Classification.— Farm crops may be grouped in several ways other than according to strict botanical relationships. On the basis of utiliza tion — the most important use of the crop being kept in mind— there are: (1) Food crops, such as potatoes, sugar beets, beans, wheat, rice; (2) feed crops, such as hay, corn, mange] wur zels and alfalfa ; (3) fibre crops, including cot ton, hemp and ,flax; (4) soil-building crops, which, as already explained, may include some qualified to fall in groups 1 and 2; (5) special purpose crops, such as tobacco, castor beans, etc.
There may also be said to be two main classes of farm crops, the first including those that are grown in widely-spaced rows, between which the soil is regularly cultivated through out most, if not all, of the growing season; and the second, including such crops as grains and grasses, which are sown in drills close together or even broadcast and allowed to grow without cultivation. This, however, may become a mat ter of preference or expediency on the part of the individual farmer, since, for example, cow peas grown for hay are usually drilled or broadcasted, while if raised for seed they are planted in rows.
From a geographical standpoint the range of American farm crops is from tropical species suited only to southern latitudes and low alti tudes, such as rice, sugar-cane and cotton to hardy forms requiring cool, northern sections or the higher elevations of the central part of the country for their best development. Of these, flax, spring wheat and the Grimm variety of alfalfa are illustrations. In this connection the work of plant breeders in developing new strains and varieties of unusual hardiness and wide adaptability is constantly modifying the early notions of crop limitations.
Perhaps the most useful and definite classi fication of farm crops, however, is one based upon somewhat loose botanical relationships combined with practical cultural considerations. Here again the secondary use of any crop may place it in a different group from that to which its primary purpose assigns it. The latter is made the basis for the following lists of Amer ican farm crops arranged approximately in order of their importance. Each of the groups includes both annual and perennial plants, which characteristic occasionally plays an im portant part in determining the value of a par ticular crop in relation to the established rota tion of farm-cropping system.
How Grown.— The cultural details for each of these crops are given elsewhere under their respective title. But there are certain re lationships which are best considered at this point of a general discussion. Good farming practice requires for various reasons a rota tion of farm crops and the most satisfactory rotations include at least one season of each of three types of crop, viz., (a) a tilled or cul tivated crop; (b) a grain crop; and (c) a le guminous crop or at least a grass crop to be plowed under as sod after it has been mowed or pastured. As illustrations of these types there may be mentioned (a) corn, potatoes, cabbage or roots of any kind; (b) any of the cereals except corn, and rice which is limited to too small a territory; (c) any of the forage crop legumes, unless the crop is to be left down for less than two or three years, in which case alfalfa is rarely chosen.
The usual sequence in such a rotation in volves growing one, two or even more crops of corn or potatoes, depending on the fertility of the soil, market demands, etc., then •sowing a hardy winter grain such as wheat or rye late in the season after the crop is harvested. In some cases a spring grain crop is substituted. In either case and clover mixture is sown with the grain in order to provide hay for a year or two after the grain is harvested and then, if desired, a year or more of pasture be fore it is plowed under in readiness for a new planting of corn.
Another type of rotation by which a soU can rapidly be built up consists of alternate crops of corn or cotton and cowpeas, soy beans, or some such legume, the latter sown between the rows of the tilled crop at the last cultiva tion. These and similar combinations are char acteristic of the most modern agricultural methods by means of which progressive farmers are striving to build up the soils that have been depleted by long years of single cropping, erosion, careless management and general ig norance.
At the same time some crops, such as to bacco, hops and flax, are so especially adapted to certain soils and localities that even success ful growers may not attempt to rotate fre quently unless forced to by the invasion of plant diseases or insect pests preferring to de pend on the use of fertilizers to maintain the productivity of the land.