84 Practical Farming 



The Role of not use phosphorus. Pure phosphorus takes 

 Phosphorus ^^^ ^ ^^^^ ^^ beinff exposed to the oxygen 

 m the Plant , , . ^, . ^ \ , "^f . 



of the air. This fact is made use of in 



the manufacture of our friction matches. Hence we 

 must get our phosphorus in some combination in which 

 it can be used by the roots of plants and can for this pur- 

 pose be dissolved in the soil water. Phosphoric acid, the 

 oxide of phosphorus, is generally found combined with 

 calcium, forming the phosphate of lime. It is found in 

 this shape in fossil rocks and in the bones of animals in 

 general. As it exists in soil it is one of the most rapidly 

 exhausted forms of plant food. The ripening grain takes 

 phosphorus from the soil. The availability of the phos- 

 phorus in the soil depends upon the form in which it 

 exists. In freshly ground bones it is sooner made avail- 

 able than in the pulverized fossil rock, because of the more 

 rapid decay of the fresh bones. But unlike nitrogen, it 

 does not rapidly leach away from the soil in the drainage 

 water, for a good loamy soil or clay soil will hold on to it 

 till some plant calls for it, but in case there is more of the 

 soluble phosphoric acid appUed than plants at once use 

 it will revert to a less soluble form and remain to become 

 more slowly available. 



The exact office which phosphorus performs in the plant 

 is less fully understood than that of other elements. So 

 far as we know it seems to be mainly useful in the transfer 

 of formed materials to points where maturity is needed, as 

 in the ripening of fruits and seeds. There may be great 

 activity in the plant through an abundance of nitrogen, 

 and yet the grain may fail to perfect through the defi- 

 ciency of phosphorus. 



