94 



that the furrows do not exceed 660 feet for ordinary loam soils and 330 

 or even 220 feet for porous sandy soils. This requires that the field be cut 

 up by two or more head ditches or head flumes fed by the supply lateral. 

 A typical wooden flume distribution system for an alfalfa field at Kenne- 

 wisk, Washington, is shown in the accompanying diagram (Fig. 75). The 

 furrows are made 3 to 6 inches deep, about the same width, and spaced 

 from 18 inches to 4 feet apart, depending on the character of the soil. The 

 furrows are commonly made by the use of a marker or furrowing sled 

 which may be a rough implement made of logs fastened together and 

 spaced the right distance apart, but preferably made of timber as shown 

 below (Fig. 76). This leaves a smooth furrow, without clods to interfere 

 with the flow. 



Fig. 70. Furrowing: Sled. 



(Farmers' Bulletin 392, U. S. Dept. Agr.) 



The water is divided and distributed into the furrows from the head 

 ditch or flume as for orchard irrigation, usually from spouts placed in the 

 ditch bank or from holes bored in the side of the flume. At first a larger 

 stream is turned into each furrow to rush it through to the lower end and 

 then the opening is regulated to give a small stream which is allowed to 

 run 12 to 24 hours for furrows 330 to 660 feet long and 24 to 48 hours for 

 furrows 660 to 1320 feet long. For porous soil a larger stream for a 

 shorter time should be used. With furrows 2 feet apart and 330 feet long 

 it will require about 1-5 miners' inch to each furrow, running for 24 hours, 

 to give a depth of 9 inches of water on the land. The practice in the 

 Yakima Valley is to make the furrows 18 inches apart when the land is 

 first seeded and to abandon every other one after the plants are well rooted. 

 2. Amount of Water Required. 



The duty of water measurements given for alfalfa (page 62) show the 

 great variations in quantity of water applied by different irrigators in dif- 

 ferent localities. These quantities do not give any idea of the correct 

 quantity of water to use. The maximum yield of alfalfa obtainable in any 

 case will depend not only on the quantity of water used, but on the time 

 when it is applied. When properly applied it has been found that different 

 quantities of water will give different yields but that the increase in yield 

 is not in direct proportion with the increase in quantity of water applied 

 and there is no. doubt for every particular case, a depth of water which will 

 give a maximum yield and any quantity applied above that is not only 

 wasted but decreases the yield because of the excess moisture in the soil. 

 Professor Fortier in 1903, when director of the Montana Experiment Sta- 

 tion, made experiments on seven plats of alfalfa to determine the relation 

 between quantity of water applied and yield. The results obtained are 

 given in the following table taken from U. S. Department of Agriculture, 

 Farmers' Bulletin 373 on Irrigation of Alfalfa. 



