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The figures taken collectively show the importance of selecting a soil suitable for the crop to be grown, the yield being doubled on Plat 2, while taken individually it is evident that certain varieties were better adapted to the environment than others. The question of which variety will best suit the environment must be determined by the grower.

Subsoiling.–Buffum', of Wyomivg, states that subsoiling may be recommended throughout that State for potatoes. The cost of subsoiling to a depth of 16 inches to 18 inches varied between $3.00 and $6.00 per acre. Hays’, of Minnesota, found it to be expensive and not profitable under most conditions in that State, and that it reduced the yields of crops on land already sufficiently open and porous. In humid climates, if attempted, it is advocated that subsoiling be done in the fall, to permit the readjustment of the soil granules before springtime, so that the moisture will be able to rise upward from the subsoil, as evaporation takes

I Wyo. Bul. 41, pp. 20, 21; Bul. 32, pp. 7, 8.

? Minn. Bul. 68, p. 609.

place at the surface, and prevent the crop being destroyed by lack of moisture. Injurious results from subsoiling in spring have been noted, probably due to the working of the subsoil when it was too wet. It does not follow that because the surface soil to the depth of eight inches is dry enough to plow the subsoil will be, and in many cases the subsoil has been puddled by spring working, and the supply of moisture from below more or less completely cut off, with disastrous results to the crop.

Preparation of the Soil.—The ideal crop to precede potatoes is timber, but as no rotation comprising this crop is in use, the preparation given after timber demands little attention. Potatoes are more commonly grown after potatoes, corn, or after clover or sod. In such cases preference is usually given to fall plowing, accomplished during October or November until freezing prevents further work. Deep plowing should be done in fall, because opportunity is then given for the storage of water in the soil during the winter and when the thaw occurs in spring. If manure is to be applied it is spread before plowing, but, if rotted, it may be applied later and disked in. The depth of plowing varies with the soil, probably six inches or eight inches being most common, although, if the soil will permit, eight inches to twelve inches will be better. When soils are deficient in humus, it is generally inadvisable to plow deeply. The humus content of such soils should be increased and the depth of plowing increased correspondingly, thus bringing the land into a higher state of production. In some districts where the snow covers the ground all winter the land is harrowed well 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

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FIG. 7-A USEFUL TYPE OF SPRING-TOOTHED HARROW

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

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FIG. 8--AN EFFICIENT PULVERIZER: THE DISK HARROW

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 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 2/2 inches is more common. Harrows differ in their action; thus, the spring-toothed harrow

1 Minn. Bul. 68, pp. 576-579.

? Utah Bul. 4.

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

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