272 THE PRINCIPLES OF SOIL MANAGEMENT 



soil, and hence require a greater proportionate amount 

 of fertility. 



133. Calcium carbonate. A determination of the 

 amount of calcium present as a carbonate is important 

 as an aid to the interpretation of an analysis of the soil. 

 Lime not so combined is generally in the form of a 

 silicate, or possibly phosphate. When there is a large 

 amount of calcium carbonate in a soil, the potash, phos- 

 phoric acid and nitrogen are always more readily soluble, 

 and smaller quantities are sufficient for crop growth than 

 where the calcium is not found in this form. The effect 

 of the carbonate of lime upon the nitrogen 1 com- 

 pounds is to furnish a base for the acids produced in the 

 formation of nitrates and its presence promotes that 

 process. It probably replaces potassium in certain 

 compounds where otherwise it would be secured with 

 more difficulty. It insures the presence of some phos- 

 phates of lime, in which form phosphorus is more 

 soluble than when combined with iron. The form of the 

 manures to be used upon the soil will also depend in 

 large measure upon the presence or absence of calcium 

 carbonate. (See page 349.) For instance, where calcium 

 carbonate is deficient, steamed bone or Thomas slag are 

 more profitable than superphosphate, and nitrate of 

 soda than sulphate of ammonium. Finally, the absence 

 of calcium carbonate indicates the need of liming, and, 

 if the analyses show a considerable amount of potash 

 and phosphoric acid, but practice shows them to be 

 somewhat deficient, it is probable that liming will be 

 all that is necessary, and that manures carrying these 



x Not determined in the hydrochloric acid extract. 



