root crop, vegetable cultivated chiefly for its edible roots, e.g., the beet, turnip, mangel-wurzel, carrot, and parsnip. All root crops have a large water content and grow best in deeply cultivated soil in cool, overcast weather when the plant's loss of water through transpiration is lowest. Because they require thorough cultivating they are often desirable in a rotation of crops—beets and turnips being most frequently so used. Root crops, especially beets, turnips, and carrots, are also grown as food for livestock.

cover crop, green temporary crop grown to prevent or reduce erosion and to improve the soil by building up its organic content. Green-manure crops are usually classed as cover crops. In orchards a cover crop is sometimes used to check the growth of some fruits when they reach maturity by supplying a plant that will compete with the tree for the nutriment in the soil. Cover crops are often the first means used to rehabilitate land that has become run down as the result of poor farming practices and neglect. Leguminous plants (e.g., clovers, vetches, and soybeans) and nonleguminous (e.g., rye, barley, wheat, and turnips) are used. See catch crop.

catch crop, any quick-growing crop sown between seasons of regular planting to make use of temporary idleness of the soil or to compensate for the failure of a main crop. It may be such rapid-maturing vegetables as radishes, onions grown from sets, or spinach (planted between rows of slower growing crops); quick-growing crops such as rye, millet, or buckwheat; or an annual legume, such as soybean, which is valuable as fodder or, when plowed under, increases the soil's fertility. See cover crop.

Successive cultivation of different crops in a specified order on the same fields. Some rotations are designed for high immediate returns, with little regard for basic resources. Others are planned for high continuing returns while protecting resources. A typical scheme selects rotation crops from three classifications: cultivated row crops (e.g., corn, potatoes), close-growing grains (e.g., oats, wheat), and sod-forming, or rest, crops (e.g., clover, clover-timothy). In general, cropping systems should include deep-rooting legumes. In addition to the many beneficial effects on soils and crops, well-planned crop rotations make the farm a more effective year-round enterprise by providing more efficient handling of labour, power, and equipment, reduction in weather and market risks, and improved ability to meet livestock requirements.

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Usually, an aircraft used for dusting or spraying large acreages with pesticides, though other types of dusters are also employed. Aerial spraying and dusting permit prompt coverage of large areas at the moment when application of pesticide is most effective and avoid the need for wheeled vehicles that might damage crops. The technique was greatly improved in the 1960s with the development of ultra-low-volume applicators, in which concentrated pesticides are distributed in extremely small amounts. Seealso spraying and dusting.

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