250 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Water culture experiments have been previously described 

 (Chapter II), and are well suited to certain purposes of experi- 

 ment. They have been used to a certain extent for studying soil 

 deficiencies, by growing the plants in an aqueous extract of the 

 soil. Conditions in water culture are radically different from 

 those in the soil, and still greater caution must be exercised in 

 applying conclusions secured by this method of experiment to the 

 soil. It is quite possible that materials will be injurious in water 

 culture which are innocuous in the soil. Hence it is necessary 

 to confirm conclusions drawn from experiments made in this 

 way by pot and field tests. 



Chemical Analysis. Chemical analysis can be used for the 

 detection of certain soil deficiencies, such as acidity, and the 

 quantity of alkali present. Chemical methods can also be used 

 to form an opinion as to the needs of the soil for phosphoric acid, 

 potash, and nitrogen, as shown in Chapter IX. Chemical analysis 

 is also useful in extending the conclusions from field experiments 

 and pot experiments to other soils under similar conditions. 



Acid Soils. Acid soils contain free inorganic or organic acids 

 or acid salts, which therefore give it an acid reaction. In some 

 cases acidity is due to the decomposition of the remains of plants 

 in the soil, forming organic acids, but it may also be due to in- 

 organic acids. 



The acidity of soils is usually neutralized by lime. A soil which 

 receives benefit from lime is not necessarily an acid soil, as lime 

 has other effects than that of correcting acidity; it makes the 

 phosphoric acid more available, liberates potash, increases nitri- 

 fication, and changes the physical properties of the soil. 



Plants behave differently towards acid soils ; some receive bene- 

 fit from liming, while others do not. The Rhode Island Experi- 

 ment Station 1 has conducted a large number of experiments on 

 an acid soil, limed and unlimed, with the addition of acid phos- 

 phate, muriate of potash and sulphate of magnesia, and nitrate of 

 soda or sulphate of ammonia. These experiments, begun in 1893, 



1 See their reports and bulletins; also Veitch, Bulletin 90, p. 183, Bureau 

 Chemistry, U. S. Dept. Agr.; Bulletin No. 66, Maryland Exp. Sta. 



