Soils, soil organisms, soil amendments, and their relation to plant health

1. Soils, soil organisms, soil amendments, and their relation to plant health Thanks to Craig Cogger Extension Soil Scientist WSU-Puyallup http://www.puyallup.wsu.edu/soilmgmt

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

3. Soil Components MineralMatter Pore Space Organic Matter

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

5. Water MovementHow quickly water moves through soilWater Holding CapacityHow 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 Bacterivorous nematodes Bacteria

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. 2. Main benefit is nutrients. 3. Relatively small amounts applied. • Soil amendment1.Low nutrient content and availability. 2. Main benefit is organic matter. 3. 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 stuffC: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.