They began using inorganic nitrogen fertilizers to replace the organic nitrogen the fields had been getting from animal manure. Nitrogen is one of the major nutrients plants need to grow. In the 1940s, farmers learned to use chemicals to kill insects and weeds. These chemicals now help one American farmer provide food and fabric for 130 non-farmers. Chemicals have caused some problems, too.
Chemical pesticides can kill other organisms besides the ones for which they are intended.
Some of the organisms they kill are useful ones that help crops grow. Chemical fertilizers also cause reactions in the soil that, over time, can make the soil less desirable for plant growth. Chemicals used in agriculture can also contaminate the water we drink. Sometimes they move through the soil and enter the underground water supply, and sometimes they are carried by rainwater into lakes, rivers and streams. Farmers are concerned about these problems.