234 SOIL ACIDITY AND LIMING 



(a) By the Use of Blue Litmus Paper. This method consists 

 in allowing well-moistened soil to come in contact with blue litmus 

 paper, which can be secured of any good druggist. When the soil 

 is moist from rain or on thawing, make a slit in it with a clean 

 knife blade and insert one end of a piece of blue litmus paper, 

 then press the soil over it and allow it to stand for fully three 

 minutes. If the paper becomes pink in spots or over the whole end, 

 the soil is acid. 



This test may also be made by placing the litmus paper hi 

 between two halves of a ball of wet soil; and, also, if the soil is 

 dry, by placing a small amount of soil in a clean dish and moisten- 

 ing it with boiled, soft water to a stiff mud. By means of a clean 

 stick, the litmus paper is placed between two portions of the 

 wet soil. 



Another way is to place a strip of blue litmus paper on a piece 

 of clean window glass, make a mud ball, break it into halves, place 

 one of the halves flat side down over the paper on the glass, press 

 the soil down firmly, and allow it to stand for five minutes. 



Precautions. Do not mistake a fading of the blue color of 

 the paper as an acid reaction; the change of color should be from 

 blue or light blue to pink or pink-red. Keep the litmus paper, 

 when not testing, in the dark and in a clean bottle or box. Do not 

 allow the portion of the litmus paper which is to be placed in the 

 soil to come in contact with perspired fingers or hands. Perspira- 

 tion is acid in character. Use water that has been previously boiled. 



The litmus paper test is simple and reliable for field use, but 

 it cannot determine the " degree" of acidity very accurately. 



(b) By Chemical Tests. Several chemical tests may be used, 

 not only to detect an acid condition, but also to determine the 

 degree of acidity and the amount of lime necessary to correct 

 this condition. 5 



(c) By Alfalfa and Clover Failures. Since alfalfa and medium 

 red and mammoth clovers are more or less "sensitive" to acidity, 

 the failure of these crops usually indicates acid soils (Fig. 149). 



(d) By the Growth of Certain Plants. Peat beds on which 

 blueberry, huckleberry and cranberry grow are acid. Uplands on 

 which blueberries grow are also acid. Clover and alfalfa fields 



5 The Truog Soil Acidity Test devised at the Wisconsin Station may be 

 mentioned as a simple and accurate test for determining the degree of acidity 

 in soils, and the amount of agricultural lime to use in specific cases. Simple 

 apparatus for making this test may be purchased of school supply houses. 



