Soil acidity

“ Sorrel is a plant popularly associated with soil acidity, but this is not through any dislike for lime. It has been observed growing in the edge of a heap. Its presence suggests acidity because it can thrive in a sour soil that will not produce plants of value which on even terms could crowd the sorrel out. There is constant competition among plants for food and water and space, and some of our worst weeds are not strong competitors of clover and grass where soil conditions are not unfavorable to the latter. ”

“ Rock-garden specialists usually indicate the preferred pH for the plants they sell.
By using a soil-test kit or, better still, sending a sample to your state agricultural service to be tested, you can easily find out whether the soil in your garden is acid or alkaline, and to what degree. Then, to make acid soil more alkaline for plants that need it, mix in small quantities of agricultural lime—the amount depends on the degree of acidity and on the plant itself. Don’t overdo it. Too much lime can do as much harm as good. ”

“ The soil wants lime in carbonate form. The oxide and hydrate change to carbonate, and therefore are good. Land plaster is a sulphate, and its tendency is to make a soil sour. It should not be considered as a means of correcting soil acidity. ”

“ Active protozoa do occur even in extremely acid soils, but their numbers in such cases are low. The common soil protozoa, in fact, appear to be as tolerant of differences in soil acidity as they are of differences in climate, for many of the same forms which occur in acid soils are found also in soils containing high percentages of chalk. ”

“ Thus, on clay soil it flocculates the particles, rendering the soil less tenacious of moisture, improving the drainage and making the soil warmer. Nor must the directly chemical results be overlooked, for in addition to those already mentioned, of liberating plant food (chiefly potash and phosphoric acid) , retaining bases, and aiding nitrification, lime acts in a special way as regards the sourness or “acidity” which is sometimes produced in land when lime is deficient. In soils that are acid through the accumulation of humic acid nitrification does not go on, and bacterial life is repressed. ”

“ Let us take up the essentials of alfalfa growing: first, that the soil must be sweet.
It is a new thought to Southern farmers, perhaps, that soils are some times sour. They may be sour upon limestone land, but are more apt to be sour away from the lime.
If they are water-logged during part of the year, they are most apt to be sour. This acidity comes probably from the decay within the soil of vegetable matter, though some soils very deficient in humus are acid. An evidence of acidity is seen when clovers fail to thrive, and certain weeds appear in the meadows. ”

“ The tests for acidity have been so many throughout our eastern and central states that the owner of land which is not productive has reason for the presumption that its percentage of lime is too low. There is danger of error, and a scientific test is surer, but in most cases the land which has been reduced from a fertile to an unproductive state has lost its alkaline nature. ”

“ There are land-owners who are not concerned with present-day knowledge regarding soil acidity because they cannot believe that it has any bearing upon the state of their soils. They know that clover sods were easily produced on their land within their remembrance, and that their soils are of limestone origin. As the clovers demand lime, these two facts appear to them final. The failures of the clovers in the last ten or twenty years they incline to attribute to adverse seasons, poor seed, or the prevalence of weed pests. ”

“ Soil Acidity.—Lime performs various offices in the soil, but farmers should be concerned chiefly about only one, and that is the destruction of acids and poisons that make the soil unfriendly to most forms of plant life, including the clovers, alfalfa, and other legumes. Lime was put into all soils by nature. ”

“ The acidity of the soil has an important effect on the bacterial processes. The acidity of soils may increase to such a point that the decomposition of plant tissues by bacteria is hindered, a peat layer being thus produced. ”

“ Our interest is only in the very small percentage of material that is composed of the four constituents which may be lacking in available form in the soil: nitrogen, phosphoric acid, potash, and lime. We believe that the only consideration that now need be given lime is as a soil-corrective and, when there is no acidity, we may assume that there is plenty of lime present. When yields of crops tend to decrease, the only plant-foods with which we are concerned are nitrogen, phosphoric acid, and potash. ”

“ Lime.—The stores of lime in the soil are not stable. The tendency of lime in most of the states between the Missouri River and the Atlantic seaboard is to get out of the soil. There is no evidence that lime is not in sufficient quantity in most soils to feed crops adequately, but within recent years we have learned that vast areas do not contain enough lime in available form to keep the soil from becoming acid. Some soils never were rich in lime, and these are the first to show evidence of acidity. ”

“ Soils Vary in Requirement. There is always the insistent question respecting the amount of lime that should be used on a particular field. Usually no definite reply can be safely made. The requirement of the present, and probably of the next few years, should be met by one application. The existing degree of acidity is an unknown quantity until a careful test has been made. There are soils so sour that several tons of fresh burned lime per acre would only meet present requirement, and there are soils so soundly alkaline that they need none at all. ”

“ The owner of such land may dismiss the matter of liming from his attention so far as acidity is concerned, though it is a reasonable expectation that a deficiency will appear at some time in the future. Experience is the basis of such a forecast. Just as coal was stored for the benefit of human beings, so was lime placed in store as a supply for soils when their unstable content would be gone. ”

“ Incidentally, the incorporation of large quantities of humus in the soil creates a condition of acidity which may call for the application of lime as a corrective.
There are many acres of land which contain too much water in the area that roots should penetrate to permit of optimum plant growth. Roots of most plants will not penetrate where there is an excess of water, and air cannot circulate where moisture is superabundant. Usually these conditions exist where the soil is of a clayey nature. The abundance of water may be caused by the inability of surface water to percolate through the soil. ”

