288 MISCELLANEOUS FARM SUBJECTS 



600 feet long. These head ditches are fed from the main supply 

 ditch of the farm, and are usually made after the field is partially 

 leveled and graded. 



The presence of an impervious hardpan near the surface causes 

 sidewide seepage of the water, a greater wetting of the surface and 

 consequent increased loss by evaporation and by accumulation 

 and run-off at the lower end of the furrows. 



Shallow irrigation furrows do not give as good results as deep 

 ones; they allow a large part of the water to rise by capillarity to 

 the surface on either side and thence to escape into the air by evap- 

 oration, while deep furrows enable the soil to receive and retain, 

 nearly all of the water applied. (Ex. S. Bui. 203.) 



Division of Water Among the Furrows. The chief trouble in 

 furrow irrigation is to divide the water in the head ditch somewhat 

 equally among a large number of furrows. The irrigator may wish 

 to turn water into fifty furrows at the same time and, unless he uses 

 some device other than a shovelful of dirt taken out of the ditch 

 bank, the distribution will not be uniform. One of the best de- 

 vices yet used for this purpose is a short pipe or spout, which may 

 be made of wood. For small amounts of water less than 1 miner's 

 inch, two pine laths cut in two and the four pieces nailed together 

 in the form of a pipe answer very well. For larger streams, requir- 

 ing from 1 to 6 miner's inches, half-inch boards of the required 

 width 'are used in place of the half laths. A pipe is inserted in the 

 lower bank of the head ditch opposite each furrow and placed 2 or 

 3 inches below the surface of the water. In some localities where 

 water is scarce and valuable, flumes and pipes of various kinds are 

 used to convey and distribute the water to furrows. (F. B. 263.) 



The main distributing laterals in the field should be placed 

 10 to 20 rods apart, depending upon the slope of the land and the 

 nature of the soil, and may be given grades of one-half inch to an 

 inch per rod. Each lateral should carry 2 to 3 cubic feet of water 

 per second, as one man can usually handle this volume with ease 

 after getting the stream set. 



The advantages of this method are : The surface soil is not so 

 apt to bake; a small head of water may be economically han- 

 dled; there is less loss of water by evaporation than with flooding. 

 The principal disadvantages are: The difficulty of maintaining 

 an equal flow in all furrows ; where the soil is not uniform in texture 

 an even distribution is hard to secure; the upper end of the field is 

 likely to receive more water than it requires; the furrows interfere 

 with cutting and handling the crop. (Ex. S. Circ. 67.) 



The check method of irrigation is confined mainly to alfalfa. 

 It consists in dividing up a field in contour, or rectangular checks, 

 each comprising, as a rule, from one-half acre to 1^ acres. Around 

 the margin of each check a low embankment or levee is formed 

 which retains the water until it has been absorbed by the soil. 



Laying Out the Field. The field to be checked is first to be laid 

 out in contour lines lines connecting points of equal elevation 

 the difference in level between any two being from 3 to 6 inches or 



