Farmers who use inorganic fertilizers exclusively add no humus or organic matter to the soil. Over time, this leads to soil compaction and decreased oxygen content in the soil. Compaction reduces the soilms ability to take up water and increases runoff. Compaction and reduced oxygen content together reduce the soilms ability to take up the nutrients provided by inorganic fertilizer, so farmers must add larger and larger quantities to achieve the same effect. Water pollution is primarily a problem of inorganic fertilizers.
Algal blooms follow, which deplete the water of oxygen.
Fish and other species find it increasingly difficult to compete for oxygen, and falling animal populations is generally the end result.