list of topics.microsoft powerpoint - soil structure intro text.pptx author: ttcf created date:...

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My name is Dr. John Galbraith. This webinar is part of the webinar series given at the Introductory level, May 28, 2015. Today’s topic is “Soil Structure and its Importance”. 1

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Page 1: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

My name is Dr. John Galbraith. This webinar is part of the webinar series given at the Introductory level, May 28, 2015. Today’s topic is “Soil Structure and its Importance”.

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Page 2: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

This webinar explains soil structure and its importance. Structure types, formation, description, relation to texture, and relevance to soil health will be discussed. 

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Page 3: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

List of topics.

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Page 4: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Learning objectives of this webinar.

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Page 5: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

This picture of a thick crust impeding seedling emergence illustrates the importance of good structure, water stable aggregates.

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Page 6: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

The most common occurrence of different shapes.

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Page 7: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

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Page 8: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

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Page 9: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Columnar only occurs where the sodium is relatively high in abundance. It is a dense, root‐limiting structure.

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Page 10: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Wedges are formed when the slip surfaces intersect. (shrink‐swell clays) 

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Page 11: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Naturally platy structure forms from ice lens compaction. Thick platy forms from compaction by vehicles and tools. 

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Page 12: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Most structure is compound – it breaks into smaller units.

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Page 13: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Without soil structure, we have clods in coherent textures, and single sand grains in sandy textures. Desiccated and divergent structure forms are unusual but do exist. Crusts form in two ways. Rock structure is really thin layering from recent or ancient deposition or mineral separation.

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Page 14: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Notice the tool marks in the compacted mine soil, because there were no soil aggregates to dig out. 

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Page 15: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

This dredged material or pond‐bottom sediment cracks into polygons when drying. Divergent masses have irregular and unpredictable shapes do to shearing.

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Page 16: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

The crust at top is from bare farmed soil and raindrops melting unstable aggregates. Siltysoils are the worst. The biotic crust stabilizes the soil from erosion but may indicate excess nutrient application and ponding. 

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Page 17: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Thin layering fro dredge flooding – left; and from weathered bedrock layering ‐ right.

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Page 18: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

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Page 19: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

This is how sand grains stay together and do not always stay as loose grains. Note the role of OM (humus). The more clay, the more micropores inside the aggregates, macropores on the outsides and open pores (higher total porosity than pure sands). 

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Page 20: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Wetting and drying, freezing and thawing, and shrinking and swelling are all associated with structure formation. They all form macropores. 

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Page 21: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Humus binds sand grains together and holds clays together. Microbes exude gels and enzymes, roots slough off cells and exude enzymes and hormones. Earthworms exude gels from their skin and excrete small, stable aggregates.

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Page 22: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Give it a grade just like a test!

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Page 23: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

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Page 24: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

The size is complex but the smaller the units, the greater surface area for water and gas exchange and root growth.

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Page 25: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Great reference, get one for free. 

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Page 26: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Shapes reviewed earlier.

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Page 27: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Put it all together. Grade, size, shape

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Page 28: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Texture triangle for reference.

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Page 29: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Sandy soil have little if any structure, clays have abundant structure if not compacted.Sandy textures have lower water holding capacity and organic matter and support fewer microbes, earthworms, insects, and roots, so have weaker structure.

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Page 30: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Compaction makes a difference. 

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Page 31: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

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Page 32: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Organic matter laid down in layers, form plates.

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Page 33: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

Compaction from humans and their tools and practices form plates or crusts (surface plates).

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Page 34: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

See the root distribution.

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Page 35: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

This soil looks like it has good structure. Good structure = good health.

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Page 36: List of topics.Microsoft PowerPoint - Soil Structure Intro text.pptx Author: ttcf Created Date: 5/29/2015 9:30:31 AM

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