104 THE ESSENTIALS OF AGRICULTURE 



a part of the phosphorus is changed to a form that is slowly 

 soluble in soil water which contains carbonic acid. Phosphorus 

 in either of these forms is considered available to plants 

 (Fig. 43). It is known commercially as available phosphorus 

 and commands a higher price than does phosphorus in an 

 unavailable form. 



120. Bone meal. There are two types of bone meal on the 

 market, raw bone and steamed bone. Raw bone is the fresh 



A BCD 



FIG. 43. Response of red clover to different soil treatments 



A, legumes, lime, phosphorus, and potassium ; Z?, legumes, lime, and phosphorus ; 

 C, no treatment ; Z>, legumes and lime 



bone finely ground. Steamed bone is bone after the fat and 

 gelatin have been extracted by steam. Raw bone contains about 

 4 per cent of nitrogen and 9 per cent of phosphorus. Steamed 

 bone contains about i per cent of nitrogen and 10 to 12 per cent 

 of phosphorus. It is more finely ground than the raw bone, and 

 the phosphorus is somewhat more readily available than in raw 

 bone. The phosphorus in both these products is largely insoluble, 

 but it is much more readily available than that in rock phosphate. 



