IOO 



SOILS AND FERTILIZERS 



NITROGEN. 



In seed sown. In plant. Gain. 



Gram. Gram. Gram. 



Clover, 2 nios o. n 0.12 o.oi 



" 3 " 0.114 0.156 0.042 



Wheat, 2 " 0.043 -4 0.003 



" 3 " 0.057 0.06 0.003 



Peas, 2 " 0.047 o.io 0.053 



Boussingault concluded that when plants in a sterile 

 soil were exposed to the air, there was with some a 

 slight gain of nitrogen, but the amount gained from 

 atmospheric sources was not suffi- 

 cient to feed the plant and allow it 

 to reach full maturity. By many 

 these results were not accepted as 

 conclusive. 



Fifteen years later (1853) Bous- 

 singault repeated his experiments, 

 but in a different way. The plants 

 were now grown in a large carboy 

 with a limited volume of air so as to 

 cut off all sources of combined nitro- 

 gen, as ammonia. By means of a 

 second glass vessel (b, Fig. 23) the 

 carboy was kept liberally supplied 

 with carbon dioxide, so that plant 

 growth would not be checked for lack of this material. 

 When experiments were carried on in this way using a 

 fertile soil, the plants reached full maturity, but when 

 a soil free from nitrogen was used, plant growth was 

 soon checked. A general summary of this work is 

 given in the following table : 4 



Fig. 23. 



Plants grown 



in carboy. 



