223 



in point of fact they were exercising their functions with maximum vigour. 

 The separate stages of nitrification mentioned above can only be secured 

 in the laboratory by a skilled bacteriologist patiently working to separate 

 the different genera of nitrifying organisms until he procures them in an 

 absolutely pure form. As may be supposed, this is very difficult to 

 accomplish. 



CONDITIONS FAVOURING NITRIFICATION. 



The further discussion of the character of the micro-organisms produc- 

 ing nitrification and their relations with each other, although highly 

 interesting from a scientific point of view, would have no great interest 

 for the practical farmer. For him the most important thing is to know 

 how to secure in the field the most favourable conditions for the develop- 

 ment of those soil ferments upon whose activity the abundance of his 

 crops so intimately depend. 



INFLUENCE OF POSITION. 



The vitality of a nitrifying organism is as a rule greatly diminished 

 as it occurs at a greater depth below the surface. For this reason it is 

 found that these ferments occur in the greatest numbers and with a 

 maximum vitality near the surface of the soil. It follows from this that 

 the conditions favouring the development of these ferments are largely 

 found in good drainage and good cultivation. In experiments conducted 

 in this division it has been found that in low, wet lands, especially those 

 standing under water for a good portion of the year, the nitrifying or- 

 ganisms are almost unknown. Such a soil may be rich in stores of ni- 

 trogenous material but even after the water has been withdrawn and 

 crops are planted it will be found that they do not grow luxuriantly by 

 reason of the deficiency of the number and vitality of the nitrifying 

 ferments. Practical farmers know very well that in reclaimed lands, 

 after the water has been removed, it is found necessary to thoroughly 

 plough the soil and leave it exposed for one or more seasons before good 

 crops can be produced. One of the chief reasons for this delay is doubt- 

 less due to the fact that it requires a considerable time for the nitrifying 

 organisms to be developed and properly distributed through the soil. 



EFFECT OF TEMPERATURE. 



Another condition favourable to the activity of soil ferments is warmth. 

 As has already been indicated, a maximum activity of these organisms 

 is shown at a temperature of from 85 to 95 degs. F. Every one who 

 has lived upon a farm knows how rapidly the growth of a crop will be 

 checked by a fall of temperature. It is evident, however, that this de- 

 pression of temperature does not diminish in the least the quantity of 

 prepared food to which the plant has access. The unfavourable influences 

 of a low temperature are doubtless found not alone in the sluggish- 

 ness of the movement of sap through the cellular tissue of the plant, but 

 also in the fact equally as patent that the diminished activity of the 

 soil ferments prevents the rootlets of the plants from absorbing their 

 normal rations of food. 



ACTION OF LIGHT. 



At this point attention might be called to a fact showing the difference 

 between the activity of the soil ferments and of the plant cells. It is well 



