1. Humus and Composting

2. Decomposition
A respiration process:
Organic matter
+ O2

3. Products of decomposition…
Energy for decomposers
CO2 + H2O
Nutrients, that were in the original organic tissue, for plants
Carbon, nitrogen, etc. for the decomposers
HUMUS !

4. What is HUMUS?
Ultimate decay product of decomposition “Amorphous, colloidal mixture of complex organic substances, not identifiable as tissue”.

5. Colloidal in size: tiny!
< mm in diameter
Nutrients and water attach to surface area of soil particles
Smaller the particle, the greater the surface area per unit volume

6. Humus <0.00001 mm Sand 0.05 – 2.0 mm Silt 0.05 – 0.002
Clay <0.002
Humus < mm
Tremendous ability to hold water and nutrients

7. Functions of humus: A supply of N, P, S for plants Holds water
Provides structure
Glue that allows soil to have spaces
Prevents erosion

8. About structure…

9. Humus sequesters carbon!!!
Carbon : organic compounds
stores energy
Cycled back and forth from atmosphere to biosphere
photosynthesis and respiration

10. sequestration
Take carbon from atmosphere and move it into long-lived soil pools where it is securely stored for very, very long time
SOIL CARBON POOLS:
Fast 1-2 yrs
Slow years
Passive (stable)

11. CARBON OUT CARBON IN SOIL Plant residues Harvesting plants Respiration
Manure
Compost
Erosion

12. Two Main Causes of Increased CO2 Emissions:
1. Fossil Fuel Burning
2. Net Loss of Soil Organic Carbon
Soil Carbon Sequestration:
Potential to offset fossil fuel emissions by 0.4 to 1.2 gigatons of carbon per year, 5-15% of global fossil-fuel emissions

13. How? Restore the humus portion!!!! Organic farming
Non-chemical no-till
Manage trees and forests
Keep green manure
Diversify crops
Compost
Mulch

14. COMPOSTING
Speeding up decomposition by making breeding grounds for decomposers

15. Composting is creating habitat for decomposers to make humus
Making soil
Need to pay attention to amounts of carbon relative to nitrogen in the organic waste you throw into the compost.
This is the C:N ratio

16. Carbon : Nitrogen ratio
C:N ratio
High C:N means not much nitrogen (“BROWN”)
Slow to decompose
Sawdust, newspaper, wood chips, straw, timothy hay; shredded cardboard; unshredded leaves
Low C:N means plenty of nitrogen (“GREEN”)
Fast to decompose
Rotted manure ; household compost, cover crops, weeds, kitchen waste, grass clippings, young alfalfa hay, beer mash from brewery, shredded leaves, ash from fires, hair, orchard litter, spoiled hay, bird cage cleanings

17. Building a Pile:
1. Originally, about twice as much BROWN as GREEN stuff layered together with thin layers of soil or compost between.
3-4 ‘ high

19. 2. Turn / Aerate prevent “smelly” anaerobic decomposers
Provides oxygen for aerobic decomposers
How often?
When cools down (approx. every 2 weeks)

20. 3. Keep adding green
When you turn the compost, the “layer cake” is messed up. That’s fine.
Keep adding green with a little soil/compost and a little straw or something brown every now and then.

21. 4. Pile should be about 1 cubic yard to have critical mass needed for heating.
5. Keep moist but not sopping wet. Decomposers prefer some moisture but too much renders the pile anaerobic.

22. Temperature in the Compost
Initially there is a mesophilic phase (1-2 weeks)
Organisms decomposing the easy waste (sugars)
After approx.1- 2 weeks, the temperature of the pile will heat up to thermophilic phase (140 – 160 °F)
Heat due to respiration
Feeding frenzy by decomposers, now tackling more difficult materials and producing humus.
Decomposers are getting C,N,P,K from compost to build their own bodies; when they have acquired all they need, temps drop.
Heat will kill weed seeds and pathogens.
Lasts 1 – 2 weeks; when cools down, need to turn again to provide oxygen for further respiration

23. Why use compost?
1. improves “texture” (Binds sandy soil; loosens clayey soil)
2. strengthens structure (Fungal mycelia, worms, humus)
3. aerates soil due to good structure
4. erosion control ( Water seeps slowly through composted soil)
5. Holds water (100 lbs humus holds 195 lbs water)
6. Neutralizes toxins:(Forms complexes with substances like heavy metals, making them unavailable for plant uptake)
7. Doles out nutrients slowly (excess nutrients don’t get leached out and end up in water)
8. Compost can stretch the growing season by darkening the soil
9. STOP THE WASTE! Why waste all of that energy that plants carefully collected from the sun and put it in a landfill???

24. What to NOT put in pile:
Any residue suspected of being treated with pesticide
Grease, oil: inhibit decomposition
Meat or animal products (eggshells okay): attracts pests
Cat litter or feces
Difficult to decompose materials: big wood, shells, corn cobs