Mulching the Landscape:

Transcription

1 Mulching the Landscape: Effects on Soil Ecology and Plant Health Dan Herms Department of Entomology The Ohio State University Ohio Agricultural Research and Development Center Wooster, Ohio

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3 Objective: Establish general principles for predicting effects of diverse sources of organic matter on soil fertility and plant health.

4 Terminology: Compost organic matter that has been subjected to decomposition process Mulch applied to soil surface Soil amendment incorporated into soil

5 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 must be replenished.

6 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

7 Trees are adapted to nutrients fluxes associated with gradual decomposition of leaf litter

8 Disrupted nutrient cycles in constructed landscapes

9 Interrupted nutrient cycles in ornamental landscapes

10 Nutrient Cycling in Ornamental Landscapes Organic Matter (Mulch) Decomposition Organic N Microbial Uptake Microbial Turnover Immobilization Mineralization Dissolved Organic N Mineral N (NH 4,, NO 3 ) Plant Uptake

11 Most labile N is tied up by microbes

12 Key principles of nutrient cycling theory: Microbes are C limited. Plants are N limited. Microbes out-compete plants for N. High C:N organic matter: greater proportion of N immobilized by microbes. Low C:N organic matter: greater proportion of N released (mineralized) by microbes.

13 How does mulch affect nutrient availability? : 1. Is the carbon available? Stability of OM 2. Who gets the nitrogen? C:N ratio of OM

14 Availability of C for microbes: rate of decomposition Slow Fast 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

15 N available for plants determined by net balance between: N mineralization by microbes. N immobilization by microbes.

16 C:N Ratio of OM and Nutrient Availability: C:N ratio > 30:1 Microbes N-limited, scavenge N from soil Available N tied up by microbes N available for plants decreases C:N ratio < 30:1 N exceeds microbial requirements N release rates increase N available for plants increases

17 Material C:N Ratio Recycled pallets 125:1 Ground pine bark 105:1 Fresh wood chips 95:1 Hardwood bark 70:1 Fresh wood chips w/ foliage 65:1 Pine straw 64:1 Freshly senesced leaves 55:1 Composted wood chips 40:1 Composted yard waste 17:1 Composted manure 12:1

18 Case study: effects of mulch on soil microbes, nutrient cycling, and plant health. Recycled organic wastes: Composted yard waste (C:N = 17:1) Ground pallets (C:N = 125:1)

19 Recyled organic waste as mulch

20 Composted mulch Ground wood pallets

21 Three Mulch Treatments: 1. Composted yard waste (C:N ratio = 17:1) 2. Ground wood pallets (C:N ratio = 125:1) 3. Bare soil control Each with and without fertilization ( NPK, 3 lbs N / 1000 ft 2 / yr)

22 Experimental Mulches Ground Wood Pallets C:N ratio = 125:1 Composted Yard Trimmings C:N ratio = 17:1

23 Experimental approach:

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28 Mulch effects on tree growth

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32 PJM Rhododendron

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35 How can mulch applied to the soil surface affect nutrient availability below? 1. Soil homogenization by abiotic and biotic forces (rapid increase in SOM in mulched plots) 2. Subterranean foraging by hyphae of fungi that have colonized the mulch. 3. It just does.

36 Mulch and IPM: Effects on Weeds and Soil Borne-Pathogens

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39 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.

40 Consistent with hypotheses: 1. Soil microbes are carbon-limited. 2. Plants are nitrogen limited. 3. Microbes out-compete plants for nitrogen. 4. Competition for N mediated by C:N ratio of OM.

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

42 Mulch volcanoes are not good for trees!

43 Mulch Volcanoes: Decrease soil oxygen. Inhibit gas exchange (bark can't breathe). Promote bark decay. Favor infection by trunk pathogens.

44 If you must make volcanoes, at least keep the mulch in the bags

45 OSU Extension Bulletin 894: Using Mulches in Managed Landscapes