Mulching and Soil Biology What’s Going On? Rex A. Bastian The Davey Tree Expert Company The Care of Trees 2371 South Foster Wheeling, IL 60090

Mulching l 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

Soil properties and root development levels resulting from wood chip mulch treatments CharacterMulchedControl Bulk Density 0.73*1.14 Moisture30.8**18.9 Root Density 6.16**3.2 Mycorrhizal Density 1.95*0.46 Soil pH5.8*6.7 Himelick and Watson, 1990 Watson, Morton Arboretum

Natural vs. Urban Systems

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%

Soil Foodweb Components l Bacteria »Decomposers – (Low C:N ratio “Green Stuff”) »Detoxifiers »Nutrient storage »Nitrogen fixers »“slime” soil »Disease suppression l Fungi »Decomposers – (high C:N ratio “Brown Stuff”) »Nutrient storage »Nutrient “pumpers” »Mycorrhizae »Soil binders »Disease suppression soilfoodweb.com

l Protozoans »Nutrient cycling »Bacterial grazing »Disease suppression l Nematodes »Nutrient cycling »Many types –Grazing –Some nematode predators Soil Foodweb Components Olympus America, Inc. soilfoodweb.com

l Arthropods »Shredders »Herbivores, predators »burrowing l Earthworms »Decomposers »Soil “mixers” »Stimulate microbial activity »Provide for improved water holding capacity and root penetration »Bury organic matter Soil Foodweb Components

The Soil Food Web

Consider These Two Systems Would the Same Types and Quantities of Soil Microorganisms Present be the Same in Both?

CA Integrated Waste Management Board Ecological Succession l Affects Soil Biology, Too l Soil organism mix changes as the above ground system changes More Fungi More Arthropods More Complex More Acidic More ammonium vs. nitrate uptake

Typical Numbers of Soil Organisms in Healthy Ecosystems GrassForest Organisms per gram (teaspoon) of soil Bacteria100 mil. -1 bil. Fungi F:B Ratio 10s – 100’s of yds 1:3 to 2: miles (conifers) 10:1 to 100:1 Protozoa1000’s100,000’s Nematodes10’s – 100’s100’s Organisms per square foot of soil Arthropods ,000-25,000 Earthworms10-50 USDA, National Resources Conservation Service

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 NH 4 vs. NO 3 Uptake

Root Biological Effects on Rhizosphere Chemistry l Biological Make-up »Host Plant Exudates »Dominant Vegetation Type »Physical Soil Characteristics l Consume Foods l Occupy Space l Tie-Up/Cycle/Release Nutrients l Release Exudates Fe-Reduction G. Neumann, 2005

Garlic Mustard Influence on Tree Mycorrhizae l Garlic mustard root extracts suppressed the growth of native tree seedlings by disrupting soil mycorrhizae Stinson, et al., 2006

Soil Biology/Soil Chemistry Interaction Nitrate vs. Ammonium Nitrogen l Nitrate (NO 3 - ) is more common in turf systems l More alkaline environment, nitrification bacteria more common, nitrate turf fertilizer use NO 3 - HCO 3 - HCO H 2 O = H 2 CO 3 + OH - pH Increases RootRhizosphere

Ammonium (NH 4 + ) is more common in woody (mulched) systems More acidic environment, fewer nitrification bacteria NH 4 + H+H+ Rhizosphere pH Drops Soil Biology/Soil Chemistry Interaction RootRhizosphere acidification G. Neumann, 2005

Natural and Cultural Differences Impact Soil Biology Mulching can Help Reestablish a Woodland Biology l Woodland Systems »More “brown” stuff –Higher C:N ratios »Lower N levels [NH 4 + ] »Fungal food sources »Acidic Secretions (tree roots and fungal dominance) –Lower rhizosphere pH l Leads to higher Fungal:Bacterial Ratio »5:1 and higher l Turfgrass Systems »More “green” stuff –Lower C:N ratios »Higher N levels [NO 3 - ] »Bacterial food sources »Higher chemical/fertilizer use »Alkaline Secretions (grass roots and bacterial dominance) –Higher rhizosphere pH l Leads to lower Fungal:Bacterial Ratio »1:1 or less –Often 1:2 or 1:3