An agrochemical is any substance used to help manage an agricultural ecosystem, or the community of organisms in a farming area. Agrochemicals include: (1) fertilizers, (2) liming and acidifying agents, (3) soil conditioners, (4) pesticides, and (5) chemicals used in animal husbandry, such as antibiotics and hormones.
The use of agrochemicals has been critical to the raising crops for food. However, some of these chemicals cause substantial environmental and ecological damage, greatly reducing their benefits.
Fertilizers are substances that are added to farmlands to encourage plant growth and to increase crop yields. Fertilizers may be chemically manufactured (synthetic) or be made from organic (living) material such as recycled waste, animal manure, or compost (decaying vegetation). Most fertilizers contain varying amounts of nitrogen, phosphorus, and potassium, which are inorganic (nonliving) nutrients that plants need to grow. Globally, about 152 million tons (138 million metric tons) of fertilizers are used each year. In the United States, the yearly total is about 21 million tons (19 million metric tons).
Liming and acidifying agents
Crops planted in soil that is either too acidic or too alkaline (basic) cannot obtain the proper nutrients they need to grow from that soil. Acidic soils, an especially common problem in agriculture, can be caused by various factors, including acid rain (precipitation that contains weak sulfuric and nitric acids) and the use of certain types of fertilizers. Acidic soils are commonly neutralized by adding compounds that contain calcium, usually in the form of powdered limestone or crushed oyster or mussel shells.
Words to Know
Fertilizers: Any substance added to agricultural lands to encourage plant growth and higher crop production.
Hormone: A chemical produced in living cells that is carried by the blood to organs and tissues in distant parts of the body, where it regulates cellular activity.
Liming and acidifying agents: Substances added to soil to bring it into balance if it is too acidic or alkaline (basic).
Pesticides: Substances used to reduce the abundance of pests, any living thing that causes injury or disease to crops.
Much less common are alkaline soils, caused by the presence of large amounts of limestone or calcium. Alkaline soils can be brought into balance by adding sulfur compounds or certain types of acidic organic matter, such as peat (rotted vegetable matter found in bogs).
Soil conditioners are materials that are added to soil, usually to increase its ability to hold water and oxygen. Materials used as soil conditioners include peat, livestock manure, sewage sludge, and even shredded newspapers. Compost is probably the best soil conditioner because it keeps soil from becoming too acidic or too alkaline and it supplies the soil with organic nutrients.
Pesticides are used to eliminate the presence of pests, any living thing that causes injury or disease to crops. Although many kinds of pesticides are used in agriculture, they can be categorized into simple groups according to the pest they are targeting. Herbicides are used to kill weeds, any non-desired plant that interferes with the growth of crops. Fungicides are used to protect agricultural plants from fungal diseases. Insecticides are used to kill insects that eat crops or stored grains. Other pesticides target snails, slugs, mites, rodents, and birds.
Very large quantities of pesticides are used in modern agriculture. Globally, about 4.4 to 6.6 billion pounds (2 to 3 billion kilograms) of
pesticides are used each year, at a total cost of about $20 billion. The United States alone accounts for about one-third of all pesticide usage.
Agrochemicals used for animal husbandry
Various agrochemicals are given to livestock. Antibiotics are administered, either by injection or combined with feed, to control infectious
diseases and parasites that often arise when animals are raised under extremely crowded conditions. Hormones are routinely administered to increase the growth and productivity of animals, such as the bovine growth hormone given to cows.
Environmental effects of the use of agrochemicals
While agrochemicals increase plant and animal crop production, they can also damage the environment. Excessive use of fertilizers has led to the contamination of groundwater with nitrate, a chemical compound that in large concentrations is poisonous to humans and animals. In addition, the runoff of fertilizers into streams, lakes, and other surface waters can increase the growth of algae, leading to the death of fish and other aquatic animals.
Pesticides that are sprayed on entire fields using equipment mounted on tractors, airplanes, or helicopters often drift away from the targeted field, settling on nearby plants and animals. Some older pesticides, like the powerful insecticide DDT (dichlorodiphenyltrichloroethane), remain active in the environment for many years, contaminating virtually all wildlife, well water, food, and even humans with whom it comes in contact. Although many of these pesticides have been banned, some newer pesticides still cause severe damage. In North America, for example, it is believed that millions of wild birds are killed each year from exposure to the agricultural insecticide carbofuran.
These and other environmental effects have prompted researchers to search for nonchemical methods of enhancing soil fertility and dealing with pests. These alternatives, however, are still quite expensive at the beginning of the twenty-first century and are not yet in widespread use. In late 2000, the United Nations Environment Program organized a meeting to draft a global treaty to restrict the production and use of twelve persistent organic pollutants (POPs), especially those used as pesticides. The twelve toxic chemicals cited, which environmentalists have called the "dirty dozen," include eight pesticides: aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, and toxaphene. Since it is still widely used in Africa to control malaria, DDT was given a special exemption. It can be used in those countries until replacement chemicals or strategies can be put into place. One hundred and twenty-two nations (including the United States) agreed to the treaty, but before it can take effect, at least fifty of those nations must also ratify it.