can be made available only when there is
sufficient moisture in the soil to permit breaking down and
decomposition.

The presence of moisture in the soil is necessary for the process of
nitrification to take place.

Soil moisture is necessary to dissolve plant food. Plant roots can
absorb food from the soil only when it is in solution, and it seems to
be necessary that a large quantity of water pass through the plant
tissues to furnish the supply of mineral elements required by growth.

Moisture is necessary to build plant tissues. The quantity of water
entering into the structure of growing plants varies from sixty to as
high as ninety-five per cent, of their total weight.

During the periods of active growth there is a constant giving off of
moisture by the foliage of plants and this must be made good by water
taken from the soil by their roots.

In a series of experiments at the University of Wisconsin Agricultural
Experiment Station, it was found that in raising oats, every ton of
dry matter grown required 522.4 tons of water to produce it; for every
ton of dry matter of corn there were required 309.8 tons of water; a
ton of dry red clover requires 452.8 tons of water to grow it. At the
Cornell University Agricultural Experiment Station, a yield of
potatoes at the rate of 450 bushels per acre represented a water
requirement of 1310.75 tons of water.

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 dryn