Alfalfa in Kansas. 215 



INOCULATION. 



It seems like a contradiction in terms to say that alfalfa both makes 

 a soil rich and needs a rich soil in which to grow, but it is a literal fact. 



Alfalfa makes heavy drafts on the soil for mineral food. It is esti- 

 mated that a ton of alfalfa hay, producing a four-ton crop for five years, 

 requires 90 pounds of phosphates, 480 pounds of potash and 1000 pounds 

 of nitrates, worth altogether about $180.* The potash and phosphates 

 can be obtained from the soil alone, but the nitrates, after the plants 

 have gotten well started, can be obtained from the nitrogen gas of the 

 air which permeates the soil. Certain bacteria, or germs in the soil, 

 attack the roots of all legumes, enter them, and cause the development 

 of root tubercles on the roots, in the cells of which they live and multi- 

 ply. These bacteria are able to use the free nitrogen gas, which consti- 

 tutes 80 per cent of the air, and which no green plant can use in its raw 

 state. This gas they build up into nitrates, which then become available 

 as plant food. By means of these powerful aids to growth the alfalfa 

 plants are finally rendered independent of the supply of nitrates in the 

 soil, and, by the decaying of their roots, considerable quantities of nitrates 

 from the plant bodies are released into the soil, enriching it for succeed- 

 ing crops. 



It must be remembered, however, that nitrates must be present in the 

 soil at the outset, in order to supply the demands of the alfalfa plants 

 until their roots become equipped with the necessary nodules. This 

 occurs ordinarily by the end of the first season. It is a prime essential 

 to ascertain whether the nodule-forming bacteria are in the soil or not. 

 If not, inoculation is necessary. 



There are many physiological varieties of the root-tubercle organisms. 

 Those which live on red clover or peas, for example, will not grow on 

 the roots of alfalfa. However, the common sweet clover, now coming 

 into such popularity, harbors on its roots the same kind of germs that 

 infect alfalfa. Any kind of land that will grow a luxuriant crop of 

 sweet clover, showing tubercles on its roots, is then already properly 

 inoculated for alfalfa. In the case of soil that needs inoculation, two 

 methods are possible the soil method and the pure-culture method. 



The soil method has been found by most of the experiment stations to 

 be the more certain and satisfactory. By this method not less than 

 400 to 500 pounds of soil per acre are recommended. This may be broad- 

 casted, or sifted, and applied with a fertilizer drill. If the inoculated 

 soil has to be brought from a long distance, then 200 to 300 pounds may 

 be used, mixed with a large quantity of the soil from the field to be 

 inoculated, and applied as before stated. The inoculated soil should be 

 kept in a cool, shady place until ready for use. If the inoculated soil is 

 broadcasted, it is best to put it on in the late afternoon of a cloudy day, 

 since the sun's rays soon kill the bacteria. Immediately after broad- 

 casting the soil should be well harrowed. 



Another method, recommended by the California Experiment Station, 

 is to take soil from an alfalfa or sweet-clover field in which the roots 



* Mo. Exp. Sta. Circular No. 6, August, 1915. 



