THE PHOSPHORUS GROUP OF FERTILIZERS 27 



acid then diffuses out again into the soil, and dissolves 

 more phosphate. Carbonic acid, therefore, acts as a carrier, 

 and though the organic acids in the root are said not to 

 pass out into the soil, they nevertheless have an important 

 relationship to the solution of phosphates in the soil. The 

 rate at which carbonic acid can be regenerated will depend 

 upon the amount of acid in the root. Phosphates are 

 especially valuable for stimulating root development, and 

 it is probably for this reason that they are so important 

 for the development of turnip seed in its early stages. 

 Phosphates usually tend to accelerate the process of ripening. 

 Phosphates are also very important in assisting nitrogen 

 fixation in the soil, either directly by bacteria in the soil or 

 indirectly by encouraging the growth of leguminous plants. 



Basic Slag. Basic slag is a by-product of the steel 

 industries. The phosphorus contained in the ores, fuel, and 

 lime accumulates in the pig iron, and is then transferred 

 to the basic slag. The basic slag, therefore, represents 

 a phosphorus concentrate, and may contain phosphorus 

 equivalent up to 40 per cent, of tri-calcium phosphate. In 

 addition to the phosphoric acid, basic slag also contains 

 a total amount of lime, equivalent to about 40 per cent., 

 with a few per cents, of magnesia and manganese, 6 to 10 

 per cent, of iron, traces of vanadium and sulphur. 



The lime is very largely in some state of combination, 

 and the amount of lime that can be extracted by such a 

 reagent as a solution of cane sugar is very small. Lime is 

 needed by soils, as is explained in Part II., Section II., for 

 several different purposes, (i) neutralizing the acid of most 

 manures (see p. 87), (2) assisting nitrification (see p. 86), 

 (3) checking disease (see p. 73). For these miscellaneous 

 purposes it has been found that calcium oxide, calcium 

 hydrate, and calcium carbonate are approximately equivalent, 

 calcium for calcium. The more basic calcium silicates are 

 easily attacked by very feeble acids, and in this case calcium 

 silicate is almost as good as other forms of lime. Looked at 

 from the point of view of the farmer, to whom the application 

 of lime to the soil is a well-known process, an equivalent to 



