1. Soils, soil organisms, soil amendments, and their relation to plant health
Thanks to Craig Cogger
Extension Soil Scientist WSU-Puyallup

2. Outline Introduction to soils Local soil types Soil organisms
Choosing organic amendments
Compost quality
How much organic amendment to use

3. Soil Components
Mineral Matter
Pore Space
Organic
Matter

4. The soil ecosystem Residue decomposition Nutrient cycling
Aggregation and porosity
Enhance plant growth
Break down contaminants

5. Water Movement How quickly water moves through soil Water Holding Capacity How much water a soil can hold available for plant growth

6. Soil pores and water movement
Macropores: Infiltration and drainage
Capillary pores: Available water
Micropores: Unavailable water

7. Soil properties that affect porosity
Soil texture
Soil structure
Compaction and disturbance
Organic matter

8. Soil Particle Sizes Sand .05-2 mm Silt .002-.05 mm Clay <.002 mm
Coarse Fragments >2 mm

10. Hand texture technique

11. Soil Structure Aggregation of sand, silt, and clay particles
Structure affects:
Macroporosity
Infiltration
Aeration

12. Formation of soil structure
Growth of roots and movement of organisms create pores and aggregates
Soil organisms break down organic residues, producing glues that stabilize aggregates
Fungi provide structural support to aggregates
Physical, chemical processes also involved

13. Urban and suburban soils
Compaction: Loss of structure and macropores
Cuts: Loss of topsoil, less structure, shallow depth
Fills: Unstructured “dirt”

14. Disturbed soil:
Cut and
compacted.

15. Effects of development on soils
Increased bulk density
Resistance to root penetration
Loss of structure
Reduced porosity
Reduced infiltration
Reduced rooting depth
Reduced nutrient and water availability

16. Consequences Increased stress on plants
Increased risk of runoff and erosion

17. Prescription
Incorporate organic matter

18. Expected benefits of organic matter
Physical: Improved bulk density, structure, porosity, permeability,
Biological: More activity
Available water: Increase depends on soil and irrigation regime
Runoff: Better structure and porosity reduces runoff and erosion
Nutrients: Significant for some materials

19. Soil Organisms
Bacteria, fungi, actinomycetes, protozoa, nematodes, arthropods, earthworms
Pictures courtesy M. Fauci and D. Bezdicek

20. Roles of soil organisms
Residue decomposition
Nutrient cycling
Aggregation and porosity
Contaminant breakdown
Nitrogen fixation
Enhance root function
Pathogens
Predators
Mary Fauci

21. Soil food web and nutrient cycling
Phytophagous
nematodes
Predacious
mites
Roots
Collembolans
Nematode
Feeding mites
Cryptostigmatid
mites
Mycorrhizae
Noncrypto-
Stigmatid mites
Predacious
nematodes
Fungivorous
nematodes
Fungi
Omnivorous
nematodes
Detritus
Flagellates
Amoebae
Bacteria
Bacterivorous
nematodes

22. Organic matter stimulates soil organisms
Formation of soil structure
Nutrient cycling
Plant disease suppression/stimulation

23. Choosing organic amendments

24. Organic materials: Fertilizers vs. Soil amendments vs. mulches
Fertilizer 1. High nutrient content and availability Main benefit is nutrients. 3. Relatively small amounts applied.
Soil amendment 1. Low nutrient content and availability Main benefit is organic matter Large amounts applied.
Mulch
1. Negative available nutrients
2. Applied to surface to control weeds and conserve moisture

25. Carbon:Nitrogen ratio
Ranges from <5:1 to >500:1 in organic materials
Low C:N supplies N to plants
High C:N ties up N by biological immobilization

26. Types of organic amendments
Hot stuff – C:N <10:1
Cool stuff – C:N 15:1 to 25:1
Woody stuff – C:N > 30:1

27. Hot stuff C:N < 10:1 Rapid N availability Use as a fertilizer
Over application leads to excess nutrient levels in soil -- potentially harming crop and water quality.

