The moisture supply, and, therefore, to a considerable extent the humidity of any locality, is an important limiting factor in the choice of crops to be grown there. Wheat, oats and barley have attained great importance in arid and semi-arid sections where they are both under irrigation and, as a result of the de velopment of drought-resisting types, by dry farming methods. Alfalfa because of its deep rooting habit is the dominant forage crop of dry-farming localities, whereas clovers are practicable only where there is natural or sup plied water. Corn is grown both east and west of the 100th meridian which roughly separates the humid from the arid territory of the coun try, but in the latter the various grain sorghums, milo maize, kaffir corn and similar forms are, because of their drought-defying qualities, more dependable croppers and, therefore, more valu able. As a general thing all the farm crops grown satisfactorily in eastern (humid) United States can be raised with equal, and often with even greater, success under irrigation in the western part of the country. The only per acre yields of potatoes, for instance, to com pare with those of the famous Aroostook sec tion of Maine are obtained on the irrigated lands of the far West. Owing to the long grow ing season in California and the Southwest, alfalfa there yields six or more cuttings a sea son, whereas three or at most four are all that can be expected in the East. Sugar beets, grasses and the cereals likewise give excep tionally fine returns wherever moisture condi tions can be controlled and maintained at the peak of their efficiency.
There is the associated and significant fact that in. the West, where dry land and irriga tion farming are carried on, the much higher annual percentage of sunshine than in humid sections stimulates all plant growth to the greatest possible extent wherever such condi tions as soil fertility and moisture supply are made favorable.
Soil.— The type of soil, though an important factor in the choosing of crops, to be grown on it, is, however, less likely to influence the larger, geographical distribution of farm crops than their location on the individual farm. For the average farm includes usually a variety of soils so that with careful planning different fields can be given up to crops especially suited to the conditions they present.
Thus a stiff, heavy clay or silt will naturally be reserved for grass and grain crops while a lighter, sandy loam will immediately be chosen for corn, potatoes, beans or some such culti vated crop. Of course the most acceptable type of farm soil — a rich, deep, friable loam will suit and permit a good growth of prac tically any crop, so the atm of the good farmer is to bring the largest possible acreage into a condition approximately this as nearly as pos sible with the least delay.
Care should be taken in planting grain and other seed crops on soils abundantly supplied with nitrogenous plant food, since on such their tendency is to develop a growth of straw and leaf surface disproportionate to the seed crop and often so weak as to cause them to or break down and mat on the ground. Such crops as hay and other forages, cabbage, silage corn, sugar-cane, and flax and hemp grown for fibre rather than seed, on the other hand, require plenty of nitrogenous stimulus for a maximum growth of tissue.
In the case of soils obviously deficient in plant food or in poor physical condition, it is generally better policy to raise soil-building crops — less valuable, perhaps, in themselves rather than more valuable and, as a rule, more exacting sorts. Buckwheat, for example, has won a well-deserved reputation as a spoor soil crop') and the first to be planted in subduing newly cleared territory. Field beans are also satisfactory yielders on land that might fail to even pay the expense of cultivating other crops. In contrast to these is tobacco, for which the soil must be carefully picked and equally carefully fitted in every particular.
The successful cultivation of many farm crops is definitely influenced by the degree to which a soil is acid, that is, deficient in lime. While a few species such as beans, corn, flax, rye and millet have been shown by experiment to be practically indifferent to an application of lime to a soil of average quality, practically all others exhibit a distinctly favorable reaction to such treatment. Kentucky blue grass, most of the clovers, and alfalfa are particularly sus ceptible to acidity, but the soy bean and the peanut are reported by scientists to be able to successfully withstand it to a considerable degree.
Poor drainage is another and a very com mon weakness of otherwise satisfactory farm crop soils. Water standing near the surface of a soil causes the development of a shallow root system. Thai, when the water level sinks in midsummer, the crops are unable to reach it and consequently suffer from an insufficient supply. Rice, which is largely grown according to a system of flooding in the course of which it remains submerged for days at a time, is a striking example of a type of crop unusual in its ability to stand °wet feet," Of the more widely distributed crops, alsike clover and red top grass may be mentioned as satisfactory substitutes for other clovers and blue grass and timothy which do not thrive on moist, heavy soils that tend toward acidity. The fact that no crop can suffer as a result of good drainage while many are seriously im peded and injured by a lack of it is ample reason for any farmer installing drains at the first opportunity whatever the crop to be grown.