Lije in the Soil 121 



matter contains nitrogen; and the decay carried on by 

 the bacteria releases this as ammonia, which is a hydride 

 of nitrogen. Then at once here are myriads of other 

 forms of these minute plants which find their food in am- 

 monia, and their oxidizing work carries it to the form of 

 a nitrite, but no further. Then other forms take up the 

 work, and the result of their growth and oxidizing influ- 

 ence is nitric acid. When nitric acid is present in the soil 

 it soon seeks a base, for there is always lime or potash or 

 some other base in the soil, and the acid becomes a salt, 

 a nitrate. 



Now, it has already been shown that green plants never 

 use nitrogen until it is in the form of a nitrate; and, that 

 when it has gotten into this form, it is readily taken up 

 by the roots of plants, and is so very soluble that if not 

 soon taken up by plants, it is washed from the soil. The 

 absorptive power of a good loamy soil is such that it will 

 take and hold on to phosphorus or potassium and keep 

 it till called for. But not so with the nitrogen, which is 

 soon leached from the soil in the drainage. The ready 

 availabiUty of nitrogen as a nitrate is well shown in the 

 use of the nitrate of soda as a fertilizer, and the speedy 

 effect it has on plants, and also the way in which it is lost 

 from the soil if not used at once. 



This process, by which the growth of bacteria in the soil 

 changes the organic nitrogen into nitrates for the use of 

 plants, is called nitrification. And, in order that it shall 

 be carried on in the soil it is necessary that there shall be 

 an abundance of food for the bacteria which do the work. 

 We can see, then, the importance of humus-making 

 material in the soil, and the loss that takes place from 



