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Saturday, October 3, 2009

Notes on Soils

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

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% Air and water in a continuum
5% Organic and living matter
45% Parent material (the underlying minerals (rock)

Soil Composition

Characteristics of Soil Components.................Property/Behavior

Water holding........Low.......Medium +......High
Drainage rate........High......Medium.......Slow/Very slow
Soil organic matter..Low.......Medium +.....High
Decomposition of organic matter
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! Read this book.

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. This is the second most important book on this list.

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.

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.


  1. Hey! Thanks for the kind words on Teaming With Microbes. I appreciate them very much! Informative and educational blog, by the way!

    Anytime you need a speaker, I do weddings and Bar Mitzvahs!


    Jeff Lowenfels
    Anchorage, Alaska

  2. Jeff -
    Not really used to the way 'comments' work, I didn't see your comment on my mention of Teaming with Microbes (made Oct.18) until today when I, faced with a writing deadline, I wanted to anything but write! I want you to know I've sold a quantity of your book down here in LA and I'm looking for a little kickback! Actually, I do want to tell you that your book confirmed some thoughts I'd been having for about 20 years and it didn't even take getting to the end before I had declared all fertilizer non gratis in my garden (except for some spastically added rock dust and compost tea and compost solids). You changed my gardening methodology and I am really grateful to you. I do hope you sell a truckload (and a big truck) of your book! Thanks!



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