Crops

Hundreds of species of plants are cultivated by humans under managed agricultural conditions. However, most of these species are tropical crops of relatively minor importance—minor in terms of their contribution to the global production of all agricultural plants. In fact, a small number of plant species contribute disproportionately to the global harvest of plant crops in agricultural systems. Ranked in order of their annual production (measured in millions of metric tons per year), the world's 15 most-important food crops are: 1) sugar cane (740 million tonnes per year); 2) wheat (390); 3) rice (370); 4) corn or maize (350); 5) white potato (300); 6) sugar beet (260); 7) barley (180); 8) sweet potato (150); 9) cassava (110); 10) soybean (80); 11) wine grapes (60); 12) tomato (45); 13) banana (40); 14) beans and peas (40); 15) orange (33).

Some care should be taken in interpreting these data in terms of the yield of actual foodstuffs. The production data for sugar cane, for example, reflect the entire harvested plant, and not just the refined sugar that is the major economic product of this crop. In contrast, the data for wheat and other grain crops reflect the actual harvest of seeds, which are much more useful nutritionally, pound for pound, than whole sugar cane (or even refined sugar).

Most agricultural crops are managed as annual plants, meaning that they are cultivated over a cycle of one year or less, with a single rotation involving sowing, growth, and harvesting. This is true of all the grains and legumes and most vegetables. Other agricultural species are managed as perennial crops, which are capable of yielding crops on a sustained basis once established. This is typically the manner in which tree-fruit crops such as oranges are managed and harvested, as are certain tropical species such as oil-palm (Elaeis guineensis) and para rubber (Hevea brasiliensis).

Some extremely valuable crops are not utilized for food, raw material, or energy. Instead, these crops are used for the production of important medicines, as is the case of the rosy periwinkle (Catharantus roseus), which produces several chemicals that are extremely useful in treatment of certain types of cancers. Other crops are used to produce very profitable but illegal drugs. Examples of these sorts of crops include marijuana (Cannabis sativa), cocaine (from Erythroxylon coca), and the opium poppy (Papaver somniferum).