

SOURCES OF FERTILIZING MATERIALS 49 



source the nitrogen is obtained. Pulverized leather scraps, hoofs, horn 

 shavings, hair, will show on analysis a good percentage of nitrogen, but in 

 such a form that plants cannot use it, being insoluble. Hence the source of 

 the nitrogen is, perhaps, of more importance than the actual amount. 



There is at all times a very small and uncertain amount of nitrogen in 

 the form of ammonia in the air. It is believed that plants do, to some extent, 

 absorb some of the ammonia, but it has never been proved that they do. 

 But there are varying amounts brought to the soil and within reach of the 

 roots in the rain water. Then, too, during thunder storms, some of the 

 nitrogen of the air is converted by electricity into nitrous acid, 

 which is further transformed into nitric acid, and this in the 

 soil forms the nitrates of lime, magnesia and other bases. It has been stated 

 that this formation of nitric acid in the air is the only source of the combined 

 nitrogen in the earth, but later studies of the work of soil bacteria have 

 developed the fact that there are other and more powerful agencies at work 

 in the getting of the free nitrogen into a form that plants can use. It has 

 been estimated that in this country about six pounds per acre of nitrogen 

 are brought to the soil annually in the rainfall, in the forms of ammonia and 

 nitric acid. 



But the greatest source of the nitrogen in the soil is in the black, organic 

 decay which we call humus. A soil well filled with the decay of plant and 

 animal life will have a large nitrogen content, while a soil from which all the 

 humus has been used up, or burnt out, will have very little nitrogen. This 

 accounts for the superior fertility of freshly cleared land. It is true that the 

 nitrogen contained in the humus is not at once in a condition to serve as plant 

 food, but it furnishes food for millions of microscopic plants known as bac- 

 teria, which are the means of carrying on the process called nitrification, 

 through which the organic matter is broken down and its ammonia changed 

 into nitrites and then into nitrates, which last is the form in 

 which green plants can use it. A soil, then, which contains a 

 large percentage of humus may be properly called a living soil, 

 while one in which there is no humus, and irom which the 

 nitrifying bacteria have been starved out and have died, may be well called 

 a dead soil. Nitrogen is an essential element in all living matter and the 

 absence of nitrogen means death either in animals or plants. 



From whence, then, are we to get the various combinations of nitrogen 

 needed in our complete fertilizers? It is always the element that gets away 

 from us most rapidly in the soil, for if it is not taken up by plants when it 

 gets into the available form of a nitrate, it quickly leaches away from the soil, 

 and therefore we need to frequently renew the nitrogen in the soil. 



