THE BIOLOGICAL FOODWEB IN SOIL
What is the biological soil foodweb?
It is the variety of microorganisms that interrelate in fertile soil. The numbers are staggering. In a teaspoon of fertile soil, the following organisms are found:
1 million to 100 million individual bacteria
5 to 60,000 meters of fungi
100 to 100,000 protozoa
5 to 500 beneficial nematodes
A few to several hundred thousand microarthropods
The interactions and diversity of these organisms form a web of life that supports all plant and animal life. If soil receives heavy treatments of pesticides, and/or synthetic fertilizers, many of the tiny organisms die. If the balance between the pathogens and beneficial organisms is upset, the opportunistic, disease-causing organisms will attack the plants.
What is the biological soil foodweb?
It is the variety of microorganisms that interrelate in fertile soil. The numbers are staggering. In a teaspoon of fertile soil, the following organisms are found:
1 million to 100 million individual bacteria
- The species of many are unknown to scientists. Bacteria break down easy-to-use organic material, and retain the nutrients, like N, P and S, in the soil. The waste products bacteria produce become humus. Humus can be used by a large number of other soil organisms, exemplifying the classic statement that "One man's waste is another's treasure". Productive soil should contain more bacteria than any other kind of organism.
5 to 60,000 meters of fungi
- Fungi break down the more difficult-to-decompose organic matter and retain those nutrients as fungal biomass. Like bacteria, fungal waste products become humus and these waste materials are used by other organisms. Soils require fungal biomass for greatest productivity, but for best crop growth, there should be an equal biomass of bacteria as compared to fungi.
100 to 100,000 protozoa
- These organisms are one-celled, highly mobile organisms that feed on bacteria and on each other. Because protozoa require 5 to 10-fold less nitrogen than bacteria, N is released when a protozoan eats a bacterium. That released N is then available to plants. Between 40% and 80% of the N in plants can come from the predator-prey interaction of protozoa with bacteria.
5 to 500 beneficial nematodes
- Beneficial nematodes eat bacteria, fungi, and other nematodes. Nematodes need even less nitrogen than protozoa, between 5 and 50 times less than fungal hyphae contains. Thus when bacterial or fungal-feeding nematodes eat bacteria or fungi, nitrogen is released, making that N available for plant growth. Plant-feeding nematodes are pests because they attack plant roots. These "bad" nematodes can be suppressed by nematode-trapping fungi.
A few to several hundred thousand microarthropods
- These organisms have several functions. They chew the plant leaf material, roots and stems into smaller pieces, making it easier for bacteria and fungi to find the food they like. Arthropods then feed on bacteria and fungi and because the C:N ratio of arthropods is 100 times that of the bacteria and fungi, they release nitrogen that is available for plant growth.
The interactions and diversity of these organisms form a web of life that supports all plant and animal life. If soil receives heavy treatments of pesticides, and/or synthetic fertilizers, many of the tiny organisms die. If the balance between the pathogens and beneficial organisms is upset, the opportunistic, disease-causing organisms will attack the plants.