The future of agriculture is dependent on soil quality. It takes nature about 500 years, in an undisturbed temperate forest, to build one centimeter of topsoil. But modern agriculture can destroy that topsoil in only 2 1/2 years. The use of tillage, synthetic herbicides, pesticides, and fertilizers destroys the life of soil. Human activities impact the quantity and quality of soil microorganisms. Two important soil organisms are earthworms and protozoa, which are found predominantly in the top 6 inches of healthy soil. What farming practices increase these plant allies to improve water infiltration, soil structure, and nutrient plant uptake?
Soil Microorganisms: Your Underground Workforce
The soil food web is made up of bacteria, fungi, viruses, nematodes, protozoa, and earthworms. It also includes the birds and mammals that feed on these smaller organisms. Plants are dependent on soil health and a balance of soil microorganisms for healthy growth.
Earthworms and protozoa are part of the intricate underground ecosystem that significantly influences soil fertility, structure, and nutrient cycling. These two soil organisms improve soil health in different ways. Earthworms feed on organic matter in the soil while protozoa feed on soil bacteria and fungi. In temperate areas, there are three numerous earthworm species and many species of protozoa in the Protist kingdom.
The Ecosystem Services of Earthworms
Some earthworms live in organic matter, while others create vertical tunnels deep into the subsurface soil. Earthworms fall into several subgroups based on their ecosystem services.
- Epigeic earthworms: live on the surface of undecomposed plant material. They’re usually small and reproduce rapidly.
- Endogeic earthworms: live in the top 6 inches of soil and create horizontal, branching burrows. They do best in rich organic soil. They eat a great deal of soil. They are wonderful decomposers of dead plant roots.
- Anecic earthworms: These are your favorite “night crawlers,” they dig deep vertical burrows but come to the soil surface to feed on manure, leaf litter, and other organic matter.
Earthworms have profound effects on the decomposition of organic matter and the formation of humus. Their burrows exist as macropores that offer a path of least resistance to plant root growth, water infiltration, and aeration. Some anecic species of earthworms can burrow through compacted soil and hardpan.
The burrows created by earthworms are lined with their rich feces, called castings, which give plant roots a nutrient-rich growing medium. Their diet includes the microbiota in the soil and protozoa are one member of the microbiome.
Protozoa and Nutrient Cycling
Protozoa are aquatic. That doesn’t mean they only live in ponds and waterways. They live in the water biofilm surrounding each soil particle. Clay soil particles are smaller than sandy soils and have larger surface areas. Water sticks to clay particles which makes for a hospitable environment for beneficial microorganisms, even if you think it makes for difficult farming operations.
Protozoa play an important role in mineralizing nutrients for plant uptake. They aid nutrient cycling by eating bacteria. Free-living protozoa are grouped into three subkingdoms:
- Ciliates: they are the largest and move around using hair-like cilia. They’re found primarily in moist or seasonally wet habitats.
- Amoebae: this group is divided into the Naked (without a covering) or Testate (with a shell-like covering). Amoebae are shape-shifters. They can get into tiny crevices and feed on bacteria that other microorganisms can’t reach.
- Flagellates: these move with a flagella, or whip-like propulsion.
It’s easy to compare protozoa to cattle, as they both graze. Cattle graze on the rich pasture cover crops available because of the ecosystem processes underground, while protozoa graze on bacteria.
Bacteria are tiny one-celled microorganisms that are major decomposers of organic matter in your soil. That’s a good thing, except that the bacteria retain the soil nutrients in their bodies (called immobilization) until they die or are eaten by predators. Enter the one-celled, but much larger than bacteria, protozoa. They are primarily predators of bacteria.
Protozoa, earthworms, and other soil microbiota keep bacterial populations in check. A single protozoan can consume as many as 5 million bacteria in a day. Bacteria are storehouses of nutrients. The protozoa’s digestion system doesn’t need as many nutrients, particularly nitrogen, the excess is excreted, aiding in soil nutrient cycling.
The populations of soil organisms are greatest in the plant root zone or rhizosphere, and when nutrients are released in the predator/prey cycle they’re close to plant roots for uptake. An increased nitrogen cycle efficiency is only one of the benefits of protozoa. The movement and feeding activities of protozoa increase decomposition rates of organic matter in the soil and improve soil aggregation. There is a constant cycling of nutrients between prey, predator, and plant.
Microorganisms are constantly dying and being replaced by new ones, creating a dynamic and diverse soil community. Earthworms and protozoa are essential members of that community, performing many functions such as decomposing organic matter, cycling nutrients, suppressing pathogens, and enhancing plant growth.
To find out how your farm or ranch could be a part of the climate crisis solution, contact our team at STBiologicals.com.
