IRRIGATION REQUIREMENTS OF THE GREAT BASIN 21 
relatively large particles belong to this type. Other soils are made 
up largely of small particles and are in consequence retentive of 
moisture and do not permit much water to percolate through them. 
Silt and clay soils are of this type and these as a rule do not require 
water as frequently as the more porous soils. 
Cropped soils having a water table near the base of the root zone 
need little, if any, water applied to the surface of the soil, since 
moisture is drawn from beneath. 
The time of irrigation is also influenced by precipitation. In 
some parts of the West enough moisture is stored in the soil, result- 
ing from rainfall or the melting of snow, to nourish plants during 
their first stage of growth. Under such conditions no artificial 
watering is needed until the roots of the growing plants threaten to 
deplete the soil moisture below the desired amount. In other parts 
of the West most of the precipitation occurs during the winter 
season and irrigation is needed shortly after crops are planted if not 
before. 
There is likewise a wide seasonal fluctuation in the flow of West- 
ern streams. To lessen the injurious effects of the lack of water 
during the late summer months, a common practice is to apply sur- 
plus quantities when there is an abundance, and this is done with 
little regard to the need of the crops for water at the time of ap- 
plication. While this practice increases the yields, it is wasteful of 
water and tends to water-log fertile land. As stated elsewhere, the 
better practice is to store a part of the surplus flow and to apply 
water from stream and reservoir as the soil and crops require it. 
This more economical method is being followed wherever funds are 
available to build works for the storage of water. 
The regulations in vogue governing the delivery of water to those 
entitled to its use exert a marked influence on the time of irriga- 
tion. For the most part water is delivered to water users in rota- 
tion. In other words, all the farms furnished water from a lateral 
ditch receive the entire stream in turn and the number of hours of 
use is apportioned to each farm in accordance with the number 
of acres watered. On small farms, the number of hours of use may 
be less than 24, while the period between water deliveries may vary 
from less than 10 days to more than 30 days. Under such regula- 
tions in respect to water delivery, it is not always possible to irri- 
gate crops at the proper time. 
Lastly, the varied and at times pressing duties of operating an 
irrigated farm often render it inadvisable to quit an urgent task in 
order to irrigate. In the Great Basin the harvesting of alfalfa often 
occurs at a time when sugar beets or other crops need irrigating. 
The delay in irrigating a particular crop by first harvesting the 
alfalfa may affect the yield of that crop. On the other hand, the 
delay in harvesting the alfalfa when ready to cut, may incur as 
great a loss. 
THE CEREALS 
The amount of soil moisture absorbed by the roots of plants and 
transpired through the foliage varies quite widely in most crops 
in accordance with the condition of the plant and the stage of 
growth. In the case of cereals, for example, a relatively small quan- 
tity of soil moisture is absorbed and transpired from the time of 
