If a plant is not growing well, there are four potential problem areas. Too little or too much light. Watering. Pests and diseases.

And the most mysterious, soil. For many people, the stuff that happens underground is a complete unknown.

One of the most important things is the organic matter content (Any dead flora, fauna or microbe), but few really understand why.

This article will explain why it is much more than just a source of nutrients for plants.

Organic matter is extremely important for providing soil its physical and chemical characteristics.

Increased microbial activity

The cycle of life is based on carbon-based compounds such as sugars, fats and carbohydrates.

“Organic” in Organic Matter means that it is Carbon-based (organic matter typically consists of 60% Carbon), which makes organic matter soils a breeding ground for organisms such as bacteria, fungi, actinomycetes, algae, protozoa, nematodes, arthropods and earth worms, also called microbes or fresh organic matter.

These microbes need carbon-based food, water, air and the right temperature and in return they help the plants with mineralization of organic matter, fixing Nitrogen, soil aggregation, producing chelates (for metals such as Iron, Zinc, Potassium, Calcium and Magnesium), protection against diseases and pests and the distribution of nutrients, water and air.

Mineralization of organic matter & Nitrogen fixation

The food of plants consists for 96% on non-mineral nutrients such as Oxygen (O), Hydrogen (H) and Carbon (C), which are absorbed from the air (CO2) and water (H2O). 

The other 4% stems from mineral macronutrients such as Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg) and Sulfur (S) and many micronutrients.

These minerals can be found in organic matter, but can’t be accessed by plants due the cell membrane protecting the cell contents such as nitrates, phosphates, sugars, amino acids, proteins, fats and carbohydrates.

Microbes excrete chemicals to break the cell membrane and then mineralize the larger molecules into simple minerals and ions, which can then be absorbed by plants (nitrates and phosphates) and microbes (sugar and other carbon-based compounds).

Much of it is also stored in soil particles for future use. This makes organic matter a long-term and continuous nutrient source.

Nitrogen is probably the key ingredient to be concerned about. It is the most abundant in plants and the one that soil is most likely lacking, especially because it is very unstable. It is easily converted from one form to another and washed away quickly. The plant-available forms of Nitrogen account for only 3% of the Nitrogen in soil. The rest is tied up as large molecules in both living and dead organic matter.

The role of bacteria in particular is very vital as they fix Nitrogen from the air.

Most of the useable Nitrogen in soil, besides synthetic fertilizer Nitrogen, is produced and provided by bacteria. Specialized nitrogen-fixing bacteria are able to take the nitrogen gas and turn it into ammonium and nitrate ions.

The plant releases root exudates into the soil, which contain a wide variety of molecules (sugars, carbohydrates and proteins), to form symbiotic relationships with microbes. Exudates influence several factors within the soil such as nutrient availability, soil pH and recruitment of bacteria and fungi.

The plant then forms a growth around the bacteria to provide an anaerobic environment and protect it. The plant feeds sugars and other nutrients into these nodules and the bacteria give nitrogen back in the form of ammonium, which is converted to nitrate. This is helpful for the plant, but also costs the plant 20% of its sugars produced by photosynthesis.

Distribution of nutrients, water and air through soil aggregation

Plants, bacteria, fungi, earthworms and other small insects all excrete juices, of which some work great as a glue, which forms aggregates in the soil. There is a direct relationship between size of aggregates and fungal biomass / mycelium.

This creates larger pore spaces, which make it easier for roots, water and air to move through the soil, increasing drainage and providing oxygen for the plant roots. This oxygen is important as roots absorb O2 and give off CO2, which allows plants to convert sugars into energy.

The structure of aggregates is fairly loose and contains many small pores that hold a lot of water. Small particles have a large surface area and many small pores. After a rain, most of the pore spaces are full of water, but that soon runs away. What is left is a lot of soil particles that are each covered in a thin film of water that lasts for days, and even weeks. Plant roots use this to get their moisture.

Nutrients also stick to the surface of particles, so a larger surface area also means that there are more nutrients available to the plants.

Besides these benefits, the aggregates also indicate a healthy soil system since they form only if the amount of dead organic matter or living microbes is high enough, both being critical for plant growth.

The role of fungi in particular is very vital as it can extend the effective root system of a plant, increasing its ability to access nutrients and water.

Just like with bacteria, 95% of plants form a symbiotic relationship with mycorrhizal fungi.

The plant shares 15% of its food in the form of sugar and other nitrogen sources to the fungi. In return the fungi forms a sheath which are able to exchange chemicals with the roots. This fungi hyphae can extend the effective root system of a plant by a factor of 1.000.

Protection against pathogenic microbes

The majority of microbes are good ones, but there are also pathogenic ones that cause diseases. The reason plants are not infected more is that there is tremendous competition in the soil. Microbes are constantly at war for space and food. Since the majority are good guys, they tend to win due to sheer numbers. The key to healthy plants and pathogen control is to maintain a large number of microbes that show a wide diversity.

Protection against chemicals

All kinds of chemicals are added to the soil. Plants, microbes and animals excrete thousands of chemicals, but also human-made chemicals and air pollution provide for a toxic soil, if it were not for the microbes who absorb and compose almost any chemical added to the soil, with the exception of Mercury and Cadmium.

Increased Cation Exchange Capacity (CEC)

Soils with a high organic matter content are negatively charged and increase the CEC.

A high CEC means that the soil can hold more positively charged ions (cations).

Many of the nutrients critical to plant growth are cations, and therefore, the ability to hold them in the soil is a key property. Nitrate f.e. is negatively charged and leaches quickly through the soil, whereas ammonium is positively charged which helps it stick to the positively charged organic matter. The downside of using ammonium is that this will lower the pH. Therefore the general fertilizer consists of 60% nitrate and 40% ammonium.

High CEC-soils also have a greater water holding capacity, because the electrical charges on the water molecules are much stronger than the force of gravity. This also reduces the evaporation.

Over time, evaporation, gravity and plants do reduce the levels of water in the soil. Normally plant roots can only grow into large pores and medium pores. Now that the surface of the root comes in contact with water, the cohesion of water and the electrical charges also attract the water from small pores.

Last but not least, acidification is more difficult, since the hydrogen ion is a cation.

How to improve the organic matter content and increase microbe populations.

·       Supply fresh organic matter with a C:N ratio of 30:1 (Compost, mushroom compost, manure, leaf mold, straw and hay, wood products, plant-based meals, agricultural by-products, peat moss and coir).

·       Provide good aeration by reducing compaction and increasing aggregation.

·       Maintain even moisture levels.

·       Keep temperatures between 25 and 37 degrees Celsius for as long as possible by using mulch.

·       Raise pH in very acidic soils (neutral pH is best).

·       Provide adequate nutrients, but not excess amounts.

·       Limit chemical treatments for pathogenic microbes. Anything that kills pathogens also kills beneficials.

**Peat soils, in comparison to sandy soils, clay soils and mineral soils, are also called organic soils with an organic content of more than 20%.**