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 
