This section is from the book "The Potato: A Compilation of Information from Every Available Source", by Eugene H. Grubb, W. S. Guilford. Also available from Amazon: The Potato: A Compilation Of Information From Every Available Source.
Fundamentally and theoretically, irrigation is the simplest operation connected with the growing of a crop on an irrigated farm.
At first thought it was intended to preface this chapter with a note to the effect that the ideas which follow will pertain only to those parts of the earth where crops can be grown only with irrigation.
The practice of irrigation, however, is simply that of supplying a plant the quantity of moisture required to bring about its most perfect, normal development. There are times when an application of water to the soil of what is called the "rain belt" would be of great benefit and result in profit to the grower.
The practice of irrigation is sure to increase as the productiveness of the acre must continually be made greater.
It cannot be made too plain that irrigation is easy as long as the operator keeps in mind the moisture needs of the plant.
The following interesting article on irrigation is from the "Irrigator's Hand Book," which is a compilation of suggestions on various agricultural subjects written in 1909, primarily for the settlers on the J. S. & W. S. Kuhn irrigation projects in southern Idaho by the authors of this work in collaboration with other members of the Agricultural Department of the Twin Falls North Side Land & Water Company, and published by H. L. Hollister of Chicago. C. J. Griffith, one of the foremost agriculturists in America, and at present Director of Agriculture for the company mentioned above, prepared the following:
Irrigation is the artificial application of water to land. It is necessary in arid regions in order that profitable crops may be grown; and it is useful in semi-arid regions to increase their production. Although most useful in arid regions, it is often practised in localities of heavy rainfall, for instance in the rice-growing districts of the South, where the annual rainfall is from forty to sixty inches.
The practice of irrigation is older than, the Pyramids of Egypt. The valleys of the rivers Nile and Euphrates have an unbroken historical record of more than 4,000 years.
In a great many places in this hemisphere there are ruins of irrigation works that antedate any written history, and the civilization of the race that built them is only surmised.
The irrigated area of all the nations of the world does not exceed 100,000,000 acres, or a land area of less than twice the acreage of the state of Idaho. Of this area India has 53,000,000 acres, and in that country may be seen some of the most expensive irrigation works in existence.
There are only 13,000,000 acres of irrigated land in the United States, and the greatest systems yet developed are in the Twin Falls country.
The preparation of land for irrigation consists in: First, putting the land in condition for farming; and, second, a proper surface grading for the even distribution of water.
There is nothing that pertains to irrigated farming that pays better than proper leveling or grading of the land. It is the key to the whole situation, and when once done it is done for all time.
It is not always necessary to change the general grade or lay of a piece of land, but it is absolutely essential to take off high places and build up low ones.
There are several implements with which to do leveling and grading; among these are Fresno scrapers, buck scrapers and land graders of different makes. Each one has a special use, some being for heavy cuts and long hauls, and some best for short hauls. The character of the work to be done will be the determining factor in the implement chosen. After the grading is done, in order to get surface smoothness, a home-made leveler or jointer made of plank should be run over the land to take out all small unevennesses. This leveler or jointer should be used every time a field is plowed. It firms and fines the soil. On some land this leveler is the only implement needed for leveling.
No hard and fast rules can be given for the laying out of the ditch system for a new tract of land, but there are a great many essential points to be considered in order to have satisfactory results. It is desirable to bring the water to the highest point on the farm, so that every part can be reached. The 'farm supply ditch' should be as short as it is possible to make it in order to lessen seepage, evaporation and maintenance. It should ordinarily be made on a grade of 1 foot (1.2 inches) to 0.2 feet (2.4 inches) fall per hundred feet, according to the firmness of the soil through which it is made. Ditches that carry over three or four second feet of water should have less grade. Whenever the current of the water picks up and carries sediment, the ditch will give trouble, because the sediment will be dropped in places where the current is slower and eventually this will choke up the ditch and cause a break. Especially in sandy soil should care be used to get an even and light grade, which should not exceed 1.5 inches per hundred feet. Where it is necessary to take a farm supply ditch down a heavy grade, drop boxes should be put in to take care of the excess grade. Farm supply ditches should be so located, if possible, to avoid dikes and flumes. A dike where absolutely necessary should be made of stiff soil, the banks should be made wide, and high, and the dirt for it should not be taken closer than four feet from the toe of the bank on each side. When water is put through it for the first few times, it should never be allowed to run all night, because the soil thus thrown up is loose and readily fills with water. After a few hours' run, the water begins to seep through the banks, and until the dirt in the fills has repeatedly soaked up and settled there is always danger of it breaking. As soon as the dikes are firm and solid, the banks should be seeded to some grass that makes a good sod. Kentucky blue grass and Brome grass (Bromus Inermus) make good sod for holding ditch banks. Sandy soil makes a very unsatisfactory dike, as it never hardens like a stiffer soil. Flumes are unsatisfactory unless well made. Galvanized iron flumes give good service. Farm supply ditches should have ample capacity. New ditches lose a great deal by seepage, and until they become silted up they do not carry as much water as their size would indicate. New land in an arid district takes more water the first year than it ever requires thereafter. For an 80-acre tract of new land the supply ditch should be made with a slip scraper and it should generally be at least one foot deep in the solid ground, to say nothing of the height of the banks made by the dirt scraped out.