THE IRRIGATION AGE. 



70 



PREPARING LAND FOR IRRIGATION AND 

 METHODS OF APPLYING WATER. 



From Bulletin US, courtesy United States Department of Agriculture. 



Many farmers prefer to go to extra expense and to 

 handle more surface earth in order to have rectangular 

 check. Fig. 8 shows the same field laid out in rectang- 

 ular checks as nearly uniform in size as the nature of 

 the ground will permit. 



In building the levees around the checks scrapers 

 are generally used. All high parts within each check 

 are first scraped down and the material thus obtained 

 is dumped along the levees. The balance of the earth 

 required to complete the banks is obtained from the 

 highest parts of the interior of the checks, which leaves 

 this space quite rough, but fairly level. 



The field is then plowed and harrowed in the usual 

 way and the seed sown. The time of sowing alfalfa 

 extend? from November to April, but in the central 



CHECK OR SLUICE BOXES. 



The check or sluice boxes, through which the water 

 is admitted into the checks, vary in width from one foot 

 to ten feet. They are rectangular boxes passing 

 through the earth embankments, and so arranged that 

 dashboards can be readily and quickly inserted and 

 withdrawn. The boxes must be water-tight, inex- 

 pensive, and so made and placed as not to obstruct farm 

 implements. 



The sketch in Fig. 9 was made from a medium- 

 sized box which was designed and used by Mr. Joshua 

 Cowell, of Manteca, Cal. 



Fig. 10 shows a cheaper box which is common in 

 Stanislaus County. 



FLOODING CHECKS. 



Many of the canals in the San Joaquin Valley are 

 operated in a manner to meet the needs of the check 

 system. Instead of delivering a small stream for a 

 long period, the practice is to deliver a large volume 

 of water for a short period. On land that is checked 





Furrow Irrigation of Sweet Potatoes 



part of the valley many prefer the first week in March. 

 The soil is then moist from winter rains and no irri- 

 gation is necessary until the plants cover the ground. 

 From twenty to twenty-five pounds of seed are sown 

 to the acre without any nurse crop. 



After -plowing and before seeding the levees should 

 be well harrowed and in some cases dragged down so 

 as to present the appearance of low embankments hav- 

 ing a wide base. In nine cases out of every ten the 

 sides of the levees are left too steep. The width of 

 the base of a levee, as a rule, should be eight times the 

 height of the crest. Thus a levee nine inches high 

 should have a base width of six feet. The height de- 

 pends on the difference in elevation of the contour 

 lines and the depth of water to be applied in one irri- 

 gation. With four-inch contours when completed and 

 settled the levees are usually nine inches high. This 

 leaves a margin of safety between the surface of water 

 in the check and the top of the levee, providing the 

 depth of water applied does not exceed six inches, 

 since a portion of the water is absorbed by the dry soil 

 before the check is filled. 



one man can handle, as a rule, four times as much 

 water as he can in flooding from field ditches. Under 

 this system a flow _of ten cubic feet per second is not 

 unusual for a forty-acre tract of alfalfa ; and since this 

 amount would cover a farm of this size six inches deep 

 in twenty-four hours, the time required for one irri- 

 gation is usually brief. On sandy soil, where the sur- 

 face is checked, a large volume is much the best. The 

 space inclosed in each check can then be rapidly 

 flooded and the water evenly distributed. In admitting 

 small streams to a check much is absorbed at the en- 

 trance end, the distribution is not uniform, and a 

 larger percentage is lost by evaporation and seepage. 



COST OF CHECKING LAND. 



The owner of an irrigated farm can prepare the 

 surface, providing he has the necessary teams and im- 

 plements, for much less money than it will cost to hire 

 it done. Work of this nature is usually done during 

 the winter months in California. Field labor on the 

 farm can be performed with more comfort in January 

 and February in the San Joaquin Valley than it can in 



