158 



THE SOIL: ORGANIC MATTER 



This can be done by applying 200 to 500 pounds of surface 

 soil from some field where the crop in question has produced 

 nodules, or where a similar crop has succeeded. The soil 

 should be harrowed in at once to prevent the sunlight from 

 killing the bacteria. In the case of alfalfa, soil from a road- 

 side where sweet clover grows is satisfactory. This practice 

 of course may introduce weed seeds or plant diseases into 

 the soil and for that reason is not always satisfactory. 



It is possible to get pure cultures of the bacteria at some 

 of the experiment stations, and from some commercial 

 sources (Fig. 37). These cultures can be mixed with water 

 and the seeds soaked before planting. The bacteria cling 



■ 



j NitnM.ii rot 



E 



» 



( / / rt itf. fit 



Fig. 37. — Cultures for Legume Inoculation. Bacteriological Department, 



Virginia Station. 



to the seeds and infect the roots when the seeds germinate. 

 The trouble with this method is to get cultures which are 

 fresh. Many preparations put out by commercial firms and 

 the scheme of the United States Department of Agriculture 

 for sending out the bacteria dried on cotton have failed 

 because the bacteria were dead when inoculation was 

 attempted. 



It must not be thought that inoculation alone is the easy 

 way to obtain nitrogen from the air and that it will work on 

 any crop. There are people who think it is a complete 

 fertilizer in vest pocket form; that corn or oats can be 

 inoculated and will gather their own nitrogen! It is not a 

 complete fertilizer and will not help any but leguminous 



