IRRIGATION 
water necessary for the crop and the fre- 
quency with which it should be applied. 
The conditions which determine the 
amount of water that should be applied 
at a single irrigation are as follows: 
(a) Amount— 
1. The capactiy of the soil and sub- 
soul to store water. The question that 
confronts the irrigator is what quantity 
of water can be stored in the soil for the 
proper growth of the plants. The range 
for sandy soils will be between 5 per cent 
and 15 per cent, the optimum being about 
10 per cent In clay loams it is safe to 
say that it is impossible to store more 
than 30 pounds (a half foot) in the first 
four feet of a silt soil. If the amount of 
water in the soil is not down to the wilt- 
ing point of plants at the time of applica- 
tion of water, the soil will not take up 
the maximum amount. 
The following table shows the lower 
and upper limit of storage capacity of a 
clay soil, and the available moisture for 
use of plants in each foot of the soil: 
Clay Loam Soil— 
Available 
Lower Upper Moisture, 
Depth Limit Limit Lbs 
First foot ...... 17.01% 25 77% 6.92 
Second foot ....19.86% 24.3% 4.11 
Third foot ...... 18 56% 24 03% 5.72 
Fourth foot ....159% 22.29% 6.786 
Total pounds per cubic foot ......... 23 54 
2. The depth of the soil stratum pene: 
trated by the roots of the particular crop. 
If the roots of a crop penetrate deeply a 
larger amount of water may be applied to 
the soil without a large amount of it go- 
ing beyond the reach of the roots. If the 
roots grow to the water the plants will 
not need to wait for the water to come 
to the roots. Plants probably root deep- 
er in arid soils and may be encouraged 
to do so by cultivation of the soil about 
Six inches in depth. Plants have been 
found to penetrate the soil with their 
roots to depths as follows: 
ADPIOS 2... cece eee ee 8 tee eee eee 9 feet 
Strawberry .......c cen eeeceavee 22 inches 
Alfalfa, 174 days old... .......... 5 to 30 feet 
3. The rate at which the soil below 
the root zone may supply water by up- 
ward capillarity to the roots. The neces- 
sary moisture may be below the roots, 
but will not travel up fast enough. 
1177 
4. The extent to which the sow and 
subsoil may become dried out. If at the 
time of irrigation the soil is very dry it 
is capable of taking up a large amount of 
water. The texture of the soil will also 
have an effect on this factor. 
(bo) Frequency. This is one of the most 
important questions that confronts the 
practical irrigator. The conditions which 
determine the frequency of irrigation 
are: 
1. The amount af avartlable morsture 
which may be stored in the soil. If the 
difference between the upper and lower 
limit is only a few per cent it will deter- 
mine the amount of water stored at one 
time. 
2. The rate at which the moisture is 
lost through the crop and through the 
soil. As to the crop it sometimes is neces- 
sary to irrigate to bring up the seed. A 
young crop will make very little de- 
mand on the water in the soil. A wheat 
crop makes the heaviest demand on the 
soil from the time it begins to head until 
it reaches the dough stage. 
3. The degree of saturation a particu- 
lar crop will tolerate before it is injured 
in quality and quantity. Irrigation will 
nearly always check the growth of the 
crop for a few days. The fewer the num- 
ber of irrigations the smaller may be the 
labor involved and the lower the cost. A 
heavy soil will store water longer, usual- 
ly, and will require fewer irrigations. 
METHOD OF IRRIGATING WITHOUT 
WASTE WATER 
H. M. GILBERT 
There is considerable alarm among 
those inexperienced in irrigation over 
the suits, court injunctions and threat- 
ening notices sent out by various canal 
companies. The accompanying illustra- 
tions will suggest to the irrigator how 
he can greatly lessen, and in many loca- 
tions entirely stop, the running of waste 
water from his land. 
The solution to the whole proposition 
of waste water is: level contour ditches 
made with a two-horse plow at the lower 
end of the irrigation rows. 
These level contour ditches should be 
sufficiently near together to irrigate the 
