SCIENCES: Biology

Biology is an intrinsic part of the unique ecosystem that exists in the soil. Each component of the soil has a specific job and all are key players to the function and the efficiency of this system. By creating an environment that promotes the biology's existence, by providing food, and by adopting farming practices that are good for the environment, wonderful things start to occur.

Biology determines quality – the mineral content of the soil and its physical structure are important for the plants well-being, but it is the life in the soil that powers its cycles and provides its fertility. It is the soil biology that makes the minerals and (added) chemicals in the soil available to the plant.

What is the Soil Food Web?

The soil food web is based around the tonnes of beneficial bacteria, fungi, protozoa and nematodes that live in soil or compost. The plants we see above the ground are in a complex symbiotic relationship with microbes in the root zone. It is soil life that provides the “living bridge” to store and make nutrients in the soil available to plants.

There are four main categories of organisms that make up the soil food web.

• Bacteria
• Fungus
• Protozoa
• Nematodes

Each group of microorganisms has a specific job in the soil.

Bacteria

Bacteria are the most numerous microbes in the soil with populations ranging from 100 million to 3 billion in a single gram of soil/compost.

Beneficial bacteria perform the following functions in the soil.

• Assist in organic matter decomposition.
• Are responsible for components of nutrient cycling and retention (especially N).
• Help build soil structure.
• Help with disease suppression.
• Help to decompose toxins in the soil.

Fungi

Soil fungi assist with the “hunting and gathering” of nutrients. Mycorrizal fungi are a key component to soil and plant health.

Soil fungi perform the following functions.

• Assist with enzymatic breakdown of cellulose, lignin, wood, hair (C).
• Decompose toxins.
• Release, recycle, store and transport nutrients. (makes Ca, P and trace minerals available)
• Helps suppress and compete with plant pathogens
• Hyphae (rope-like tubed structure of the fungi) tie soil together to give structure. Fungal glues (glomalin) stick it all together.

Mycorrizal Fungus is a type of fungi that attaches itself to the root of the plant. It has a very special symbiotic relationship with the plant root. By entwining itself around the root, it provides for better protection of the root from predatory bacteria, fungi, and nematodes.

Mycorrizal Fungi perform the following functions.

• Symbiotic function with the roots of the plant.
• Hyphae of the Mycorrizal fungi grab the nutrients that are unavailable to the plant and make them available via the enzymes in the fungi.
• Also does this with water for the plant.
• Mycorrizal fungi builds walls around roots, protecting infection sites and producing antibodies.
• The plant gives the fungi food in return. (simple sugars, proteins, carbohydrates).
• They are present in most growing situations.

Protozoa

The protozoa group is made up of flagellates, amoebae, and ciliates. Excess numbers of ciliates indicate an anaerobic state in the soil.

Protozoa perform the following functions.

• Feed on bacteria, making nutrients immediately plant available.
• Responsible for 40% of the net mineralization.
• When bacteria, with a C: N of 5, get eaten by a protozoan with a C: N of 30. N will be released in a plant available form.

Nematodes

Nematodes are the “living store house of nutrients”. There are 5 main groups of nematodes: bacteria feeders, fungal feeders, fungal/roots feeders, roots feeders, and predators.

Nematodes perform the following functions:

• Beneficial nematodes eat and digest bacteria, fungi and protozoa making nutrients available to plants.
  
• Building soil structure – make tunnels, creating aerobic conditions in the soil.
  

Some nematodes eat and digest the meat of the root-feeding nematodes.

“The Fifth Group”

Microarthropods are sometimes referred to as the fifth group of the soil food web. Some are visual to the human eye, and therefore do not always qualify as microbiology. Despite their size, they still are responsible for important jobs in the ecosystem.

The functions of Microarthropods are:

• Eat organic matter, fungi, and bacteria to make nutrients available to the plants.
  
• Stimulate reproduction of bacteria and fungi.
  
• Build soil structure via tunneling.
  
• “Taxicabs” for bacteria and fungal spores.

Food Web Disturbances – practices that hinder or harm the biology of the soil.

• Clear cutting, thinning
  
• Compaction
  
• Fertilizers
  
• Pesticides, herbicides
  
• Temperatures (hot and cold)
  
• Moisture
  
• Deep or repetitive tillage
  
• Cropping practices
  
• Organic Matter (timing, type, placement)
  
• Air Pollutants
  

(Soil Food Web Canada)

Balance between Bacteria and Fungi depend on the crops to be grown. (This ratio is based on weight of the organisms, not numbers.)

• Weeds - F:B - 1:10
• Early Grasses F:B - 3:10
  
• Mid-grasses, vegetables F:B - 3:4
  
• Late grasses, row crops F:B - 1:1
  
• Shrub, vines, bushes F:B – 2:1 – 5:1
• Coniferous, old growth forests F:B – 100: 1 – 1000:1

Basic Soil Biology tests will give you information you need to determine if your soil ratio is right for your desired crop. For more information, go to www.soilfoodweb.ca.