soils, soil organisms, soil amendments, and their relation to plant health
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DESCRIPTIONSoils, 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. Outline. Introduction to soils Local soil types Soil organisms Choosing organic amendments Compost quality - PowerPoint PPT Presentation
Soils, soil organisms, soil amendments, and their relation to plant health
Thanks to Craig CoggerExtension Soil Scientist WSU-Puyalluphttp://www.puyallup.wsu.edu/soilmgmt
•Introduction to soils
•Local soil types
•Choosing organic amendments
•How much organic amendment to use
Mineral MatterPore Space
Residue decompositionNutrient cyclingAggregation and porosityEnhance plant growthBreak down contaminants
•Water MovementHow quickly water moves through soil
Water Holding CapacityHow much water a soil can hold available for plant growth
Soil pores and water movement
•Macropores: Infiltration and drainage
•Capillary pores: Available water
•Micropores: Unavailable water
Soil properties that affect porosity
•Compaction and disturbance
Soil Particle Sizes
Sand .05-2 mm
Silt .002-.05 mm
Clay <.002 mm
Coarse Fragments >2 mm
Hand texture technique
Soil StructureAggregation of sand, silt, and clay particles
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
Urban and suburban soils
•Compaction: Loss of structure and macropores
•Cuts: Loss of topsoil, less structure, shallow depth
•Fills: Unstructured “dirt”
Disturbed soil:Cut and
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
•Increased stress on plants
•Increased risk of runoff and erosion
•Incorporate organic matter
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
Bacteria, fungi, actinomycetes, protozoa, nematodes, arthropods, earthworms
Pictures courtesy M. Fauci and D. Bezdicek
Residue decompositionNutrient cyclingAggregation and porosityContaminant breakdownNitrogen fixationEnhance root functionPathogensPredators
Roles of soil organisms
Soil food web and nutrient cycling
Organic matter stimulates soil
•Formation of soil structure
•Plant disease suppression/stimulation
Organic materials:Fertilizers vs. Soil amendments
•Fertilizer 1. High nutrient content and availability. 2. Main benefit is nutrients. 3. Relatively small amounts applied.
•Soil amendment 1. Low nutrient content and availability. 2. Main benefit is organic matter. 3. Large amounts applied.
•Mulch1. Negative available nutrients2. Applied to surface to control weeds and conserve
•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
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
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.
•Packaged organic fertilizers
•Fresh grass clippings
•Fresh, undiluted rabbit manure
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.
•Compost (yard debris, most manures, biosolids)
•Mixed fresh yard debris
•Cover crop residues
•Dairy manure solids
Woody stuff, C:N > 30:1
•Need to add N along with organic amendment
•Use as mulch or bulking agent for compost
•Horse manure rich in bedding
Why use compost as a source of
•Locally produced, recycled material
•Home, farm, or commercial
•Can usually be applied at high rates to increase organic matter benefits
•Hot composting kills pathogens
What is composting?
•Biological transformation of raw organic materials into biologically stable, humus-rich substances suitable for growing plants
What can compost be made of?
•Feedstocks includeyard debriswood wastebiosolidsdairy solids feedlot manurepoultry manure fair wasteand more
Compost Quality•Quality depends on specific use (landscape incorporation vs. mulch vs. potting mix component)
Compost Quality: Important things to
Compost moisture affects handling
•Dry compost (< 35% moisture) is dusty
•Wet compost (> 60% moisture) is clumpy
Compost particle size•Particle size < 1 inch is good for incorporation in landscape beds
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)
Keys to compost nutrient availability
•Carbon to Nitrogen (C:N) ratio
•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
•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.
•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.
Other organic amendments
•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)
Amending soil with organic materials
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.
•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.
•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.
•Cover ground, reduce erosion
•Reduce growth of weeds
•Buffer surface soil temperature
•Decompose to become part of soil organic matter
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
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