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Introduction to Soils

Kitty O’Neil, Ph.D.

Cornell Cooperative Extension, NNY

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Introduction to Soils

• At end of today’s discussion, you should…

–Understand why soil is important

– Explain to someone what soil is made of

– Explain to someone how soil was/is formed

–Understand that soils are highly variable in space and time

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Introduction to Soils

• Importance of soil – Soil functions

• Definition of soil • Components of soil

– Mineral, organic matter, air, water

• Soil formation, weathering – Parent materials – Soil formation processes – Soil differs from parent material

• Soils vary in space and in time

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Why do we care about soil?

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Why do we care about soil?

• Soil resources were and are a central factor in shaping human history and development.

• Survival of humans and animals is dependent on light, water, air and soil.

• Good, productive soil is a basic human need. – Grow our food, clean our water, clean our air

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Why do we care about soil?

“All civilization is basically dependent upon natural resources. All natural resources …are soil or derivatives of soil. Farms, ranges, crops and livestock, forests, irrigation water, and even water power resolve themselves into questions of soil. Soil is therefore the basic natural resource.”

- Aldo Leopold, Erosion and Prosperity, 1921

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Why do we care about soil?

• “Man—despite his artistic pretensions, his sophistication, and his many accomplishments—owes his existence to a six-inch layer of topsoil and the fact that it rains.”

- Author unknown

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What does soil DO?

OK, so soil is important.

Why? What does soil actually DO?

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What does soil DO?

1. Soil serves as a natural medium for the growth of plants,

2. regulates and purifies water,

3. recycles organic wastes and nutrients,

4. provides habitat for soil organisms, and

5. serves as physical support for building and construction.

= Soil functions

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What is ‘soil?’

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What is ‘soil?’

Soil = the unconsolidated mineral and organic material on the immediate surface of the earth.

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Soil = solids + pore space

From Univ. of Massachusetts Extension Vegetable Program, Soil Basics, part I

Composition of typical soil, by volume

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Mineral particles

from Hillel, 1998, Environmental Soil Physics, Academic Press

0.05 – 2.0mm, don’t stick together, gritty

<0.002mm, sticky when wet, hard clods when dry

0.002 - 0.05mm, smooth when wet

> 2.0mm = Gravel

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Organic matter

• Wide range of organic materials – Living organisms

• Plants, roots

• Insects, nematodes

• Fungi, bacteria

– Non-living OM, products of decomposition of living things

• Continuously decomposed, new compounds synthesized by other microorganisms

• Holds mineral particles together to form aggregates

• Over time, OM is lost from soil as CO2

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Pore space = air + water

• Air space provides gas exchange to organisms and plant roots

• Water is needed by plants and organisms

• Soil water also contains dissolved mineral compounds & nutrients needed by plants and organisms

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Where did soil come from?

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Where did soil come from?

Soil has been formed by 5 major factors:

1. Parent material (original form)

2. Climate (precipitation and temperature effects)

3. Macro- and microorganisms

4. Topography (elevation, slope, position)

5. Time

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Where did soil come from?

Parent material

Climate Organisms Topography Time

x

Soil

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Where did soil come from?

Parent material

Climate Organisms Topography Time

x

Soil

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Soil Formation or ‘weathering’

from Brady & Weil, The Nature and Properties of Soils, Prentice-Hall publ.

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Soil Formation or ‘weathering’

From T.H. Cooper, Soil 2125, U. Minnesota, http://www.soils.umn.edu/academics/classes/soil2125/index.html

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Weathering varies with climate, organisms

From T.B. Walther, Introduction to Geography, http://www.geography.hunter.cuny.edu/~tbw/ncc/

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Weathering varies with topography

From Smith, et al, Soil, in AccessScience@McGraw-Hill, http://www.accessscience.com, DOI 10.1036/1097-8542.631500; after Simonson et al., Understanding Iowa Soils, Brown, 1952

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Soil originated from ‘parent material’

As a result of weathering, soil differs from the parent material :

a) physically,

b) chemically,

c) biologically, and

d) structurally.

…this is an ongoing process…

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Soils vary widely

Parent material

Climate Organisms Topography Time

x

Soil

Variable

Variable

Really Variable

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Soils vary widely

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Soils vary widely

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Soils vary widely

• Identify soil type

– NRCS Soil Classification

– Determine best land use

– Plan buildings and plantings

– Maps

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Lecture 1 - overview

• Importance of soil – 5 Soil functions

• Definition of soil • 4 Components of soil

– Mineral, organic, air, water

• Soil formation, weathering – Parent materials – Soil formation processes – Soil differs from parent material

• Soils vary in space and in time

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Questions?