200 THE BOOK OF ALFALFA 



cially from distant and unknown fields. In one of its bul- 

 letins the United States Department of Agriculture has 

 summarized its advice as to inoculation as follows: 



When Inoculation is Necessary. — Inoculation is nec- 

 essary — 



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

 viously borne leguminous crops. 



2. If the legumes previously grown on the same land 

 were devoid of nodules, of "nitrogen knots," thus show- 

 ing the need of 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 nod- 

 ules will often fail to produce nodules on alfalfa when 

 sown with the latter crop for the first time. 



When Inoculation May Prove Advantageous. — Inocu- 

 lation 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 favorable. 



When Inoculation is Unnecessary. — On the other hand, 

 inoculation is unnecessary and offers little prospect of 

 gain— 



