Chapter 46

CONTROL OF SOIL MOISTURE

Value of Water in the Soil.--The amount of water in the soil each day of the growing season determines in large measure the possibility of securing a profitable crop from land. Observant farmers have noticed oftentimes that the differences in yields on the farms of a region are less in a wholly favorable season than in one of deficient rainfall. The skill of the farmer in conserving the moisture supply in a wet season is less well repaid because it is less needed. The poverty of a worn soil is less marked in a favorable season. The land is accounted poor because the supply of plant-food is inadequate for a drouthy year in which a considerable percentage of the time produces little growth, but most agricultural land has enough plant-food for a fairly good crop when water is present all the time to carry daily supplies into the roots. It is the amount of moisture in the soil that is the limiting factor in the case of most land that is not in a high state of productiveness.

The Soil a Reservoir.--The rains of the summer rarely are adequate to the needs of growing plants. Some water runs off the surface, some passes down through crevices beyond the effect of capillary attraction, and much quickly evaporates. The part that becomes available is only a supplement to the store of water made by the rains of the fall, winter, and early spring.

If the soil were viewed as a medium for the holding of water to meet the daily needs of plants, and were given rational treatment on this basis, a long step toward higher productiveness would have been taken. As has been stated, rotted organic matter gives a soil more capacity for holding water. It is an absorbent in itself, and it puts clays and sands into better physical condition for the storage of moisture. An unproductive soil may need organic matter for this one reason alone more than it may need actual plant-food.

Fall-plowing for a spring crop enables land to withstand summer's drouth if it gains in physical condition by full exposure to the winter's frost. It is in condition to take up more water from spring rains than would be the case if it lay compact, and it does not lose water by the airing in the spring that plowing gives.

Early spring-plowing leaves land less subject to drouth than does later plowing. As the air becomes heated, the open spaces left by the plowing serve to hasten the escape of moisture. If a cover crop is plowed down late in the spring, the material in the bottom of the furrow makes the land less resistant to drouth because the union of the top soil with the subsoil is less perfect, and capillary attraction is retarded. It is usually good practice to sacrifice some of the growth of a cover crop, even when organic matter is badly needed, and to plow fairly early in the spring in order that the moisture supply may be conserved.

The Land-roller.--The breaking-plow is a robber of soil water when used in warm weather. The air carries the water away rapidly. The air-spaces are large. The corrective of this condition is the land-roller. It presses the soil together, driving out the excess of air. Large crumbs are pressed down into the mass, and are kept from drying into hard clods. The roller never should be used on land when fresh-plowed in a moist condition, and it is not needed after fall-plowing, or early spring-plowing in most instances, but land broken when the season is advanced should be rolled before much water evaporates.

The Plank-drag.--An excellent implement on a farm is the plank-drag. It is usually made of over-lapping heavy planks, and when floated over the surface, it both pulverizes and packs the soil. The effectiveness is controlled by the weight placed upon it, and oftentimes the drag is to be preferred to the roller.

The Mulch.--In conserving the supply of water in the soil the mulch plays an important work. The dry air is constantly taking up the water from the surface of land, and when the surface is drier than the soil below, the moisture moves upward if there is no break in the structure of the surface soil. The mulch is a covering of material that does not readily permit the escape of water.

The only available material for a mulch in most instances is the soil itself. Experience has taught that when the top layer of soil, to a depth of two or three inches, is made fine and loose, the water beneath it cannot escape readily. It is partly for this reason that the smoothing-harrow should follow the roller after land has been plowed. The plow is used to break up the soil into crumbs that will permit air to enter. The loosening is excessive when the planting must follow soon, permitting rapid escape of water. The roller or plank-drag is employed to compress the soil, and to crush crumbs of soil that are too large for good soil conditions. The harrow follows to make a mulch of fine, loose soil at the surface to assist in prevention of evaporation.

A sandy soil will retain its mulch in effective condition for a longer time than a fine clay, if no rain falls. When the air is laden with moisture, clay particles absorb enough water to pack together and form an avenue for the rise of water to the surface, where the dry air has access to it.

Mulches of Foreign Material.--The truth that moisture is a leading factor in soil productiveness is evidenced by the value of straw and similar material as a mulch. A covering of straw around trees in an orchard, or bush fruits, or such plants as the potato, may give better results than an application of fertilizer when no effort is made to prevent the escape of water. People so situated that little attention can well be given to the fruit and vegetable garden obtain good results by replacing tillage with a substantial mulch that keeps the soil mellow, prevents weed growth, and retains an abundant supply of water.

In grain-producing districts where all the straw is not needed as an absorbent in the stables its use as a mulch on thin grass lands, or wheat-fields seeded to grass, is more profitable than conversion into manure by rotting in a barnyard. The straw affords protection from the sun, and aids in the conservation of soil water, when scattered evenly in no larger amount than two tons per acre, and a less amount per acre has value. The sod is helped, and as the straw rots, its plant-food goes into the soil.

Plowing Straw Down.--The practice of plowing straw under as a manure is unsafe, when used in any large quantity per acre. It rots slowly, and while lying in the bottom of the furrow it cuts off the rise of water from the subsoil which is a reservoir of moisture for use during drouth.

The Summer-fallow.--Bare land loses in total plant-food, but may make a temporary gain in available fertility. The practice of leaving a field uncropped for an entire season has been abandoned in good farming regions. Where moisture is in scant supply, and a soil is thin, there continue instances of the summer-fallow. In a crop-rotation containing corn and wheat, the corn-stubble land is left unbroken until May or June, and then plowed. In August it is plowed again, and fitted for seeding to wheat. The practice favors the killing of weeds, and the soil at seeding time may contain more water than would have been the case if a crop had been produced, because its mellow condition enables the farmer to hold within it nearly all the moisture that a shower may furnish after the second plowing.

The Modern Fallow.--The modern method of making a grass seeding in August partakes of the nature of the old-fashioned summer-fallow. The desire is to eradicate weeds, secure availability in plant-food, and fit the soil to profit by even a light rainfall. Thin soils lend themselves well to this treatment, which is described in Chapter VIII, and there is no better method for fertile land. The benefit of the fallow is obtained without serious loss of time.