20 AGRICULTURE OP MAINE. 



reduced the nitrogen supply of the soil by nearly 700 pounds 

 per acre, although the wheat itself used but 98 pounds. Con- 

 tinuous cropping with oats and barley caused even greater losses, 

 but a rotation in which clover entered once during the four years 

 increased the amount in the soil by nearly 250 pounds, although 

 the crops themselves had used much more than did the wheat 

 crop. Were there not some way of reclaiming this lost nitrogen, 

 this earth would long since have been barren, for with the best 

 of management some loss is inevitable. This loss is made good 

 in two ways: One class of germs which work in the soil are 

 able to fix free nitrogen directly in the soil, to a limited extent, 

 so that soil which is frequently stirred and tilled gradually grows 

 richer in nitrogen if there are no wastes. The amount has been 

 supposed to be too small to have much practical value, but no 

 one really knows how great the gain may be. 



In spite of the fact that every plant is surrounded by a wealth 

 of nitrogen in the air, our common crops, such as cereals, corn, 

 potatoes, etc., are unable to make use of this supply. The clover 

 family and its relatives, the peas, beans and vetches, have the 

 ability to get hold of this exhaustless supply. It is done, how- 

 ever, by means of still other types of soil organisms or bacteria, 

 which work upon the roots of these plants. The nodules to be 

 found upon the roots of the clovers, the beans and the peas are 

 teeming with bacteria. In some way these minute organisms 

 make use of the nitrogen contained in the air of the soil for their 

 own growth and thereby enable the plant to use it for its growth. 

 We may grow a crop of clover, harvest it and carry it to the 

 barn, and still leave behind in the roots and stubble more nitro- 

 gen than the soil contained before the crop was sown. Note 

 that here again air in the soil is essential. 



Another essential is that the soil shall not be acid, for these 

 organisms will not thrive in a sour soil. If that is its condition 

 lime will be necessary to enable them to do their work properly. 



The importance of these organisms has led to attempts to 

 introduce them into the soil by artificial means. Several years 

 ago a German preparation was advertised which it was hoped 

 would add to the ability of soils to take nitrogen direct from the 

 air, thereby benefiting such crops as oats and corn by the intro- 

 duction of the particular germs which do this work. The 



