SOURCES AND FORMS OF SOIL WATER

The soil which is occupied by the roots of plants receives moisture in the form of rain, snow and dew from above and free and capillary water rising from below.

“Free water is that form of water which fills our wells, is found in the bottom of holes dug in the ground during wet seasons, and is often found standing on the surface of the soil after heavy or long continued rains.  It is sometimes called ‘ground water’ or ’standing water,’ and flows under the influence of gravity.”  Free water is not used directly by plants unless they are swamp plants, and its presence within eighteen inches of the surface is injurious to most farm plants.  Free water serves as the main source of supply for capillary water.

“Capillary water is water which is drawn by capillary force or soaks into the spaces between the soil particles and covers these particles with a thin film of moisture.”  It is a direct source of water to plants.  Capillary water will flow in any direction in the soil, the direction of flow being determined by texture and dryness, the flow being stronger toward the more compact and drier parts.  If the soil is left lumpy and cloddy then capillary water cannot rise readily from below to take the place of that which is lost by evaporation.  If, however, the soil is fine and well pulverized, the water rises freely and continuously to supply the place of that taken by plant roots or evaporation from the surface.

TOO MUCH WATER

Some farm lands contain too much water for the growth of farm crops; for example, bottom lands which are so low that water falling on the surface cannot run off or soak down into the lower soil.  The result is that the spaces between the soil particles are most of the time filled with water, and this checks ventilation, which is a necessary factor in soil fertility.  This state of affairs occurs also on sloping uplands which are kept wet by spring water or by seepage water from higher lands.  Some soils are so close and compact that water falling on the surface finds great difficulty in percolating through them, and therefore renders them too wet for profitable cropping during longer or shorter periods of the year.  Nearly all such lands can be improved by removing the surplus water through drains. (See Chapter XXV.)

Percolation and ventilation of close compact soils can be improved by mixing lime and organic matter with them.

NOT ENOUGH WATER

In some sections of the country, particularly the arid and semi-arid sections of the West, the soil does not receive a sufficient supply of rain water for the production of profitable yearly crops.  These soils are rendered unfertile by the lack of this one all important factor of fertility.  They can be made fertile and productive by supplying them with sufficient water through irrigation.