Category: Soils and Growing

A Training Manual For Soil Analysis Interpretation in Northern California

A Training Manual for Soil Analysis Interpretation in Northern California

A Masters Thesis by Gregg A. Young

Phosphorus Fertilizers for Organic Farming Systems

Discussion and test results on the effect of various organic phosphorus fertilizers on high pH soils in Colorado.  From the Colorado State University Extension.  PDF

Phosphorus Fertilizers for Organic Farming Systems

Humus and Worm Castings

Humus and Worm Castings

Gary Kline

Humus and Humility – Recently we sent out an article that I (GK) wrote entitled “Understanding Humus”.  It was fairly long, so probably not many read it.  However, a few who did gave it what has to be described as high praise.  Try as I might, being self-effacing, at some point, becomes suspect.  Fortunately, I continue to make enough mistakes to remain authentically imperfect and unavoidably modest.  An example is in the Humus article.


Castings Correction – In the section about composition of worm castings, I stated that worms accumulate high levels of minerals; and what I should have said, or explained, is that they transform unavailable minerals into available nutrient minerals as soil particles pass through their intestines.  More than two thousand years ago Aristotle proclaimed that earthworms were the intestines of the earth.  Smart guy.


Classical Content – Gardeners have long known that the presence of earthworms in their soil is a sign of good soil health, and their absence a sign of something being wrong.  There is an often quoted reference to the mineral content of castings compared to the mineral content of surrounding soil (aka, dirt).  Thus, castings are said to contain 5 times the nitrogen, 7 times the phosphorus, 11 times the potassium [and 1.5 (?) times the calcium, and 3 times the magnesium] as ordinary topsoil.  How can that happen?  The extra minerals can’t come out of thin air, nor, seemingly, out of thin soil.  Transmutation of elements would be a stretch.


Enigma Explained – Initially, I figured the worm must somehow extract and concentrate the minerals as ingested soil moves through its body and is then excreted.  Here’s what Sir Albert Howard, in Soil and Health (1947), had to say about the process and the make-up of castings:


“The casts are manufactured in the alimentary canal of the earthworm from dead vegetable matter, and particles of soil.  In this passage the food of these creatures is neutralized by constant additions of carbonate of lime from the 3 pairs of calciferous glands near the gizzard, where it is finely ground prior to digestion.  The casts which are left contain everything the crop needs – – – nitrates, phosphates, and potash [NPK] in abundance, and also in just the condition [soluble?] in which the plants can make use of them.”


Further Explanation – Howard goes on to cite that often-mentioned analysis as follows:  “Recent investigations in the United States show that the fresh casts of earthworms are 5 times richer in available nitrogen, 7 times richer in available phosphates and 11 times richer in available potash than in the upper 6 inches of soil.”  It’s that word “available”, in contrast with previously non-available, which explains the higher content of nutrient minerals in the castings coming out, versus the “soil” and organic matter going in.  As near as I can tell, these numbers came from a single USDA study done in Connecticut in July, 1944.


Restoration Tool – Very large portions of the earth’s soil have been eroded and exhausted over the past 5,000 years all around the world.  In recent centuries the rate has been stepped-up many times the rate of natural soil formation.  The earthworm potentially is a major tool (if properly fed) for restoring and rebuilding those soils.  Here’s further explanation from Dr. Thomas J. Barrett’s 1947 and 1959 book Harnessing the Earthworm:


“In the chemical and mechanical laboratory of the earthworm’s intestines are combined all the processes of topsoil-building.  The earthworm swallows great quantities of mineral earth with all that it contains of vegetable and animal remains, bacteria and microscopic life of soil.  – – – Finally, it is ejected in and on the surface of the earth as castings – earthworm manure – humus, a crumbly, finely-conditioned topsoil, richly endowed with all the elements of plant nutrition in water-soluble form.”


