Soil Minerals and Soil Prescriptions for Organic Gardeners
 

Why get a soil test?

Reading and Understanding Soil Test Results for Organic Gardens

Throughout history, all farmers and gardeners have faced this dilemma:  Why does the food grown on this patch of ground taste better than the food grown on that patch of ground?  Why are the cattle grazing on that pasture fat and healthy, while the cattle on this pasture are thin and sickly?  Until less than two hundred years ago no one knew, and they had no way of finding out.  If they were fortunate enough to have soil that grew flavorful fruit and vegetables, that grew strong stands of grain that made good bread, if they had pastures where the livestock thrived, and they were also good farmers and gardeners, they took care of their land the best they could, returning plant and animal waste to the land as compost and manure.  If they didn't return anything to the land, its fertility was soon exhausted

If they were growing crops and animals on poor land, even returning the plant and animal waste to the land didn't help much.  They could only truly improve the land by bringing in compost from rich land and manure from animals fed crops grown on that rich land.  Organic matter, when dry, contains around 95% fibers and carbohydrates formed from elements in the air and water. If it is burned, 95% returns to the atmosphere as gases. The difference between the organic matter from the rich land and that from the poor land lies in the 5% that is left as ash, and that 5% is the minerals that the plants have taken up from the soil.

The difference between rich, fertile soil and poor, infertile soil is essentially this:  the mineral composition of the soil.  The flavor and nutrition in fruit, grains, and vegetables are based on the soil minerals available, not the amount or type of organic matter. If a needed mineral is missing, it is just that, missing, and no amount of organic matter will make up for it.  No amount or combination of the air elements Carbon, Oxygen, and Hydrogen will add Zinc to your soil, and all plants and animals need Zinc. They also need Copper and Iron and Manganese, Calcium and Magnesium and Phosphorus, and at least seven other essential minerals, and they need them in an available and balanced form.   Rotting organic matter may release growth stimulants like Nitrogen and Potassium, but the other minerals are what create sweetness and flavor and nutrition in food.  Without these other minerals you may achieve high production, but you will not achieve the highest quality.

That is why, if you are serious about gardening or farming, you must know the mineral content of your soil, and the only way to find that out is with a good soil test.

The last eight or ten thousand years of agricultural history have largely been luck and guesswork regarding soil nutrients.  It doesn't need to be luck and guesswork anymore.  We now know which minerals plants need to thrive and be healthy, and which minerals must be in the food we feed our animals and ourselves, and we know how much of which mineral and in what form it must be to be used.  For those who are paying attention and are willing to learn, this is the dawning of a new age in agriculture. No matter how poor the soil you are starting with, by adding the missing minerals and bringing them into balance, you can create as fine a soil as is found anywhere in the world, and you can do it with precision, not guesswork.  Care to re-create the soil of the vineyards of Bordeaux, the buffalo-grass prairies of the Dakotas, or the Nile Valley?  It starts with a soil test.

So let's take a look at a soil test. The results below are from good garden soil, from a sample submitted in early 2007.  The format is based on that developed by Professor William Albrecht during the 1940s when he was working with the Friends of the Land group at Louis Bromfield's Malabar Farm in Ohio.  It packs a lot of information into a small area, and is the same format that we use today at soilminerals.com.  

The test gives the results for 11 essential mineral nutrients plus Aluminum and free Hydrogen, pH, Exchange Capacity, and the Base Saturation percentage of the major cations.

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Element
Results

Reading a Soil Test

Taking it from the top, the first line below "Element" is Exchange Capacity Exchange Capacity or "EC" is a measure of the cation (pronounced cat-eye-on) nutrient holding ability of your soil. Cations are positively charged + ions. Sand has a low exchange capacity, most clays and organic matter have a high exchange capacity. How much water a soil will hold is a good analogy. This number will range from a low of around 5 to a high of around 40.

Next line down is pH.  Most of us are familiar with pH; it is a measure of the acidity or alkalinity of your soil. This soil's pH is 5.9, a little too acid for most crops. 6.0-6.5 is ideal.

The third item is the percentage of organic matter in your soil.  Many soil scientists say that 4-5% organic matter is ideal, but that depends on the climate. In a cool, rainy climate 10% organic matter may be common.

