1180 
the case of pipes, the material out of 
which it is made determines in some de- 
gree the amount of friction. Wood pipe 
is supposed to have less friction than 
cement pipe, and iron pipe less friction 
than wood. 
To find how much water will discharge 
at a given point, multiply the velocity 
by the cross section in square feet, 
which gives the number of cubic feet 
per second of time. 
A. second-foot of water on ordinary 
soil will irrigate from 80 to 160 acres. 
The water necessary to mature cer- 
tain kinds of crops is estimated as fol- 
lows: 
Tomatoes, 24 inches in depth over the 
ground, or two acre-feet. Potatoes, 17 
inches; onions, 36 inches; strawberries, 
27 inches. 
Orchards of tree fruits are variously 
estimated, depending on the climate, 
soil, kinds of fruits and the age of the 
trees. Young orchard trees can be grown 
with less than half the water required 
for old trees in full bearing. 
One foot deep per acre is 43,560 cubic 
feet, equal to the number of square feet 
per acre. 
IRRIGATION OF ORCHARDS 
It is impossible to give any correct 
rules for irrigation that will apply to all 
cases. There are so many conditions of 
soil, rainfall, seepage, climate and kinds 
of crops that the orchardist must neces- 
sarily learn from the experience of others 
who have lived for a considerable time 
in the community where the orchard is 
located. However, the following may 
be helpful in determining the amount of 
water needed. 
Varieties which mature their fruits 
early require less water than those 
which mature late. For this reason cher- 
ries, early peaches, prunes and apricots 
require less water than late peaches, 
pears and winter apples. 
The non-deciduous fruits require more 
water than those which drop their leaves 
in autumn, not only because there is 
little evaporation from the tree during 
the winter, but because of climatic con- 
ditions. There are, however, exceptions 
ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
to this rule, for the leaf and root sys- 
tem of the olive are so constructed that 
they will bear with less water than is 
required for the peach 
More water is required for large than 
for small trees, and the larger the tree, 
other things being equal, the more water 
required. Shallow rooting trees will gen- 
erally require more frequent irrigation 
than those of the deep rooting habit. 
Trees with tap roots, such as apples 
and pears, must be irrigated with special 
reference to the supply of water for the 
tap roots as well as the lateral roots. 
In the fine volcanic-ash soils, in adobe, 
or in scab soils that puddle or cement, 
or harden when dry, or in any other way 
tend to become impervious to the air, 
there should be more than usual care to 
see that the water goes below the roots, 
and that the soil is sufficiently aerated. 
This may be done by growing alfalfa, 
or dynamiting the soil, or by digging 
holes to considerable depth to let the 
water down below the puddled section. 
Where the water does not penetrate 
about the roots of the trees, there will 
be manifestations of disease such as die 
back, yellows, rosette, etc. These may 
also result from excess of water. Lack 
of moisture may also prevent bearing the 
following year, since it may prevent the 
proper development of fruit buds. 
Irrigate the Center 
For a number of years the general 
practice, in irrigating an orchard, was 
to run the laterals about three feet apart 
between the rows of trees with the lateral 
nearest the tree not nearer than two and 
one-half feet. This left the center of 
the space in which the tree stood without 
a lateral. The laterals on either side be- 
ing two and one-half feet from the tree 
row made a space of five feet occupied 
by the tree row. This seems to be all 
right for the lateral roots, which tend to 
reach out toward the center, but it leaves 
the tap roots often without water. In 
making some experiments, we found that 
when the center was watered by a small 
lateral, made with a shovel, that this lat- 
eral required much more water than 
either one of the others. This suggested 
