Transcript It All Comes Down to

Land, then, is not merely soil; it is a foundation of energy flowing through a
circuit of soils, plants and animals”. Aldo Leopold
“ Soil is the hidden, secret friend, which is
the root domain of lively darkness and
silence”
Francis Hole
Soil by parts:
5% organic, 50% space, 45% mineral

Living, dead, decomposing, decomposed
%
10%
5%
dead & decomposed
plant roots
living
85%
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What is special about Organic compounds?
They have ENERGY
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Food chain passes energy along through
photosynthesis and respiration
Photosynthesis:
CO2 + H2O + solar energy
C6H12O6 + O2
organic !
Respiration:
C6H12O6 + O2
ENERGY + CO2 + H2O
Energy is passed from one
trophic level to the next.

What is an organic compound?
 Bank of energy
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More living biomass below ground than
above!
▪ Beneath 1 acre: equivalent to 12 horses
▪ 1 cubic meter of soil:
 50,000 earthworms
 50,000 insects and mites
 12 million roundworms
▪ 1 pea-size bit of soil:
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30,000 protozoa
50,000 algae
400,000 fungi
Billions of bacteria
fungi
earthworms
Beetles
Springtails
bacteria
mites
actinomycetes:
geosmin, antibiotics
nematodes
pseudoscorpion
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Arthropods
 Invertebrates with
external skeleton
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Spring or hop
Detrivores
100,000 / m3 topsoil
Arthropods; order Coleoptera
400,000 species (40% of all
known insect species)
Some omnivores, some
eat plants, fungi, some
are carnivores
Larvae (grubs)
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Arachnid
 Joint-legged
invertebrate
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Carnivorous: eat
larvae, ants, mites, flies
Annelids
Some 2700 different
types
 3 categories:
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 Epigeic (leaf
litter/compost dwelling )
 Endogeic (topsoil or
subsoil dwelling )
 Anecic (deep burrow
drillers)
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Giant
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Benefits to soil
 Move air in and out of
soil
 Castings are rich in
available nutrients
▪ Produce 10 lbs / yr
Roundworms
Occupy many positions
in soil food web
 > 28,000 species
 Most microscopic
 Can be predatory or
parasitic
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arachnids
Extracted from one ft2 of top two inches
of forest litter and soil
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Abundant; most important decomposers
Adaptable
Specialized:
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Non-photosynthetic
Photosynthetic
Oxidize ammonium, nitrite, iron, manganese
Oxidize sulfur
Nitrogen-fixing
Aerobic, anaerobic
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1 ton / acre
Bacteria and fungal hyphae

Break down OM, esp important where
bacteria are less active

branched hyphae form mycelium: bears
spores

attack any organic residue
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Mycorrhizae: s

Symbiotic ; infecting plant roots, formed
by some fungi
 normal feature of root systems, esp. trees
 increase nutrient availability in return for
energy supply
 plants native to an area have well-developed
relationship with mycorrhizal fungi

Higher fungi have basidium : club-shaped
structure , bearing fruiting body
 toadstools, mushrooms, puffballs, bracket fungi
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Filamentous
morphology varies
adaptable to drought
neutral pH
usually aerobic heterotrophs
break down wide range of organic
compounds
A respiration process:
Organic matter
+ O2
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Energy for decomposers

CO2 + H2O
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Nutrients, that were in the original organic
tissue, for plants

Carbon, nitrogen, etc. for the decomposers
 HUMUS !
Ultimate decay product
of decomposition
“Amorphous, colloidal
mixture of complex
organic substances,
not identifiable as
tissue”.

< 0.00001 mm in diameter
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Nutrients and water attach to surface area of
soil particles
 Smaller the particle, the greater the surface area
per unit volume
 Sand 0.05 – 2.0 mm
 Silt 0.05 – 0.002
 Clay <0.002

Humus <0.00001 mm
▪ Tremendous ability to hold water and nutrients

A supply of N, P, S for plants

Holds water

Provides structure
 Glue that allows soil to have spaces

Prevents erosion

Carbon : organic compounds
 stores energy
 Cycled back and forth from
atmosphere to biosphere
▪ photosynthesis and respiration
▪
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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 15-100 years
Passive (stable) 500-5000
CARBON OUT
CARBON IN
Manure
SOIL
Respiration
1. Fossil Fuel Burning
2. Net Loss of Soil Organic Carbon
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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
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Restore the humus portion!!!!
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Organic farming
Non-chemical no-till
Manage trees and forests
Keep green manure
Diversify crops
Compost
Mulch
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Speeding up decomposition by making
breeding grounds for decomposers
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Making soil
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Need to pay attention to amounts of carbon
relative to nitrogen in the organic waste you
throw into the compost.
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This is the C:N ratio
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Carbon usually makes up 45 – 55% of dry
weight of tissue
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Nitrogen can vary from 0.5% - 6.0%
For a residue with:
50% carbon and 0.5% N, C:N ratio would be ?
100:1 (wide/high C:N)
50% carbon and 3.0% N, C:N ratio would be ?
16:1 (narrow/low C:N)
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C:N ratio
 High C:N means not much nitrogen (“BROWN”)
▪ Slow to decompose
▪ Sawdust 600:1 ; straw 80:1 ; newspaper 120:1
 Low C:N means plenty of nitrogen (“GREEN”)
▪ Fast to decompose
▪ Rotted manure 20:1 ; household compost 15:1
 Break-point between high and low = 25:1
 WHY?
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Soil microbes’ cells need 8C: 1N
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Only 1/3 of C from compost is taken into the
cells
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Therefore they need compost with 24 : 1
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Intense competition for N
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Microbes will build their bodies first, then
give up N for plants; N deficiency
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Plenty of N to be released for plants
1 compost
4”green”
1 compost
8 “brown”