Autotoxicity is a form of allelopathy

Allelopathy

Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have beneficial or detrimental effects on the target organisms...

 in which a species inhibits growth or reproduction of members of that same species through the production of chemicals that are released into the environment.

This mechanism will result in reduced competition between members of the same species.
Inhibition on the growth of other plants will increase the availability of nutrients.

In cultivation, autotoxicity can make it difficult or impossible to grow the same species after harvest of a crop. For example, this is known in alfalfa

Alfalfa

Alfalfa is a flowering plant in the pea family Fabaceae cultivated as an important forage crop in the US, Canada, Argentina, France, Australia, the Middle East, South Africa, and many other countries. It is known as lucerne in the UK, France, Australia, South Africa and New Zealand, and known as...

 and the tree Cunninghamia

Cunninghamia

The genus Cunninghamia is a genus of one or two species of evergreen coniferous trees in the cypress family Cupressaceae. They are native to China, Taiwan and northern Vietnam, where they may reach 50–55 m in height....

 lancealata Other species displaying autotoxicity include the rush Juncus effusus and the grass Lolium rigidum.

In alfalfa

Autotoxicity in alfalfa is produced from the first seeding of the plant. The plant emits a chemical or chemicals into the soil that reduce the effectiveness of further alfalfa seedings. Studies show that the chemical is extractable from fresh alfalfa, is water soluble, reduces germination, and prevents root growth. Some believe that a chemical called medicarpin is responsible for autotoxicity. Roots of affected plants can be swollen, curled, discolored, and lack root hairs. Lack of root hairs reduces the plants ability to gather nutrients and absorb water.
Crop rotation

Crop rotation

Crop rotation is the practice of growing a series of dissimilar types of crops in the same area in sequential seasons.Crop rotation confers various benefits to the soil. A traditional element of crop rotation is the replenishment of nitrogen through the use of green manure in sequence with cereals...

is used to counteract autotoxicity in alfalfa.