Effects of Pesticides on Soil Micro-Organism

Crop dusting with pesticides.

The effects of pesticides on soil micro-organisms can cause a ripple effect that can last for years. Micro-organisms are essential to healthy soil. Without them, your plants will not reach their true potential.

What are Micro-Organisms?

Micro-organisms are organisms that are too small to be seen with the human eye. They live on the top-most layer of soil. There are many micro-organisms which live in the soil including:

  • Bacteria
  • Fungi
  • Algae
  • Protozoa

Micro-organisms are responsible for the decomposition and recycling of organic materials in the soil. They aid in the plant's absorption of essential nutrients. An example of this is the nitrogen fixing bacteria, Bradyrhizobium, which lives in a nodule on the soybean plant. It provides nitrogen to the plant and boosts growth.


Biopesticides are micro-organisms that can help a plant defend itself against pests. These micro-organisms include antimicrobial metabolites, antibiotics and extracellular enzymes. The potential of these biopesticides has not been fully examined by scientists. It is hopeful that science will be able to re-produce the effects of the biopesticides, which will help to eventually eliminate the need for harmful chemical pesticides.

What Pesticides Do

Pesticides are designed to kill bugs that are harmful to plants. Pesticides kill specific pests on plants such as slugs, beetles and flying insects. The chemicals used in most pesticides can kill more than just garden pests; they can kill the helpful organisms that live in the soil. Some of these chemicals can remain in the soil for years, effectively keeping necessary micro-organisms from working the soil.

Common chemical pesticides that are used in gardens and by large-scale crop producers include the following:

  • Basic Copper Sulfate
  • Silica Gel
  • Sodium Fluoride
  • Carbon Disulfide
  • Hydrogen Cyanide
  • Methylchloroform
  • Fenthion
  • Boric Acid

There are literally hundreds of pesticides that have been manufactured and applied to soil in the past. We are beginning to understand the ramifications of using these toxic chemicals on the soil. In places where the chemicals are used extensively, plants will no longer grow at all, or will fail to thrive.

The Effects of Pesticides on Soil Micro-organisms

Unfortunately, many pesticides can kill more than just their intended targets, namely the necessary micro-organisms in the soil. When chemicals are used for a period of time on plants in an area, they will eventually leach into the soil. Once in the soil they can kill the micro-organisms living in the soil that break down organic material and aid in plant growth. It can take years before micro-organisms can once again live in soil that has had toxic chemicals applied to it.

Alternatives to Harmful Chemical Pesticides

For the average gardener, the use of organic pesticides can keep a healthy balance in the soil. Many organic pesticides are made of minerals or other plant materials that will keep pests at bay and break down quickly in the soil. Examples of some common organic pesticides include the following:

  • Cayenne pepper spray--Can be sprayed on the leaves of plants to deter harmful insects.
  • Soap spray--Also sprayed on plants to get rid of aphids.
  • Tobacco powder--A spray can be made from the finely ground tobacco leaves and water. It is used to kill sucking insects on plants such as aphids, thrips and spider mites.
  • Pyrethrin--Made from the chrysanthemum plant. This organic pesticide is used to knock out flying insects and ground pests such as grubs.
  • Neem--Derived from the neem tree. Used to control Gypsy moths, leaf miners, mealy bugs, whiteflies and caterpillars.
  • Sabadilla--Derived from the sabadilla lily. Used to control caterpillars, leaf hoppers, stink bugs and squash bugs.


For decades people have believed that harmful chemical pesticides were the only true way to rid gardens and crop fields from pests. Soil pollution has occurred from the use of pesticides and it takes years and sometimes decades for some of these chemicals to break down. Luckily there are many organic chemicals that are just as effective. The effects of pesticides on soil micro-organisms are less invasive when organic pesticides are used.People need to break the habit of using harmful pesticides and switch to using organic ones that break down quickly in the sunlight and in the soil. The faster a chemical breaks down, the sooner the soil can return to a healthy state. Most organic pesticides are also safe to use around people and pets. They can easily be washed from fruits and vegetables making them healthier for you and your family to eat.

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Effects of Pesticides on Soil Micro-Organism