No. 6. DEPARTMENT OF AGRICULTURE. 437 



Froiu tliis casual ciiuiiK'ratiou ol' physical conditions we see the 

 value of such a study of the soil; but with all Ibis knowledge, the 

 farmer will not know anything of the chemical composition of his 

 soil, its crop producing power, due to fertili/jug elements, con- 

 tained in it, nor the fertilizer that should be api)lied to it. In short, 

 physically considered, a soil is made up of disintegrated rock mixed 

 with organic matter; chemically considered, it is made up of a large 

 number of simple and complex chemical compounds. In considering 

 these chemical compounds, we should confine ourselves to those in 

 whicli the soils are usually deficient, such as nitrogen, phosphorus, 

 potash and lime. 



The classes of compounds formed in the soil with these elements 

 are organic and inorganic. The inorganic compounds of nitrogen are 

 the nitrate and nitrite of potash and the nitrates of lime and soda. 

 All of these are very soluble in water, and therefore there are usually 

 very small quantities of them in. the soil, because being so easily dis- 

 solved they are readily washed out by the rain and lost or carried 

 down into the sub-soil. The phosphates and phosphoric acid in the 

 s^oil amounting from 1000 to 8000 pounds per acre, are supposed to 

 have been derived from the remains of marine animals and sea water, 

 and during geological times to have undergone many changes and 

 occur now as the inorganic phosphates of lime, aluminum and iron, 

 and are mostly unavailable for plant food. 



The potash of the soil amounting to from 3,000 to 12,000 pounds per 

 acre is present in the form of silicates. It is derived from feldspar, 

 the cementing material of many rocks, such as granite. Feldspar 

 is more readily acted on by atmospheric agencies than the other 

 minerals of which the rock is composed, and consequently the rock 

 gradually falls to pieces, and when the feldspar is further decom- 

 posed it forms clays and potash compounds. Mica also contains 

 potash, and soils formed by the decomposition of micacious rock are 

 usually fertile. The formations of clays by these decompositions 

 brings about a condition for the formation of zeolitic minerals, which 

 contain potash, members of the potash family and water. These 

 zeolitic minerals have the power of fixing and holding plant food in 

 an insoluble and yet available condition for plants. Lime is present 

 in the soil in the inorganic forms of common limestone, the various 

 silicates, dolamite and sulphate or gypsum; all of which are im- 

 portant factors in the fertility of the soil. 



The organic compounds, however, perform the vital functions in 

 the soil for it is through this agency that chemical action is kept up, 

 and the inorganic fertilizing substances are made available and that 

 the micro-organisms which produce nitrification are maintained. 



Humus is the chief organic constituent of the soil and is derived 

 from animal and vegetable matter, and is in an intermediate state 



