566 VARIOUS FERTILITY FACTORS 



mixed with the plowed soil. Hence, we should know what the 

 plowed soil of an acre contains of the different important con- 

 stituents and the relations between the amounts contained in the 

 soil and the amounts applied in fertilizers and removed in crops. 



This book is not a text on chemistry, but space is taken in the 

 Appendix for a description of the details of soil analysis, such as 

 are given in the " Soil Fertility Laboratory Manual," which is 

 designed to accompany this text for use in schools and ^colleges. 

 Every student of soil fertility, even though not a chemist, should 

 understand how to make a few simple and very important tests. 



Soil Acidity. To test for soil acidity, make a ball of the fresh, 

 moist soil, break it in two, place a piece of blue litmus * paper 

 between, and press the soil firmly together again. After a few 

 minutes examine the paper. If it has turned pink or red, soil 

 acidity is indicated. It is especially important to test the sub- 

 soil for acidity for reasons already mentioned. 



To examine the soil thoroughly, samples should be tested from 

 the surface and subsoil at several different places in the field; 

 and the tests should be made by the landowner in the field rather 

 than by the chemist in the laboratory. The amount of acidity is 

 indicated to some extent by the intensity of color and the rapidity 

 with which it develops. The litmus-paper test 2 for soil acidity is a 

 long-established, trustworthy, and very useful test. It can also 

 be used as a test for acidity in other materials, as in acid phosphate 

 or in mixed fertilizers which contain acid phosphate. Place two 

 or three spoonfuls of the fertilizer in a glass, add half a glass of 

 water, stir well, let settle, and then insert a strip of blue litmus 

 paper, which will be quickly reddened by the acid solution. 



A positive test for carbonates in the soil precludes the presence 

 of soil acidity, because the carbonates are easily decomposed by 



1 Litmus is an organic coloring matter which turns red in acid solutions and 

 blue in alkaline. Litmus paper is made by moistening paper with a solution of 

 litmus, the paper then being dried. The prepared litmus paper ready for use 

 can be obtained at most drug stores put up in packages of 20 or 30 pieces for 5 

 cents a package. 



2 Cameron has reported experiments intended to show that the litmus-paper test 

 has little or no value, because he was able to change blue litmus red by contact with 

 absorbent cotton, the change being attributed by him to absorption; but it develops 

 that bleached cotton may retain sufficient acid used in the bleaching process to 

 produce the change of color in litmus. 



