NITROGEN 119 



compounds in the same way that other plants do. They 

 require much more nitrogen than other plants do, and 

 have two ways of obtaining it. 



It is very hard to determine what proportion of the 

 nitrogen in a legume comes from the air and what pro- 

 portion comes from the soil. It is certain that a con- 

 siderable part comes from the air under usual farm 

 conditions. One German investigator grew twenty-eight 

 successive crops of lupines (a legume) on the same land 

 with no nitrogen added. But, in spite of the removal of 

 these crops, the field gained in nitrogen. We can readily 

 see how important it is to have some legume like alfalfa, 

 clover, or cowpeas in a crop-rotation. 



117. Fixation of Nitrogen without Legumes. During 

 the last few years, a great deal of attention has been 

 given to legumes as a source of nitrogen. But the fixa- 

 tion without legumes is probably a more important 

 source of nitrogen. Lipman grew millet in boxes of soil 

 that had been given different treatments. 1 In all cases, 

 the amount of nitrogen in the soil was determined at the 

 start, and that in the soil and crop was determined at the 

 end. A few of his results follow: 



(1) No fertilizer used, no crop grown, soil kept bare, 

 a gain of 1.02 grams of nitrogen. 



(2) No fertilizer used, millet grown; slight gain of 

 nitrogen. 



(3) One gram of nitrogen added to the soil in the 

 form of nitrate of soda, millet grown; a gain of 3.73 grams 

 of nitrogen. 



(4) One gram of nitrogen added in the form of barn- 



: New Jersey Experiment Station, Bulletin No. 180 



