SOILS AND FERTILIZERS 625 



an inch in length, or it would take about one and one-half millions 

 in a cube to make a mass large enough to be seen with the unaided 

 eye. Bacteria are omnipresent. They are in the air we breathe; in 

 the crust of the earth ; on trees, grass, hay, flowers, fruit, vegetables ; 

 in lakes, creeks, rivers, oceans, the water we drink, in our food in 

 fact, they are everywhere, except in the interior of the earth and the 

 upper layers of the atmosphere. A fertile soil teems with countless 

 millions of various kinds of micro-organisms constantly active in 

 breaking down and nitrifying organic matter. The food require- 

 ment varies according to the species. As a rule, bacteria, like other 

 non-chlorophyllic plants, require performed organic food; although 

 some soil bacteria apparently thrive best, or only on mineral foods. 

 Generally speaking, bacterial food resembles closely the food of 

 man ; thus, milk, an excellent human food, is also an excellent bac- 

 terial food. Bacteria digest their food by ferments secreted by their 

 bodies ; the process in general is the same as that of man. The food 

 thus digested is absorbed by the bacteria, a part of it being used in 

 the construction of new protoplasm, and a part to produce en- 

 ergy in the form of heat, motion, and possibly light. (Y. B. 1902; 

 Kansas Ag. Col. B. 117.) 



Nitrogen Necessary. Nitrogen is absolutely essential to all 

 plant life. It is a part of plant food that must be supplied if the 

 soil does not contain it, and at the same time it is the most costly 

 if the farmer has to buy it. Under normal conditions this nitrogen 

 must be obtained by the plants through the roots in some highly 

 organized form. Other substances, such as phosphoric acid, potash, 

 iron, etc., which plants must have, can be obtained through the 

 soils, but nitrogen is so much greater and in one sense so much 

 more important that the question of the available nitrogen supply 

 in the world has come to be looked upon as lying at the founda- 

 tion of agriculture and demanding the most careful consideration. 



How Nitrogen Is Lost. In the first place, the conditions of 

 life on the ordinary farm are such as to cause the constant loss of 

 this valuable element through the removal of the crops taken from 

 the soil. If every crop that grew on the land could be returned to 

 it, nature has made provision for getting it back in suitable form 

 for plant food. In the case of nitrogen, neither plants nor animals 

 are able to produce this substance directly in an available form. 

 It is necessary that certain bacteria take hold of plant and animal 

 products, and by means of peculiar changes produce nitrates from 

 their fats, sugars, starches, etc. Without these bacteria everything 

 would have come to a standstill long ago, for unless decay takes 

 place and the decomposed elements are rearranged into definite 

 nitrogenous salts no plant is able to use them. Thus, it will be seen 

 that certain bacteria in the soil play as important a part in the food 

 supply of the earth as do the animals and larger plants upon which 

 we think we are so dependent. 



It is hardly necessary to refer to the vast waste of nitrogenous 

 material that is involved in modern sewage methods. Millions of 

 dollars' worth of nitrogen which would naturally return to the soil 



