Rotation tends to protect crops from injurious insects and diseases. If one kind of crop is grown continuously on one piece of land the soil becomes infested with the insects and diseases which injure that particular crop. If the crop is changed, the insects and diseases find difficulty in adapting themselves to the change and consequently diminish in numbers. Rotation helps to keep the soil free from weeds. "If the same kind of crop were grown year after year on the same field, the weeds which grow most readily along with that crop would soon take possession of the soil." For example, chick weed, dock, thistle, weeds peculiar to grain and grain crops tend to increase if the land is long occupied by these crops. Rotation helps the farmer to make a more even distribution of labor throughout the year. This is because crops differ as to the time of year at which they are planted and harvested. Rotation of crops enables the farmer to provide for his stock more economically. Live stock fares better on a variety of food, which is more cheaply secured by a system of rotation than otherwise. THE TYPICAL ROTATION A typical rotation for general farming should contain at least: One money crop which is necessarily an exhaustive crop. One manurial crop which is a soil enricher. One feeding crop which diminishes fertility only a little. One cleansing crop, a hoed or cultivated crop. CONDITIONS WHICH MODIFY THE ROTATION There are certain conditions which tend to modify the rotation or to influence the farmer in his choice of crops. They are as follows: First of all the climate will set a limit on the number and varieties of crops from which a choice can be made for a given locality. The kind of farming which he chooses to carry on, whether stock raising, grain farming, truck farming, or a combination of two or more of these, or others. Kind of soil. Certain soils are best adapted to particular crops. For example, heavy soils are best suited to wheat, grass, clover, cabbages, etc. Light, sandy soils to early truck, certain grades of tobacco, etc. The demand for crops and their market value. Facilities for getting crops to market, good or bad country roads, railroads and water transportation. The state of the land with respect to weeds, insect pests and plant diseases. GENERAL RULES A few general rules may be made use of in arranging the order of the crops in the rotation though they cannot always be strictly followed. Crops that require the elements of plant food in the same proportion should not follow each other. Deep-rooted crops should alternate with shallow-rooted crops. Humus makers should alternate with humus wasters. Every well arranged rotation should have at least one crop grown for its manurial effect on the soil, as a crop of cowpeas, or one of clover, to be turned under.