All soils have a range of permanent soil-borne disease organisms. But these are kept in check in a balanced soil containing many non-pathogenic microorganisms. There are many factors that affect the balance of soil including drainage, soil temperature, soil composition, pH level, quantities of disease suppressing microorganisms, and the adjacent surroundings.
25% of the Earth’s species live in the soil and are microscopic. These include bacteria, fungi, protozoa, and nematodes. They are all important in the soil for cycling of carbon and nutrients, soil fertility, water filtration, and soil aggregate formation. Pathogenic microorganisms can become dominant only if certain soil and atmospheric conditions are met.
Anaerobic vs. Aerobic
What do these terms mean?
An anaerobic soil contains little to no oxygen. Examples are wetlands, rice paddy fields, mud flats and hydrothermal vents. These are areas that are high in sulfur, nitrate, sulfate, and fumarate. You can tell an anaerobic area by its “rotten egg” smell if the soil is high in sulfur or by its foul odor. Some of that odor is methane, a dangerous greenhouse gas. Your compost pile can become anaerobic if it isn’t turned. You’ll know by how it smells. If your compost has become anaerobic (smelly) there will be a different community of microorganisms breaking down the organic matter than if it remains aerobic through turning. An anaerobic soil leads your crop to struggle.
An aerobic soil is well oxygenated. It will also contain soil water pores. There isn’t the foul odor associated with anaerobic soil. The microorganism community in an aerobic soil is quite different than the anaerobic community.
But just because a soil is aerobic and has diverse microorganisms doesn’t mean it won’t contain pathogens that can cause soil-borne diseases in plants, humans, and animals.
Soil-borne Diseases And A Balanced Soil
Whether anaerobic or aerobic, soil has to have a balance of bacteria, fungi, nematodes, protozoa, and all the other macroorganisms that make up the Soil Food Web. A minority of soil microorganisms are pathogenic. They are opportunistic and may infect plants, people, or other animals in numerous ways. They may also end up in a body of water through water erosion. If you have cattle drinking that water, or you’re pumping that water for farm use you’re cycling pathogens back into your soil.
More pathogenic organisms are found in disturbed soil than in forests. This means that humans are responsible for a great deal of the soil-borne disease pathogens. Through agricultural and gardening practices we have disturbed the soil balance.
What Part Of The Soil Microbial Community Is Pathogenic?
Pathogenic microorganisms are part of the soil ecosystem. It’s only when there is an imbalance of types of microorganisms that the microbial community becomes pathogenic.
Pathogenic organisms are natural in soil but when humans add animal urine and feces, or manure, which are major sources of disease pathogens, an imbalance of soil microorganisms occur that may lead to pathogen imbalance. Once in the soil they can survive for extended periods of time. E. coli is an example of such a soil-borne organism. Many studies have been conducted and found:
- Poor hygiene. Farms and processing facilities that do not have a strict protocol regarding restroom usage and hand washing have seen more outbreaks of E. coli than other farms and facilities.
- Contaminated irrigation water. As water is becoming a more valuable resource much irrigation water is being recycled. Regular water tests will save you money and your reputation.
Although the soil does contain pathogens, keep in mind that the vast majority of microorganisms in soil are part of an ecosystem that provides many essential benefits to plants, people, and animals. Understand the ecosystem conditions and farming practices that promote disease. Regularly monitor your crops to catch any issues before they become major, and you will avoid plant pathogenic problems on your farm.
How Does Soil Health Impact Human Health?
Soil-borne diseases can become a health concern due to several reasons. If you step on a piece of rusty metal you need to get a tetanus shot (unless you’ve had one recently). The bacteria Clostridium tetani (which causes tetanus) may be on the rusty metal but it actually lives in soil, dust, and manure. The fact that it is still alive on the metal attests to its ability to survive.
Bacteria are the most abundant microorganism in the soil. Salmonella, E. coli, and Campylobacter are common bacteria found almost worldwide that we usually consider pathogenic. But each of these bacteria have diverse families, some members may be pathogenic, while most are not. E. coli has a strain that carries a soil-borne disease, but most E. coli are harmless and are even a part of a healthy human intestinal tract.
Soil-borne diseases impact immunosuppressed people the most. But even people with healthy immune systems can become ill. The majority of soil-borne diseases are caused by opportunistic microorganisms. They infect plants, people, or other animals by ingesting the pathogen, inhaling it, or through an open wound. As the wound heals over our body creates a perfect environment for the microorganism to grow. A healthy immune system will take care of that foreign microorganism.
Farming practices also impact human health. When you’re discing your field and creating dust, you’re putting pathogens that were in your soil in the air. If it’s a windy day those soilborne pathogens may end up at your neighbors. Breathing in that dust is also breathing in soil-borne disease pathogens.
How To Reduce Soil-Borne Diseases
There are several common-sense practices we all can do to decrease the chance of becoming ill from a soil pathogen. There are also some practices we need to consider.
- Wear gloves when gardening or farming. This seems to take some of the joy out of “playing in the soil” but if you know your soil doesn’t have any raw manure you can take them off.
- Wash your hands after touching soil, animals, or materials that may have manure on them. Manure is the #1 source of pathogens. When you get done gathering the eggs, walking your fields for monitoring, or harvesting - wash your hands.
- Reconsider discing your fields. Consider cover crops. Airborne pathogens are just as dangerous as soil-borne and can be avoided by agricultural practices that use no-till or minimum till.
Healthy soil is soil in balance. There are bacteria, fungi, nematodes, protozoa, and other organisms in your soil that act as prey and predator. When we disturb this balance, we create opportunities for soil-borne disease pathogens to dominate the Soil Food Web. When we try to solve the imbalance with pesticides and herbicides, we create a greater problem.
Working with nature instead of against her will right the imbalance. Pathogens in the soil won't have a chance against an army of beneficial microorganisms. Soil health is important to human health. The pathogens that create soil-borne diseases that affect human health become less virulent with a balanced soil and when we understand the impacts, we, as humans, have on our own health.