
4) Temperature cooled down to ambient temperature
5) signs of macro life (redworms, sowbugs, springtails)
6) Dark brown to blackish-brown in color
7) Earthy smell
8) Feels greasy
What are some additional ways of assessing compost maturity and stability?
Measurements of of carbon dioxide and ammonium levels. This is commonly done in large-scale and commercial composting operations