The Effect of Crop Protection Chemicals on Soil-Dwelling Microorganisms

Microorganisms are an important component of the soil environment, and they play a key role in the decomposition of organic matter, the circulation of elements in the natural environment and the preservation of soil fertility. Microbes enhance the overall health of plants. In the rhizoplane, ectorhizosphere and endorhizosphere, high populations of microbes dwell around plant roots which secrete biogenic substances. Soil-dwelling organisms protect the plant against pathogens. Bacteria and actinomycetes are important contributors to plant health – by forming symbiotic associations with roots, they supply the plant with nitrogen. Symbiotic fungi also exert a beneficial effect – they facilitate the supply of water and minerals, as well as protect the plant against pathogens and heavy metals. One gram of soil contains thousands of prokaryote species whose populations can be measured in billions. Soil is not only a habitat of macroorganisms and microorganisms, but it is also an environment that absorbs man-made xenobiotics that affect its physical, chemical and biological properties to a varied extent. This group of substances is inclusive of pesticides. The use of crop protection chemicals, collectively referred to as pesticides, dates back to the late 19 century. Owing to intensified agricultural production and the need to protect crops against pest, microorganisms and their metabolites, such as mycotoxins, the use of pesticides became widespread, contributing to an increase in the number and the diversity of the available products. To maximize crop yield, farmers around the world use herbicides, fungicides, insecticides and nematicides, often during the same growing season. Crop protection chemicals contain substances that do not occur naturally in the environment. They are composed of one or more chemical compounds, which are active substances of the commercial product, as well as additives – adjuvants. Pesticides are applied to prevent, damage, repel and alleviate the harmful effects of pests and weeds. They are classified in view of their purpose, time and type of action as well as chemical composition. Pesticides contain both organic and inorganic substances. Many pesticides persist in the environment for years, the most notable examples being DDT and chloroorganic insecticides which have been present in