IRRIGATION 



3064 



IRRIGATION 



.RRIGATION, iriga'shun. Nearly every- 

 one has had some experience with flower cul- 

 ture and knows how important it is that the 

 plants should be watered at certain stages of 

 their growth. Though other plants are less 

 delicate, they are no less dependent on water, 

 and if all that they require does not come to 

 them in the form of rain or of moisture in the 

 soil, it must be given to them by man. Irriga- 

 tion, or artificial watering of vegetation, has 

 been practiced in simple ways for thousands of 

 years, but only within the last half century has 

 scientific knowledge been applied to watering 

 the waste places. Men knew that with the aid 

 of water crops could grow in the desert, but 

 they did not know how much water was needed 

 for the best results, when to supply it, or how 

 to handle it without waste. 



How Lands Are Irrigated. There are a num- 

 ber of methods for distributing the water over 

 fields. In more than nine-tenths of the irriga- 

 tion in the United States and Canada water is 

 brought to the fields through ditches. The 

 main ditch or canal takes the water from the 

 source of supply, and head ditches join the 

 main ditch on each side at regular intervals. 

 A gate prevents the water from entering the 

 head ditch when it is not needed. At the 

 time of irrigating this gate is opened. The 

 plan of distributing the water over the field is 

 determined by the crop. Fields on which 

 alfalfa, wheat or other crops of similar char- 

 acter are grown are usually flooded, which is 

 done by placing a portable dam usually made 

 of canvas across the ditch at intervals of about 

 three rods. When the water has flooded one 

 strip the dam is moved on to another, the 

 process being repeated until the field is irri- 

 gated. 



Fruits, potatoes, corn and other crops 

 planted in rows are usually irrigated by run- 

 ning the water in furrows between the rows. 

 Sprinkling and the use of underground pipes 

 are other methods used to some extent in 

 gardens and on truck farms, bu.t both are 

 expensive. 



Whatever the method used, the ground must 

 be prepared for the proper flow of water before 

 planting. A slope from ten to twenty feet to 

 the mile will usually allow the water to flow 

 freely and without currents that may carry the 

 surface soil along with them. Where the land 

 slopes too rapidly checking is necessary, that is, 

 ridges are raised around the edges of small 

 plots, which are made practically level. The 

 same rule holds in irrigating by furrows. The 

 grade must be slight or the current will cause 

 damage. 



Development in the United States. Long 

 before the white man came to America irriga- 

 tion was carried on by the city-dwelling Indians 

 of New Mexico and Arizona. In that region, 

 and throughout most of Utah, Nevada and 

 Southern California and parts of Colorado, 

 Wyoming, Idaho, Washington and Oregon, less 

 than ten inches of rain falls each year. This 

 will sustain only such vegetation as the sage- 

 brush and the cactus, which nature had 

 adapted to arid regions. The Spaniards who 

 came to America knew something of the irri- 

 gation systems which the Moors had estab- 

 lished in Spain, and they taught the Indians 

 to build masonry dams and reservoirs. The 

 Mormons and other early settlers in the 

 West found irrigation indispensable. When 

 the pioneer gold-seekers were mining the Cali- 

 fornia gold by washing it from the stream beds, 

 many ditches were dug, some of which after- 

 ward proved even more valuable as irrigatic 

 ditches. But not until the last quarter of 

 nineteenth century were there more than a 

 thousand acres of land under irrigation in 

 whole United States. Then progress was ra] 

 and the census of 1890 reported nearly 4, 

 000 acres of irrigated land. In 1894 Congress 

 passed the Carey Act, which granted land to 

 the states if the latter would build irrigation 

 works. This law did not prove popular, and in 

 1902 a national Reclamation Act gave power 

 to the Department of the Interior to construct 

 irrigation systems. Of the more than 14,000,- 

 000 acres irrigated in the United States in 1910, 



