108 SOILS AND FERTILIZERS 



1 1 6 . At water ' s Experiments . — Atwater carried on 

 similar experiments in this country. 40 Some of his 

 results indicate that when seeds germinate they lose a 

 small part of their nitrogen, and when grown in a 

 sterile soil, thev fail to fix any of the free nitrogen of 

 the air. 



In all of the work of the different investigators prior 

 to 1888, plants were grown in a sterilized medium, 

 and under these conditions they are unable to make 

 use 7 of the free nitrogen of the air. 



A 117. Field and Laboratory Tests. — Experiments 

 with sterilized soils do not represent the normal 

 conditions of growing crops, where all of the 

 bacteriological agencies of the soil, the air, and the 

 plant, are free to act. Experiments have shown that 

 these agencies have an important bearing upon plant 

 growth. 



In a five years' rotation of clover and other legu- 

 minous plants, Lawes and Gilbert found that a soil 

 gained from tw r o to four hundred pounds of nitrogen 

 in addition to that removed in the crop, while land 

 which produced wheat continuously had gradually 

 lost nitrogen. The amount in the subsoil remained 

 nearly the same. All of these facts plainly indicated 

 that crops like clover have the power of gaining 

 nitrogen from unknown sources. The results of 

 prominent German agriculturists led to the same con- 

 clusion. It was known that wheat grown after clover 



