GS THE farmers' handbook. 



From what we know of the process of nitrification, we can lay down with 

 tolerable certainty the following conditions as being favourable to the 

 process : — 



We must have free access of air and moisture, a certain degree of warmth, 

 and the presence of nitrogenous organic matter prone to oxidation (repre- 

 sented by humus). The presence of reducible mineral matter, such as 

 sesquioxide of iron or metallic sulphates, is also favourable. A sufficiency of 

 basic substances to combine with the nitric acid appears to be advantageous 

 to nitrification. 



Putting on one side the bacteriological aspect of the phenomena involved, 

 we shall find that the formation of nitrates within the soil is due primarily 

 to oxidation, and that within certain limits the power of oxidation which 

 the soil possesses is also the measure of its nitrifying power. 



We are, therefore, justified in assuming that a soil will be most favourable 

 to the development of the nitric ferment which combines the following 

 characteristics : — 



1st. A proportion of humus. 



2nd. Warmth. 



3rd. Provision for free access of air and of moisture (these depend upon 



its porosity, and are determined by its capillary power). 

 4th. Good drainage, to prevent stagnant water accumulating. 

 5th. A certain proportion of basic substances. 



These conditions are more fully discussed on page 76, but it will be seen 

 that, beyond the presence of certain mineral and organic matter, the con- 

 ditions favourable to nitrification are those whose presence otherwise indi- 

 cates fertility — namely, fineness of texture and absence of excessive water. 

 If the capillary power of the soil is low, it indicates an unfavourable con- 

 dition for nitrification. 



It has been stated that the presence of nitrates in the soil assists in ren- 

 dering soluble the potash in such insoluble combinations as felspar, which is 

 an additional mode by which the nitric organism promotes fertility. 



Provided then, that the condition of the soil, as indicated by the physical 

 properties above enumerated, is favourable to the metabolism of plant-food, 

 its fertility will depend upon the amount of that plant-food, and it is imma- 

 terial whether that food be now in a soluble state or not. If the mineral 

 and nitrogenous matters are present in sufficient quantity, and the soil pos- 

 sesses high absorptive capacity, high capillary power — in short, is of good 

 texture, and possesses the conditions conducive to nitrification — it may be 

 fairly expected to prove a fertile soil ; and, in cases where one or more of the 

 conditions conducive to fertility are absent, we may look to improved 

 methods of cultivation to attain that fertility. 



The above considerations lead us to attach special importance to two 

 factors in particular besides the chemical nature of the soil. One factor io 

 the texture of the soil, its porosity, and the second is the amount of humus 

 or decaying organic matter it contains. 



It may be worth while to study these two points a little more in detail. 



Texture of Soil. 



We have seen that the texture is of first importance in determining the 

 fertility of the soil. We will now discuss some of the conditions which 

 affect the texture and some of the means to be adopted to promote the 

 desired porosity of texture. 



