Assessing Soil Health

by Dennis K. Howard

Assessing Soil Health

Assessing soil health is something every good gardener should understand. I talk about it in almost every article I write.  Soil health is at the core of our organic systems.  How can you tell if your soil is healthy since most of the organisms that contribute to soil health are microscopic and nothing short of a sophisticated lab test will tell you if your soil has all the essential nutrients in the right ratios?  It’s not as daunting as you might think.

Defining Soil Health

The USDA defines soil health or soil quality as:

 the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans.[i]

In many ways, the definition of soil health depends on who you are and where you are.  Farmers might tell you that healthy soil will hold enough water, contains enough nutrients, and provide pest control to produce sustainable crops.  A homeowner could view healthy soil as providing a foundation for a lawn and garden. 

I like to think of soil as a living ecosystem and a part of the larger ecosystem in which we all exist, in which a diverse set of organisms live and which is the primary source of nutrition for every other plant and animal.

Thinking of soil in this way conveys my belief that the health and well-being of everything that walks or grows on the soil are fundamentally connected. 

Is your soil healthy?

There are a few ways you can judge for yourself if your soil is healthy.  They are sophisticated, but they can tell you a few things about your soil and provide some clues that can help you regenerate or further improve your soil health.

What is in your soil?

You really should understand what makes up the soil structure.  If you understand the basics, you can grasp the importance of the other tests and the remedies.

Soil is made up of three major components; sand, silt, and clay.  The proportions of each in your soil determine the type of soil.  The graphic included is a quick guide to determining the makeup of your soil.  If you could separate the three components, you could feel the difference.  Sand would feel gritty.  Silt is slick and smooth.  Clay would feel sticky and gummy.

Assessing soil health - soil types

In the proper proportions, the soil that results is called loam. Soil with these three components in a proper ratio will, when damp, compress easily into a ball that holds it’s shape, but when poked or tapped, breaks apart into clumps.  That is a quick test to determine if your soil has the proper ratio of sand, silt, and clay.

As you can see in the graphic, when the soil contains almost equal amounts of clay, silt, and sand, you get a loam that is ideal for most plants.

To get an idea of where your soil falls on this chart, rub a bit between your fingers.  Look at it and feel it.  Is it gritty?  It probably contains a lot of sand. When wet, does it turn sticky?  That is an indication of a predominance of clay.  A smooth slick feel indicates a high percentage of silt.

A more visual test.

Soil Compnenet Seperation

Take a sample of your soil and put it into a large glass jar.  Fill the jar about 1/3 full of soil.  Fill the jar to the neck with water and cap it tightly.  Now shake.  Shake it hard.  You want the soil to be thoroughly dispersed in the water.  Now sit the jar somewhere for 24 hours.   It should be in a place that you can look at it later without having to pick it up or disturb it.  In 24 hours, the soil will have settled back to the bottom of the jar.  You should notice right away that it has layered into its constituent parts.  At the bottom, you should see sand as it is heavier and bigger than the other components.  The next layer should be silt, and the clay should settle out at the top.  Your water may still have clay particles suspended, making it cloudy.  Carefully measure each layer.  The measurements will allow you to calculate the percentage of each component in your soil.

Soil Compaction

Healthy soil resists compaction.  The easiest way to test for soil compaction is with a soil probe.  A soil probe is nothing more than a straight stiff shaft of some sort that you can push straight down into the soil.  I use the shaft I cut from an old golf club. Measure how deep you can easily push the probe into the soil at various places in your landscape.  Don’t strain too hard to push the probe.  It should push in easily, and when you begin to feel stiff resistance, stop.  Ideally, the probe should drive easily into the ground for 12 inches.  In turf, if you can push your probe into the soil 8 to 10 inches without much difficulty, your soil is in good shape. 

Soil that is penetrable to a depth of 12 inches encourages plant root development and the growth of the other organisms in the soil.  If you find that your soil is compacted, there are a few remedies.  First, aerate your soil.  Using aeration equipment is the easiest way to do this.  We strongly encourage you to use the type of machine that removes a plug of soil rather than just pushing a spike into the ground.  Amendments such as compost applied generously to the soil will eventually help alleviate the problem.  Avoid driving heavy equipment or vehicles over your soil.  Physical compaction is one of the major problems.

Infiltration

Healthy soil will allow an amazing amount of water to infiltrate deep into the soil.  Compacted soil resists infiltration creating runoff problems and surface erosion.  To test your soil for its infiltration properties requires a bit of work.

First, dig a hole roughly 12 inches square and 12 inches deep.  Fill the hole with water and allow it to drain completely.  When it is empty, refill the hole and measure how much time passes before the hole is empty again. 

What is the lesson here?   If the second filling takes less than 2 hours to drain away, your soil drains too quickly.  This can be good or bad, depending on the types of plants you want to grow.  Some plants don’t like to sit in damp soil, so they want the water to drain quickly and infiltrate deeper.  Other plants like damp soil and will not do well in this type of soil without frequent watering.

IF there is still water in your hole after 6 hours, your soil does not infiltrate water well.  It may be compacted, or it may contain a large percentage of clay.  Adding organic matter to this type of soil can help.  If you are gardening vegetables, installing raised beds might be an answer.

Who is living in your soil?

One of the best indicators of the condition of your soil is the presence of earthworms.  Earthworms are the soil contractors of the gardener’s world.  As they move through the soil feeding on the organic matter that is present, they convert that organic matter into the best and richest compost you can imagine. 

assessing soil health

At various locations in your landscape turn over a shovel full of dirt, sift through it with your fingers.  Your first look should tell you a lot.  If the soil appears dry, it is hard to penetrate with the shovel and comes out in one big hard lump that you cannot break easily with your fingers; you have soil problems.

If your shovel turns over a moist but not soggy lump that you can easily break apart with your fingers, you probably have at least the beginnings of healthy soil.  Ideally, you should find at least five earthworms in every shovel full of dirt that you turn.  Ther should also be other bugs.  These are all indications of healthy soil.

Before you return that soil, smell it.  It should have a clean earthy smell.  You will recognize it quickly.  It is almost a sweet smell.  If there are any foul or noxious odors, you have another problem.  Bad smells in the soil indicate the presence of anaerobic bacteria, which are never a good sign.

Tilth

What?  What is tilth?  Tilth is the summary of the agricultural prospects of your soil.  More simply, it is an indication of how well your soil will support plants.  Tilth is a combination of all the other things we have talked about; aeration, moisture, composition, and infiltration.  It tells you how ready your soil is for planting. 

We test by again using our senses.  Take a handful of soil and compress it into a ball.  It should not ooze water.  It should hold together in a ball when you release your hands after compressing it.  If you poke it gently with your finger, it should crumble easily.  Smell it.  It should have a sweet earthy smell that is pleasant. 

Healthy soil will exhibit these properties and offers excellent prospects for planting.  If your soil will not compress and hold its shape, it probably is to dry, to sandy or lacking in the organisms that we would expect in healthy soil.  F it compresses but doesn’t crumble, it is likely to wet or too dense with clay or silt.

Conclusion

These simple tests will tell you a great deal about the composition and condition of your soil.  Knowing those two things gives you great insight into your next steps in building a healthier microbiome in your soil. 

or more information about fixing damages soil, see our article Fixing Damaged Soil

If you have more questions, visit our Facebook page.  Search for us @westtexasorganicgardening.


[i] USDA, Natural Resources Conservation Service, https://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/health/