20 
BULLETIN 1340, IT. S. 
DEPARTMENT OF AGRICULTURE 
This method, however, is costly and not well suited to arid conditions. 
Ordinarily crops grown in the West are irrigated with large quanti- 
ties of water at certain periods and when these periods are limited 
to two or three in the growing season, it is not easy to determine 
in all cases the proper time to use water. 
While it is generally true that the more foliage a plant has the 
more water it transpires and the greater is its need for soil moisture, 
cases arise like that of a newly cut alfalfa field where the transpira- 
tion is small, yet the need for water is urgent in order to start the 
new growth. 
When the growth of plants is checked — especially at a time when 
it is most rapid — by a lack of moisture, complete recovery is not 
possible, and a smaller yield, depending upon the severity of the 
check, is the result. To guard against such an occurrence, an ade- 
CROP 
ALFALFA 
1911 in Tanks 
at Nevada Experiment 
Station Farm. Reno, New. 
ALFALFA 
1312 in Tanks. 
Same Location 
WHEAT 
I9t3 in Tanks. 
Same Location 
Note: Tank No. 5 sprang a leak and was abandoned 
9-ro 
ll-!2 
13-14 
250 200 ISO 100 50 
OATS 
19/3 in Tanks. 
Same Location 
Fig. 10 
. — Relationship between amount of water applied and crop yield for alfalfa, 
wheat, and oats as determined by tank experiments at Reno, Nev. 
quate amount of soil moisture should be maintained during the 
critical stages of growth, because when crops suffer a setback on ac- 
count of drought no subsequent waterings will repair the damage 
done. It is also true that the application of water to many crops 
approaching maturity results in injury rather than benefit. 
Before taking up the question of the proper time to apply water 
to typical crops, it will be necessary to consider briefly the influence 
which several secondary factors exert in causing more or less de- 
parture from theoretical conclusions based solely upon the water 
requirements of the crops under consideration. 
Of the secondary factors, the character of the soil is one of the 
most important. Some soils when irrigated retain little water, ne- 
cessitating frequent light waterings in order to supply enough soil 
moisture for the use of crops. Sandy and gravelly soils having 
