The Key to Optimum Soil and Plant Health: Giving Life to the Soil


Those who study life in the soil point out that the population of beneficial living organisms that grow and thrive there determines to what extent that soil will grow and produce abundant, healthy crops.  The life in the soil and the health of the soil are intertwined.  To determine what promotes the greatest amount of life in the soil will also then provide the greatest support for soil health.

Time after time, the healthiest soils are found to be those with the most active living organisms.  Soil life is a major factor in determining soil health.  The most critical needs for sustaining all life are also the most critical to life in the soil.  Assuring the correct amount of life’s most critical requirements is the real “trunk of the tree” in regard to building better soil health.

There are four basic needs for life – shelter, food, water and air.  Which one of these on average can more likely be missing and life could go on the longest?  First would probably be shelter, then food, then water, then air. Air is the most critical of all since we can only live a very short amount of time without it.

Air in the Soil

When considering clay soils, much like the human body, insufficient air is considered one of the most significant problems. This is usually caused by too much water in the soil, which prevents the air from reaching to the proper depth causing interference in microbial activity.  Far too many individuals working in agriculture fail to recognize the significance of the correct amount of air needed in the soil, let alone the methods that must be involved for correctly solving this problem when having sufficient air is not the case.  That may be one of the reasons it is not pointed out as the greatest problem affecting soil life and soil health.

Just how important is air for soil health?  It is a major key for humus formation.  Humus is formed within the soil’s aerobic zone. The aerobic zone is the depth of soil to which air remains sufficiently available for the most beneficial microbial activity and good plant health in each different type of soil.

Due to the abundance of air, microbiologists say that on average 70 percent of all humus is formed in the top two inches of soil.  Ninety-five percent of humus is formed in the top five inches, and 100 percent is formed within the depth of each soils’ aerobic zone.

One good measurement to determine each soils’ aerobic zone (how deep the microbes that depend on air can get enough to live and function) is to remember that it as deep as a fencepost will rot in each particular soil.  This is generally between 6.5 to 8 inches deep.

How many people who advocate for building better soil health even consider providing an adequate amount of air to the soil as the most critical step to building excellent soil health?  And even so, if the soil lacks aeration, is there anything that can be universally done to change or correct that lack?

Changing Soil Structure

Air is needed to keep a healthy set of microbes to supply plant nutrients and build humus in our soils.  But what can be used to determine if the correct amount of air – not too little and not too much – is present?

This is an important question that too few can answer.  When soil aeration is lacking, how can farmers and growers detect that actually is the case?   What provides the proper amount of aeration to the soil to best promote soil life and soil health?  There is a way to determine this answer that many in agriculture reject because it does not translate into immediate sales and profits, though it is very profitable for the farmer and the land in terms of soil health.

That answer has to do with measuring and correcting the physical structure of each different soil.  The physical structure of a soil (how well it works up, takes in water and provides the needs for plant roots) determines the amount of air and water that is present in relation to the soils’ mineral content.  The ideal soil has a specific physical structure.  That is 25 percent air, 25 percent water, and 50 percent mineral content – of which 5 percent or more of that mineral content would ideally be humus (see related pie chart.)

Textbooks on soil science illustrate the physical structure of an ideal soil as 50 percent solids and 50 percent pore space.  However, none of those books go on to provide what changes are needed in order to enable soils that are lacking such qualities reach that correct physical structure.

Achieving the ideal physical structure for each soil – the proper amount of air in relation to water in each soil – can only be correctly determined by measuring the percentage of saturation of the elements that have a major influence on pore space in that soil.  To correctly understand and farm the soil, those elements are calcium, magnesium, potassium and sodium.

In order to bring the physical structure of a soil into alignment with the textbook definition of an ideal soil; first measure and adjust the base saturation percentages of calcium, magnesium, potassium and sodium to match the correct percentages needed for the total exchange capacity (TEC) of that particular soil.  The pie chart in this article shows those needed relationships.

Making any needed corrections will help promote the proper nutrient uptake, the proper physical structure, and the ideal biological environment for the soil and the crop.

In other words, to optimize needed soil aeration the correct relationship between specific elements, namely calcium, magnesium, potassium and sodium must be achieved.  When there is too much of any one of these, there will usually be too little of one or more of the others.  Until any excesses or deficiencies of any of these four elements are corrected, the soil will not have the ideal amount of air in relation to water.

Since calcium and magnesium are by far the most needed and thus provide the most influence of the four elements involved for building the proper soil structure, always consider correcting them first.  This is the place to begin if soils do not already have the ideal physical structure and thus the ideal amount of air to provide for optimum biological activity.

Balancing Calcium and Magnesium

Before correcting calcium and magnesium levels, there are three basic points that need to be understood.

First, the base saturation percentage of calcium plus magnesium always needs to equal 80 percent in order to achieve the correct physical relationship between air and water in the soil.  In other words, the proper relationship between calcium and magnesium ultimately determines the friability of each soil – whether it is too tight or too loose or works up as it properly should.  This relationship applies to every soil with a TEC of 4.16 or higher.  (Lower TEC soils must be treated differently and require a separate course to explain all the differences to consider.)

The second point is concerned with the reaction of calcium and magnesium to one another in terms of changes in the soil’s base saturation.  The change is generally expected to be 1:1.  This means that for every 1-percent increase in calcium, the magnesium will decrease by 1 percent.  And also, for every 1 percent magnesium goes up without adding more calcium to counteract it, the calcium will decrease by 1 percent.  (But watch higher TEC soils.  Some have magnesium trapped between the layers of clay, while others may have an abnormally high pH, or percentage of potassium or sodium that affects magnesium availability.)

This brings up the third point which is, the principle of nutrient balance involves correcting the obvious deficiencies in order to help control any excesses.

Here is the basic foundational key to excellent soil health: Work to supply each soil with the proper amount of needed air and that soil will be most equipped to perform at its best.  And only a detailed soil analysis will provide the necessary information to show what is needed to promote the needed air in each soil.

Cover crops, compost, adding carbon and nutrients can all help contribute to soil health, but until there is enough air in the soil, that most critical component will still slow the way to excellent soil health.

Once the required percentages of calcium, magnesium, potassium and sodium are met, then the soil chemistry is working at its best and providing the proper physical structure for air and water to function as they should due to well aerated soil.  Will it always be perfect?  No.  Too much rain can reduce aeration, not enough water can cause problems as well.  But once the soil nutrients are there in the correct proportions, only then does the soil have the best means of re-adjusting to the most ideal conditions in the shortest period of time.  Until the conditions are met for proper aeration in each soil, there is no chance of achieving what is needed for an ideal in terms of soil fertility and plant health.

Neal Kinsey is owner and President of Kinsey Agricultural Services, a consulting firm that specializes in restoring and maintaining balanced soil fertility for attaining excellent yields while growing highly nutritious food and feed crops on the land.  Please call (573) 683-3880 or see for more information.