No. G. DEPARTMENT OF AGRICULTURE. :J«1 



CHEMICAL COMPOSITION OE SOILS. 



Chemically considered tlie soil is a body of great complexity. 

 Plants contain fonrteen elementary substances which are necessary 

 to their growth: Carbon, hydrogen, nitrogen, oxygen, phosphorus, 

 sulphur, chlorine, silicon, calcium, iron, magnesium, manganese, po 

 tassium and sodium; of these, all except carbon are derived almost 

 exclusively from the soil. Of these, only nitrogen phosphorus and 

 potassium are likely to be deficient in the soil. The importance of 

 seeing that all the necessary plant ingredients are present in the 

 soil in proper quantities will at once be properly estimated when it 

 is stated that the absence or insufficiency of any one of these three 

 elements is capable of preventing the growth of the plant even 

 though the other two may be present in abundance. But in consid- 

 ering the chemical properties of soils, a simple consideration of the 

 dilTerent ingredients is not enough, we must also consider their 

 chemical condition. Before any plant food can be assimilated by the 

 roots of plants it must first be rendered soluble. The quantity of 

 soluble or available plant food in the, soil is very small, but is being 

 constantly added to at least during the growing season. From 

 one point of viev/ chemical analysis is of little value in giving evi- 

 dence of actual fertility. While the potential fertility may be read- 

 ily ascertained bv chemical analvsis, the available fertilitv cannot be 

 ascertained in this manner. 



A point of considerable interest is the quantity per acre different 

 soils contain of nitrogen, phosphoric acid and potash. When these 

 ingredients are calculated in pounds per acre, they are found to be 

 in large excess of the amounts likely ever to be removed by crops. 



BACTERIA OF THE SOIL. 



The soil of every cultivated field is teeming with bacteria whose 

 function it is to aid in supplying plants with their necessarj^ food. 

 The presence of these organisms is indispensable to the fertility of 

 the soil. The nature of, and the function performed by these or- 

 ganisms differ very widely. One very important class prepare the 

 food of plants by decomposing the organic matter in the soil into 

 substances readily assimilated b}^ the plant. Plant life is unable 

 to live upon the complex compounds of the organic matter in the 

 soil and if it were not for these organisms these substances would 

 remain unavailable. There are organisms in the soil which have 

 the power of reversing the w^ork of nitrification, so that the action 

 of bacteria is not wholly beneficial. From what is at present known 

 of these organisms they may be divided into three classes. First, 

 those whose function it is to oxidize the soil ingredients; every soil 

 is probably teeming with this class. The second class are those tiat 



