30 FUNDAMENTALS OF AGRICULTURE. 



taining it were present in the soil. Certain plants 

 (mainly bacteria), have the power of making use of 

 this atmospheric nitrogen. When these plants die 

 their decay adds this nitrogen to the soil's supply. Of 

 greatest benefit to the agriculturist in this connection 

 are the bacteria which form tubercles on the roots of 

 plants of the bean family (legumes), such as bean, 

 pea, clover, alfalfa, cowpea, velvet bean, beggarweed, 

 soy-bean, lespedeza, etc. These bacteria use the ni- 

 trogen of the air and then when they die, the plant in 

 which they live uses them to get nitrogen from. Thus 

 plants of this sort instead of reducing the nitrogen 

 supply actually increase it. 



Inoculation of the Soil Sometimes Is Necessary. 

 The particular bacterium attaches itself only to the 

 kind of legume to which it is suited. Bacteria accus- 

 tomed to forming tubercles on cowpea roots will not 

 grow on clover roots. If it is wished to grow cow- 

 peas on soil where there are no suitable bacteria pres- 

 ent, it is necessary to inoculate the soil, either by sowing 

 soil from a field that has produced good cowpeas, 

 or, if such cowpea soil cannot be found, by inocu- 

 lating the seed before sowing with a pure culture of 

 the proper bacteria which have been isolated from 

 cowpea tubercles. Such cultures may be obtained 

 from the U. S. Dept. of Agriculture as well as from 

 various dealers. If the soil is used for inoculating 

 the field, extreme care must be taken that it comes 

 from a field free from any diseases of the crops to be 

 grown subsequently. It is easy to convey various 

 fungus diseases and insect and other pests (e. g., root 

 knot, nematodes, etc.) if soil is taken from fields 

 where such troubles are present. The same condi- 

 tions as herein mentioned apply to many of the other 

 legumes. 



Plants Use a Large Amount of Water. Far more 

 water is taken up by the roots than the plant really 

 needs for the manufacture of food. Large quanti- 

 ties, however, are lost by evaporation from the leaves 



