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21 September, 2007

22 Sept. Handout: Notes for Soils Lecture

We know more about the movement of celestial bodies than about the soil underfoot. Leonardo da Vinci

(note to class: the figures do not appear in this post, but all the data is the same)

Soil Formation

1. Climate – including temperature and rainfall
2. Organisms – from the itty bitty (microscopic) to the biggies (macroscopic)
3. Topography – (the book calls relief) – land surface
4. Parent material – the original rock
5. Time – the factor that weathers us all.

Components of Soil

50 % Water/air – in proportion to one another
45% Parent Material – underlying rock
5% Organic matter (OM) – more or less
Soil Composition

Characteristics of Soil Components

Property/Behavior Sand Silt Clay
Water holding Low Medium + High
Aeration Good Medium Poor
Drainage rate High Medium Slow/Very slow
Soil organic matter Low Medium + High
of organic matter Rapid Medium Slow
Speed of warming Rapid Medium Slow
Compactability Low Medium High
Storage of nutrients Low Medium High
Resistance to pH change Low Medium High

Soil Texture

Is defining how the proportion of these differing components are found in a given soil. An ideal soil is a mix of all these different components. While it is possible to have a soil that is composed of one or the other component, the likelihood is that it will be a combination of all three. The proportion of one to the next determines how you call your soil.

Each shovel of soil holds more living things than all the human beings ever born.


The following books were used in the development of this lecture with my notes on each.

Dirt, The Ecstatic Skin of the Earth,
Logan, William Bryant, 1995, Riverhead Books; A series of passionate essays pleading to respect the earth and to rethink how we define ‘dirty.’

Elements of the Nature and Properties of Soils,
Brady, Nyle et al, 2000, Prentice Hall; This is the simple version of the text I had in my soil class. It is really dense and a good reference when you settle in to teach soils, but unless you have a lot of organic chemistry under your belt, it will probably serve you as a door stop more than a book.

Out Of The Earth: Civilization and the Life of the Soil, Hillel, Daniel. 1991 Free Press; The paperback is published by University of California Press. Not strictly a soils text, I recommend this book very highly. It is a grand overview of how soils shape civilization and how failure to understand and conserve them has resulted in the fall of civilizations – much more than even losing battles! Worth every second you invest in it!

Soil Science Simplified, 4th Edition, Dohnke, Helmut et al, 1995, Waveland Press; Just like the title says it is very much a simplification of the concepts and scientific principles of soil. A lot of big scientific words, and not light reading, but still highly recommended.

Teaming with Microbes, A Gardener’s Guide to the Soil Food Web, Lowenfels, Jeff et al, 2006 Timber Press; Look up all the titles in the Timber Press catalog – one of the more important horticultural publishing houses in business today! I wish I had this book when I started gardening – this book presents the latest research on the ecology of the soil. A must read! My next book review in Touch the Soil will be on this book and, after careful reconsideration, I think this is one of the most important books to come out on soils and gardening in many a decade.

The Gardeners’ Guide to Better Soil, Logsdon, Gene, 1975, Rodale Press; The first book to turn me on to soils and a real page turner, although it’s out of print and a real bear to find. Gene Logsdon is brash, outspoken, political and opinionated. He goes on tangential tirades about the price of gas (in 1975!), but, in part because he is brash, outspoken and opinionated, still he pulls off a book that is informative and easily read and digested.

The Soul of Soil; A Guide to Ecological Soil Management, Gershuny, Grace et al, 1986 Gaia Services; This is a small book, only 109 pages including back notes, but is chock full of information about how to care for your soil. The ‘ecological’ in the title cues you to know that it’s a total organic approach. A great text and easy to read. This is a classic.


Converting Agricultural Measurements for Home Horticulture

Pounds Per Acre Equivalent Quantity per 100 Square Fee
100 3.5 oz.
200 7.5 oz
300 11 oz
400 14.75 oz
500 1 lb. 2.5 oz
600 1 lb. 6 oz.
700 1 lb. 10 oz.
800 1 lb. 13 oz.
900 2 lb. 1 oz
1000 2 lb. 5 oz.
2000 4 lbs. 10 oz.

Some Common Materials and Their Conversion

Material Pounds per Acre Pounds 100 Sq. feet Pounds per 1000 Sq. feet
Blood meal 100 @.25 (¼) 2.5
Sulfur 1000 2.3 23.
Mixed fertilizer
(i.e. 10-10-10) 1000 2.3 23.

Useful conversions
100 pounds per acres = 0.2296 lbs. per 100 square feet
.01 pound = .16 oz
144 sq. inches = 1 square foot
9 sq. feet = 1 square yard
43560 sq. feet = 1 acre
4840 sq. yards = 1 acre

ton = 2000 pounds

How to Take A Soil Sample Test

 Remove as much surface organic matter as possible before taking your soil sample.
 Put approximately one cup of soil into a straight-sided quart jar with lid.
 Add approximately one tablespoon of alum or Calgon bath beads.
 Fill the jar with water almost to the top.
 Shake vigorously for several minutes to get all the soil moistened.
 Let the jar stand undisturbed for at least one hour.
 The soil mix will separate into layers. The longer it sits, the more distinct the layers will appear.
 Figure out the percentages of sand, silt, clay, and organic matter. The sand will be the bottom layer. Silt will be the next layer, followed by clay. Organic matter will float on top of the water.
 Determine soil type by comparing percentages with soil triangle. Follow arrows in example—15% sand, 70% silt, and 15% clay—to merge at silty loam category.
 Understanding soil type will help you know how to properly amend, fertilize, water, and plant so that you will have healthy, disease-resistant, and pest-resistant plants.

What to do and How to do it:

Follow these steps to determine the name of your soil texture:

1. Place the edge of a ruler at the point along the base of the triangle that represents the percent of sand in your sample. Position the ruler on or parallel to the lines which slant toward the base of the triangle.
2. Place the edge of a second ruler at the point along the right side of the triangle that represents the percent of silt in your sample. Position the ruler on or parallel to the lines which slant toward the base of the triangle.
3. Place the point of a pencil or water soluble marker at the point where the two rulers meet. Place the top edge of one of the rulers on the mark, and hold the ruler parallel to the horizontal lines. The number on the left should be the percent of clay in the sample.
4. The descriptive name of the soil sample is written in the shaded area where the mark is located. If the mark should fall directly on a line between two descriptions, record both names.

Feel the texture of a moist soil sample. Sand will feel "gritty", while silt will feel like powder or flour. Clay will feel "sticky" and hard to squeeze, and will probably stick to your hand. Looking at the textural triangle, try to estimate how much sand, silt, or clay is in the sample. Find the name of the texture that this soil corresponds to.


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