26 



furnish again the nitrogenous food in an available form. This practice 

 should never be neglected in fields which lie over during the winter in 

 preparation for planting during the following spring Of course, this 

 statement does not apply so particularly to fields which may be 

 ploughed late in the autumn, after the activity of the nitrifying fer- 

 ments is practically suspended for the winter. In a temperate climate 

 fields may be ploughed late in November or during the month of De- 

 cember, and the freshly turned soil be exposed to the action of the 

 weather during the winter without great danger of loss 



In many localities even an earlier period might be chosen for the 

 autumn ploughing, which should be deep or accompanied by sub-soiling, 

 The loosened soil should be brought into good tilth, and thus form an 

 absorbent which will hold large quantities of moisture, becoming avail- 

 able for the following season during the period of deficient jains. 



THE SUPPLY OF RAW MATERIAL FOR THE ACTION OF FERMENTS. 



A field is as poor as its most deficient fertilizing principle. A plant, 

 like an animal, demands a balanced ration. It can not live upon phos- 

 phoric acid alone. In order to secure the most economic method of fer- 

 tilizing, the peculiarities of each field must be carefully studied and its 

 particular deficiency in plant food determined. In the case under con- 

 sideration it may happen that a field will have an abundant supply of 

 potash and phosphorus and be deficient only in nitrogen. In such a 

 case its pristine fertility will be restored by the application of nitrogen 

 alone, provided the other conditions in the composition of the soil are 

 favourable to the development and activity of the ferments which oxi- 

 dize nitrogen. Virgin soils as a rule are extremely rich in nitrogen. 

 This arises from several causes. In the first place, such soils usually 

 contain a large quantity of humus, and this humus is exceptionally rich 

 in it« nitrogenous elements. In the second place, a virgin soil is apt 

 to be well protected frum leaching. This is secured either by a forest 

 growth or, on prairie land, by the grass. In the third place, there is 

 a well-marked tendency in soils, especially those covered by grass, and 

 presumably those also protected by forest growth, to develop ferments 

 capable oi oxidizing the free nitrogen of the air. When virgin soils 

 are subjected to cultivation, it is found that their nitrogen content, as a 

 rule, diminishes most rapiuly as compared with that of the other lead- 

 ing plant foods. Hence, it becomes necessary sooner or later, if maxi- 

 mum crops aie to be maintained, to supply nitrogenous food Atten- 

 tion has already beeu called to the use of tke stores of nitrogen which 

 have already been oxidized for fertilization. It is evident, however, 

 that only a very small part of the nitrogenous needs of arable fields can 

 be supplied in this way. Further than this, it must not be forgotten 

 that in the use of a substance like Chili saltpetre, there is added to the 

 soil a material which can in no manner foster the growth and develop- 

 ment of nitrifying organism. To feed a soil with a food of this kind 

 alone, therefore, would be to virtually produce a famine in respect to 

 the nitrifying ferments which it contains. 



It is therefore highly important that additional methods of supplying 

 the nitrogenous foods of plants should be practised. Stall manures and 

 the refuse of cattle and poultry yards furnish considerable quantities of 

 nitrogenous materials suited to the needs of the soil ferments, and use- 



