85 



Usually the furrows are made parallel to the rows of trees. As the 

 trees grow older it is not possible to get the furrows near the trunk which 

 leaves a space between the trees in a row which is comparatively dry. To 

 wet the soil more uniformly the land is'fcrpss furrowed so as to form zig- 

 zag furrows around the trees (Figs. 73, 74). The furrows indicated by the 

 dotted lines are first made, then crossed at right angles and the necessary 

 cuts and fills made with a shovel. Because of the greater length, slower 

 velocity and the larger area wetted, the zigzag furrows receive a larger 

 stream. Frequently only the lower half, third, or fourth of the furrows is 

 zigzagged. This will tend to give the lower part of the orchard as much 

 water as the upper part which otherwise receives a greater quantity. 



The length of the furrows ranges usually from 330 to 1320 feet, which 

 is the length of a 40 acre tract. As a rule the furrows should not exceed 

 660 feet and preferably 330 feet. On sandy soil, especially, short furrows 

 not over 330 feet long are desirable; otherwise the upper side of the 

 orchard receives a large excess of water before the lower part has received 

 sufficient. 



The grade of the furrows varies widely with the topography or lay of 

 the land. Some orchards on flat valley soils do not permit of a steeper 

 grade than 1 inch to 100 feet while orchards on steep side hills may re- 

 quire placing the furrows on much steeper grades. The proper grade de- 

 pends much on the character of the soil. On ordinary soil a flat grade of 

 3 to 6 inches in 100 feet is preferable. On steep hillsides flat grades for 

 the furrows can often be obtained by setting out the trees so that the fur- 

 rows will run across the slope. Some soils that do not wash badly are 

 irrigated successfully with furrows as steep as ten or twelve feet to the 

 hundred, but usually such grades are excessive and require that very small 

 streams be turned into the furrows and great care taken to prevent wash- 

 ing of the soil. Where steep grades are not avoidable short furrows 

 should be used. 



APPLICATION OF WATER. 

 1. When to Irrigate Orchards and Quantity of Water to Use. 



Most orchardists have their opinion as to when irrigation is necessary. 

 They may be guided by the appearance of the fruits and the leaves, but the 

 best way to determine the necssity for irrigation is by a study of the soil. 

 This is best done by borings or excavating trenches to determine where 

 the roots are and how much free moisture there is in the soil. The method 

 of taking soil samples and the determination of percentage of free moisture 

 in the soil have been explained (page 65). After the orchardist has be- 

 come familiar with his soil and knows the best percentage of moisture for 

 his trees, he may be able to tell readily by taking a sample of the soil in 

 his hand whether there is sufficient moisture or not. 



It has been stated above (page 65) that the minimum amount of free 

 soil moisture in four feet of soil to keep apple trees in good growing con- 

 dition has been found to be from 2.5 to 3 per cent, by weight. Dr. Lough- 

 ridge found in his experiments on citrus orchards in southern California 

 that the moisture content in the upper four feet varied from about 4.7 per 

 cent, by weight before irrigation, to 9.64 per cent, immediately after irri- 

 gation for a sandy soil, from about 6.81 per cent, before irrigation to 11.27 

 per cent, immediately after irrigation for a sandy loam, and from about 

 5.47 to 10.86 per cent, for a heavy loam. The percentage of free moisture 



