The Problem Of Alkali Soils

Between the Missouri River and the Rocky Mountains, in parts of California, and in a few other parts of the West, are large areas of alkali soils. They are found almost entirely in arid or semi-arid regions. These soils produce an insignificant growth of a few native plants and are wholly unfit for cropping until properly treated. They are called alkali soils' because they contain large quantities of various salts, mostly common salt and carbonate of soda, which is ordinary washing soda. Otherwise they are normal. Thousands of acres of once valuable land have been made too alkaline for crops by seepage waters. The surface of alkali soils is often covered with crystals of the salts, making it look whitish. This is caused by the evaporation of water from the soil, leaving behind on the surface the salt that was dissolved in it.

Over-irrigation, especially on heavy lands, often makes them alkaline and may ruin them. But all soils that are white on the surface are not alkali. Excellent limestone soils have sometimes been mistaken for alkali, because they had a coating of carbonate of lime on the surface. Quite frequently there are alkali spots in an otherwise fertile field, the spots varying from several feet to several acres in extent. There are two common types of alkali soils, "black alkali" and "white alkali." The former contains chiefly carbonate of soda, which decomposes the humus in the soil and makes it very black; while the latter is a mixture of several salts, chiefly common salt and sulphate of soda. Black alkali is much more injurious to plants than white. The effect of alkali upon plants depends chiefly upon the kind of plant and upon the amount of salt in the first foot or two of soil. Some plants cannot stand alkali at all, some are tolerant of it, a very few prefer it. The plants that tolerate it are mostly native salt bushes and grasses. Of cultivated plants, sugar beets, alfalfa and sweet clover are most tolerant, especially sugar beets. The grains are impatient of it, but rye and barley appear to stand it better than the other cereals.

Practically all the common farm crops will not thrive in alkali soils, but after the salts are removed from these soils they are found to be remarkably fertile and produce very large crops. How to Treat Alkali Soils. — There are two methods of improving alkali soils; the alkali may be removed, or it may be changed into another form. The most common and most efficient way of removing alkali, whenever non-alkaline water can be had in abundance, is to irrigate the land and drain it. If persisted in, irrigation and drainage usually effect a permanent cure. Irrigation washes the salt out of the soil and drainage carries it off. The waters of some streams and wells, however, contain much alkali and are not suitable for irrigation. Irrigation without drainage may make a soil more alkaline, by bringing more of the salts to the surface. Under-drainage alone is usually effective, especially for small areas that can be drained at slight expense, but it is too expensive to be practicable except for land having a high valuation. In irrigating alkali land the entire surface of the soil should be flooded to remove the salts.

In experiments by the Bureau of Soils in Utah a 40-acre tract of waste land containing 2 1-2 per cent, of salt, or 6,650 tons to a depth of 4 feet, was flooded with 57 inches of water per year. Of this amount 45 inches were recovered as drainage, and this drainage water contained 2,401 tons of salt. In other words one-third of the alkali was removed in one year. The cost of this work is from $16 to $30 per acre. The injurious salt may be changed into another material that is less harmful by dressing the soil with gypsum, or land plaster. An application of four to six hundred pounds per acre is considered sufficient. This treatment is valuable only for black alkali. When a quarter or more of the salt is on or near the surface, as is often the case, it is sometimes practicable to scrape the surface and cast the scrapings elsewhere. Certain plants, notably greasewood and the Australian Salt-bush, thrive on alkali soils and take large quantities of salts from them. Occasionally it is practicable to crop soils that are very alkaline with these plants for several years, to remove part of the salts. The plants should not be burned on the land, however; ashes of all kinds and especially these, make the soil more alkaline. A crop of Australian salt bushes produces 15 to 20 tons of excellent green forage per acre, or 3 to 5 tons of dry forage. This plant grows well upon black alkali. Some soils that are very badly alkaline may not be worth the attempt to reclaim; those that are only mildly alkaline it will certainly pay to reclaim, providing they possess the other requisites of a fertile soil. Usually it takes several years to completely remove the objectionable salts, but if the soil is under-drained a fair crop can be grown upon it the second season. Deep plowing should be given to all soils that are more or less alkaline. Thorough tillage lessens the evaporation of water and hence lessens the amount of salt deposited upon the surface. Hilgard says, " When the alkali is not very abundant nor very noxious, frequent and deep tillage may afford all the relief needed. More than half the alkaline land in this state (California) that the people are afraid to touch requires no more remedy than thorough, deep tillage, maintained at all times." Liberal dressings of manure, especially horse manure, are very beneficial.

Alkali soils are apt to be deficient in nitrogen, because the nitrogen-fixing germs are not able to do their work when there is much alkali present. It is stated by Snyder that if a few loads of soil from fertile land are sprinkled on alkali spots the beneficial germs will be introduced and much good will result. After steps have been taken to remove the excess of salts the land should be cropped first with plants that are not very impatient of alkali. Oats is considered one of the best crops for this purpose. Practically all farm soils contain some alkali, but wherever rainfall is plentiful the salts are washed away before they accumulate sufficiently to injure plants. A very little alkali in a soil is beneficial. In fact, it is necessary to apply lime to some acid soils in order to make them sufficiently alkaline to be most productive, as is noted in Chapter XIV