In Summation – I’m not sure that all (or most) topsoil is from worm castings which are, in turn, humus.  Recall that this was the claim of Barrett and Darwin.  Darwin calculated that worms deposit 10 tons of castings per acre each year.  Sir Albert Howard figured it was 25 tons.  In some parts of the world these deposits have been measured to far exceed those amounts.  Whether or not topsoil is castings and castings are humus, or that humus requires soil and clay for its formation, the creation of 25 tons per acre or more of new topsoil per year is nothing to sneeze at.  This represents a too-often overlooked means of restoring billions (yes, billions) of acres of ground lost to the plow, it’s modern successors, and a century of reckless chemicalized agriculture that are soon going to be necessary to the survival of civilization.  In ancient Egypt it was a crime to kill earthworms.  Let’s not forget the lowly earthworm.  It’s the least we can do.    GLK


© 2013 Gary L. Kline

All Rights Reserved


Black Lake Organic

4711 Black Lake Blvd. S.W.
Olympia, WA 98512

Mulder’s chart of mineral interactions

Chart showing how the presence or absence of various elements influences the uptake of other elements by plants.

Mulder’s chart of nutrient interactions

Presley: Calcium and Seedlings

Article by Presley and Leonard




Published with the approval of the Director, Mississippi Agricultural Experiment
Station. Paper No. 140, New Series.

Received January 4, 1948

Tiedjens: Soil Acidity and Calcium Requirements

Article by V. A. Tiedjens



Soil samples from many sections of the United States and Canada show a paucity of
available calcium even though the pH reading seems satisfactory. Studies made on these
soils show that the pH test, accurate for most purposes, does not indicate the available
calcium in the presence of other fertilizer ions. A high pH does not necessarily indicate
adequate calcium in the soil.

THE OHIO JOURNAL OF SCIENCE 65(4): 227, July, 1965

Tiedjens: Assimilation of Nitrogen




Plants absorb ammonium and nitrate nitrogen in varying quantities,
depending partly on the rate of assimilation2 of either ion in the plant.
That certain specific conditions are necessary for the most efficient assimilation
of either form of nitrogen has been pointed out (40). Different species
vary in the efficiency with which they utilize the nitrate or ammonium ion
under a given set of conditions (29). The hypothesis that both ions probably
are finally utilized as ammonium, even though external requirements
may be different, involves an interesting study, a preliminary report of
which has been published (40). A continuation of these studies has established
certain relationships affecting the assimilation of nitrate and ammonium
nitrogen. Such factors as hydrogen-ion concentration and available
carbohydrates have a direct bearing on the assimilatory processes.
That these relationships vary with the source of nitrogen, and that the
location of the initial assimilatory processes varies with the type of plant,
will be pointed out.

Tiedjens: Available Calcium and Salt Balance

Article by Tiedjens



By Victor A. Tiejens and L. G. Schermerhorn

Foth and Ellis: Soil Fertility

Soil Fertility by Henry D. Foth and Boyd G. Ellis

This book is a hard-to-find item because it is out of print. It provides perhaps the simplest explanations around for the basic science behind soil advising. To make much use of this book does require remembering the basics from high school inorganic chemistry.





This book has been written to serve as a text for a soil fertility course at the
j u n i o r – s e n i o r level and at the master’s level for students who have had an
introductory course in soil science and several basic science courses. We
have chosen to cover the most essential topics and not produce an all-inclusive
text to serve as a reference book. T h e treatment is an evolutionary one
which considers soils as dynamic, ever-changing bodies.
There has been major progress over the past three decades in the
accumulation of new knowledge and development of theories in the fields
of soil science, agronomy, plant physiology, and plant nutrition. Thus, the
production of this book has been an exciting challenge to integrate the most
recent information about soil fertility with the knowledge and theories
about weathering and soil evolution, mineralogy, exchange chemistry, soil
taxonomy, fertilizer technology, and plant growth and nutrition.
Soils are one of the world’s most important resources. We hope that
the information put forth in this book will help to increase the food supply
for the world’s expanding population.
We extend our special thanks to Mary Foth for the graphic art work
and to Nate Rufe for photographing the mineral models.
Henry D. Foth
Boyd G. Ellis
East Lansing, Michigan
June 1988

Whitlark: Soil Testing Procedures for Calcareous Soils

An excellent article on testing calcareous soils by Brian Whitlark


Soil Testing Procedures for Calcareous Soils

“Well-established soil testing methods on soils containing calcium carbonate or
gypsum often underestimate fertilizer and soil amendment requirements.”