158 SCIENCE AND SOIL 



If the element calcium becomes deficient in the soil (and it does 

 in some cases), the most economic source is ordinary limestone ; 

 and, if magnesian limestone is applied, both calcium and mag- 

 nesium are thus added to the soil. Kainit also supplies magnesium. 



Sulfur would be furnished in applications of acid phosphate, 

 land-plaster, potassium sulfate, or kainit, as well as in magnesium 

 sulfate and sodium sulfate, both of which are sometimes to be had 

 as waste products or by-products. 



Iron sulfate (FeSO 4 ) is a common by-product in certain manu- 

 facturing processes, and strenuous efforts have been made from 

 time to time to encourage its use as a fertilizer. Since numerous 

 investigations have been conducted both in Europe and America 

 to ascertain its fertilizing value, it is easily possible to select, from 

 the many results thus secured, some few which indicate appre- 

 ciable or even marked benefit. These results, however, have 

 failed of verification. As a general average, iron sulfate produces 

 less benefit than land-plaster, and sometimes detrimental effects 

 are shown. A fair consideration of all results of carefully con- 

 ducted experiments certainly leads to the conclusion that the use 

 of iron sulfate as a fertilizer cannot be recommended in systems 

 of soil improvement ; although, like common salt (NaCl), it may 

 sometimes produce a stimulating action sufficient to cover the cost 

 where it can be secured at less expense than land-plaster, common 

 salt, or other soluble salts. 



