Mulching the Landscape:

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Mulching the Landscape Beyond Aesthetics
Dan Herms Department of Entomology The Ohio
State University Ohio Agricultural Research and
Development Center Wooster, Ohio herms.2_at_osu.edu
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Objective
Establish general principles for predicting
effects of diverse sources of organic matter on
soil fertility and plant health.
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Terminology
Compost organic matter that has been subjected
to decomposition process Mulch applied to soil
surface Soil amendment incorporated into soil
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Soil quality the central role of organic matter
(SOM)

• Key determinant of soil structure
• oxygen, drainage, water / nutrient holding
• capacity.
• Source of essential nutrients for plants.
• Foundation of soil food web.
• Continuously depleted and replenished.

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The living soil
In an average cup of healthy soil Bacteria
200 billion Fungi 60 miles of
hyphae Protozoa 20 million Nematodes
100,000 Arthropods 50,000
From S. Frey, Ohio State University
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Hypothesis trees are adapted to the nutrient
fluxes and signals associated with gradual
decomposition of leaf litter
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Disrupted nutrient cycles in constructed
landscapes
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Interrupted nutrient cycles in ornamental
landscapes
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Nutrient Cycling in Ornamental Landscapes
Organic Matter (Mulch)
Organic N
Decomposition
Mineralization
Microbial Turnover
Dissolved Organic N Mineral N (NH4,, NO3)
Microbial Uptake
Immobilization
Plant Uptake
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Most labile N is tied up by microbes
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• Key principles of nutrient cycling theory
• Microbes are C limited.
• Plants are N limited.
• Microbes out-compete plants for N.
• High CN organic matter greater proportion
• of N immobilized by microbes.
• Low CN organic matter greater proportion
• of N released (mineralized) by microbes.

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How does mulch affect nutrient availability?
1. Is the carbon available? Stability of OM
2. Who gets the nitrogen? CN ratio of OM
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Availability of C for microbes rate of
decomposition Slow Inorganic
mulch (stone, shredded tires)
Softwood bark (mature trees)
Softwood bark (immature trees)
Hardwood bark Ground wood
Wood chips Composted yard
waste Sawdust
Composted Manure Fast
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• N available for plants determined by net balance
  between
• N mineralization by microbes.
• N immobilization by microbes.

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• CN Ratio of OM and Nutrient Availability
• CN ratio gt 301
• Microbes N-limited, scavenge N from soil
• Available N tied up by microbes
• N available for plants decreases
• CN ratio lt 301
• N exceeds microbial requirements
• N release rates increase
• N available for plants increases

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Material CN
RatioRecycled pallets 1251Ground pine
bark 1051Fresh wood chips 951Hardwood
bark 701Fresh wood chips w/ foliage
651Pine straw 641Freshly senesced
leaves 551Composted wood chips
401Composted yard waste 171Composted
manure 121
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• Case study effects of mulch on soil microbes,
  nutrient cycling, and plant health.
• Recycled organic wastes
• Composted yard waste (CN 171)
• Ground pallets (CN 1251)

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Recyled organic waste as mulch
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Composted mulch
Ground wood pallets
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Three Mulch Treatments 1. Composted yard
waste (CN ratio 171) 2. Ground wood pallets
(CN ratio 1251) 3. Bare soil control Each
with and without fertilization (18-5-4 NPK, 3 lbs
N / 1000 ft2 / yr)
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Experimental Mulches
Composted Yard Trimmings CN ratio 171
Ground Wood Pallets CN ratio 1251
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Experimental approach
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Mulch effects on tree growth
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Nitrate as signaling molecule gene expression
and regulation of carbon allocation in
Arabidopsis High soil nitrate Up regulation of
genes for shoot growth, protein synthesis. Down
regulation of genes for secondary metabolism,
root growth. Low soil nitrate Down regulation
of genes for shoot growth, protein synthesis. Up
regulation of genes for secondary metabolism,
root growth. Scheible, et al. 2004. Plant
Physiology 1362483-2499. Zhang and Forde. 2000.
Journal of Experimental Botany 51 51-59.
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Hypothesis trees are adapted to the nutrient
fluxes and signals associated with the gradual
decomposition of leaf litter
Can trees be tricked into maladaptive allocation
patterns?
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PJM Rhododendron
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• How can mulch applied to the soil surface affect
  nutrient availability below?
• Soil homogenization by abiotic and
• biotic forces (rapid increase in SOM in
• mulched plots)
• Subterranean foraging by hyphae of
• fungi that have colonized the mulch.
• 3. It just does.

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Mulch and IPM Effects on Weeds and Soil
Borne-Pathogens
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• Conclusions
• 1. Both mulches increased
• soil organic matter
• microbial biomass and activity
• 2. Yard waste increased, ground wood decreased
• nutrient availability
• plant growth
• 3. Yard waste suppressed root rot disease.

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• Consistent with hypotheses
• 1. Soil microbes are carbon-limited.
• 2. Plants are nitrogen limited.
• Microbes out-compete plants for nitrogen.
• 4. Competition for N mediated by CN ratio of
  OM.

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• Prescription mulching
• Low CN mulch (e.g. composted yard trimmings)
• degraded soils
• increased plant growth
• new landscapes
• High CN mulch (e.g. recycled pallets)
• slow to moderate growth
• established plantings

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Soil management regimes for highly disturbed,
inverted sub-soil profiles.
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Design and Construction of Sub-Soil Plots
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• Mycorrhizae research
• Colonization in subsoil
• 2. Effects of soil treatments
• 3. Interactions between native and inoculated
• mycorrhizae

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Mulch volcanoes are not good for trees!
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• Mulch Volcanoes
• Decrease soil oxygen.
• Inhibit gas exchange (bark can't breathe).
• Promote bark decay.
• Favor infection by trunk pathogens.

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If you must make volcanoes, at least keep the
mulch in the bags
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Acknowledgements Dr. John
Lloyd Department of Plant, Soil, and
Entomological Sciences University of Idaho Drs.
Harry Hoitink and Pierluigi (Enrico)
Bonello Department of Plant Pathology OARDC / The
Ohio State University Dr. Ben Stinner AgroEcosyst
em Management Program OARDC / The Ohio State
University
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Funding Sources USDA National Research
Initiative USDA Forest Service National Urban
and Community Forestry Council International
Society of Arboriculture
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OSU Extension Bulletin 894 Using Mulches in
Managed Landscapes
http//ohioline.osu.edu/b894/pdf/b894.pdf