How Pesticides Affect Soil Microbes

  • 13 March 2015

In a natural soil environment, a cooperative relationship exists between microbes and plants. Plants like grass, trees and food crops depend on microorganisms in the soil to obtain water, solubise nutrients, protect from pests and pathogens, prevent nutrient loss and break down compounds that could inhibit growth. These soil microbes, in return, benefit from the health of plants growing in the soil and substances secreted from the plants root system. This relationship creates a dynamic living system that is easily broken by conventional systems that use pesticides, herbicides and fertilizers. The chemicals that we use to enhance plant growth can actually destroy the soil system, killing or causing mutation pressure on the soil microbes that all other organisms in the ecosystem need to survive.

What Soil Microbes Do for the Ecosystem

A small handful of healthy soil will include millions of microscopic organisms that are beneficial to the soil systems where healthy plants grow, including fungi, nematodes, protozoa, microathopods and other beneficial bacteria. These microbes decompose organic material while they absorb water and nutrients that would otherwise get lost in the soil; the absorbed water and nutrients then get used by more and more complex creatures. This ecosystem ranges from the tiniest bacteria to the largest mammal predators. Any damage suffered by one part of the system can affect the health of all the others.

Three Levels of the Soil Ecosystem

The first level of the soil ecosystem is made up of bacteria and fungi that consume leftover organic matter, nitrogen and nutrients. These organisms act like a nutrient bank that plants can use when they need it. The second level of organisms consists of predators that feed on the bacteria and fungi. Nitrogen and nutrients are metabolized and released into the soil at a slow rate that is beneficial to plant growth. Higher-level predators, like millipedes and earthworms, make up the third level. These animals keep the second-level organisms in check, helping the plants maintain a healthy growth rate. The third level is also made up of bigger predators that keep the smaller ones from over eating. This extensive bio-diversity is what makes all life in the soil ecosystem possible.

How Pesticides Affect Soil Microbes

Pesticides include a large group of chemical agents that attempt to eliminate destructive biological forces in agriculture. These include herbicides for killing plants, insecticides for killing insects, fungicides for killing fungus and bactericides for killing bacteria. While these chemicals supposedly only target specific species, repeated use inevitably kills microbial life that is beneficial to the soil system. Microbes that survive can be genetically altered in a way that is no longer beneficial to the soil ecosystem and be resistant to the chemical intended to kill them. The destruction or alteration of first-level microbes can affect the entire soil ecosystem all the way up to the largest mammalian predators.

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