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Importance of Soil Moisture 
Of all the factors which influence 
growth, moisture is without doubt the 
most important. Plants suffer more fre- 
quently for want of proper moisture 
conditions than they do for want of 
chemical elements of plant food. Moisture 
is a carrier of plant food on the soil and 
in the plant. There is a wide range in 
which the moisture content will be fav- 
orable to growth, but for each soil there 
is a low limit at which plants wilt for 
want of moisture, and there is also a 
line of excessive wetness above which 
nothing but water plants will thrive. 
Moisture is necessary to bacteria of the 
soil. It gives turgidity to the plant cells 
and makes plant food available. 
Supply 
The amount of water in the soil is not 
always greater in the region of greater 
rainfall. Soil of a wet climate may dry 
and bake quickly after rains. The ini- 
tial amount of water will depend on the 
rainfall, and stored supply as for irriga- 
tion. A thing that is more important is 
the supply during the growing season, so 
the amount of rainfall is not so vital as 
the time of occurrence. The rate of loss 
and the retentive capacity of the soil will 
modify the amount available during the 
growing season. 
Forms 
1. Hydrostatic water. This can be 
seen and is free to move by gravity. It 
is removed in drains. 2. Capillary moist- 
ure. This is held against the force of grav- 
ity by surface tension. It is the form 
used by plants. There is no distinct line 
between this and free water. 8. Hydro- 
scopic moisture This is absorbed by dry 
soil from the air. 
Limitations 
The maximum amount of the different 
kinds of soil moisture depends on texture, 
structure and content of organic matter. 
Movements 
Percolation. This is more rapid in tile 
after small streamlets have formed in the 
soil about the tile, and in coarse grain 
soils. Run-off may remove a large per- 
centage of the rain. Evaporation. Most 
ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
of the rain not lost by percolation is 
lost by evaporation. Capillarity. Relieves 
congested condition at the surface when 
water first comes to the soil. Capillarity 
depends on gravity, surface tension and 
pressures. 
Control of Capillarity—Increase by 
Irrigation—Decrease by 
Drainage 
We will for the present omit the meth- 
ods for increasing the moisture content 
of the soil, and take up the methods of 
decreasing the water content. The three 
ways of doing this are: 
1. Cultivation. We can hasten evapora- 
tion by early spring cultivation of the 
soil. By increasing the air circulation and 
leaving the soil with an uneven, rigid sur- 
face which exposes a greater surface for 
evaporation. Rolling a light sandy soil 
causes upward capillarity and increases 
evaporation at the surface. When rain 
falls on the soil it can be lost by run-off. 
Cultivation will check excessive run-off 
It will also increase the water capacity 
and there will be less percolation. 
2. Growth of Plants. Crops of any 
sort, weeds and cover crops will dry the 
soil by transpiration of the water through 
the leaves. This may be taken advantage 
of in taking out the excess water in the 
early spring. We can take advantage of 
this in the fall, when the cover crop is 
planted in the orchard to take up the 
moisture and check the growth, so the 
buds will prepare for winter. 
38. Drainage. Drainage consists es- 
sentially in the direct removal of gravi- 
tational water from the root zone of the 
soil by affording free passages for its 
percolation and flow. This is the chief 
means of decreasing the supply. 
History of Drainage 
The subject of drainage is attracting 
more widespread attention throughout the 
country at the present time than ever 
before. It becomes more important as 
the agricultural resources of a country 
are developed. There are over 1.000,000 
square miles in the United States that 
must be drained before they can be util- 
ized. Thirteen per cent of the irrigated 
