el ial ee 
TRRIGATION EXPERIMENTS IN IDAHO. 25 
cated that the maximum yields were made with approximately 1 
foot of water per acre, and that applications in addition to this quan- 
tity made a considerable decrease in the yield. There is no doubt 
that had the fertilized plots of the Gooding experiment been more 
fertile the largest yield would have been made with the 1 foot per 
acre. 3 
This Gooding experiment, together with the other experiments 
which have been made, seems to prove conclusively that less water 
4s required for the production of a given yield of crop on fertile soils 
than is required for the same yield of crop on infertile souls and empha- 
sizes the necessity of maintammg a high state of fertility m cases 
where a high duty of water must be secured. It does not mean, 
however, that less water is required by the fertile soils, for, as shown 
by figure 3, fully as much is required for maximum crop production, 
a greatly increased yield being produced on the fertile soils. 
RESULTS SECURED WITH INDIVIDUAL CROPS. 
In order to show the results secured from single crops on the same 
type of soil, curves are shown in figures 5, 7, and 8. Each of these 
curves is based upon five years’ results at the Gooding experiment sta- 
tion. The average amount of precipitation during the growing sea- 
son for four of these five years was 2.92 inches. Considering that 
— each of these curves is based upon a number of experiments, that this 
station lies at the average altitude for southern Idaho, and that the 
soil, which is a medium clay loam, rather impervious, and averaging 
6 to 8 feet in depth, is representative, it is believed that the results 
plotted are typical of what may be expected throughout the State, 
and that they show within a reasonable limit the yield of crop which 
may be produced with a given quantity of water. These curves do 
not necessarily indicate a proper duty of water under good practice 
in Idaho, since, as is later stated, local economic features enter largely 
into all such problems. 
The curves in figure 5 show the average results secured from 96 
plots of staple varieties of spring wheat grown during the five seasons. 
One curve shows yields per acre, and the other yields per acre-foot of 
water applied. Considering the large number of plots upon which 
these curves are based, they should be very dependable. The curve 
showing yield per acre agrees with the data secured elsewhere through- 
out the State, in that it shows that the yield of graia will normally 
increase as the water applied is increased until an amount varying be- 
tween 1.4 and 1.8 acre-feet per acre has been applied, after which.the 
application of more water will decrease the yield of grain and in many 
cases the yield of straw as well (fig.6). The curve showing yields per 
acre-loot of water (fig. 5) shows that the highest efficiency from water 
applied to spring grains is secured where the smaller quantities are 
