All sustainable farming systems and practices recognize one fundamental principle: Soil is not merely a dead substance or planting medium, it is a complex, living ecosystem. This ecosystem, comprised of bacteria, protozoa, fungi, insects, invertebrates, plants and small animals are in constant activity. It is this this biological activity which creates fertility and structure in the soil. Let us take a closer look at how this all works.
Organic matter is the fuel for this entire system. Plant and animal substances such as stems, leaves, roots, fruits, manures, organs and even hair, wood and bone are all examples of organic matter. These substances provide food for the entire ecosystem. They also provide other benefits such as structuring the soil, allowing for good drainage leading to oxygen rich environments that soil organisms need to thrive. Organic matter also brings the PH of the soil closer to the 6.5-7 PH that microbial life prefers.
Some organic matter is more appropriate than others however. In general, decomposed plant matter and manure of ruminants (cows, buffalo, horses, goats and rabbits) are more appropriate and can be added in large amounts. Others, such as animal by-products and manure of omnivores and carnivores should be processed properly and used in measured amounts.
The best way to break down organic matter is through composting. The method of composting will determine the speed of decomposition and microbial life that is created. The materials used in the compost will determine the if there more is Humic or Fulvic acid created. Composts made with material that is high in Carbon will create more fulvic acid, which is what builds up soil structure. When building composts, pay attention to the Carbon- Nitrogen ratio of the materials. If your composts contain relatively more nitrogen, it will result in more Humic acid, which is where most of the plant nutrition is found. In addition, physiologically active substances are also found in the humic acid portion of the composts. These substances can confer greater pest resistance as well as drought and waterlogging tolerance.
Fungi are sessile (immobile) organisms, kind of like plants. They are made up of two parts, the mostly hidden mycelium, which are similar to plant roots, and the mushroom, the reproductive part of fungi, which we see above ground. Fungi is able to break down organic matter that is very tough to decompose like wood, bone and even stone! Mycelium is able to penetrate into the smallest of spaces and digest the matter there. These mycelial networks can sometimes stretch across vast areas. In fact, the largest organism in the world is a fungus, encompassing several states.
These are living organisms that are extremely small, and invisible to the naked eye. They can however be observed by microscope which is what has allowed us to learn so much about them.
Bacteria are the first on the scene. These single cell organisms feed on certain parts of organic matter, namely carbohydrates, acids and fats, quickly multiplying in number. This in turn attract protozoa and other multicellular organisms that feed on bacteria. As these organisms feed on bacteria, they produce waste, some of which is plant available nitrogen. Through this activity, much of the nutrition a plant needs is generated in a controlled manner.
These are the critters which we can see without need of magnification. Earthworms, Millipedes, Pill Bugs, Springtails and beetle larvae are just a few of the many macro-organisms that live in the soil. These creatures feed on bacteria, protozoa and each other, and in turn create waste which is also plant available. This allows for a complete plant food to become available in the soil. Due to their relatively large size, the movement of these creatures also till the soil. Earthworms are extremely valuable in this respect. They feed on bacteria found on decomposing organic matter, and will burrow all over the top 3-4 feet of soil to find their food. As the earthworms move around, they create many tunnels that are lined with their waste. These tunnels serve as pathways for plant roots. Not only that, the vermicast lining these pathways are a potent natural fertilizer.
Larger animals to a smaller extent play a role in maintaining soil health. Some, like rodents, bats and birds feed on the macroorganisms and their waste serve to enrich the soil. Ruminants, such as bovines, goats, horses and rabbits have special bacterial cultures in their digestive systems, designed to break down cellulose in tough plant matter. Their manure is rich in this bacteria, which supplements the soil ecology.
Plant Biological Activity
Plants also have the ability to encourage biological activity in the soil. Through photosynthesis, they are able to synthesize carbon dioxide from the atmosphere and convert it into carbohydrates and fats which they pump into the soil through their root systems. This action encourages bacterial colonization of the root zone. Apart from jump starting the processes described above, the good bacteria provides protection to the plant roots simply by being there. It has been proven that large amounts of good bacteria can eliminate the presence of pathogen- causing bacteria. Furthermore, plants that are able to practice this exchange become better at it, as do the following generations as a product of epigenetic biology.
The processes outlined above are what allow sustainable farmers to do away with the costly conventional system of tilling the soil and manually adding all the nutrients that the plants require. By simply adding appropriate organic matter, sustainable farmers are able to reap all the benefits that biological soil activity can provide.
Microorganisms provide fertilization and protection, macroorganisms till the soil and provide further nutrition. While it takes time to reach this point, you will find that your input and efforts decrease while yields and plant vitality increase.
Aside from all the articles cited on this page, one very strong proof of this is shown in the experiments conducted by the Rodale Institute, who have been growing crops using all possible systems side by side for 50 years now. The system that consistently provides the highest yield is organic no-till. This is undeniable proof that Soil Biological Activity creates the fertility you need to grow healthy plants!