28. Examples: Poultry manure Packaged organic fertilizers
Fresh grass clippings
Fresh, undiluted rabbit manure
Heat-dried biosolids

29. Cool stuff, C:N 15:1 to 25:1 Slow N availability
Can add large amounts without risk of over-fertilization
Use as a soil amendment
Expect some N immobilization (tie-up) shortly after application.

30. Examples: Compost (yard debris, most manures, biosolids)
Mixed fresh yard debris
Cover crop residues
Dairy manure solids

31. Woody stuff, C:N > 30:1 N immobilization
Need to add N along with organic amendment
Use as mulch or bulking agent for compost

32. Examples:
Straw
Sawdust
Paper waste
Horse manure rich in bedding

33. Compost Quality

34. Why use compost as a source of organic matter?
Locally produced, recycled material
Home, farm, or commercial
Can usually be applied at high rates to increase organic matter benefits
Hot composting kills pathogens

35. What is composting?
Biological transformation of raw organic materials into biologically stable, humus-rich substances suitable for growing plants

36. What can compost be made of?
Feedstocks include
yard debris
wood waste
biosolids
dairy solids
feedlot manure
poultry manure
fair waste
and more

37. Compost Quality
Quality depends on specific use (landscape incorporation vs. mulch vs. potting mix component)

38. Compost Quality: Important things to know
Moisture
Particle size
Organic matter
Nutrient availability
Salts
Biological stability
Contaminants

39. Compost moisture affects handling
Dry compost (< 35% moisture) is dusty
Wet compost (> 60% moisture) is clumpy

40. Compost particle size
Particle size < 1 inch is good for incorporation in landscape beds

41. Compost organic matter
Typically 40 to 60%
If a compost contains large amounts of soil, the organic matter content will be lower (this may be true of backyard and feedlot composts)

42. Keys to compost nutrient availability
Carbon to Nitrogen (C:N) ratio
Biological stability

43. Soluble salts
Less of a problem in humid climates than in arid climates
General recommendation is soil:compost blend < 2.5 to 6 mmho/cm, depending on sensitivity of plants

44. Biological Stability
Unstable compost can harm plants (phytotoxic compounds include organic acids and high levels of ammonia).
Indicators include color, odor, very low or high C:N, stability test kits.

45. Compost contaminants Inerts (plastic etc.) affect aesthetic appeal.
Metals (lead, cadmium etc.) tend to be low in Northwest composts.
Pesticides: Clopyralid was a concern in some composts, but no problems have been reported since 2001.

46. Other organic amendments
Cover crops
Yard debris (leaves, grass clippings)
Uncomposted manures (horse, dairy solids, rabbit, goat, etc.)
Class A biosolids (such as Tagro)
Food waste (coffee grounds, vegetable trimmings)

47. Amending soil with organic materials

48. How much to add?
Physical benefits are most apparent with high rates of amendments.
Materials must have low nutrient availability to avoid potential N leaching when high rates are used.
Most research has been done on agricultural soils.
Maximum rates studied are about 1/3 by volume.

49. Landscape plantings
Most research has focused on amended planting holes.
Little or no benefit of amending holes.
Not much data available for planting beds.
Recommend 1/3 by volume based on results from ag research and field experience.

50. Annual Beds
Establishing raised beds. You can use up to 30 to 50% by volume of suitable material. Expect settling.
Annual amendments. One half to one inch per year to maintain OM.

51. Organic Mulches Cover ground, reduce erosion Reduce growth of weeds
Reduce evaporation
Buffer surface soil temperature
Decompose to become part of soil organic matter

52. Organic Mulches for Landscapes
Coarse, woody material (bark, wood chips) are good for weed control in landscapes
Apply 3” deep, keep away from trunks
Compost mulches may not control weeds well after the first few months
Woody mulches may slightly reduce N availability to plants in first year after application

53. Which mulch where? Landscapes: Woody mulches
Annual gardens: Mulch in winter with compost or straw, or grow cover crops (living mulch)
Turf: Do not mulch