Acid Soils and Nitrification 179 



crops growing on the manured land are more vigorous 

 and leave greater amounts of root and stubble residue 

 in the soil, hence, also, more nitrifiable material. It 

 has been demonstrated that the nitrogen of organic 

 matter is not all capable of nitrification to an equal 

 extent. A portion will change to nitrate quite readily, 

 the following successive portions less and less readily, 

 until, finally, a stage ( is reached when the remaining 

 nitrogen nitrifies with extreme difficulty. The great 

 resistance to the activities of nitrifying bacteria is 

 characteristic of the humus in exhausted soils. On the 

 other hand, the nitrogen of ammonia salts, of liquid 

 manure, or of such compounds as dried blood, nitrifies 

 very rapidly. 



It has already been stated that the application of 

 ammonia salts in the fall is wasteful because of its 

 ready conversion into nitrate, even in the late fall. 

 In fact, nitrification seems to go on until the soil is 

 almost frozen. When a crop is occupying the land, 

 the nitrate as it is formed is taken up by the plants 

 and but little allowed to escape into the drains. When 

 the land is kept bare, the nitrates formed are washed 

 into the deeper layers of the soil and may be carried 

 off by the drainage. It is for this reason partly that the 

 continuous growing of wheat is a wasteful procedure. 

 The land is kept bare at a time of the year when the 

 nitrification processes in the soil are most active, resulting 

 in the loss of very considerable quantities of nitrates. In- 

 vestigations have shown that in the continuous growing 

 of wheat there may be four to six pounds of nitrogen lost 

 from the soil to every pound removed in the crop. 



