Understanding the Soil

February 1, 2018

Do you really need to "replace what you remove" when growing a crop?

For thousands of years, nature has sustained all living things through natural soil fertility. This remains true today, with one exception: Farmers have been managing their soils with the idea that “what you remove, you must replace.” While this is not totally wrong, the most important piece has been left out—how we replace nutrients.

The Balance Sheet Theory

In 1840 German chemist Justus Von Liebig produced the “balance sheet theory.” It stated that the soil is a medium—devoid of life—that merely stores water and inorganic minerals. Von Liebig observed that plant growth and yields were in exact proportion to the mineral nutrients removed from the soil. This discovery led those in agriculture to believe that the solution to sustainable soil management was to replace, in any form, the mineral content that was removed by the plant, thereby maintaining soil fertility. 

This is wrong. If we accept this principle, how can we explain nature’s ability to support life when chemical fertilizers are not added? Why do the great forests survive and flourish? How were the grasslands of the Great Plains maintained before man came along? Obviously, we have overlooked something. If this theory were relevant, the problems of soil degradation would not be a consideration today. Science has since determined that Von Liebig’s theory has no foundation in nature’s fertility. 

In USDA's 1957 Yearbook, Von Liebig’s theory was discounted as having no basis in the overall picture of soil management.

Von Liebig himself denounced the balance sheet theory before his death.

Von Liebig’s theory leaves out the most important consideration—the interactions of the biological life cycle in the soil. The fundamentals of soil fertility begin with the living organisms that inhabit the soil.

Despite science disproving it, why have agricultural research establishments held on so tightly to the balance sheet theory? Could it be possible that it inflates the profits of multi-national corporations involved in the manufacturing of farm fertilizers and chemicals? It is well documented in western society that the science of exploitation is the most finely honed, financed, and researched science in the world today. 

Unfortunately, the steward of the soil—the farmer—is the easiest prey. It is also well known that most research today is contingent on private funding from these major corporations. Imagine how easy it is to come to a (profitable) predetermined “answer” to today’s problems in agriculture.

We can accept these conclusions of modern research, or we can open our eyes to what scientists, without the influence of these ingrained soil management principles, have been saying for many years. The fundamentals of soil fertility begin with the living organisms that inhabit the soil. 

Life in the Soil

There is a far greater abundance of life within the soil than above it on the surface of the earth. Within soil lies the key to survival for all life forms on the surface of the earth. Soil contains so many diverse life forms that, even today, the study of these organisms is one of the most complicated and misunderstood sciences. You can compare soil organisms to our society above ground: every individual is dependent on others for certain needs. Therefore, soil harbors complexity that you can’t ignore or simplify, as in Von Liebig’s balance sheet theory. We must consider each soil organism as a piece of the overall system. We know that as essential pieces decline in the system, so does the strength of the complete community. Like a chain, the soil’s ecosystem is only as strong as its weakest link.

To understand this complex system, we must learn about the various types of organisms living in the soil. There are five basic families of microorganisms:

  1. Bacteria
  2. Algae
  3. Fungi
  4. Protozoa
  5. Actinomycetes
In one gram of healthy, fertile soil, billions of microorganisms may thrive.

Of all microorganisms, bacteria make up the greatest number. They are an extremely diverse species and perform a wide variety of functions. 

Bacteria control the nitrogen, carbon, sulfur, and iron cycles in the soil and are responsible for nitrogen fixation from both the air and minerals. They are also predominant in the creation of enzymes and the breakdown of mineral elements into plant-available nutrients.

Algae flourish in high-moisture conditions. The blue-green variety are very efficient at nitrogen fixation, but their valuable services diminish with moisture loss in the soil. 

Fungi are mainly decomposers and generally work deeper in the soil than the other species. 

Protozoa are amoeba that consume bacteria, thereby concentrating and passing on nutrients.

Actinomycetes are primarily involved in the breakdown of organic matter and produce incredibly fertile soil. 

Microorganisms can be either plant-like or animal-like in form, and must compete in a constant struggle for survival. Some microorganisms are aerobic (oxygen-requiring). They use elements from the air in the production of plant nutrients. Others are anaerobic (cannot live with air). They live deep in the soil and produce toxins that further break down organic matter and minerals into forms that plants and other organisms can use.

There are many factors that determine the number of microorganisms in the soil. The most important factor is their food source. Many species rely on crop wastes and organic matter incorporated in the soil for food. Still others may live off the remains of other dead organisms. Hence, nature achieves a balance between species so that none of them becomes predominant. However, the use of toxic chemicals in modern agriculture has profoundly affected this balance. Since some of these organisms are plant-like in nature, does it not seem correct to assume that a herbicide that can kill a 24-weed-spectrum would have devastating effects on these tiny organisms? Beyond this problem lies another—these microorganisms must clean up any substance polluting the soil. As the microbes work to break down toxic substances, their dead bodies are being used as a food source for other organisms in the soil. These toxins are carried up through the food chain to plants and animals, including humans. 

Another method that nature uses to control the various microbial populations includes the build-up of excrement, or by-products, of that organism. A good example is nitrogen-fixing bacteria. If high quantities of nitrogen are added to the soil, certain species will assume that their “job” is complete based on the amount of by-product in the soil. The numbers of nitrogen-fixing microbes can be seriously diminished, while other microbes concerned with the breakdown of this nitrogen will flourish. Thus, by applying high quantities of nitrogen, we have created an imbalance that has other repercussions. What about the organisms that use this nitrogen fixer as a food source? It would make sense that a decline in available food would make the population of these organisms decline also. While all this is happening, other organisms dramatically increase in number. What happens to their remains? Is there another group of microbes that, with an expanded food supply, will increase in number?

Disturbing the balance of nature usually leads to disaster. 

Remember: any chain is only as strong as its weakest link.

There are many larger life forms in the soil that compete for survival. They include mites, springtails, ants, millipedes, sow bugs, rotifers, and worms, to name a few. This group also includes the ultimate soil engineer—the earthworm. This fantastic mobile soil factory carries out many worthy functions. As the earthworm burrows through the soil, it carries tons of organic matter deep into the soil. On its return trip, it brings up minerals for plants and other microorganisms to utilize. In its travels, the earthworm also consumes microorganisms and organic matter, leaving behind nutrient-rich castings (excrement). 

Earthworm castings contain 5 times more nitrogen, 9 times more phosphorus, 19 times more potassium, 3 times more calcium and 4 times more magnesium than is naturally present in the soil surrounding it.

Earthworms produce their own weight in castings each day (about ½ pound per year per worm). An acre of fertile soil can contain as many as one million earthworms. This means that as much as 500,000 pounds of castings can be created in a single acre each year—the equivalent of nearly 9,000 bushels of corn per acre by weight. There is no denying the value of the earthworm’s services to the farmer.

Right now, poor soil management practices have degraded the soil to levels that are seriously threatening the soil organisms. Fortunately, nature can be forgiving if we work within its laws. Good soil management practices will quickly stimulate a rebirth in soil organisms if the environment is improved. As farmers, we must strive immediately to gain a new perspective in dealing with the natural fertility cycle.

Continue reading the subsequent article on Understanding the Soil Fertility Cycle.

George Sims