SOIL ALIVE!
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
5% Organic
Living, dead, decomposing, decomposed
Organic portion composed of:
%
dead & decomposedplant rootsliving
85%
5%10%
“organic”
What is special about Organic compounds? They have ENERGY
Food chain passes energy along through photosynthesis and respiration
Green plants can directly use sun
Photosynthesis:
CO2 + H2O + solar energy C6H12O6 + O2
organic !
Rest of us are only indirectly solar-powered
Respiration:
C6H12O6 + O2 ENERGY + CO2 + H2O
Food Chain Concept
Energy is passed from one trophic level to the next.
What is an organic compound?
Bank of energy
Organic materials in soil: 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:▪ 30,000 protozoa▪ 50,000 algae▪ 400,000 fungi▪ Billions of bacteria
SpringtailsBeetles
pseudoscorpion
earthworms
nematodes
mites
actinomycetes:geosmin, antibiotics
bacteria
fungi
Springtails
Arthropods Invertebrates with
external skeleton Spring or hop Detrivores 100,000 / m3
topsoil
Beetles
Arthropods; order Coleoptera
400,000 species (40% of all known insect species)
Some omnivores, some eat plants, fungi, some are carnivores
Larvae (grubs)
pseudoscorpons
Arachnid Joint-legged
invertebrate Carnivorous: eat
larvae, ants, mites, flies
earthworms
Annelids Some 2700
different types 3 categories:
Epigeic (leaf litter/compost dwelling )
Endogeic (topsoil or subsoil dwelling )
Anecic (deep burrow drillers)
Giant
Benefits to soil Move air in and out
of soil Castings are rich in
available nutrients▪ Produce 10 lbs / yr
Nematodes
Roundworms Occupy many
positions in soil food web
> 28,000 species Most microscopic Can be predatory
or parasitic
Mites
arachnids
Extracted from one ft2 of top two inches of forest litter and soil
Bacteria
Abundant; most important decomposers Adaptable Specialized:
Non-photosynthetic Photosynthetic Oxidize ammonium, nitrite, iron, manganese Oxidize sulfur Nitrogen-fixing Aerobic, anaerobic
bacteria
1 ton / acre
Bacteria and fungal hyphae
Fungi
Break down OM, esp important where bacteria are less active
branched hyphae form mycelium: bears spores
attack any organic residue
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
Actinomycetes
Filamentous morphology varies adaptable to drought neutral pH usually aerobic heterotrophs break down wide range of organic
compounds
Decomposition
A respiration process:
Organic matter + O2
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 !
What is HUMUS?
Ultimate decay product of decomposition
“Amorphous, colloidal mixture of complex organic substances, not identifiable as tissue”.
Colloidal in size: tiny!
< 0.00001 mm in diameter
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
Functions of humus:
A supply of N, P, S for plants
Holds water
Provides structure Glue that allows soil to have spaces
Prevents erosion
About structure…
Humus sequesters carbon!!!
Carbon : organic compounds stores energy
Cycled back and forth from atmosphere to biosphere▪ photosynthesis and
respiration▪
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 yrsSlow 15-100 yearsPassive (stable) 500-5000
SOIL
CARBON IN CARBON OUTPlant residues
Manure
Compost
Harvesting
plants
Respiration
Erosion
Two Main Causes of Increased CO2 Emissions:
1. Fossil Fuel Burning2. 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
How?
Restore the humus portion!!!!
Organic farming Non-chemical no-till Manage trees and forests Keep green manure Diversify crops Compost Mulch
COMPOSTING
Speeding up decomposition by making breeding grounds for decomposers
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
Carbon usually makes up 45 – 55% of dry weight of tissue
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)
Carbon : Nitrogen ratio 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?
…because microbes have needs too!
Soil microbes’ cells need 8C: 1N
Only 1/3 of C from compost is taken into the cells
Therefore they need compost with 24 : 1
If C:N is > 24:1
Intense competition for N
Microbes will build their bodies first, then give up N for plants; N deficiency
If C:N < 24:1
Plenty of N to be released for plants
1 compost4”green”
1 compost
8 “brown”
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