soil architecture – texture and...
TRANSCRIPT
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Soil Architecture – Texture and Structure
Ecological Agriculture Program 1-12-06 TESC
Steve Scheuerell
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(Weaver, 1926)
Plant growth is directly limited by multiple soil physical properties. These properties further
Interact with chemical and soil biotic factors.
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Soil Physical Properties
• Soil Color• Soil Texture• Soil Structure
• Not covering heat transfer• Hydrology will be covered later• Soil as an engineering medium – opposite
goals than for growing plants in the soil
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Percent by Volume
Soil physical properties
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NRCS Soil Biology Primer
Soil as habitat
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Soil color is an indicator of Oxidation – Reduction (Redox) conditions
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Percent by Volume
Soil Texture – size distribution of mineral particles in the soil
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Soil Texture“You play the hand you are dealt”
• Managing field soil doesn’t modify texture
• In contrast, manufactured soils and potting mix are designed and texture can be chosen– Landscape architecture projects spec soil– Plant propagation e.g. rooting in sand– Potting mix– Green roofs
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Soil Texture – proportion of sand, silt, and clay
Environmental Soil Physics. 1998. Daniel Hiller
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Soil particle classification systems – particle size
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Particle-size distribution across soil textures
Figure 4.9
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Soil textural classesfigure 4.6
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Soil texture by feel
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Physical properties of soil particles – surface area to mass ratio. Clays have much more reactive surface area than sand
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Clay Physical PropertiesInternal spaces, negative electrical charge, colloid formation
Figure 8.3
Kaolinite Montmorillonite Mica
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Intrapedmicropores
Soil macropores between soil particles (sandy soil)
and soil aggregates(clayey soil)
Also micropores within clayey aggregates
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Soil Texture vs. Soil Structure
• Texture• Termed soil particles
or separates• Sand • Silt • Clay
• Structure• Termed aggregates
or peds• Arrangements of soil
particles• Described based on
shape and size of aggregates/peds
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Percent by Volume
Soil Structure – arrangement of pores and particles – how they fit together
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Soil pore network (2 mm soil block)
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Soil pore types – packing pores, interpedpores, and biopores
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NRCS Soil Biology Primer
Biopores
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Environmental Soil Physics. 1998. Daniel Hiller
Soil aggregates or peds
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Soil Structure – Aggregate Formation
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Soil aggregates - Humus structure
Figure 8.3
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Aggregate Formation – role of humus colloids and cation bridging
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Aggregate stability – Native prairie compared to cultivated soil
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Aggregate stability – organic polysaccharides (P) excreted by microbes
Figure 4.31
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Aggregate stability – fungal hyphae, in this case mycorrhizae
Figure 4.30
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Aggregate stability – fungal hyphae and glomalin from mycorrhizae
Box 4.6
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Aggregate stability – effect of soil organic matter content
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Percent by Volume
Soil Compaction – affects texture or structure?
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Compaction decreases macropores(figure 4.26)
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Hardpan limits rooting depth
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Root elongation in compacted soil
The Plant Root and Its Environment. 1974. E.W. Carson
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Soil compaction – 110 years after wagon trail abandoned in Minnesota
Box 4.4
Compaction - Increasing Bulk Density
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Plow pan - Moldboard plow
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Soil compaction – wheel traffic and plow pan.Note soil bulk density values
Figure 4.19
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Soil compaction and plant rooting
Figure 4.21
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Subsoiling to reduce soil compaction
Figure 4.20
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Soil crusting and seedling germination
(Capon, 2005)
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Soil Crusting
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Flocculation and Dispersion of soil clays – effect of Calcium verses Sodium
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Soil Conditioners
• Polysaccharides– PAH– Yuccah plant extract
• Gypsum– Calcium sulfate
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Expanding soils – clay drying and wetting
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Swelling soils – type of clay and sodium (Na)
Environmental Soil Physics. 1998. Daniel Hiller
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Roots follow vertical shrinking crack in clay
The Plant Root and Its Environment. 1974. E.W. Carson
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Swelling soils – effect on soil structure over time
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Example of managing soil for increased structure with tillage
systemsUC Santa Cruz Farm and Gardens
Key is organic matter additions
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Greatly modified soil structure
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Increased Soil Organic Matter LevelsCompost and Cover Crops
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Increased Soil Organic Matter LevelsCompost and Cover Crops
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Study questions Brady and Weil
• Chapter 4. Questions 2-5, 7-8