2019 MG Soil/Fert 1
Soils
Claudia Groth
Master Gardener Program Instructor
2020 Master Gardener TrainingWhat you can grow depends on your soil
The Part Soils Play
Most productive soils
Least productive soils
19.03%
30.76%
38.63%
21.67%
Global US
Mineral
Water
Air
Organic Matter
Soil TextureHow coarse or fine a soil is
The proportion of sand, silt, and clay
The arrangement of sand, silt, and clay
Soil Structure
2019 MG Soil/Fert 2
Relative Sizes of Soil Particles
(University of Nebraska, Lincoln)
Particle Size and Surface Area
volume = 64
surface area = 384
volume = 64
surface area = 96
4 1
Soil Texture
Sandy
Clay‐like
Soil Texture and Water‐holding
¾ ‐ 1 in/ft 1½ ‐ 1¾ in/ft 2 ‐ 2½ in/ft
Impacts of Texture
Nutrient‐holding or cationexchange capacity (CEC) high low
Water‐holding capacity high low
Drainage and permeability slow fast
Spring warming slow fast
Clay‐like Sandy
Determining Soil Texture
•Soil surveys (Web Soil Survey/SoilWeb app)
– Silt loam predominates in Metro area
•Professional soil test
•Ribbon test
– Messy, but interesting
•Home jar test or “shake method”
– Pretty accurate – easy and fun
2019 MG Soil/Fert 3
Soil Survey – Hood River East Soil Survey – Hood River West
Determining Soil Texture
•Soil surveys (Web Soil Survey)
•Professional soil test
– Laboratory analysis ~ $16 (w/o nutrient test)*
•Ribbon test
– Messy, but interesting
•Home jar test or “shake method”
– Pretty accurate – easy and fun
*EM 8677 Laboratories Serving Oregon: Soil, Water, Plant Tissue, and Feed Analysis
Soil Test Results
Ribbon MethodTexture by Feel
sand
silt
clay
Texture via “Soil Shake”
•1/3 to 1/2 soil
•Fill with water
•Shake 5 minutes
•Measure
2019 MG Soil/Fert 4
Soil Texture
Soil Shakeor
Jar Test
Clay
Sand
Silt
Using the
Soil Triangle
Sand: 40%
Silt: 40%
Clay: 20%
40% sand
40% silt
20% clay
Loam
Using the
Soil Triangle
Sand: 40%
Silt: 40%
Clay: 20%
40% sand
40% silt
20% clay
Loam
Using the
Soil Triangle
Sand: 33%
Silt: 33%
Clay: 33%
Clay Loam
33% sand
33% silt
33% clay
Just Add Sand??
particle in. percentSand 2.2 20%Silt 6.6 60%Clay 2.2 20%
11.0
10’ x 10’ = 100 sq ft.
particle in. percentSand 3.2 27%Silt 6.6 55%Clay 2.2 18%
12.0
Add 1 in. sand(830 lbs.)
What About Gypsum?
Calcium Sulfate
Gypsum won’t improve drainage
in Pacific NW clay‐based soils
Gypsum doesn’t change soil pH
2019 MG Soil/Fert 5
We Can’t Change Soil Texture
We Can Change Soil Structure
Improving Soil Structure
Soil Habitat
S. Rose and E.T. ElliottMycorrhizae3
Actinobacteria1
Rhizobia2
1No. 14 from Soil Microbiology and Biochemistry Slide Set. 1976. J.P. Martin, et al., eds. SSSA, Madison, WI 2Stephen Temple, New Mexico State University3Mycorrhizal Applications, Inc., Grants Pass, Oregon
Biology Helps Create Structure Improving Soil Structure
Fine Soil Coarse Soil
Well‐aggregated Soil
2019 MG Soil/Fert 6
Organic Matter Amendments(soil conditioners)
Are there “bad” amendments?
•Bark dust/sawdust/wood chips– Amending vs. Mulching
–Adding nitrogen
• Top soil –Source???
Top Soil?
Reclaimed Portland soil and decomposed plant material from yard excavations. Screened to 3/8˝.
Contains forest wood products and composted bark
Clean and screened topsoil
One or more of the following: (peat, forest products, rice hulls, native soil, food waste, and/or compost) and sphagnum peat moss.
Oregon's Own Topsoil Can You Have Too Much Organic Matter?
•Uneven/unpredictable release of nitrogen
•Some lab testing may be unreliable
•Phosphorus build‐up
Study shows some urban gardens contain too much organic matter
January 24, 2020
Kym Pokorny, OSU Extension
‐Insufficient Data
‐Low
‐Fair
‐Intermediate
‐High
Percent P2O5
Phosphate Found in US Soils
Tilling vs. No‐till
•Advantages
–Fast incorporation
–Weed control
–Faster decomp
–Nutrient mixing
•Advantages
–Microbes
–Winter crops
–Fewer weeds
–Slower decomp
2019 MG Soil/Fert 7
Inorganic Amendments(also soil conditioners)
•Hardened clay or diatomaceous earth
– Turface/Profile
– Amturf Ultra Soil Conditioner
– AXIS
•Gravel
– Quarter‐ten (1/4 ‐10)
•Volcanic pumice
100 sq. ft. estimates
Compaction Destroys Structure Compaction Creates an Interface
Layering impedes water movement
and root growth
Preventing Compaction
Beware foot and equipment traffic
Don’t dig in soggy soil
Cover bare ground
Avoid excessive tilling
Raised Beds
