1905.] 



Soil Inoculation. 



283 



view, however, of the interest which is being taken in the ques- 

 tion, and the fact that the preparations are now obtainable com- 

 mercially in this country, it may be well to point out that it is 

 only under certain conditions that the use of cultures is claimed 

 to offer any possibility of gain. 



These conditions, which have been referred to in the previous 

 articles, are summarised * by the United States Department of 

 Agriculture as follows : — 



When Inoculation is Necessary. — Inoculation is necessary — 



1. On a soil low in organic matter that has not previously 

 borne leguminous crops. 



2. If the legumes previously grown on the same land were 

 devoid of nodules, or " nitrogen knots," thus showing the need 

 for the nodule-forming bacteria. 



3. When the legume to be sown belongs to a species not 

 closely related to one previously grown on the same soil. 

 For instance, soil in which red clover forms nodules will often 

 fail to produce nodules on lucerne when sown with the latter 

 crop for the first time. 



When Inoculation May Prove Advantageous, — Inoculation 

 may prove advantageous — 



1. When the soil produces a sickly growth of legumes, even 

 though their roots show some nodules. 



If the cultures introduced are of the highest virility, their 

 use will often result in a more vigorous growth. 



2. When a leguminous crop already sown has made a stand, 

 but shows signs of failing, owing to the absence of root 

 nodules. 



The use of the culture liquid as a spray or by mixture with 

 soil and top-dressing may save the stand if other conditions are 

 favourable. 



When Inoculation is Unnecessary. — On the other hand, 

 inoculation is unnecessary and offers little prospect of gain — 



1. Where the leguminous crops usually grown are producing 

 up to the average, and the roots show nodules in normal 

 abundance. 



Cultures of nitrogen-fixing bacteria are not to be regarded in 



* United States Department of Agriculture, Bureau of Plant Industry, Bulletin 

 72. Part IV. : Inoculation of Soils with Nitrogen — Fixing Bacteria. 



