THE IREIGATION AOE. 



can be flooded if it is considered best. A better plan is 

 to furrow the floor of each check as shown in Figure 24. 

 The water is admitted through the check box which was 

 used for the alfalfa and conducted into a short head ditch, 

 from which it is distributed to the furrows. The chief 

 objection to this method is that the checks are too small 

 for orchard tracts in furrow irrigation. 



Time to Irrigate Orchards. 



The best orchardists believe that frequent examina- 

 tions of the stem, branches, foliage, and fruit are not 



enough. The roots and 

 soil should likewise be 

 examined. The advice 

 of such men to the inex- 

 perienced is: Find out 

 where the bulk of the 

 feeding- roots is located, 

 ascertain the nature of 

 the soil around them, 

 and make frequent tests 

 as to the moisture which 

 it contains. In a citrus 

 orchard of sandy loam 

 samples are taken at 

 depths of about 3 feet 

 and the moisture content 

 determined by exposing 

 the samples to a bright 

 sun for the greater part 

 of a day. It is consid- 

 ered that 6 per cent by 

 wei?ht of free water is 



Fig. 84. Combination of Check and 

 Furrow Methods. 



sufficient to keep the trees in a vigorous condition. 



Doctor Loughndge, of the University of California, 

 in his experiments at Riverside, Cal., in June, 1905, found 

 an average of 3.5 per cent in the upper 2 feet and an aver- 

 age of 6.16 per cent below this level in an orchard which 

 had not been irrigated since October of the preceding year. 

 It had received, however, a winter rainfall of about 16 

 inches. On examination it was found 

 that the bulk of the roots lay between 

 the first and fourth foot. These trees in 

 June seemed to be merely holding their 

 own. When irrigated July 7 they be- 

 gan to make new growth. A few days 

 after the water was applied the percent- 

 age of free water in the tipper 4 feet of 

 soil rose to 9.64 per cent. The results of 

 these tests seem to indicate that the per- 

 centage by weight of free moisture 

 should range between 5 and 30 per cent 

 in orchard loams. 



Many fruit growers do not turn on 

 the irrigation stream until the trees be- 

 gin to show visible signs of suffering. 

 as a slight change in color or a slight 

 curling of the leaves. In thus waiting 

 for these signals of distress, both trees 

 and fruit are liable to be injured. On the 

 other hand, the man who ignores these 

 symptoms and pours on a large quantity 

 of water whenever he can spare it, or 

 when his turn comes, is apt to cause 

 greater damage by an overdose of water. 



Number of Irrigations Per Season. 



For nearly half the entire year the 

 fruit trees of Wyoming and Montana 

 have little active, visible growth, whereas 

 in the citrus districts of California and 

 Arizona the growth is continuous. A 

 tree when dormant gives off moisture 

 but the amount evaporated from both soil and tree in win- 

 ter is relatively small, owing to the low temperature, the 

 lack of foliage, and feeble growth. A heavy rain which 

 saturates the soil below the usual covering of soil mulch 

 may take the place of one artificial watering, but the light 

 shower frequently does more harm than good. The num- 

 ber of irrigations likewise depends on the capacity of the 

 soil to hold water. If it readily parts with its moisture, 

 light but frequent applications will produce the best re- 



sults, but if it holds water well a heavy application at 

 longer intervals is best especially when loss by evapora- 

 tion from the soil is prevented by the use of a deep soil 

 mulch. 



In the Yakima and Wenatchee fruit-growing district of 

 Washington the first irrigation is usually given in April or 

 early in May. Then follow three to four waterings at inter- 

 vals of 20 to 30 days. At Montrose, Colo., water is used 

 three to five times in a season. At Payette, Idaho, the same 

 number of irrigations is applied, beginning about June 1 in 

 ordinary seasons and repeating the operation at the end of 30- 

 day intervals. As a rule, the orchards at Lewiston, Idaho, 

 are watered three times, beginning about June 15. From two 

 to four waterings suffice for fruit trees in the vicinity of 

 Boulder, Colo. The last irrigation is given on or before 

 September 5, so that the new wood may have a chance to 

 mature before heavy freezes occur. In the Bitter Root Valley, 

 Montana, young trees are irrigated earlier and oftener than 

 mature trees. Trees in bearing are, as a rule, irrigated 

 about July 15, August 10 and August 20 of each year. In 

 San Diego county, Cal., citrus trees are watered six to 

 eight times, and deciduous trees three to four times in a 

 season. 



Duty of Water in Orchard Irrigation. 



The duty of water for 1 acre as fixed by water con- 

 tracts varies all the way from one-fortieth to one four- 

 hundredths of a cubic foot per second. In general, the 

 most water is applied in districts that require the least. 

 Wherever water is cheap and abundant the tendency 

 seems to be to use large quantities, regardless of the re- 

 quirements of the fruit trees. In Wyoming the duty of 

 water is seldom less than at the rate of a cubic foot per 

 second for 70 acres. In parts of southern California the 

 same quantity of water not infrequently serves 400 acres, 

 yet the amount required by, the fruit trees of the latter 

 locality is far in excess of that of the former. 



In recent years the tendency all over the West is toward 

 a more economical use of water, and even in localities where 

 water for irrigation is still reasonably low in price it is rare 



00 



Fig. 25 Average 



duty per month under Riverside Water Company, December 1, 1901, to 

 November 30, 1908. 



that more than V/2 acre-feet per acre is applied in a season. 

 This is the duty provided for in the contracts of the Bitter 

 Root Valley Irrigation Company of Montana, which has 40,000 

 acres of fruit lands under ditch. Since, however, the water 

 user is not entitled to receive more than one-half of an acre- 

 foot per acre in any one calendar month, it is only when the 

 growing season is long and dry that he requires the full 

 amount. 



In the vicinity of Boulder, Colo., the continuous flow of a. 



