Excessive application of chemicals by farmers or spills and leaks of petroleum products and toxic substances by other users kill soil organisms. Soil is a complex living food web, where a variety of organisms interact to process organic matter, recycle nutrients, and nurture plants. Please use organic fertilizers and organic methods for pest management.
According to soil scientist Elaine Ingham at Oregon State University, just one gram of healthy agricultural soil contains around 100 yards of threadlike fungal material, 100 million bacteria, tens of thousands of one-celled organisms called protozoa, and up to 2000 tiny worms called nematodes. Growth of plants depends upon the presence of these microorganisms, which interact to retain nutrients and make nitrogen available. Higher up the food chain are the springtails and mites that prey on fungi. Larger still are the earthworms, ants, termites, millipedes, and beetles that fragment the organic debris, aerate the soil, and form channels for infiltration of water.
If you want healthier plants then support your soil food web by putting organic matter, which increases the population of beneficial soil organisms, in your soil medium. Please support the fight against soil quality and erosion by visiting http://www.basic-info-4-organic-fertilizers.com/soilorganisms.html where you can find lots of detail information about the kinds of beneficial soil organisms.