Anions

Next we come to a couple of Anions, Sulfur and Phosphorus.  Anions are negatively charged atoms. They are designated by the - minus symbol. Sulfur is important for many life processes including formation of protein.  Most soils in high rainfall areas are deficient in Sulfur as Sulfur is easily leached away in water.  Onions, Garlic, and members of the cabbage family all require a lot of Sulfur to grow well. At 13ppm, this soil is far too low in Sulfur.

Large amounts of Phosphorus are needed by all living things. Plants use Phosphorus to make sugars.  Animals use Phosphorus to make bones and teeth, and to generate energy in the body cells. An apple or watermelon that looks perfect but isn't sweet was likely grown in a Phosphorus deficient soil. This soil has a good level of Phosphorus.

Cations
(pronounced cat-eye-ons)

The cation elements are the most critical nutrients for a healthy soil. If they are missing or out of balance nothing will grow really well. Cations are bases: that means they have a + charge, and the Exchange Capacity of your soil is a measure of the amount of cation elements it can hold.  Base saturation is a measure of how much of the EC is filled by each element.  On this soil test 64.58% of the EC is filled by Calcium, just about the perfect amount.

The critical importance of the cation nutrients is poorly understood by many gardeners.  A really fertile soil contains more Calcium than all of the other mineral nutrients combined!  A soil with the right amount of Calcium will remain loose and workable.  Calcium is the major transporter of other minerals and nutrients, including sugars.

An atom of Magnesium is at the center of each molecule of chlorophyll that plants use to convert sunlight into food and fiber.  The Calcium to Magnesium ratio should be about 7:1 by weight in most soils.  Magnesium  and Calcium are necessary for proper nerve and muscle function in animals.

Potassium is a powerful growth stimulant for plants and is needed in large quantities by animals too, but unfortunately it is too often overused.  Large amounts of Potassium will encourage lush growth but the plants will be weak. Note that you never need more than 5% base saturation of Potassium.

Sodium is also an essential nutrient for plants and animals, and one that is frequently in short supply in high-rainfall areas.

Hydrogen in the soil is not considered a nutrient.  It is more of a place-holder.  Plant roots and soil microorganisms exchange Hydrogen for nutrient cations.  The higher the level of exchangeable Hydrogen, the more acid the soil.

The Minor elements

These are only "minor" in the amounts required compared to other minerals.  They must be available and in balance for truly healthy soil, plants, animals, and people.

Boron is needed in tiny amounts in order for plants and animals to properly utilize Calcium.  For each thousand pounds of Calcium only about one pound of Boron is necessary. Boron can easily reach toxic levels if it is over-applied. 3-4 parts per million is all that is needed even in a high Calcium soil.

Iron is needed by plants and animals.  Our blood contains an atom of Iron at the center of each hemoglobin molecule. The 196ppm of Iron in this soil is plenty.

Manganese is needed for a plant to set fertile seeds and is also an essential nutrient for animals.

Copper and Zinc work together and need to be in a balance of about 1 part Copper to 2 parts Zinc.  They are both essential for hundreds of life processes. In this soil they are out of balance, as there is 6 times as much Zinc as Copper.

Aluminum is the second most abundant mineral on Earth, and it is found in all soils.  High Aluminum levels are usually only found in very acid soils.  Anything under 2000ppm is normal.

For more examples of soil tests and recommendations click HERE.

To see the prices for soil tests and the procedure for taking a soil sample, click HERE.

Exchange Capacity
9.72
pH of soil sample
5.90
Organic Matter %
10.24

 

 

 

Anions
Sulfur-   (parts per million)
13
Phosphorus- as P2O5   (lbs per acre)
955

 

 

Cations

Calcium Ca++
lbs per acre

Desired
Found
Deficit
2643
2510
-133
Calcium base saturation 60 to 70%
64.58%
Magnesium Mg++
lbs per acre
Desired
Found
Deficit
279
212
-67
Magnesium base saturation 10 to 20%
9.09%
Potassium K+
lbs per acre
Desired
Found
Deficit
303
156
-147
Potassium base saturation 2 to 5%
2.06%
Sodium Na+   lbs per acre
31
Sodium base saturation .5 to 3%
.70%
Other Bases (Fe,Mn,Cu,Zn etc)
5.60%
Exchangeable Hydrogen H+ 10 to 15%
18.00%

 

 

 

 

Minor Elements (parts per million)
 
Boron B
0.51
Iron Fe+
196
Manganese Mn+
43
Copper Cu+
1.05
Zinc Zn+
6.25
Aluminum Al+
1545
©2008
  
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