64 BULLETIN 355, U. S. DEPARTMENT OF AGEICULTUEE. 



the acidity in order to secure a good growth of these plants. Some 

 other legumes, such as yellow lupine, serradella, and cowpeas are 

 usually able to grow well on distinctly acid soils, though in some 

 cases even these plants seem to be benefited by lime. The beneficial 

 effect of lime on alfalfa and the other first-mentioned crops is in 

 changing the reaction of the soil from acid to neutral or alkaline, 

 while the benefit occasionally reported in the case of serradella and 

 lupine is possibly due to the fact that on certain soils these plants 

 do not find sufficient calcium for their growth, and the lime supplies 

 this element. 



Detection oj acidity (Ref. No. 1, p. 247).— The presence of acidity 

 may be detected in various ways. Perhaps the simplest method is 

 by the use of litmus paper. This is cheap and can be purchased at 

 any drug store. A strip of blue litmus paper is placed in the bottom 

 of a drinking glass and covered with white blotting paper or filter 

 paper on which the soil to be tested is placed. Clean rain water 

 is added slowly until the soil and the litmus paper become damp. 

 If the paper turns distinctly pink it shows that the soil is acid. It 

 may be well to wait for ten minutes or more before coming to a final 

 decision. The degree of acidity is roughly indicated by the rate at 

 which the change in color takes place and its final intensity. Red 

 litmus paper turns blue in the presence of alkalinity. It will often 

 add to the interest and value of the test if strips of both red and 

 blue litmus paper are placed in the bottom of the glass. 



A method of determining the presence of limestone and the con- 

 sequent absence of acidity is to drop dilute muriatic acid upon moist 

 soil. Any perceptible bubbling, or effervescence, indicates the presence 

 of lime. The character of this effervescence may easily be learned 

 by dropping some of the acid upon a piece of limestone or marble, 

 or into a little baking soda dissolved in water. The presence of 

 lime in the subsoil may sometimes be shown by this test when the 

 surface gives no positive test. A failure to detect the presence of 

 limestone by this test should not be interpreted as proof of acidity in 

 the soil. 



The best indication of the need for lime is the type of plant growth 

 that the soil bears. Where alfalfa, red clover, and sweet clover 

 grow vigorously no lime is needed. The predominance of sorrel, 

 broom sedge, white daisy, or redtop indicates a need for lime. 



Correction of acidity (Ref. No. 7, pp. 382-390; or No. 6, pp. .303- 

 313). — The practical means for correcting the acidity of soils are 

 (1) drainage, where needed, and (2) the application of lime in some 

 form. Lime suitable for use in correcting soil acidity may be in any 

 one of three forms. The first is the carbonate; second, burned or 

 quicklime; and third, water-slaked or hydrated lime. These forms 



