93 
IRRIGATION EXPERIMENTS IN IDAHO. 5 
e well represented in Plate II, figures 1 and 2, which show the 
average soil of the first, second, third, and fourth foot of two of the 
_ experimental tracts. 
. 
4 
MOISTURE DETERMINATIONS. 
The primary object of this investigation having been to determine 
| the quantity of irrigation water required by the soils and crops of 
_a farm or project, it was not considered advisable or practical on 
account of the large territory involved to go to the expense of mak- 
ing exhaustive soil-moisture determinations on all tracts throughout 
\ the season. A careful determination of the moisture in the first, 
second, third, and fourth foot of soil of each plot experimented upon 
was made, however, before the first irrigation and about the time 
plants started to grow in the spring. This was done by securing a 
large number of representative samples from each tract and drying 
_ them in an oven at a temperature of 108° C. While the available 
soil moisture has not been taken into consideration in averaging the 
‘quantities of water used and the yields obtained, these determina- 
tions have permitted of a careful comparison of the results secured 
from the different experiments. 
REIMBURSEMENT OF LOSSES. 
The owners of the various experimental tracts included in the 
- investigation have been reimbursed for all crop losses that have 
been experienced because of variation of the water-supply. The 
yield of the plot selected and handled by the owner himself was used 
In each case as a basis for determining the loss. Reimbursement 
was found necessary in connection with less than one-third of the 
tracts included in the investigation. 
METHOD OF INTERPRETING RESULTS. 
The correct and proper analysis of the results has been the most 
difficult part of the entire investigation. Even when the greatest 
care is used in agricultural experiments there are many factors 
other than those under observation which may influence the yields. 
Normally it has been assumed that the plot which produced the 
best yield in each experiment received the best application of water. 
In many cases, however, the largest yield has exceeded the yield — 
of one of the other plots by not more than 2 to 5 per cent, when 
_ the quantity of water applied for the maximum yield exceeded that 
applied to the next largest yield by as much as 100 per cent. In 
such cases it is apparent that if economy of time and water is to 
be considered, it is better practice to apply the smaller quantity 
of water. The investigation as a whole has emphasized the fact 
that the results from single experiments can not be depended upon, 
