tailieunhanh - STORING WATER IN THE SOIL

The large amount of water required for the production of plant substance is taken from the soil by the roots. Leaves and stems do not absorb appreciable quantities of water. The scanty rainfall of dry-farm districts or the more abundant precipitation of humid regions must, therefore, be made to enter the soil in such a manner as to be readily available as soil-moisture to the roots at the right periods of plant growth. In humid countries, the rain that falls during the growing season is looked upon, and very properly, as the really effective factor in the production of large. | STORING WATER IN THE SOIL The large amount of water required for the production of plant substance is taken from the soil by the roots. Leaves and stems do not absorb appreciable quantities of water. The scanty rainfall of dry-farm districts or the more abundant precipitation of humid regions must therefore be made to enter the soil in such a manner as to be readily available as soil-moisture to the roots at the right periods of plant growth. In humid countries the rain that falls during the growing season is looked upon and very properly as the really effective factor in the production of large crops. The root systems of plants grown under such humid conditions are near the surface ready to absorb immediately the rains that fall even if they do not soak deeply into the soil. As has been shown in Chapter IV it is only over a small portion of the dry-farm territory that the bulk of the scanty precipitation occurs during the growing season. Over a large portion of the arid and semiarid region the summers are almost rainless and the bulk of the precipitation comes in the winter late fall or early spring when plants are not growing. If the rains that fall during the growing season are indispensable in crop production the possible area to be reclaimed by dry-farming will be greatly limited. Even when much of the total precipitation comes in summer the amount in dry-farm districts is seldom sufficient for the proper maturing of crops. In fact successful dry-farming depends chiefly upon the success with which the rains that fall during any season of the year may be stored and kept in the soil until needed by plants in their growth. The fundamental operations of dry-farming include a soil treatment which enables the largest possible proportion of the annual precipitation to be stored in the soil. For this purpose the deep somewhat porous soils characteristic of arid regions are unusually well adapted. Alway s demonstration An important and unique demonstration of the .