in fall and left nearly ready for planting, thus facilitating spring work. Where the frost penetrates deeply, or the soil is apt to run together, the land is better left rough plowed all winter and fitted in spring; but this entails some loss of time, and prevents the early planting of potatoes.

Sometimes it is necessary to plow in spring, and in many cases it is profitable to replow when a fall plow

ing has been given. Under such conditions a depth of not more than six inches or eight inches is advised, because plowing land is attended by loss of moisture, and in most cases the amount of moisture held in the soil or supplied as rainfall during the growing period is insufficient to insure maximum yields; hence, care should be taken to conserve all the moisture possible by plowing judiciously, making and maintaining a mulch of the surface soil, thus checking evaporation,

and by enriching the soil in humus either by manuring or a suitable rotation. Humus affects the physical properties of the soil considerably-among other things, enabling it to hold more moisture without injury to the plants in a wet time, and to endure drouth in a

dry time. Even where irrigation is practiced the above factors cannot be economically neglected.

Surface-fitting Tools.-The Acme harrow is one of the best tools for making a soil mulch before the crop is planted, and in trials made by Sanborn' was shown to be the most efficient type of harrow for pulverizing soil. On stony land, or where roots of trees interfere, the spring-tooth harrow (Fig. 7) is preferred for deep tillage of the soil, while under other conditions

1 Minn. Bul. 68, pp. 576-579. 2 Utah Bul. 4.

the disk harrow. These tools work deeper than the Acme harrow, and may be used to prepare the soil to a depth of four to six inches, which seems to be as deep as is necessary. Few farmers prepare land to this depth, as it requires three horses on a six-foot harrow on a loam soil. Two to 21⁄2 inches is more common. Harrows differ in their action; thus, the spring-toothed harrow

and the smoothing or spike-tooth harrow tend to compact the soil while fining it, while the disk type (Figs. 8 and 9) and Acme harrows tend to lighten it and make it more open when they fine it. For potatoes and corn for wheat the former.

the latter are preferable, while Whatever tool is used the land should be well fitted. Few farmers prepare the land well enough, and many

would find it more economical and profitable to spend another week working the land than to rush the crop into a badly prepared seed-bed. The soil under the plants and near them cannot be touched when they have been planted, while wide tools may be used before.

CHAPTER IV

ROTATION

In some cases potatoes are grown continuously for several years on the same soil, but a rotation of crops is preferable for many reasons-among others, to lessen the dangers of attacks of diseases and insects, and to bring the soil into a suitable physical condition for growing this crop. Some rotations suggested by Wheeler, of the Rhode Island Experiment Station,' are as follows: three-year rotation-potatoes, winter rye, common red clover; four-year rotation-corn on clover sod, potatoes, winter rye, clover. This can be made into a five-year rotation by seeding timothy and redtop with the clover, and leaving the mixture down two years, thus reducing the labor bill to some extent. Trials of these and other rotations were made on land so poor that corn attained a hight of but 4 or 5 inches, while the first crops of salable potatoes were but 65 bushels per acre. During later years, with management similar to that given the first year, and the application of a similar amount of fertilizers, the yields ran up to 350 bushels of salable potatoes per acre. A common Maine rotation is a four-year course of potatoes, oats, clover and grass, the latter for two years-it being noted that clover thrives on good potato land. In deciding upon the rotation it is important

1 R. I. Bul. 74, 75, 76.