IRRIGATION EXPERIMENTS IN IDAHO. 85 
the months of June and July. Many instances have come to the 
attention of the writer where the advocates of a high duty have over- 
looked the unequal requirements of the different months of the season, 
and it is desired to emphasize the fact that this must not be ignored 
if the best use of the water is to be secured. 
Table XVIII gives a general summary of the results that have been 
obtained upon porous, sandy, and gravelly soils. This table has 
been constructed by averaging the requirements of grain and alfalfa 
on these soils during the first two years of the investigation in the 
same manner used with the clay soils, there not having been a sufficient 
number of tracts of this type of soil experimented upon during the 
last two years of the investigation to be included in such a summary 
table. 
Taste XVIII.—Average depths of water applied to 21 selected fields of grain and alfalfa 
on porous, sandy, and gravelly soils. 
[Altitudes ranging from 2,600 to 5,800 feet.] 
l 
Depth of water applied. | 
\ 
Num- | | Total 
Crop. Season. | ber of April— Septem ber— for 
plots. i ev ACCT ee season. 
| May. June. | July. gust.| 7 
1-15 | 16-30 1-15 | 16-30 
Feet.| Feet. | Feet.| Feet.| Feet.| Feet.| Feet.| Feet Feet. 
AINE CS 5 a eae 1910 7h Rae | 5 583 4) tbe We Le O) |i) | ede ees Sele oo ee cae 6.43 
(Garis es es Se 1910 LOWS aiecece .03 | 1.44 . 66 eS GM arses as |e eee 2.49 
ANIMES 5, Sea ae ea 1911 Gy | eee 18 CPA dbs tees ei SPW OBPAD laces Soce 6.58 
Cian: SS eesseeeas ees 1911 Si les oe remcelh sere cis | OSEID |) USWIO es GREE eco ose een 2.90 
Aenea ean ee eS ett eae 5G ee Be er er eo 4.60 
IRGe Coy Ol Woe alidcaSopacolanacceca|soccer 3.9 |11.3 32.0 ioe PANO to MISES lew eels Renee e 
Table XVIII shows that porous soils require a larger supply of 
water for their efficient irrigation than the medium soils, the exact 
quantity required being governed by the porosity of the soil, the 
method of preparation, and the skill used in the application of the 
water. The results shown in this table indicate that an application of 
4.6 feet to the acre per annum will be required for this type of soil, 
of which 3.9 per cent will be required during the last half of April; 
11.3 per cent during the month of May; 30 per cent during June; 26 
per cent during July; 25.6 per cent during August; and 1.3 per cent 
during the first half of September. 
SURFACE WASTE. 
The measurements just given do not include waste from irrigated 
lands. In the variation experiments the waste from the various 
plots was measured, with the results shown in Table XIX. 
