Effect of pesticides on soil microflora

     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, solubilize 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 the use of 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 in the ecosystem for survival. Pesticides include mainly 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.

Soil microflora is also actively involved in enhancing soil fertility and crop productivity. Microbial activity in soil has a strong impact on its physical properties and biocontrol of phyto-pathogens in agricultural soils. Soil microorganisms have thus been accepted as the bioindicators of soil health and activity. Fertilizers and pesticides affect the soil microflora thereby disturbing soil health. Amendment of soil with fertilizers and pesticides strongly influences soil functions and properties like rhizo deposition, nutrient content of bulk and rhizospheric soil, soil organic carbon, pH, moisture, activities of soil enzymes and many others. All these factors indirectly lead to a shift in the population dynamics of soil microflora. Other direct effects of fertilizers and pesticides include toxicity and altered substrate availability profile of the soil.

Soil health management is crucial for sustainable agricultural productions. Fertilizers and pesticides are a necessary evil for industrial agriculture with well-known adverse effects on environment and human health. They also strongly influence the microbial properties of soil. Such effects are variable depending on many biotic and abiotic factors ranging from soil characteristics to crop variety. Still, it has been well established that long term and excessive chemical inputs in soil undoubtedly influence the soil microbial communities in terms of their structural and functional diversity.

Integrated Pest Management (IPM) and replacing chemical pesticides with biopesticides and cultural practices is the most effective method to reduce pesticide damage because it reduces the use of chemical pesticides  and adopts safer alternatives like:

1. Use of Biopesticides instead of Chemicals
Use Bt, Trichoderma, Pseudomonas, Neem, etc. These are non-toxic to soil microbes and safer for the environment.

2. Adopt Cultural Practices

Crop rotation, Intercropping, Use of resistant varieties, proper sanitation and weed control. These reduce pests and the need for pesticides.

3. Use Minimal Chemical Pesticides
Apply pesticides only when necessary and only where needed. Use recommended dose and avoid overdosing. Use soil-friendly formulations. Avoid persistent and broad-spectrum chemicals.

4. Maintain Soil Organic Matter
Add compost and green manure. Maintain healthy soil which supports microbial diversity and growth.