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Soil – Model and testing

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

-Leonardo da Vinci

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

David King (first to tell me)


Soil Happens: What you get is what you get, fortunately we can work with most soil and grow appropriate edible plants.

Soil Formation is a long term issue

1. Climate – including temperature and rainfall

2. Organisms – from Micro to Macro

3. Topography – the face of the Earth

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 (sand (beach ball) silt (baseball) and clay (speck))

5% Organic matter (OM) – living and dead…  link to Compost, worms and teas…

Soil Composition – meet the parents


Your soil composition affects how water flows through your soil – and this affects many other things – size matters:  X = diameter of clay

Property/Behavior Sand   1000X Silt   10X Clay  X
Water holding Low Medium High
Aeration Good Medium Poor
Drainage rate High Medium Slow/Very slow
Soil organic matter Low High
Decomposition of organic matter Rapid Slow
Speed of warming Rapid Slow
Compactability Low High
Storage of nutrients Low High
Resistance to pH change Low High

So, whether you have sandy or clay soil, you’ll add lots of amendments.

Soil Test – below is a test for soil composition – but if you are going to eat food from the garden the big issue is heavy metals and you’d like to know what nutrients your soil needs and this demands a professional soil test – if you have heavy metals talk to an expert and don’t eat anything except maybe fruit from trees planted there – no greens or root plants…

An adequate $15 soil test (plus almost $5 shipping):

How to Test Soil Texture

  1. Get a straight sided quart jar (like a mayonnaise or canning jar) – be aware this exercise requires that you allow the jar to sit undisturbed for 24 hours…
  2. Fill the jar 2/3 full with clean water, collect soil: scrape off top compost/much, take a slice out with your spade, preferably to a depth of 4-8 inches, break up soil and add a couple cups of to the jar of water.  Make sure you have at least 1” of open space at the top.
  3.  Shake that jar until all particles are largely separated and suspended in the water (~2 minutes)
  4. Set jar down in it’s settling point (viewable / measurable / and not to be moved for 24 hours)
  5. After one minute mark the level of soil settled –  This is the sand.
  6. After one hour make the level of the soil – the difference from the last mark is your Silt
  7. After one day make the level of the soil – the difference from the last mark is your Clay – the OM is floating on top.
  8. Measure each and divide into the whole  (e.g. 2 inches sand, one inch silt and one inch clay: total is 4 inches – 2/4 is sand, ¼ is silt, and ¼ is Clay)
  9. Interpret using soil triangle


An acre is a football field without the endzones

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 1.2 11.5*
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

100 Square feet = 0.002296 acre

144 sq. inches = 1 square foot

9 sq. feet   = 1 square yard

27 cubic feet = 1 cubic yard

43560 sq. feet = 1 acre 

4840 sq. yards  = 1 acre

David King’s Bibliography from Master Gardener Class

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


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.

In Defense of Food, An Eaters’ Manifesto, Pollan Michael, 2008, Penguin Press;

This is the ‘sequel’ to The Omnivore’s Dilemma: A Natural History of Four

Meals both of which are damning to the past view of macronutrients. Drawing on

strong modern science, with no dog in this fight, Pollan shows that relying solely on

NPK has hurt our environment and our health. Get ready for the new paradigm – a soil

ecology! Both

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


Teaming with Microbes, A Gardener’s Guide to the Soil Food Web,

Lowenfels, Jeff et al, 2006 Timber Press; No fooling: This introduces soil science for

the new century. Gone are the days when NPK ruled – now it really is about a soil

ecology. Before you dig, this is a must read!

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, he pulls off a book on soils that is informative and easily

read. No small feat!

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 the least expensive soil testing service I’ve found.

UMass Soil and Plant Tissue Testing Laboratory.

Author: Mark Rice

I’m a UC Master Gardener with a huge interest in growing my own food, beekeeping, medicinal herbs and living sustainably. I also have a passion to share these journeys with like minded souls. I work with many off site communities and manage an educational organization and two outdoor learning facilities.

One thought on “Soil – Model and testing

  1. Pingback: Fall 2011 Victory Garden at Coral Learning Garden | Pasadena Learning Gardens Network

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