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gredient of plant food. It is the most fugitive. Our largest suppljr 

 comes mainly from organic matter which by a process of oxidation 

 through the work of organisms, is converted into nitric acid. The 

 salts of nitric acids, are extremely soluble, and if not utilised at once by 

 growing plants, are washed out by heavy rains. Hence, a gradual 

 development of nitric acid during the period of growth of plants, and 

 the process by which this oxidation is accomplished, is called " nitrifica- 

 tion." This oxidation is going on in every fertile soil, and when stopped, 

 even though the soil be rich in vegetable matter containing nitrogen, 

 the plants thereon must also stop growth. 



The nitro-bacteria taking part in complete nitrification are of three 

 distinct types of genera: First those which convert nitrogenous mntter 

 into ammonia. (Second, those which convert ammonia into nitrous acid. 

 Third, those which convert nitrous acid into nitric acid Each are 

 necessary to the complete transformation of nitrogenous matter into 

 nitric acid, the form of nitrogen chiefly available as plant food. A 

 complete demonstration of this transformation can be made in any 

 laboratory by analyses of samples of the same soil, after the lapse of a 

 month, the one sterilised and the other not. The unsterilised soil will 

 always give the largest amounts of nitric acid. These ferments work- 

 together synchronously, each one waiting on the other. 



It is the aim of every cultivator to maintain his fields in conditions 

 most favourable to the development of these soil ferments, upon whose 

 activity the abund ance of his harvests so intimately depends. Wnat 

 are these conditions ? 



1. They are the most numerous and active near the surface, dimin- 

 ishing in quantity and vitality as one descends. Hence, surface culti- 

 vation required for all crops for maximum results. 



2 A eration —an abundance of air needed The necessity of deep 

 preparation or breaking of land to insure thorough aeration of soil. 



3. A high temperature. The maximum activity is developed be- 

 tween 85 degrees and 100 degrees. We all know how rapidly plants 

 grow when both days and nights are warm, and how they are checked 

 by a fall of temperature. 



4. The absence of light. While parts of plants above the ground 

 require sunlight for their functional full activity, these soil ferments 

 diminish in activity to the vanishing point as the sunlight intensifies. 

 Hence shading the ground in any way enables them to work nearer the 

 surface, and warm nights are more favourable to their development 

 than waim days Hence many plants make phenomenal growth dur- 

 ing warm nights. 



5. A certain amount of moisture. Excessive moisture must be re- 

 moved by drainage, since it excludes air needed for nitrification, yet a 

 certain amount is indispensable to these ferments. For the most rapid 

 work, experience has shown that from one-third to one-half of the 

 capacity of the soil is the proper amount. 



6. Since the final action of these organisms results in nitric acid, it 

 is necessary that there be present in the soil some base which can neu- 

 tralize it and prevent its accumulation in the soil ; killing the ferments 