“ The United States has thus far been using up the original materials stored in the soil by nature, but these have not been sufficient to yield anything like the crop output per acre of the more highly fertilized soils of Europe.
In addition to the nitrates, phosphates, and potassium salts, important amounts of lime and sulphuric acid, and some gypsum, are used in connection with soils. Lime is derived from crushed [Pg 100] limestone (pp. 82-83) , and is used primarily to counteract acidity or sourness of the soil; it is, therefore, only indirectly related to fertilizers. ”

“ As the lower layers rot, new layers of leaves and twigs are being constantly deposited, so that the forest soil, in the course of time, fairly reeks with nourishing plant food, which seeps out more or less to enrich neighboring soils." The forest is also a soil former. "Even the most tender rootlet, because of its acidity, is able to dissolve its way through certain kinds of rock. This, together with the acids formed in the decomposition of humus, is a potent and speedy agent in the production of soil. ”

“ In the latter a man rows against the current, and if livestock farming is not employed to furnish manure, and if the manure is not supplemented by tillage and drainage to secure aeration, or if lime is not applied, the land reaches such a degree of acidity that it loses the power to yield any profit.
Nature's Short Supply. The total area of lime-deficient soil is large, comprising certainly much more than half of all the land east of the semi-arid belt of the United States. ”

“ A Practical Test.—The importance of alkalinity in soils is so great, and the prevalence of acidity has such wide-spread influence to-day, limiting the value of the clovers on a majority of our farms, that a simple and more convincing test is suggested here. ”

“ However, ammonium sulfate does not eliminate or reduce worms when the soil contains large amounts of chalk or other forms of calcium that counteract acidity.
The truth of the matter is that worms eat decaying organic matter and any soil amendment that increases plant growth without acidifying soil will increase earthworm food supply and thus worm population. Using lime as an antidote to acid-based fertilizers prevents making the soil inhospitable to earthworms. And many chemical fertilizers do not provoke acid reactions. The organic movement loses this round-but not the battle. ”

“ In our limestone areas, however, acid soil conditions are developing year by year, limiting the growth of clover and affecting the yields of other crops.
The situation is a serious one just in so far as men refuse to recognize the facts as they exist, and permit the limiting of crop yields, and consequently of incomes, through the presence of harmful acids. The natural corrective is lime, which combines with the acid and leaves the soil friendly to all plant life and especially to the clovers and other legumes that are necessary to profitable farming. ”

“ In general, I may say I should prefer a soil slightly on the acid side for any and all tree and farm crops if I had an eye to future fertility. Lime breaks down vegetable matter and makes its constituent plant foods quickly available, but prevents a build-up of humus in the soil. The effect is very pronounced in times of drought, the alkaline soil crops drying up much more quickly than do those on acid soil. On the other hand, such soil elements as phosphorus seem to require the lime as a flux to prevent the phosphates from becoming fixed and unavailable to crops. ”

“ The presence of acid, by restraining the productive powers of the soil, has, in a great measure, saved it from exhaustion; and after a course of cropping, which would have utterly ruined soils much better constituted, the powers of our acid land remain not greatly impaired, though dormant, and ready to be called into action by merely being relieved of its acid quality. A few crops will reduce a new acid field to so low a rate of product, that it scarcely will pay for its cultivation; but no great change is afterwards caused, by continuing scourging tillage and grazing, for fifty years longer. ”

“ From these analyses it appears that the air contained in the pores of the soil is much richer in carbonic acid than the atmosphere, the poorest soil containing about 25 times, and a recently manured soil 250 times as much. This carbonic acid, which is obviously produced by the decomposition of the vegetable matters and manure, acting partly as gas and partly dissolved in the soil water, exerts a solvent action on its constituents. ”

“ I think I can almost see my way through in this matter; we are to correct the acid with limestone, to work the legumes for nitrogen, and turn under everything we can to increase the organic matter, and if we find that the soil won't furnish enough phosphorus, potassium, magnesium, or calcium, even with the help of the decaying organic matter to liberate them, why then it is up to us to increase the supply of those elements. ”

“ Rock-phosphate, known as floats, is not a profitable source of plant-food for soils deficient in organic matter, when compared with acid phosphate. It is more nearly profitable in an acid soil than in one that has no lime deficiency. It gives more satisfactory results when mixed intimately with stable manure than when used upon land that remains deficient in organic matter. Applications should be in large amount per acre—500 to 1000 pounds—in order that the amount of readily available phosphoric acid may meet the immediate need of plants. ”

“ Peter shook his head. "It is lime water and does not belong in the acid class, but to one which is exactly opposite to the acids, the alkalies. Soils ought to be neither acid nor alkaline, but neutral, as it is called. An alkali will help make neutral an acid. If the soil is acid it is bad for your crop. Put a little lime water on the litmus which the acid has turned red." ”

“ The cerealia require the alkalies and alkaline silicates, which the action of the lime renders fit for assimilation by the plants. If, in addition to these, there is any decaying organic matter present in the soil supplying carbonic acid, it may facilitate their development; but it is not essential to their growth. If we furnish the soil with ammonia, and the phosphates, which are indispensable to the cerealia, with the alkaline silicates, we have all the conditions necessary to ensure an abundant harvest. The atmosphere is an inexhaustible store of carbonic acid. ”

“ The alkali conditions in the arid or semiarid regions of the West are thus produced. But in humid sections where more or less of the rainfall leaves the soil as underdrainage the regular loss by leaching is so much in excess of the rise by capillarity that soils which are not affected by erosion or overflow steadily decrease in fertility even under natural conditions, with no cultivation and no removal of crops. Of course this applies at first only to the mineral plant foods, as phosphorus potassium, magnesium, and calcium. ”