Herbicides

Definition of Herbicides

 Herbicides are pesticides used to kill unwanted plants

Selective herbicides kill specific targets, while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic mimics of natural plant hormones.

Herbicides used to clear waste ground, industrial sites, railways and railway embankments are not selective and kill all plant material with which they come into contact. Smaller quantities are used in forestry, pasture systems, and management of areas set aside as wildlife habitat.

Some plants produce natural herbicides, such as the genus Juglans (walnuts), or the tree of heaven; such action of natural herbicides, and other related chemical interactions, is called allelopathy.

Herbicides are widely used in agriculture and landscape turf management. In the US, they account for about 70% of all agricultural pesticide use

Plant nutrition

 It is  defined as the chemical elements and compounds that are necessary for plant growth  and development  also of their external supply and internal metabolism. In 1972 according to E. Epstein two criteria for an element to be essential for plant growth:

1.  in its absence the plant is unable to complete a normal life cycle; or

2.        that the element is part of some essential plant constituent or metabolite.

This is in accordance with Liebig's law of the minimum.There are 14 essential plant nutrients. Carbon and oxygen are absorbed from the air, while other nutrients including water are obtained from the soil.