Understanding the microbiology and biochemistry of the soil is an important part of understanding how plants grow, but what are soil microbiology and soil biochemistry? And how do they influence plant health and nutrition? To answer these questions, let’s turn to the soil.
The Soil is a Living Environment
The soil is a living environment, full of organisms that influence plant growth and health. These organisms include visible inhabitants, such as earthworms, as well as a multitude of microorganisms – including bacteria, fungi, protozoa, nematodes and microarthropods. Together, soil organisms large and small make up about 5% of the soil organic matter. Plants – through their growing roots – are also part of this living environment. Many microorganisms live in close proximity to plant roots, an area known as the rhizosphere, where there is a rich food source for them in the form of exudates released from the roots.
Soil-plant system
As soil organisms interact with each other and with the soil, they influence the soil-plant system physically, chemically and biochemically. Temperature, moisture, aeration, pH, soil pore spacing, and types of food sources affect how active soil organisms will be, as well as how many and what types of species will be present.
Key beneficial roles of soil microorganisms:
- Decompose organic materials
- Recycle nutrients in the soil by converting organic materials into forms plants and other soil organisms can use (mineralization)
- Generate oxygen in the atmosphere, which is important for plant respiration
- “Fix” nitrogen from the atmosphere by converting it to ammonium (nitrogen fixation), making it available to plants
- Retain nutrients such as nitrogen or carbon in their cells, keeping them in the root zone (immobilisation)
- Feed on each other, releasing immobilized nutrients in their excretions (e.g., protozoa and nematodes that excrete excess nitrogen when they eat bacteria and fungi)
- Give plant roots access to soil nutrients by transporting them to the plant (i.e., the mycorrhizal fungi that colonize plant roots)
- Bind soil particles into aggregates, helping with soil structure and water dynamics
- Help to suppress plant diseases by competing with or feeding on pathogens
- Degrade soil pollutants.
Soil Microorganisms in Plant Health and Nutrition
Microorganisms play many beneficial roles in plant health and nutrition. Through their activities, they help plants extract the nutrients they need for growth and functioning. They also affect the soil structure, influencing water dynamics on, in and through the soil. In addition, although some microorganisms can cause disease, many more help protect the plant from pathogens.
Biochemical Interactions in the Soil-Plant System
Many of the interactions in the soil-plant system – whether among the microorganisms and between microorganisms and plants – occur through biochemical signaling, particularly in the rhizosphere. Biochemical compounds produced by microorganisms and by plant roots are the tools by which biochemical signals are created and transmitted. They are the tools that microbes need to function in the soil, and determine their ability to process nutrients (including the nutrients in fertilizers), stimulate root growth and perform other functions critical to plant health and nutrition. With up to 50 billion microbes in a teaspoon of soil, imagine the number of biochemical compounds that are produced during their lifecycles. Each of these microorganisms may be the source of unique biochemical compounds that affect a variety of soil, plant and microbial community functions.
Biochemistry: The Backbone of Soil Microbial Functioning
Biochemical compounds produced by soil microorganisms include:
- Enzymes that break down organic matter, transform N for energy and perform many other functions
- Proteins that signal changes in microbe response
- Chelators that mobilise nutrients
- Antibiotics that reduce competition
- Compounds that induce plant rooting, change physiological functions, induce immune responses and increase salt tolerance.
Spotlight on N-P-K
When it comes to the “big three” macronutrients that plants need – nitrogen, phosphorus and potassium – why do soil microbiology and soil biochemistry matter?
- Nitrogen: In the soil profile, the great majority of nitrogen (>90%) is typically in an organic form (e.g., in crop residues, manures, litters, composts) and needs to be converted into inorganic forms – that is, ammonium (NH4 +) or nitrate (NO3 -) – that plants can take up and use. This transformation is called the mineralization process. Biochemical compounds produced by microbes in the soil profile mineralize organic nitrogen into an inorganic form that plants can use.
- Phosphorus: A good portion (25%-65%) of phosphorus in the soil profile can be tied up in organic matter. Biochemical compounds help to dissolve, solubilise and mineralise soil phosphorus, transforming it into inorganic forms (H2PO4 – or HPO4 2-) that are available for plant use.
- In the soil, potassium quickly gets locked in between soil layers, becoming unavailable to the plant. Unlike nitrogen or phosphorus, where mineralisation or solubilisation is necessary, potassium remains in the K+ form in both the soil and the plant – but requires a release from the soil profile. Biochemical compounds produced by microorganisms help to improve the soil structure and a plant’s ability to take up potassium.
Soil microbes and the biochemical compounds they make play a major role in nutrient release and nutrient use efficiency. By taking care of soil health -including by using products that enhance the microbial and biochemical activity in the soil – growers can capture the power of soil microbiology and biochemistry and improve the productivity of their growing operations.
Agricen has released a free booklet on Understanding the microbiology and biochemistry of Soil: Click here to download your digital copy of the booklet.
