PHOSPHATE FERTILIZERS 2OQ 



phosphate undergoes a change to more available forms, 

 as described, and the nitrogen is rendered more available. 

 Dissolved bone contains from 2 to 3 per cent of nitrogen 



and from 15 to 17 per cent of phosphoric acid. 







240. Bone Black. When bones are distilled, bone 

 black is obtained. It is extensively employed for refin- 

 ing sugar, and after it has been used and lost its power 

 of decolorizing solutions it is occasionally sold for fertili- 

 zer. It is a concentrated phosphate fertilizer, containing 

 about 30 per cent phosphoric acid. 



241. Use of Phosphate Fertilizers. -- The amount of 

 a phosphoric acid fertilizer that it is 'advisable to apply 

 to crops varies with the nature of the soil and the kind 

 of crop to be produced. On a poor soil 400 pounds of 

 acid phosphate per acre is an average application. It is 

 usually applied as a top dressing just before seeding, and 

 may be placed near but not in contact with the seed. It 

 is not advisable to make heavy applications of superphos- 

 phates at long intervals, because fixation may take place 

 to such an extent that crops are unable to utilize the 

 fertilizer. Lighter and more frequent applications, as 

 100 to 200 pounds per acre, are preferable. Phosphates 

 should not be mixed with lime carbonate before spread- 

 ing, but be applied directly to the land. 22 Phosphates 

 may be used in connection with farm manures. Many 

 soils which contain liberal amounts of phosphoric acid 

 are improved by a light dressing of phosphates, 75 pounds 



