mulching and soil biology what’s going on? rex a. bastian the davey tree expert company the care...
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Mulching and Soil BiologyWhat’s Going On?
Rex A. BastianThe Davey Tree Expert Company
The Care of Trees2371 South Foster
Wheeling, IL 60090
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Mulching
Overall, proper
mulching is considered
one of the best, long
term tree health
practices» Usually focus on the
physical and chemical
benefits over the
biological benefits
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Soil properties and root development levels resulting from wood chip mulch treatments 1979-1983
Character Mulched Control
Bulk
Density
0.73* 1.14
Moisture 30.8** 18.9
Root
Density
6.16** 3.2
Mycorrhizal
Density
1.95* 0.46
Soil pH 5.8* 6.7
Himelick and Watson, 1990
Watson, Morton Arboretum
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Natural vs. Urban Systems
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soils.usda.gov
Components of Soil Organic Matter
Decomposing organic matter(active fraction) 33% - 50%
Stabilized organic matter
(humus) 33% - 50%
Fresh residue <10%
Living organisms
<5%
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Soil Foodweb Components
Bacteria» Decomposers
– (Low C:N ratio “Green Stuff”)» Detoxifiers» Nutrient storage» Nitrogen fixers» “slime” soil» Disease suppression
Fungi» Decomposers
– (high C:N ratio “Brown Stuff”)» Nutrient storage» Nutrient “pumpers”» Mycorrhizae» Soil binders» Disease suppression
soilfoodweb.com
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Protozoans» Nutrient cycling» Bacterial grazing» Disease suppression
Nematodes» Nutrient cycling» Many types
– Grazing– Some nematode
predators
Soil Foodweb Components
Olympus America, Inc.
soilfoodweb.com
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www.freewebs.com
Arthropods» Shredders» Herbivores, predators» burrowing
Earthworms» Decomposers» Soil “mixers”» Stimulate microbial activity» Provide for improved water
holding capacity and root penetration
» Bury organic matter
Soil Foodweb Components
www.wildaboutbritain.co.uk
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The Soil Food Web
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Consider These Two Systems
Would the Same Types and Quantities of Soil Microorganisms Present be the Same in Both?
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CA Integrated Waste Management Board
Ecological Succession
Affects Soil
Biology, Too
Soil organism mix
changes as the
above ground
system changes
More Fungi
More Arthropods
More Complex
More Acidic
More ammonium vs. nitrate uptake
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Typical Numbers of Soil Organisms in Healthy Ecosystems
Grass Forest
Organisms per gram (teaspoon) of soil
Bacteria 100 mil. -1 bil. 100 mil. -1 bil.
Fungi
F:B Ratio
10s – 100’s of yds
1:3 to 2:1
1-40 miles (conifers)
10:1 to 100:1
Protozoa 1000’s 100,000’s
Nematodes 10’s – 100’s 100’s
Organisms per square foot of soil
Arthropods 500-2000 10,000-25,000
Earthworms 10-50 10-50
USDA, National Resources Conservation Service
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Higher pH
Lower pH
Acidic Tree Root
Secretions
Tree
Root
Rhizosphere
Zone of intense biological and chemical activity
Biological Effects on Tree Rhizosphere Chemistry
Acidic Fungal
Secretions
Selective
NH4 vs. NO3
Uptake
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Root
Biological Effects on Rhizosphere Chemistry
Biological Make-up» Host Plant Exudates» Dominant Vegetation
Type » Physical Soil
Characteristics
Consume Foods Occupy Space Tie-Up/Cycle/Release
Nutrients Release Exudates
Fe-Reduction
G. Neumann, 2005
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Garlic MustardInfluence on Tree Mycorrhizae
Garlic mustard root
extracts suppressed
the growth of native
tree seedlings by
disrupting soil
mycorrhizae
Stinson, et al., 2006
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Soil Biology/Soil Chemistry InteractionNitrate vs. Ammonium Nitrogen
Nitrate (NO3- ) is more common in turf systems
More alkaline environment, nitrification bacteria more
common, nitrate turf fertilizer use
NO3-
HCO3-
HCO3- + H2O = H2CO3 + OH-
pH Increases
Root Rhizosphere
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• Ammonium (NH4+) is more common in woody
(mulched) systems
• More acidic environment, fewer nitrification bacteria
NH4+
H+Rhizosphere
pH Drops
Soil Biology/Soil Chemistry Interaction
Root Rhizosphere
Rhizosphere acidification
G. Neumann, 2005
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Natural and Cultural Differences Impact Soil Biology
Mulching can Help Reestablish a Woodland Biology
Woodland Systems» More “brown” stuff
– Higher C:N ratios
» Lower N levels [NH4+ ]
» Fungal food sources
» Acidic Secretions (tree roots
and fungal dominance)
– Lower rhizosphere pH
Leads to higher
Fungal:Bacterial Ratio» 5:1 and higher
Turfgrass Systems» More “green” stuff
– Lower C:N ratios
» Higher N levels [NO3- ]
» Bacterial food sources» Higher chemical/fertilizer use» Alkaline Secretions (grass
roots and bacterial dominance)– Higher rhizosphere pH
Leads to lower Fungal:Bacterial Ratio» 1:1 or less
– Often 1:2 or 1:3
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