ABSTRACT
Agricultural production increased greatly during the 20th century, freeing much of the world from food shortages. Chemical methods contributed to this increase, especially through production of nitrogen fertilizer, herbicides, and insecticides. The Haber–Bosch process for conversion of nitrogen from air to ammonia by reaction with hydrogen was introduced in 1915 and now accounts for >99% of commercial nitrogen fertilizer. Synthetic herbicides and insecticides were commercialized soon after WWII, based on the discovery of 2,4-dichlorophenoxyacetic acid (2,4-D) and 1,1,1,-trichloro-2,2-bis-(4-chlorophenyl)ethane (DDT) during and immediately before the war. Many different types of herbicides were subsequently developed by research at chemical companies. More than 20 different classes have been recognized, based on mechanism of action. Agrochemical companies, the Department of Agriculture and the Environmental Protection Agency have developed information on optimal use and regulations that establish specific instructions for use. Nevertheless, two problems persist. One is the development of herbicide-resistant weeds and the other is herbicide residues on food crops. There are also several groups of insecticides, but most target the insect central nervous system. Some have substantial toxicity to other species, including humans. As with herbicides, regulations establish the specific conditions for use. Biotechnology has permitted the development of plant varieties that incorporate tolerance to specific herbicides and/or toxicity to certain insects. These have been widely adopted for major agricultural crops such as corn, cotton, and soy beans. Considerable public concern about the use of pesticides in food production has given rise to increased demand for “organic” or “natural” foods.
