SOIL IMPROVEMENT III 



Pure Culture of Nitrogen. After many experiments by scientists, 

 a method has been discovered of growing these bacteria, so as to 

 give legumes a start on land where they have not been cultivated. 



This is done by means of what is called a ' pure culture ' of 

 nitrogen; it supplies bacteria raised under conditions that make 

 them depend upon the air instead of the soil for their supply of 

 nitrogen. This ' pure culture ' is applied to the seed or to the soil. 

 It is similar in action to a yeast cake, and like yeast the bacteria 

 must be raised carefully according to directions. 



The practical value of this method is doubted . by many 

 scientists. Certainly it is not enough to inoculate the seed or the 

 soil. The soil should be well prepared, and there should be 

 supplied mineral food, potash and phosphoric acid, and lime 

 if the soil is acid. If these elements be furnished in abundance, 

 the legumes make a rank growth. 



EXPERIMENTS 



1. Obtain the 'pure culture' from the Department of Agriculture 

 or from your State Agricultural Experiment Station, and experiment 

 with it. Fill two boxes with quartz 



sand which has been heated red- 

 hot in order to burn out nitrates. 

 Supply both with potash and phos- 

 phoric acid. Plant wheat in one, 

 and in the other plant peas inoc- 

 ulated with the ' pure culture.' 

 What happens to each when the 

 nitrogen stored in the seed is ex- 

 hausted ? At the left, crimson clover on uninoculated 



2. Plant crimson clover Seed in a soil; at the right, crimson clover on inocu- 



paper box of soil from a field lated soil - 



in which clover has been grown. When the plant blooms, put the box 



in water and soak the soil from the roots ; examine the tubercles. 



