The Clovers. Red clover can make growth in some soils that have a lime deficiency. If all other conditions are favorable, the lime requirement may exceed one-half a ton per acre of fresh burned lime and not affect the clover adversely, but farm experience throughout the country has demonstrated that when soil acidity is only slight and clover grows with difficulty, an application rarely fails to favor the clover in a marked degree. Experience has taught the land owners to fear soil acidity when red clover does not thrive where formerly it made good growth.
The prevalence of alsike clover in a farming region is indicative of lack of lime. This clover thrives in a calcareous soil, but is more indifferent to a small lime supply than is the red clover. As red clover seedings begin to fail, the alsike gains in popularity, and where a soil is decidedly sour the alsike is most in evidence. The latter has less value to the farmer, rooting nearer the surface of the soil, and making less growth of top, but it has gained in favor with farmers as soil acidity has increased.
The Grasses. Timothy is more resistant to acidity than red clover, but often fails to make a heavy sod where the deficiency in lime is marked. Rhode Island Bent, known as redtop, is less exacting, and where it thrives to the exclusion of timothy, or is in evidence in grass lands, the inference is fairly safe that a test would show that the soil is sour.
When Production Decreases. It is not a matter of any moment to the owner of a productive soil whether or not his soil would give an acid or an alkaline reaction under test. Returns from his labor are satisfactory. Some land in this class is not strictly alkaline. The man most interested in the effects of lime applications is the one who is not satisfied with yields. 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.
Naturally Thin Soils. Nature may be prodigal in supplies of nearly all the elements of plant food to land and yet skimp its supply of lime, but naturally poor soils are quite surely in the acid class. The exceptions in our humid region are not extensive. When improvement is planned for, involving additions of organic matter and plant food, the application of lime to correct acidity is the first requirement. If such land could be given the characteristics of a limestone soil so far only as the lime factor is concerned, the building up of fertility would be relatively easy. Liming must form the foundation of a new order of things. The ability to grow the clovers and to furnish rich vegetable matter to the soil, which naturally is poor in humus, rests upon lime application first, and then upon any supply of plant food that may continue to be lacking.
CHAPTER V
TESTS FOR ACIDITY
The Litmus Paper Test. A method of testing soils for acidity, which has been in use for many years, is the simple litmus paper method. Because of its simplicity and fair degree of accuracy, the litmus paper test is still used to a considerable extent in estimating the degree of acidity of certain soils. The best manner of using litmus is to place a strip of the blue paper in the bottom of a glass saucer, covering it with filter paper or other paper which is neutral—that is, paper which is neither acid nor alkaline.
A small quantity of the soil to be tested is moistened with rain or distilled water and placed on this paper. If the acid is present the blue paper will be changed to a reddish color, varying in intensity according to the degree of acidity in the soil. Two objections to the use of litmus paper are to be noted: One of these is that the red color may be produced by carbonic acid gas without a trace of more powerful acids being present, and this may give a wrong impression to the operator. Another objection to the use of litmus is that the degree of acidity is not accurately indicated, and therefore the farmer is sometimes at a loss to know just how much lime should be applied to make soil conditions favorable for growing crops.