In order to eliminate pests in farmland, human beings have invented more than 30,000 kinds of pesticides. Although they have temporarily controlled the pests, they have also eliminated the natural enemies of insects and bees, making it impossible for some vegetables, melons and fruits to be pollinated. Weeds compete with crops for nutrition, water and space, so someone invented herbicides, which temporarily control weeds, but also promote the evolution of weeds, making them more difficult to deal with. To make matters worse, herbicides also eliminated beneficial microorganisms in the soil, harming some nitrogen-fixing bacteria that had the ability to fix nitrogen, and even denitrifying bacteria that reduced excess nitrogen to nitrogen in the atmosphere. Without the care of weeds, farmland becomes plank, and the rainy season is very easy to cause soil erosion.
The harm caused by the disturbance of the existing agro-ecosystem is the most important part of this passage.