SPECIAL ASPECTS OF NUTRITION OF PLANTS 12$ 



bacteria in their roots, be spread on soil poor in combined nitrogen 

 where these or related crops have not been grown recently, the 

 clover or peas will develop a greater number of root tubercles and 

 consequently more nitrogen will be fixed to the benefit of the crop 

 and to the enrichment of the soil in combined nitrogen. This 

 inoculation of the soil has been put into practice in a number of 

 different ways. One of the more recent methods is by preparing 

 in the laboratory " pure " cultures of the bacteria on nitrogen- 

 poor culture media in small tubes which can be sold and sent by 

 mail to persons who wish to inoculate their soils.* The object in 

 growing them on nitrogen-poor substances is to create in them 

 " nitrogen hunger," for they will then more readily attack the 

 roots of the clover, etc., in order to put them in a condition to 

 " fix " the free nitrogen. In soil rich in combined nitrogen they 

 do not readily attack the roots of the legumes. It is, therefore, 

 not good policy to inoculate soils rich in combined nitrogen, for 

 the clover, etc., will find a sufficient amount in the soil already. 

 There have been some successes and many failures in inoculating 

 soils with the root tubercle bacteria. Some of the failures are to 

 be ascribed to a poor condition of the inoculating material. Other 

 failures are probably due to the fact that the soil is already rich in 

 combined nitrogen, and still others are probably due to the fact 

 that there are a sufficient number of organisms already in the 

 soil. Some of the conditions under which one might hope for 

 good results are, first, when the soil is poor in combined 

 nitrogen and Ihere are few root tubercle bacteria already in 

 the soil; second, when the soil is poor in combined nitrogen 

 and the root tubercle bacteria may be plentiful, but of a 

 " race " different from that which readily attacks the kind of 

 legume it is desired to grow. For example, the race of bacteria 

 which attack the roots of clover will not readily attack the roots 

 of the soja bean. Those which attack peas will not readily 

 attack the locust, etc. 



* See Bull. No. 71 Bureau PI. Ind. U. S. Dept. Agr., Soil Inoculation for 

 Legumes : Bull. No. 72, Pt. IV, Inoculation of Soil with Nitrogen-Fixing 

 Bacteria. 



