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STATE BOARD OF AGRICULTURE. 



the making available of phosphorus, potassium and other elements of 

 plant-food as well as the favorable effects it has on lower organisms, 

 germs or bacteria that are beneficial. This material must decay in the 

 soil, consequently if a proper supply is maintained provision must be 

 made for regularly renewing it. This is another condition essential to 

 soil fertility. 



Nitrogen may te taken from the air hy legumes. The soil does not 

 furnish all of the nitrogen that some crops contain. The legumes or 

 those plants that form seed in pods such as the clovers, alfalfa, peas, 

 beans, cowpeas and vetch may obtain nitrogen from the soil air by 

 means of germs or bacteria that are present in the soil or added to it. 

 These attack the tender portions of the roots and cause galls, tubercles 



Figure .2. — It Is much better to have straw rot in the soil than In the pile or stack or 



to be burned. 



or nodules to form. In these are large numbers of germs or bacteria 

 which are able to take the nitrogen from the soil air and pass it on to 

 the plant in such form that it makes use of it in its growth. In the 

 light of our present knowledge we may say that such crops derive about 

 two-thirds of their nitrogen from the soil air and one-third from the 

 soil. This relationship is shown by figures 3 and 4. 



Nitrogen may be fixed in the soil by other organisms. Some germs or 

 organisms take nitrogen from the soil air and fix it or place it directly 

 in the soil in such condition that it may be utilized by crops. This may 

 proceed in the absence of growing crops. It is agreed that the activity 

 of these varies greatly in different soils and they are encouraged by 

 many conditions that are favorable to the common crops such as heat, 

 moisture, lime, phosphorus, vegetable matter, good tilth and others. 



