PHOSPHORUS. 113 



shells, and where it is also laid down in the deposits of lime material 

 that may, in later ages, form new limestone rocks. But, aside from 

 this future possibility, the bacterial agencies of the earth's surface 

 are constantly dissolving the limestones and adding them to the 

 soil to be subsequently carried away by drainage. 



In recent years calcium cyanid has become much used as a 

 fertilizer. It furnishes lime and results in distinct nitrogen gains 

 to the soil. In the utilization of this material bacteria are necessary 

 to convert it into ammonium salts before it can be assimilated by 

 plants. 



PHOSPHORUS. 



Vegetation needs only very small amounts of phosphorus, but 

 these small amounts are requisite to the production of good crops, as 

 has been many times appreciated by the farmer who finds decidedly 

 increased crops following the application of phosphate fertilizers to 

 the soil. There are many substances containing phosphorus which 

 may be used to supply the amount needed by the soil. They are: 

 i. Mineral compounds, of which the chief are ground phosphate rock 

 (floats), superphosphates and a by-product of steel manufacture 

 called Thomas slag. 2. Organic compounds. A considerable quan- 

 tity of phosphorus is contained in the humus, likewise in bone, which 

 is used as a fertilizer chiefly for its phosphorus. The solid part of 

 barnyard manure contains phosphorus, and a variety of other 

 sources, are also utilized ground fish, tankage, castor pomace, and 

 the like. The phosphorus in some of these substances is readily 

 soluble in water, and this must always be the case before it can be 

 utilized by plants. 



Apparently the solution of the phosphates is dependent upon 

 bacterial action. It is easy to understand how the phosphorus from 

 organic sources is rendered available through the agency of the soil 

 organisms. As these bacteria decompose the various organic prod- 

 ucts in the soil, the phosphorus contained in them is set free from 

 its combinations. Bone, for example, is vigorously attacked by the 

 bacteria, and is in time completely disintegrated, the phosphorus 

 being, of course, freed from its relations. The entire series of 



