206 



THE ESSENTIALS OF AGRICULTURE 



when legumes are introduced on soils on which they have not 

 grown before. Inoculation is usually accomplished by scattering 

 uniformly over the surface, at the rate of three hundred or four 

 hundred pounds per acre, the soil taken from land where the 

 legume in question has been grown. The field should be har- 

 rowed soon after the soil is scattered, to cover the bacteria and 



FIG. 96. Root tubercles on soy-bean plants 



All but one of these plants were artificially innoculated, being placed for different lengths 



of time in solutions containing the proper kinds of bacteria. A, all night; B, one 



hour ; C, ten minutes ; Z), not placed in the culture. The plants were grown separately 



in test tubes. (Photograph from Kentucky Agricultural Experiment Station) 



thus prevent their injury by drying or the sun's rays. Recently 

 there has come into use a method of inoculation of the soil with 

 prepared cultures of the desired bacteria. These are proving 

 fairly satisfactory. In most parts of the United States soils 

 seldom need inoculation for the clovers, cowpeas, or field peas. 

 Inoculation is frequently desirable or necessary for alfalfa and 

 soy beans in fields where these plants have not previously been 

 grown. 



