116 HORTICULTURE, FORESTRY, FLORICULTURE 



Time to Irrigate Orchards. The best orchardists believe that 

 frequent examinations 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 inexperienced 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 ex- 

 posing the samples to a bright sun for the greater part of a day. It 

 is considered that 6 per cent by weight of free water is sufficient to 

 keep the trees in a vigorous condition. 



Many fruit growers do not turn on the irrigation stream until 

 the trees begin 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 Ari- 

 zona the growth is continuous. A tree when dormant gives off mois- 

 ture, but the amount evaporated from both soil and tree in winter 

 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 number of irrigations likewise depends on the capacity of the 

 soil to hold water. If it readily parts with its moisture, light but fre- 

 quent applications will produce the best results, but if it holds water 

 well a heavy application at longer intervals is best, especially when 

 loss by evaporation from the soil is prevented by the use of a deep 

 soil mulch. 



Duty of Water in Orchard Irrigation. The duty of water for 

 1 acre as fixed by water contracts 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 requirements 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 irri- 

 gation is still reasonably low in price it is rare that more than 2^2 

 acre-feet per acre is applied in a season. 



The most reliable and in many ways the most valuable records 

 pertaining to duty of water on orchards have been obtained by the 



