Soil Testing

See what you look at!

This was the charge Dr. Carey Reams drilled into Dan Skow over and over again. Nowhere is this more important than when dealing with the foundation of human health: soil. The soil test is our eye into the complex world beneath our feet. This leads us to the ever-important question of what soil test should be used to help us see what we are looking at.

Types of soil tests

There are many different kinds of soil tests that have been developed over the years. Without getting into the chemical complexities, let's explore the basic concepts of the various types of soil tests.

Chemical analyses of soil nutrient levels involve mixing soil with water and an additional chemical that extracts or dissolves nutrients from the soil. This mixture of soil, water, and chemical extract is then filtered and tested to determine the level of nutrients in the soil.

The extract solutions can be divided into 3 basic classes:

  • Strong Acids
  • Weak Acids
  • No Acid just uses water A.KA. Water Extract

Strong acids

Most testing laboratories and state agricultural colleges use strong acids. This type of extract can test the total amount of nutrients in the soil and compute Base Saturation and Cation Exchange Capacity. Dr. Reams rejected this type of soil test for one basic reason; this test didn't let him really see what he was looking at.

With this test, nutrient levels (Base Saturation and Cation Exchange Capacity) might all be in the desired range and yet the plants could show deficiency symptoms of various elements and yield poorly. Why? Because the amount of nutrients dissolved by strong acids is not the same amount made available by the weak acids in the exudates given off by the plant roots.

No acid

An equally poor choice is to use no acid at all. This measures only the amount of nutrients that is dissolved by water. Plant exudates are weak carbonic acids that will extract more nutrients from the soil than just water. Dr. Reams rejected this type of soil test for the same reason as the strong acid test—neither of them squared with what was actually available to the plant.

Weak acids

The test of choice for Dr. Reams and International Ag Labs is the weak acid test. This test uses a chemical extract that was patterned after the exudates that roots give off. It is called the Morgan Extract. The Morgan extract is a "universal" extractant, meaning all major nutrients (including phosphorus) and many micronutrients can all be measured in the one extract. Dr. M.F. Morgan developed the Morgan extract in the 1930's and 40's at the University of Connecticut.

This test more accurately reveals what the plant can actually utilize from the soil. This was the test Dr. Reams used to see what he was looking at. What was Dr. Reams really looking to see with this test? Nutrients that are biologically active. This test closely relates to the visual symptoms plants display. Plants may be grown directly above limestone bed but show a calcium deficiency. The Morgan test picks this up and shows a low reading of biologically calcium even though there is plenty of calcium in the soil.

Through out the years the weak acid test has stood the test of time and it has produced brilliant results. Dr. Reams built on this test and determined the ideal nutrient levels and ratios that we use today as benchmarks. When the soil is balanced according to the available nutrients it produces an abundance of high-quality produce.

How to take a soil test

Take a sample by digging a vertical hole to a depth of 6 inches. Take an even slice off the side from top to bottom with a clean spade and put into a clean bucket. Take several samples like this throughout the garden or field. Once all samples are collected, mix soil thoroughly and take out 1 1/2 cups of soil. Soil may be submitted in soil sample bags or plastic Ziploc bags. Include a completed Garden Soil Test Order Form or Field Data Sheet.

The lab only needs 1 1/2 cups of soil per sample!

Note: International Ag Labs is no longer able to accept foreign soils (exception is Canadian Soil--see below) due to soil permit expiration. We are very sorry for any inconvenience this may cause.

Canadian Soil: According to new regulations International Ag Labs is now allowed to receive Canadian soil for soil testing. This does not include potting soils or growing media. You must fill out the form below and include it in the soil package.

Canadian Soil Sample Form

Canadian Soil


Question: What is the best time to take a soil sample?

Answer: Anytime is better than not taking a sample. Generally fall or the beginning of the dormant season is best because it allows time to secure the nutrients your soil needs. If you apply the broadcast in the fall it gives the minerals more time to digest in the soil before the planting season. A second good option is just after the spring thaw. This still gives you time to get the soil to the lab and get the nutrients needed for your soil before planting.For lawns and turf midsummer works good.

Question: How should a soil test be taken?

Answer: Take a soil sample by digging a vertical hole in your garden or field to a depth of 6 inches. Take an even slice off the side from top to bottom with a clean spade that is not rusty. Place in a clean bucket that does not have any feed, salt, or fertilizer residues. Take several more samples like this in other areas of the garden or field. Mix all the soil together thoroughly in the bucket. After mixing, put 1 ½ cups into a soil bag or plastic Ziploc baggie. Don't worry about drying the sample.

Please submit your soil sample with either a field data sheet or a garden soil test order form. If it is for a backyard garden please use the garden form. For anything else use the field data sheet. Only fill out what makes sense since some may apply to different farming operations.

Wendell Owens

of International Ag Labs

Wendell Owen

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